poor running 454 TBI

[Cowboy_Customs]

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.

 

[Captkaos]

Sounds like what my Burb was doing...  Check your fuel pressure.  You can clamp the return off and see if it makes a difference.

[VileZambonie]

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.

[joesgarage71]

 #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.

[Cowboy_Customs]

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!

[Captkaos]

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.

[Cowboy_Customs]

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

[Captkaos]

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...

[VileZambonie]

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?

[Cowboy_Customs]

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.

[VileZambonie]

Did you check the engine coolant temp sensor?

[Cowboy_Customs]

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.

[Captkaos]

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/cfmtechfuelpsiguageadaptorforgmtbi2843505774.aspx

[VileZambonie]

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.

[Cowboy_Customs]

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???