73-87chevytrucks.com
General Site Info => General Discussion => Topic started by: Dr_Snooz on April 05, 2015, 05:03:53 pm
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Hi guys,
I've been fighting this for awhile with no real luck. The newly rebuilt 454 in my 90 1-ton TBI lacks power. The idle surges and all the power evaporates at mid-throttle. It struggles up hills and has been slowly getting worse for the last few weeks.
I've replaced the cap and rotor. Plugs and wires are relatively new. Coil tested fine. Pickup coil tested fine. Timing is dead on 4 deg. BTDC with the EST in bypass mode. Fuel pressure is 13 psi at idle and the fuel pressure regulator is new. Fuel filter is also fairly new and the fuel injector pattern is not noticeably bad. I re-gapped the plugs when I installed the new engine ~2,000 miles ago, though I haven't checked them recently.
This sucks and I'm out of ideas at this point. Can anyone help?
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Oh yeah, the ICM is also new after the old one left me stranded a few weeks ago.
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I tested the TPS today. It's supposed to get a 5V supply. Mine is getting 0.818V. Hmmm. I assumed the ECM would flash a CEL if I had sensor problems, but I guess not. The "Service Engine Soon" light does come on when I turn on the key and turn off a couple seconds later, so it does work. According to my Chilton's manual, I have either a problem with the wiring to the TPS or a problem with the ECM. I dug into my GM manual to verify that, but of course, that section is in a manual I don't have. Grrr. I am in the process of downloading the GM manual now and will dive into it later.
When I had the engine out I took time to rewrap my engine loom, which had fallen apart. I'm a pretty careful guy, and don't often screw stuff up without knowing that I've done so, but it's possible I broke a wire. Of course if I had, I'd be getting zero volts to that TPS. So I'm leaning toward the ECM. Is it common for GM ECMs to go bad? Is there a way for me to test mine at home? Are they expensive? Does anyone have a pinout from the ECM so I can run a jumper wire to my TPS and verify that the wiring isn't bad?
Thanks.
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think the tps is supposed to be .5v at idle and 5v at wot
http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0
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Yes, across terminals B and C I should be getting 0.5V at idle. Across terminals A and B, however, I'm supposed to be getting 5V constant and I'm only getting 0.818V.
Did some reading last night and I guess those ECMs are pretty notorious for going bad. They aren't terribly expensive on Rock Auto (<$200). I downloaded the "Light Duty Truck Fuel and Emissions Manual" which covers all the engine electronics and the first thing they have you check is the ECM. So I'm leaning even more toward the ECM now.
There are some basic diagnostics for the ECM, which I'll perform and see what I learn. I notice that the new ECMs are all reman units, which gives me the creeps, frankly. I've never found reman electronics to live very long. They also require me to reuse my PROM unit, and I'm wondering if the PROMs also go bad?
Incidentally, this link contains a trove of GM manuals in *.pdf form:
http://67-72chevytrucks.com/vboard/showthread.php?t=545416
I'm trying to find the location of my ECM right now and some more description on my ALDL link, what it looks like, where to find it, pinouts, etc.
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TPS pin A should be signal return (ground), C should be 5-volt reference, and B should be TPS signal (~0.6-5v dependent on throttle opening). So, with the ignition ON, engine OFF, throttle closed to idle, your DVM should measure: zero volt A-to-ground, ~5 volts C-to-A, ~0.6 volt B-to-A.
Actually, the ECMs on these trucks are pretty durable. Reverify the 5v reference, check all ECM grounds and the ECM pin connections, before condemning the ECM. A floating ECM ground may not set a diagnostic trouble code.
Have you test driven it with a fuel pressure gauge connected while it is acting up?
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TPS pin A should be signal return (ground), C should be 5-volt reference, and B should be TPS signal (~0.6-5v dependent on throttle opening). So, with the ignition ON, engine OFF, throttle closed to idle, your DVM should measure: zero volt A-to-ground, ~5 volts C-to-A, ~0.6 volt B-to-A.
Okay. Well, I know Chilton isn't the final word on these things, but they're telling me that the 5V should be across A and B. With terminal B as ground. Autozone is saying the same thing (http://www.autozone.com/repairinfo/repairguide/repairGuideContent.jsp?pageId=0996b43f80c90e96). GM's manual is completely useless on this topic. I'll have to go out tomorrow and see what's what. FWIW, I did poke around on the other wires on the TPS and never got any kind of voltages that made sense. There's something squirrely going on there for sure.
check all ECM grounds
I'll go looking for those, unless you want to tell me where they are...?
Have you test driven it with a fuel pressure gauge connected while it is acting up?
I haven't because my super duper Harbor Freight gauge doesn't seal very well. It drips gas everywhere. If it helps, I did gun the engine and the pressure didn't flicker.
Tonight I went out and did the Tap Test (http://www.napaechlin.com/GM-Tap+Test/Content.aspx) and the ECM passed. I basically just beat on the case with a ratchet. If the ECM is bad, it's supposed to make the truck hiccup. That isn't the kind of test that inspires my confidence frankly. With a German or Japanese car, the tests are very specific and detailed. With GM, they are like "beat on it with a tool or something." Seriously?
At any rate, the SES bulb lights when I turn the key on, flickers once and stays steady until startup. So that's also a pass. I put the ECM in diagnostic mode and it flashed a code 12, which is another pass.
Without verifying the TPS pinout, I'm still leaning toward the ECM at this point. At the very least, the ECM should flash a trouble code if the TPS is sending out bad voltage readings.
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you can always do the ohms test. 5v wont be on a and b if your not opening the throttle 100% (WOT). if you only got .8 at wide open throttle then you would return to idle when you go wide open. if you turn the tps the volts should gradually increase with no dead spots. if you hit .8 while at 100% then that would be a dead spot
T.P.S.
(Throttle Position Sensor)
Symptoms of a Defective TPS
The 'Check Engine' Light is On
Bucking and Jerking/Hesitation while Accelerating
Idle Surging
Sudden Stalling of the Engine
Sudden Surge in Speed While Driving on the Highway
Testing
Test between blue and black wire.
.5v idle to 5v WOT
the readings should gradualy change hitting no dead spots
Or you can test with a ohms meter
TPS Actuator Arm at rest: Pins Values (ohms)
A to C = 5.88k
A to B = 2.44k
C to B = 8.32k
Rotating the TPS Actuator Arm: At Rest Rotated
A to B = 2.44k 8.26k
C to B = 8.32k 2.39k
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Since there are contradictions between references, if the TPS wire colors on your engine are gray, black and dark blue: gray should be +5 volt reference, black should be sensor ground and blue should be the TPS signal to the ECM. Testing as before, black-to-ground should measure zero volt, gray-to-black should measure +5v, and blue-to-black should measure ~0.6-5v depending on throttle opening from idle to WOT, respectively.
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Thanks guys.
My wire colors are:
A=black
B=blue
C=gray
Terminal C does supply 5V to the sensor, so Chilton and Autozone get the big raspberry blown at them for being lame. Thanks for clarifying that bd. I would have been chasing my tail for years trying to figure that out.
I did some more testing with my multimeter today and didn't get much good.
With ignition on, I got the following readings between terminals.
A->C 5V
A->B 3mV and declining
B->C 0V
Okay...?
With the engine running, I got
A->C 60mV and declining
A->B 0V
B->C 0V
Huh?
With the key off, I checked continuity to a known ground (the battery negative terminal).
A= no continuity
B= ~1 kOhm
C= ~1 kOhm
Not sure what that tells me. I was just looking for the ground wire and not finding it. Without power to the ECM, I guess terminal A doesn't go to ground.
I need to think this all over and take a fresh run at it tomorrow now that I know what terminals are what. Thanks Irish for posting that info. I need to test the sensor itself to make sure its output is correct and your info will help a lot.
Thanks bd for keeping me out of the weeds where Chilton had steered me.
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Those figures are no good. I backprobed for them and it didn't give good results. Today, I pierced the wire insulation and got better numbers.
With key on:
A->C = 4.99V (s/b 5V)
A->B = 0.832V (s/b 0.5V-1.2V) increasing smoothly to 4.3V (s/b 5V) at WOT
So if my Chilton's manual is correct, the TPS and circuitry is working within tolerance.
I also tested the resistance with the TPS unplugged.
A->C = 5.04kOhms (s/b 5.88)
A->B = 2.14kO increasing to 5.74kO (s/b 2.44kO -> 8.26kO)
B->C = 5.52kO decreasing to 1.94kO (s/b 8.32kO -> 2.39kO)
I'm a little outside those ranges and am not sure if that warrants a replacement or not. My only symptoms are a surging idle and no power after pressing the throttle past a certain point. The TPS is $100, so I'd like to make double certain it's bad before buying a new one.
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Disregard TPS resistance measurements - they aren't reliable. The voltage measurements you posted are within the acceptable range. As long as the voltage transition across A/B is uniform/controlled/consistent, the TPS does not need replacement. However, you might perform a "wiggle & gentle tug test" on the wires connecting to the TPS and MAP sensors with the engine idling
Buy/rent/borrow a fuel gauge that doesn't leak and has the correct adapters, then monitor your fuel pressure while driving under load. Check the exhaust for restrictions (best accomplished using a pressure gauge plumbed into an air injection or O2 sensor port, etc).
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But/rent/borrow a fuel gauge that doesn't leak and has the correct adapters, then monitor your fuel pressure while driving under load.
Yeah. Before it leaves me stranded, right?
I did spring for the much more expensive kit that alleges to work on TBI. It just doesn't seal very well and requires the fuel filter to be removed before using. Thus, it's no help in diagnosing a plugged fuel filter. I'm tempted to plumb a fitting into the fuel line that allows one to use a regular gauge without some leaky adapter.
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Will something like this work?
http://www.ebay.com/itm/TBI-Throttle-Body-Injection-Fuel-Pressure-Gauge-Adapter-/260732758647?hash=item3cb4e22a77&vxp=mtr
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Haven't used that adapter, but it appears workable. You can check the fuel filter by draining it and then blowing through it. If there's any restriction, replace it.
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We installed the fuel pressure gauge tee and ran a hose some could zip tie it to a windshield wiper
That way we could see it and if it dripped a little it was outside the cab
Sent from my iPhone using Tapatalk
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I fiddled with my HF adapter today and was able to get it to seal. Fuel pressure was 11.5 psi at all times under all conditions, including hard throttle, up a hill, towing my tool trailer. The fuel filter is not clogged.
I'm flummoxed.
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Assuming the vehicle displayed symptoms during your road check, the fuel pressure is okay. Did you check exhaust backpressure with a gauge as previously suggested?
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It was displaying symptoms on the road test. I haven't checked the back pressure yet. It's next on my list.
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dual tanks?
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Single tank.
Since we're getting to the outlier possibilities, I thought of a couple possibilities last night. First, when I pulled the engine the injectors were hard wired to the loom. There was no Molex-type connector between the injectors and the loom. When I pulled the engine, I had to cut the wires. When I put it back together, I wired in a cheap Molex-type connector from Radio Shack. The connector I used looks more like the connector you'd find on the fan inside your computer than what you'd find under the hood. In other words, it's not really the right connector to use. It makes good contact and is not corroded. In my research, I wasn't able to find that injectors are very picky about voltage drops or amperage draws or anything that could be related to that connector, so I can't think of any reason why it would be causing problems. Nevertheless, there's always that possibility. Anyone have thoughts or experience on that? If the connector is no good, how do I reconnect those wires better? My preference is to have a proper Molex-type connector rather than butt crimps or wire nuts or something.
Second, the catalytic converter is only two years old. My smog test was last month and the numbers were epic. It ran super clean, so I know the cat works well. However, upon first start of the new engine, I got gallons of water blowing out the tailpipe. It did this solidly for two days and then tapered off in the next week. Now it doesn't do it at all. I speculate that the tailpipe filled with condensation during the month I had the engine out and the pipes open. The shed in which the truck was sitting had a lot of condensation dripping from the tin roof during that time and some of it could have fallen in. It seems very unlikely that all that water came from a dripping roof, but that's the only thing I can think of. The question is whether all that water blocked the exhaust flow somehow?
I'm just brainstorming here. I know. TLDR.
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What do you mean the injectors were "hard wired?" The injector harness should be terminated with this (http://www.autozone.com/fuel-delivery/fuel-injector-wiring-connector/gp-sorensen-fuel-injector-wiring-connector/79638_0_0/). Post a pic. Nonetheless, the Molex connector shouldn't cause an issue as long as the wires were clean and crimped properly to their terminals.
Is the radiator coolant level low? If it is, run a compression check. Otherwise, check the exhaust backpressure.
Be careful about reaching for wild conclusions! Proper diagnosis is systematic and methodical.
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Yeah, those are the connectors. Unfortunately, the wires coming off them go through a small hole in the aluminum throttle body, then disappear into the loom. There's no way to remove them without cutting them. :(
Coolant level is fine. Doesn't leak. Doesn't smoke.
I might buy one of those ALDL cables so I can monitor the sensors in real time and see what's going on when it loses power.
I'm trying to scare up a backpressure tester locally. I checked spark voltage today based on someone else's recommendation and it's 30kV, so that checks okay too.
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I swear I typed up this post a few days ago, but I guess it didn't take. I can't find an exhaust pressure tester locally and I don't want to send away for one, so I threw my vacuum gauge on the truck the other day. With an exhaust restriction, the vacuum should fall off at higher revs. Mine stayed steady, which is what it's supposed to do. My cat is just over 2 years old and the truck passed its smog check two months ago with flying colors. I mean, the emissions levels were amazingly low. I don't think I have a clog, but if you guys think I should buy the gauge to confirm, let me know.
In other news, I replaced the PCV valve for kicks and the situation is noticeably improved. Not 100%, but better. So I'm thinking vacuum leak? Any suggestions for spotting vacuum leaks aside from the spray carb cleaner deal?
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Don't buy a backpressure gauge. Does your vacuum gauge also register pressure? At ~2000 RPM, exhaust pressure should measure no more than 1.5 - 2 PSI.
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Well, the truck is running better and better with that new PCV. Tonight coming home it was almost normal. I unplugged the battery to reset the ECM and clear out the old maps when I got home. We'll see how it runs tomorrow. I might have solved my problem.
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Spray a little B12 through the PCV and down the throats of the throttle base to see if that makes any improvement. Then pull the vacuum line off the MAP sensor and do the same to wash out the line all the way into the TBI base. Could be as simple as carbon building up under the base, restricting vacuum signals.
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It was a fun couple days, but now it's worse than before. Aaaarrgh.
I'll try cleaning the vacuum lines next.
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Getting back to this after a long absence. This problem is ongoing and exasperating enough that I just want to sell the truck. Too bad that it's all set up for me: overload springs, wiring to run the camper, trans cooler, oil cooler, battery isolator, inverter, etc. So I soldier on.
I found in the GM manual a troubleshooting section devoted to low power complaints. It's pretty thorough covering:
- check air fiter
- check timing
- check condition of plugs, wires, all vacuum lines
- check EGR operation
- check for silicone contaminated O2 sensor
- check exhaust backpressure (using a vacuum gauge)
- check compression
- check valve timing (ie: timing chain/cam problems)
I followed the procedure, checking everything right up until check compression, timing chain and other things gone horribly wrong with a rebuild. So far, everything checks out great. Plugs show signs of maybe running a little lean, but nothing that would completely emasculate my truck, I think. The O2 sensor looks good to me, but I'm no expert.
Pics are below and second opinions welcome. (Okay, there's only 7 plug pics because I'm an idiot. Suffice it to say that they all look the same.)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2704_zpsur2thmdp.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2703_zpslss6o1lp.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2701_zpstbk68ulz.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2702_zpshfyhcrox.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2700_zpslzznyxle.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2699_zpspbtnkwly.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2698_zpscpiblqhy.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2706_zpsajjyhraz.jpg)
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2705_zpswsipzyjp.jpg)
Anyway, when I connected my vacuum gauge to do the backpressure test, I noticed that the needle whipped erratically around ~19Hg. As I increased the throttle, it whipped erratically over a much wider range. From what I can research, this indicates weak valve springs. I'll try to get a video of the gauge later today, but would weak springs cause a low power problem with a rough and surging idle? I assume it would. If I have valve problems, then it's something I need to take up with the rebuilder, right? How hard is it to change valve springs?
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The spark plugs appear fine, although from the color change on the ground electrode, they are burning a little hot. You might consider changing to an AC R43CTS next tune up. The condition of an O2 sensor cannot be judged by appearance, only by monitoring its function with a scanner.
I am curious...
...when I connected my vacuum gauge to do the backpressure test, I noticed that the needle whipped erratically around ~19Hg. As I increased the throttle, it whipped erratically over a much wider range. From what I can research, this indicates weak valve springs. I'll try to get a video of the gauge later today, but would weak springs cause a low power problem with a rough and surging idle? I assume it would....
Were you trying to check exhaust backpressure?
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Thanks. Part of the diagnostic was to check for RTV contamination of the O2 sensor, which shows up as a white powdery buildup. Mine looks okay to me.
And yeah. I was checking exhaust back pressure. It was hard because the needle on the vacuum gauge was gyrating over such a wide range at higher RPMs. The vacuum never fell off like with an exhaust restriction, so I'm not worried about that. I'd take a video of the needle movement, but I misplaced my gauge. I'll do that when I find it again.
I talked to my rebuilder the other day about the possibility of weak valve springs. He checks valves during building with some kind of special tool that compresses them and measures tension, so that kinda answers that question for me. He wants to put it on their scope to see what's up.
Will post again when I learn more.
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Not sure if this is your problem, but in the past I've had a similar problem and the cause end up being the distributor. The bushing's we worn just enough to give these "gremlin" type problems and because the distributor still "works" you get these on again off again problems with no codes. And for what its worth also had an issue with a "known new good distributor" that was bad also.
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Update on my useless slug of scrap iron. I promised to take a vid of the bizarre vacuum signal I'm getting and here it is. I'm trying to figure out what it means and am open to suggestions. Timing chain off a tooth? Valves screwed up? Bad Feng Shui? What?
http://vid441.photobucket.com/albums/qq132/dr_snooz/MVI_1425_zpsxdqwnkhx.mp4
Bear in mind there aren't 10,000 miles on this engine. My new '89 Suburban TBI is rock steady at 19 w/ 90k or so miles. This engine flops all around and has no power at all.
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Unable to open the file.
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Well. Try these I guess.
http://s441.photobucket.com/user/dr_snooz/media/MVI_1425_zpsxdqwnkhx.mp4.html
(http://i441.photobucket.com/albums/qq132/dr_snooz/th_MVI_1425_zpsxdqwnkhx.mp4) (http://i441.photobucket.com/albums/qq132/dr_snooz/MVI_1425_zpsxdqwnkhx.mp4)
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BTW, the MAP sensor tests good. The only thing I haven't tested is compression, which is next. Followed by something drastic.
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Here is my album. It's the first video.
http://s441.photobucket.com/user/dr_snooz/library/?sort=3&page=1
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Scroll down to the image of the gauge and 'click' on the various scenarios: How to Use and Interpret a Vacuum Gauge (http://www.secondchancegarage.com/public/186.cfm). Now, go back to 5. Does it run smooth, or is there a little miss?
Where did you have the gauge plumbed in at the time?
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Now, go back to 5. Does it run smooth, or is there a little miss?
I'm not able to look at the scenarios on that page. I had so much trouble with Adobe Flash, I had to uninstall it. Is Scenario 5 the "weak valve springs" diagnosis?
That's a wonderful site, BTW.
The idle is not right. It does miss, most of the time. At other times, it surges. The gauge was piped into the throttle body in place of the PCV hose.
A couple other notes. The truck runs fine at a steady speed on flat ground. When you get harder on the throttle is when everything unravels.
Sometimes, the cab fills with the smell of burning brown sugar. ?! Especially if I've been driving the truck under load.
If I mess with the vacuum, introduce a vacuum leak, bypass the PCV, etc., the truck runs slightly better for the next couple days.
I swear I'm not making any of this up.
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You should author a mystery novel.... Really.... ;D
Scenario 5 is "sticking valves." I wasn't able to get a steady stream via your link, but the ol' sticky valves routine seems the best fit - or similar valve issues. I wanted you to see it and compare for yourself. Does it pop back through the intake if you aggressively snap the throttle wide open? The surging is probably fuel management trying to compensate for the misfire. Are you sure the 'brown sugar' smell isn't coolant or oil coking on the exhaust?
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Okay, so it does seem like there is something up with the valves. What would make the valves sticky on a newly rebuilt engine? Is there anything I can check that doesn't involve a tear down? My rebuilder is super highly respected in town, especially among the farmers. He inherited the business from his dad and has been in business forever. He's very careful and I can't imagine anything meaningful escaping his notice. A bad cam lobe or bent valve or whatever would have been seen upon inspection and I would have received a call. The strange thing is that the truck passed CA smog with really good numbers running this way. Valve trouble would tend to prevent that, but this is so bizarre, who can say?
The truck has never backfired, even at WOT. I haven't tried blipping the throttle though, so I'll see. My hunch is that it will merely stumble and hesitate. I get a lot of stumbling and hesitation off the line. The truck has never lurched or bucked or backfired. It just has a subtle misfire and no power.
I think the brown sugar is a wire loom or relay cooking itself. I've spilled enough oil down the side of the block to know what that smells like and coolant smells different than this.
I'll do a compression test next. It's really hard to believe that this is mechanical, given that my symptoms aren't consistent, but I'm really out of ideas. Everything I test is dead perfect. The only thing wrong is this screwy vacuum signal and I don't know what it means.
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Burning electrical components produce a distinctive rank, almost rancid, odor.
Go ahead and run the compression and/or cylinder leak down tests. They will tell you basic mechanical condition. What will remain is fuel management and ignition.
What recent discussion had you with the rebuilder? Did he ever check engine function using his scope?
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I went in a couple weeks ago to tell him what I'm dealing with. He went over some basic troubleshooting stuff, fuel pressure, vacuum leaks and the like, then promised to ask around. He called back a few days later having talked to a tech at the local dealership. He suggested some additional fuel pressure tests, which I haven't done. They are largely redundant, given that my pressure held at 11.5 psi, going uphill at hard throttle with the relief button on the gauge held open. His tech has to scare up his scope and they'll look at it then.
I told him about the vacuum shake and suggested weak valve springs. He did check the springs during the build and we didn't have a vacuum gauge to confirm the shake, so we left it there. He also wanted some compression numbers, so I have to get those now.
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Compression test results:
#1 - 110 psi
#2 - 122
#3 - 118
#4 - 119
#5 - 118
#6 - 121
#7 - 120
#8 - 111
That's definitely lackluster, but not enough to make my truck such a dog.
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Those compression numbers are underwhelming, but they aren't unacceptable. That alone shouldn't make the truck a complete dog. Something is going on with the valves, but something else is going on too in the engine electronics. My hypothesis is that the squirrelly vacuum signal is messing with the MAP sensor. I'll check valve lash next and hope it calms that vacuum signal.
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I'm noticing a really bad misfire in the mornings on first start. It cleans up after the truck has idled a bit, but if I don't wait, it feels like someone is hitting the truck frame with a hammer. The misfire is random and erratic, not like a specific cylinder misfiring.
Performance is getting bad enough that I worry about making it up the one hill here. The idle is noticeably rough too now. Before, it alternated between rough and surging. Now it's really rough all the time. Sometimes, performance improves if I turn off and restart the truck. Gawd I hate this truck.
Any ideas?
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just thinking of something else but what happens when you unplug the cts?
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I'll have to find out. Stay tuned.
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Okay, I swapped out the MAP sensor with an old one I didn't know I had. That seems to have resolved all of my lesser symptoms. The idle is smoother. The hesitation from stops is gone. Misfire is greatly improved. No more surging. The bogging out at mid throttle is all gone. Unfortunately, my main symptom, POWER, remains. My performance now seems more consistent with a low compression engine. Especially one with a vacuum signal that goes to crap at higher RPMs.
I'm pretty sure a valve job is in my future and I'm pretty sure it's because of weak valve springs. That is, after all, what the vacuum gauge is telling me. The machine shop insists that they test springs before re-installing, so I'd like to confirm this diagnosis before negotiating for a warranty valve job. Does anyone know a way to test spring pressure WITHOUT removing the heads and disassembling them? Moroso sells this rascal right here for that purpose.
(http://www.jegs.com/images/photos/700/710/710-62390.jpg)
http://www.jegs.com/i/Moroso/710/62390/10002/-1
It would give me a nice solid number to confirm or negate the diagnosis. Unfortunately, $90 is well outside the budget right now. Anyone have any other ideas for me or should I just save up?
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You can remove the valve springs on one cylinder at a time by getting the piston to almost TDC on the compression stroke. Then feed some rope through the spark plug hole and turn the engine to squish the rope a bit, it will hold your valves up without fear of them falling into the cylinder. Mark the rocker arm nuts and count how many turns/threads it takes to get them off. You can get a tool that's pretty much a lever with a cutout for the valve stem to compress the springs and remove the keepers. I'm sure the shop would test them for free or much cheaper than buying that tool. It would be pretty time consuming to do every cylinder this way but I think if you did a couple of cylinders (one at a time) it would let you eliminate the valve springs.
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Another update on my Gypsy Curse Truck. It keeps running worse, misfiring, hesitating, idling rough, etc. In desperation, I unplugged the ECT sensor and the truck started running better for a day, then started getting worse each day. I replaced the ECT and again, the truck ran better for a day, then progressively got worse until it was the same as before. FINALLY, the stupid thing gave a feeble pop and died near my mailbox. No spark. I tested all the ignition components again for the 50th time and they all checked out fine. I pulled the distributor and started tearing it down when I realized that the reluctor assembly was completely caked with rust. I replaced the distributor with a Richporter unit from O'Reilly and the truck ran again! It even ran well, though still with no power.
But the Gypsy Curse still holds, so each day it runs a little worse. Good grief.
I did a leakdown test the other day and found ~70% leakage on all cylinders, past the rings. So this engine is a total loss. I knew the valves were screwy and was hoping I could massage them without pulling the engine, but with bad rings, there's no point. I'll get a different truck.
What a Charlie Foxtrot this has been.
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I went to the machine shop yesterday and talked with the owner. He has agreed to warranty the engine for me and do another rebuild. I still have to pull the engine and all, but at least it's not a total loss. The problem right now is that I'm driving the truck daily for work. I'm saving up for another truck right now, so this all will have to wait until there's yet another truck in the yard. LOL
I'm planning to swap the rebuilt engine into my '86 (AKA Chester), along with some other stuff that I'll detail in another thread.
All in all, this is a positive development.
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If you were chasing a weak spark condition and it persisted even after replacing the coil, the distributor and the ICM, what would you do next?
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Oh, and an update. Now it's running pig rich with a steady misfire that makes the truck hop at stop lights, but also a lot of random misfiring. It gets dreadful mileage and Civics are passing me on hills now. I'm shopping for another truck, ~2000, ~150k miles, 4x4, ext cab, long bed and they don't exist. No lie. There's nothing. I believe I have a weak spark condition and have a test to confirm that, but it doesn't seem weak enough to make it run this bad. Moreover, the entire ignition system is new, so now what?
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Solved the problem. I bought a new-to-me '09 Silverado.
The '90 is at another shop for a last Hail Mary effort before it gets parted out. The shop has spent $500 of my money and found bad plug wires. Correction: they have found BAAAAAAAD plug wires. They are literally burned up. When they went to pull the boots, the wires tore apart leaving the metal connectors on the plugs. They tell me the boots had holes burned in them. I told them that those wires were only 3 weeks old and good NAPA wires, not some Chinese junk from eBay. Now we're all scratching our heads. The entire ignition system is new from stem to stern. New coil, new distributor, new ICM, new cap, new rotor, new wires, new plugs. But the wires were still completely toasted.
I'm done with this truck. Every dollar I spend on it makes it run worse. I've spent a fortune on it and I'm not one iota closer to fixing the problem. I want no part of this truck anymore. I don't want the TBI. I don't want the long block. I don't want a single piece of trim or a solitary screw to remain in my possession. I don't even want a picture to remind of this misery. It's all gonna go, along with the Gypsy curse that is on it.
Good riddance.
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Are you going to junk it?
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I think I finally figured it out. It was the cat. It's completely plugged. The shop tested it and told me it was bad. I Sawzalled it out and I have a 454 again! What a nightmare this has been. The restriction heated up the exhaust manifolds and cooked the wires, leading to the misfire. It didn't cause the truck to overheat though, I guess because I have a big radiator in it. ?
Normally for a power loss complaint, the cat is among the first things you'd test, and I did very early in this process. I tested it according to the GM manual and it tested fine. Shows what the GM manual is worth. I keep being disappointed by their manuals. Now that cat wasn't a year old when I dropped the new engine in, yet somehow it was cooked at that point. I'm not exactly sure how that happened but I do remember that the exhaust pipe was spitting lots of water for a few days immediately after the swap. The engine was out for almost a month but the truck was in my brother-in-law's metal shed the entire time, so I have no idea how the exhaust system filled with water. Maybe my nephews were screwing around? I'm not even sure if the water would mess up the cat, but I didn't have the problem before the rebuild so I don't know. To make the problem still more difficult was that the old distributor had some rust in it. That would corrode up the electrodes on the distributor cap periodically, making accurate diagnosis more difficult by pointing me in the wrong direction.
I'm still ironing out some final bugs, but I think I'm past the worst part. This is a low-mileage 1990 1-ton with a fresh rebuild, new tires, nice interior, good condition overall. It's set up to carry my camper with overload springs, battery isolator, etc. The paint is rubbish, but that's theft-proofing as far as I'm concerned. I'll keep it around because I really do need it.
Thanks everyone for your help on this.