Another TBI running rich

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thinger2

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I just went through similar drama with my truck. In the end it ended up being a rolled and split o-ring on 1 injector. The split o-ring leaked a little at idle and blocked 50% of fuel feed at load. I replaced just about every sensor and the fuel pump before I finally decided to pull the injectors in desperation. The spray patern looked good in the shop, but on the road it didn't run quite right.

It would start and die 3 times before it would hold an idle. I would put my foot in it and it would run like crap for 10 seconds then idle fine. After getting it going it would miss until it warmed up and then run mostly okay.
Yep, That happens alot during tbi rebuilds. thats a pretty good tip.
 

opus

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I bought a bunch of tbi stuff from a guy who was going out of business.
Got it all dirt cheap and threw it on cuz why not?
Ended up with the same damn problem and its all NOS GM delco delphi
Deffinetly temperature related.
First thing, set your timing back to 0 tdc with the engine warm and the dist reference wire diconnected.
A stock GM TBI will never work right unless its at 0
When you get timing set and reconnected.
Run it for a while before you reset the idle air control.
It will run like crap but thats part on the relearn.
Make sure the pintle on the IAC is pushed in before you screw it back in.
You didnt mention if youve rebuilt the throttle body.
The passage behind the IAC gets plugged full of carbon and so does the EGR system.
Look for throttle shaft wear on the linkage side of the TBI. Really common problem. Try to wiggle it around. it shouldnt move.
A worn throttle shaft is a vacuum leak.
I spent about a week and 60 bucks on beer trying to find the "one thing" that caused the problem.
Turns out, it was about ten things that added up beyond what the computer could compensate for.
You already spent the money brother, Maybe all you need now is the beer.
Good Luck, hope it helps

Tb is tight. No shaft play or carbon build up. Done the IAC relearn a bunch of times and replaced it too. Will do timing tomorrow.
 

thinger2

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Tb is tight. No shaft play or carbon build up. Done the IAC relearn a bunch of times and replaced it too. Will do timing tomorrow.
Cool. it really made a difference on mine once I set the timing hot and let it relearn before I reset the IAC.
Let me me know if that works. That would be awesome info for everybody
 

Schurkey

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I have looked at the data stream.
I don't know how clues to this could NOT be shown in the data stream.

The problem happens with great regularity. There's got to be SOMETHING in the data stream to show problem origin.
Commanded idle speed vs. actual idle speed
O2 voltage and/or O2 crosscounts
Open vs. Closed loop operation--or the transition between them
TPS voltage signal appropriate to the throttle position? Doesn't "drop out" with throttle motion or other influence?
Intake air temp sensor (if equipped) providing reasonable data?
TCC operation? Not trying to apply the converter clutch, stalling the engine?

Actually, when its 40 or so, it barely will start because its in "that mode". Which makes me think it is strictly temperature related.
Engine still has a properly-operating thermostat of correct temperature rating?

Of course, you've checked that the computer is showing appropriate temperature before the engine starts...right?

The heated-air intake is intact and functional? No throttle icing?

Correct "special" TBI intake manifold gaskets, having the very-restricted coolant passage? Forces coolant flow under the fuel/air passages so the manifold warms evenly? Coolant flow through the heater core is still functional?

AIR system (if your engine has this) diverts to the air cleaner during "closed-loop" operations?
 
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Redneckgeriatric

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i would double check ect, and do some serious wiggle testing between it and the firewall if ect tests good. its quick and easy, and will eliminate that area of diagnostics so you can get back to the expertise of mr. playingwithtbi and evilunclegrimace. they are well versed with the tuning wares.
 

evilunclegrimace

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Try and force a check engine light. Remove the ECT sensor plug or the TPS plug and see if the ECM will recognize a fault code.
 

evilunclegrimace

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Sorry, its been a while. It does what its supposed to do. Isnt it supposed to run when its fully seated? A set amount of air is allowed through, if I recall correctly. Wither way, I recalibrated it a few times, then replaced it....for giggles.

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You still have not answered the question. Does the truck idle with the IAC pintel fully extended and unplugged?This is a test to see if the base idle is set correctly. It eliminates the computers control over the idle speed.
 

opus

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You still have not answered the question. Does the truck idle with the IAC pintel fully extended and unplugged?This is a test to see if the base idle is set correctly. It eliminates the computers control over the idle speed.

The base idle is set correctly. I drilled the hole and checked/reset and calibrated the TBI multiple times. Like I said above, its been about a year since I have fiddled with it. I did the whole IAC check thing and it turned out that it was working properly. It was fully seated and I adjusted the idle speed. TPS voltage is correct by testing as I was told to test it.

I can sure enough do the IAC thing again this coming week.

I've wiggled every wire multiple times. If it was a o-ring or a bad connection, it wouldnt happen so perfectly everytime, it would be more of a constant issue, not just a 40 second issue.

CEL works properly as well. However, this never throws a code.

Correct thermostat, multiple CTS too. I still dont know what the "ECT" is, that was mentioned above. There is no air intake sensor or heated anything.

I thought it might be staying in open loop too long but according to someone that can read the logs, this isnt the case.

It cant be coolant temp related because by the time the coolant rises a degree, its all done and over with. Yes, the temp the logs state is the correct ambient temperature outside.

Not trying to be difficult and I appreciate your input but for 3 years I've been dealing with this and everyone is stumped. It cant be this difficult.
 

mike73

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I don't really know as much about this as the others, but I'll throw out some ideas:

-Check with a vacuum gage while running. I don't remember a lot of details, but you can tell a lot about engine health by how the needle moves- I would do a thorough test for vacuum leaks as they are common on these engines. As they tell people in medical school- an uncommon manifestation of a common problem is more likely than a common manifestation of an uncommon problem. If you hear hoofbeats, think horses, not zebras.

-You said it was rich, but I didn't see black smoke in your video or any significant amount of soot on the exhaust pipe. Can you smell raw fuel (either rich or poor atomization), or can you smell NOx (raw no-cat exhaust smell- somewhat normal on cold starts since cat is less effective cold, but an excessive amount of it, especially while running hot, might suggest a lean condition)?

A vacuum leak would probably be a lean condition, but weird stuff might happen when the computer tries to compensate for it (surging, sputtering, etc.). Vacuum leaks could come from a lot of places- intake gaskets, brake booster, hoses, etc. and electric/vacuum devices like EGR valves
 
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