73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Cowboy_Customs on February 27, 2008, 04:14:35 pm
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I need some help here, my '91 runs like crap. I have no codes, and the IAC checks out, I have used seafoam, and throttle body cleaner (runs great with that stuff pooring through it) Here are my issues
1) wont idle, kind of lopes a little bit (not cause of a cam) stumbles n dies
2) When trying to give it fuel its like it drowns out, but as soon as u let off the throttle from trying to rev it and it stumbles, it revs up some, then dies down n trys to die.
I did replace the plug wires, cap rotor and coil, they all needed replacing pretty bad. This made NO difference. The distibutor is pretty nasty with rust in it.
My thoughts are its like the truck isnt getting the spark, or timing advance required to fire the fuel. The plugs were OK, maybe 10-15K left on em, but within reason.
??? ??? ??? ??? ??? ???
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Sounds like what my Burb was doing... Check your fuel pressure. You can clamp the return off and see if it makes a difference.
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Check the stuff I recommended in your other post.
#1 disconnect the EGR to make sure it isn't hanging open at idle.
#2 make sure your TBI base gasket didn't get sucked in. While it's idling spray some carb clean at the base of the tbi and see if it effects the idle.
#3 check your fuel pressure
#4 verify firing order and ignition timing.
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#5 Check your advance weights and springs under the rotor cap. Lube them lightly
#6 Check fuel filter.
#7 Check for a good spray pattern from the injectors and that both are working.
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I started reading that thread Kapt. but havent finished yet. Did you ever get that issue resolved? A good mechanic friend of mine dealt with the exact same issues on a 350 TBI before but stopped working on it for whatever reason and it basically defeated him. So hes helping me on this for a chance to "redeem" himself. lol
Anyway, Its insanely cold here today, so im going to pull the truck in the barn if it'll stay running long enough. Where can I pick up those plastic vacuum lines that are everywhere?? I like stock LOOKING for clean appearances other wise id go buy a 25 foot roll of hose and have at it.
The TBI base gasket is ok, I sprayed the base with carb cleaner and no change in idle or anything, we did fix a vacuum line on the manifold, I am going to pull the distributor, and check the cam position sensor. The distributor had a lot of rust in it, and the rotor was rusted to the shaft so we had to break it off to replace it yesterday (the rotor) I swear this is almost a timing/timing advance issue as the truck seems to drown itself when u give it fuel. I did note that I have to key off 50% of the time after it dies to refire the motor. Someone mentioned somewhere that the CPS is the culprit here. I will get a fuel pressure reading in the next day here, the injectors fire, and well, even though the TBI looks to have been on fire at one point, the injector connectors are melted and Im going to have a fun time getting them off the injectors for replacement, but do spray, and spray well.
The truck was parked because of this issue about a year ago I was told, and it just all of a sudden happened while on the road. So it wasent a gradual death, but a quick one.
Sorry for the long post, just trying to be thorough. Will post back later!
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I fixed my Burb, it runs fine now. BTW, #5 above isn't necessary to check, there is only a module in there.
I ended up checking everything on there and swapped TBI's, but there was still a problem, ran better with a different TBI, it would stay running and if you weren't in a hurry it wouldn't die all the time. I pulled the stock one apart and the spring in the regulator was basically non existant and the diaphram was junk. So I rebuilt it completely. Once I got it on there one of the injectors started to spray funky, so I replace both of those also. Put it on the truck and it ran as the other but would still die. I figured I might as well check the distributor again. I had already replaced the rotor ( I had to break it off to replace it so that wasn't it) with no luck, so I dug deaper into the distributor. I pulled it out and the pickup was rusty and I believe it was either the module or the rusty pickup as the truck also sat for about 1.5 years. It was cheaper to buy a distributor than rebuilt it so I got a new one and it ran fine after those two pieces.
If you fuel pressure is fine, I would either rebuild or replace the distributor first, and if that doesn't solve the problem, tear into the TBI. I wouldn't ever put a carb on one of these. It is something simple. I have the pictures of where I rebuilt my TBI that I plan to put in a tech article I can push it forward if you need me to.
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Thanks Capt.
I did find I had a nearly destroyed distributor, the internals were cracked or missing or falling out.
However I replaced it today (used) still no help. Im trying to work up the ambition to go back out and check the timing. I have noticed that the TBI distributors seem to get quiet rusty inside, this one i put in was no gem, but in much better condition.
This brings me to a question, is there anyway to check the electronic advance in one of these things? Like put some voltage to it and see if the advance ring moves?
I think im just going to look into a rebuilt unit and go from there, I got a great shop over the hill for stuff like that.
Answers:
1)no Vacuum to EGR ??????
2)nothing happens when sprayin carb clean
3)Havent done yet
4)Done, need to check time
5)
6)OK
7)good pattern, lots of spray, good pulse
Oh, what exactly does the IAC do? should something happen when the truck is warm, and idiling and I unplug it? (yields no change, and no codes)
MAP sensor vacuum line unplugged when warm and iding sends the idle into orbit
TPS unplugged when running and warm, the truck doesnt like that at all
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If you unplug the IAC you probably won't notice a difference.
I found all the originals were rusty messes, I ended up getting one from NAPA or O'Rielley for $100. I has a new design pickup on like the later ones as far as I can tell...
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Randomly unplugging sensors and actuators will do little more than set a false DTC. You need to put the ignition system into BASE timing when checking the timing. The advance is controlled electronically and there is no mechanical check to be made of any advance.
The EGR should not have vacuum to it at idle and the valve should be closed.
Your used distributor is probably a bad idea - get a reman and set the timing with the EST in bypass.
The IAC is a controlled stepper motor that allows air to bypass the throttle plate to acheive the desired idle speed. The ECM controlls it in step counts that can be read on a scan tool.
Fuel pressure is critical so make sure you check it.
Does it matter if the engine is cold or warm when it acts up?
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Thanks again guys. After some thought, and reading im going to ditch the used distributor.
As far as being warm or cold when it acts up. Yes, when its cold, or under like 150, it will NOT stay running on its own. After that, it will run with out assistance, but still up and down. Its issues seem to be multiplied greatly when its not up to temperature.
Before I shut it down tonight it was ideling rather high, just a guess here without a tach. but around 1300? and thats after running for probably 45 minutes.
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Did you check the engine coolant temp sensor?
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OK, Advance auto parts reman and updated distributor went in today, NO change whatso ever. other then going in one tooth off becase of the oil pump, (which im going back out in a minute to correct)
But why the heck is it purring like a kitten right now, up to operating temp, with the MAP sensor unplugged???? It runs like a top with out the MAP plugged in from idle to 5 grand. Remember I get no codes from the computer except now that the map is unplugged.
Im going to be checking the TPS, and MAP voltages shortly. If I can get my hands on a timing light im going to check timing as well today.
Here is another question, how the heck do I check fuel PSI on this thing??? I see no schrader valve anywhere.
I will get a video of whats going on to help everyone out.
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You have to get a TBI Adapter to check the pressure, it will fit after the filter. The do make them that replace the rear feed for the TBI on the back though.
Have you tried clamping the return line?
This is the TBI Pressure piece I was talking about:
(http://marine-performance-parts.com/images/products/detail/tbifuelpsifitting.JPG)
http://marine-performance-parts.com/cfmtechfuelpsiguageadaptorforgmtbi2843505774.aspx
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Check your map voltage at idle with the vacuum hose connected then check your map voltage key on engine off. backprobe cavity B the light green wire. And yes you'll have to tee in after the fuel filter.
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OK, little update. I finally got around to checking the timing today, with everything plugged in (minus the MAP sensor which has no issues ???) forget running under 12* BTDC at 8* it will run for about 15 seconds on its own. Im going to get a fuel PSI fitting on the way, possibly look into rebuilding the throttle body. I know what I would like to do with that, but thats for another discussion.
My question is this, According to Chiltons the Camshaft position sensor if it goes bad, the truck will continue to run, mine will not if I unplug it. I only did this thinking this is the lil item that needs to be unplugged to check timing without the puter doing the work???? Chiltons manual is VERY vague about this. >:( So how do I really check the timing like its supposed to be done?
SO, now what? Im thinking the timing chain is jumped? Im having a VERY hard time with this thing as it ran exactly like it does now with a detroyed distributor, now with a new one its the same, plus I think it went in a tooth retarded, but I think I did get it right after turning the oil pump. These things are all compounded in my thought process so I am having a hard time diagnosing it.
What would you do? Pull the motor and start from scratch?
I THINK the better route would be to pull the motor and just throw all new gaskets at it, and degree the cam and replace the timing chain, and toss a nice truck cam at it, and get the valves properly adjusted. But thats just me, plus I dunno if my stand will handle the 454 fully assembled.
What would YOU do???
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I doubt it's your timing chain jumped.
Time it correctly. Did you put the EST in bypass mode? Tan wire with the black tracer needs to be disconnected. If it's a 454 it's near the distributor taped to the harness. With the EST in bypass set the timing to 4° BTDC
Once you do this and lock the distributor down, shut it off and reconnect the the bypass wire. Then clear the DTC you set by disconnecting the battery.
Once you do this then report on how it behaves with any symptoms that come back.
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Hmmm, tan wire with a black tracer...... I'll go out n have a looksie right now, I gotta go on a road trip for a day or 2. (yeppy, back to VT, canada border again.) Its a PITA for me to get back in there to look around, between the A/C and my belly..... :o
Thanks for the tip. I will report back soon.
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I can not find any wire any where thats on or in that loom. The only wire I can find thats taped to anything near there is the Tach lead off the coil, and pair of wires (one tan or white and one black) that come out of the loom and bolt to the back of the passenger side head which serve as a ground? It may be there but I just can not get to it, there are so many wires and vacuum lines on this thing. Should it really be this difficult to locate this darn wire?
Every darn wire on this thing thats supposed to be white or tan are all tan with black on em lol
Is there anywhere that have a picture of it or am i going to be stuck with pulling the distributor again just to locate it?
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It will be taped to the outside of the conduit with a black connector.
Look toward the bulkhead connector to the left of and below the wiper motor
(http://i6.photobucket.com/albums/y228/Sabaka454/c133.gif)
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OHHHHH! Its down there! I have been looking by the distributor!!! THANK YOU!
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OK, timing checked and set. No change. The computer is adjusting the timing for sure when its not in bypass. Were pointing the finger at the throttle body now, SO, im going to go ahead and get a TBI rebuild kit from Advance or NAPA tomorrow and see what happens. Also getting the pressure check fitting for the throttle body on the way as well.
Oh, what is the stock PSI rating SUPPOSED to be pre throttle body? I think I remember seeing it somewhere being 15 PSI?
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12-18 before the regulator. Make sure you get the WHOLE kit for the TBI. Gaskets and the regulator pieces, they have a kit that has it all....
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Key on engine off fuel pressure should be 9-13 psi. Did you check the engine coolant temp sensor?
Resistance 185 ohms at 210 deg F
450 ohms at 160 deg F
1800 ohms at 100 deg F
3400 ohms at 70 deg F
7500 ohms at 40 deg F
13500 ohms at 20 deg F
25000 ohms at 0 deg F
100700 ohms at -40 deg F
When the coolant temperature is low, the sensor produces a high resistance. When the coolant temperature is high, the sensor produces a low resistance
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Im going out to tinker with it some more today. No I havent checked that yet, i will today and report back, n finally get that video of what its doing like i said id do.
I have rebuilt the fuel pressure regulator, just for grins, I figured it probably hasent ever been done. I did take the whole Tbody off and clean the heck out of it, it wasent really bad at all. Put new base gasket on, regulator and associated gaskets. Im going to put on the new injector pigtails today as well. I may run a compression test as well, I usually do that the first time i pull plugs but havent yet.
I have been running "Seafoam" fuel treatment to give the system a good cleaning, plus ran some straight through the Tbody like it said to do. To date, with the tinkering ive done its ate 6-7 gallons of 93 just in my driveway! ( I only run decent fuel, no crap gas in my gas burners )
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87 vs 93 isn't crap gas. You are actually going to get worse mileage and performance out of 93 than out of 87 in your truck. 93 is less combustible at lower temperatures and is designed for higher compression ratio engines. If you don't have the benefits of a higher compression ratio you will see no benefits from higher octane fuel. Odds are you are not creating as much cylinder pressure as you would with 87 and are not completely burning all of the 93 in combustion plus you are paying more per gallon of gasoline. Unfortunately gas companies lead you to believe otherwise by labeling fuel pumps, "regular - mid grade - and premium" which is false advertisement in a way.
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Ditto on what Vile said on the octane. Think of it this way. If you put your gasoline on a scale from highly flamable to water, 93 would be on the water end and 87 would be the highly flamable end. Not only will it get more mileage, the engine will make more power, this has been proven several times.
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ARGH! so I got my fuel pressure gauge fitting deal for the truck, tried installing. No go. I bought one from xtremefi on fleabay for the back of the throttle body, I cant mount the giggered thing!! I have to modify and re flair my supply line to clear the stupid distributor and coil. Will it mount back at the fuel filter?? I would try it, but I have welding class in an hour, and after that im going out of town again till late tomorrow night. I did get a video of what the truck is doing BTW and will get that posted thursday.
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Just tee in at the filter. You shouldn't need any special gadget other than your TBI fuel pressure gauge. Autozone sells them for like $15- $20 bucks
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What does it look like? The one from autozone is what I have. it just tees into the line at the filter.
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;DBINGO! ;D
Fuel pressure! Fortunatly for me I didnt go to VT last night 8)
So today I put my lil valve in at the filter. I discovered 2 maybe 3 PSI. Then discovered some tard has cobble jobbed my fuel system. It goes like this, from the driver tank (passenger tank in the bed right now) about 6 inches before the switcher valve someone put in a stupid lil clear plastic filter, and completly bypassed the switcher, except for the electronic portion of it, then onto the factory system with the stock filter. AND NEVER changed the additional filter after it was put in. ::)
I removed the plastic POS and ran the lines BACK into the switcher, so now its factory again. The switcher works by the way (moron!) and now have 5PSI pre filter. With that 2-3 psi jump the truck WANTS to run again!!!!
So, now when I get paid I will be putting in a new fuel pump.
here is a link to the lil valve I bought BTW (if u by this, it will NOT work on the back of the t-body w/o modification, it will screw directly into the stock filter)
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEBTOX:IT&item=260187275488&_trksid=p3984.cTODAY.m238.lVI
OH quick question, Bosch has an upgraded "turbine" pump, is it worth the extra couple bucks, and 26PSI? (that might come in handy later down the road) plus, do I REALLY NEED a strainer??
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Yes you need a pump and strainer. 26 PSI is too much. 9-13 PSI for TBI
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ITS ALIVE! ITS ALIVE!! New pump installed, engine runs GREAT!! Thank you to everyone who helped, and big thanks to Vile and Capt.!!! You guys are awesome! ;D
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The part you linked is the same one that you can get from Autozone. You will never get it hooked up to the back of the TBI...
The one I linked and posted a pic of is designed to replace one of the TBI fittings and the gauge screws into it permanently.
It was in this Post BTW (page 1): http://forum.73-87chevytrucks.com/smforum/index.php?topic=7421.msg45202#msg45202