Most puzzling (and wastefully expensive) car problem ever.

[dragon.breath 10+ year member]

replace the coolant temperature sensor. when they go bad they start reading colder. the ecm 'thinks' its 30 degrees below 0 when its really 60 degrees .the ecm then goes into 'cold start' mode and runs full rich.

 

[tommyk90 5,000+ posts]

replace the coolant temperature sensor. when they go bad they start reading colder. the ecm 'thinks' its 30 degrees below 0 when its really 60 degrees .the ecm then goes into 'cold start' mode and runs full rich.

I've already done this too. lol.

The one in the intake and the one on the passenger side of the block. I will say that my temp gauge was reading low until I switched those out. But something else is still screwed up somewhere.

 

[dB-r 10+ year member]

I have owned at least 6 of these TBI motor trucks. They are EASY.

The most common problem with ALL of them is this:

1. Bad EGR Valve. The spring gets weak the valve opens just off idle, causes stalling. Way to find out if yours is a problem, simple, unplug the vacuum hose from the EGR valve and loop it back to the extra "teat" on the nearby control solenoid (or just plug the line off to prevent vacuum leaks) If problems go away, just buy a new EGR valve, install it, done, fixed.

2. Blocked passages on bottom of TBI unit. Take it off the motor, look underneath it "YUCK!" Clean all those little passages, carb cleaner, small screwdriver, whatever you can use to get that clean like new, (I sandblasted mine, no shiz...) you would be amazed at how gunked up the bottom of that TBI unit gets and causes, the IAC and the PCV valve not to to work right and throws everything for a loop. Causes uneven idle speeds, to the point that the engine won't idle eventually. 1 way to check the severity of this problem, is while the engine is running, pull the PCV valve out of the valve cover, put your finger over the bottom of the PCV valve, there should be a (moderately strong) pulsating suction going on with the little metal valve inside the PCV valve itself, if it aint doing nothing, try replacing the PCV valve first with a new one, check the hose for leaks or replace hose and PCV Valve, if still nothing, PCV port on bottom of throttle body is completely clogged/blocked off with oily gunk. Remove throttle body and clean thoroughly all passages on bottom of TBI unit.

3. Stopped up Catalytic converter. This is inevitable. Replace it. Causes low power at higher RPMs, and you can actually feel a DROP in power as you give it more gas, i.e. when you are accellerating hard and you push past 1/4 throttle, and you feel the engine actually make less power till you raise back up off the accellerator back to 1/4 throttle, stopped up cat!

4. Ignition Module. The ignition module, may work seemingly FINE, however take it an autoparts store and let them test it on the machine, likely it will fail a couple of the tests, also will likely be VERY hot (overheating module) after testing, should not be that hot, if really hot, and/or fails any 1 out of 5 test runs on the machine, replace it.

5. CTS (coolant temperature sensor) causes the ECM to dump massive amounts of fuel into the engine in attempt to start it up. Engine will not start, smells of gas, really really bad when attempted. Replace sensor.

 

[tommyk90 5,000+ posts]

4. Ignition Module. The ignition module, may work seemingly FINE, however take it an autoparts store and let them test it on the machine, likely it will fail a couple of the tests, also will likely be VERY hot (overheating module) after testing, should not be that hot, if really hot, and/or fails any 1 out of 5 test runs on the machine, replace it.

Where can I locate the ignition module? This is one thing I haven't checked on my truck yet. I don't think its the catalytic converter since I don't have necessarily a loss in power, but I'm pretty sure I have a misfire of some sort.

 

[dB-r 10+ year member]

I think it's in the bottom of the distributor like the old schools. Take the cap off, look under the rotor. Been a while, haven't owned one of these trucks for years now, my 2004 has been top-notch, 90,000 miles, never had to turn a wrench on it!

 

[#45 10+ year member]

Where can I locate the ignition module? This is one thing I haven't checked on my truck yet. I don't think its the catalytic converter since I don't have necessarily a loss in power, but I'm pretty sure I have a misfire of some sort.

it won't always cause a loss in power, depends i think

problems you listed as #1,2 and 6 is what we had wrong with a couple of our work trucks, swapped em out and they were fine. Might be worth at least having it checked, ya never know seeing as you have done so much already.

 

[Liquid Bass 10+ year member]

What happened to the denali???

 

[cotjones 10+ year member]

well today i rebuilt the entire TBI unit, including replacing the fuel pressure regulator. AND.....

NOTHING! no change. Pics coming... also just bought a donut for the exhaust so I can fix that and go tell the dealership to give me my gaddam 300$ back for telling me nothing and costing me another 400 bucks in unneeded repairs (who says i didn't have a mechanic do the work)? lol

 

[cotjones 10+ year member]

Dude I Can't freaking get to the bolts to replace the doughnut between the pipe and manifold, the sucker is froze solid and there doesn't seem to be a way to turn a wrench in there, I'm not sure how the he'll I'll get to these freaking bolts. I may be able to reach one from the bottom with a really long extent ion but the other one right next to the steering Shaft has not easy angle of attack and I don't see any easily removable parts to get to it... Arrrrrog this is driving me nuts

 

[dB-r 10+ year member]

That's what I used on them a couple extensions till it clears enough to turn the ratchet. Soak the bolts overnight with PB Blaster, that will make them come loose like gravy.

 

[audioatg 10+ year member]

That's what I used on them a couple extensions till it clears enough to turn the ratchet. Soak the bolts overnight with PB Blaster, that will make them come loose like gravy.

O god. I wish it was always that simple.

 

---------- Post added at 05:54 PM ---------- Previous post was at 05:53 PM ----------

 

Not sure. But have you checked fuel pressure yet.

 

[cotjones 10+ year member]

That's what I used on them a couple extensions till it clears enough to turn the ratchet. Soak the bolts overnight with PB Blaster, that will make them come loose like gravy.

Good call on the PB blaster, that is some serious stuff. Got them lose and i'm noticing a few things. #1 there was no gasket on the exhaust manifold, #2 the doughnut was indeed shot. #3 the pipe and manifold don't line up perfectly, and #4 they are supposed to be connected by spring bolts and someone had put regular bolts on them, probably the reason the doughnuts have had a tendency to go bad, cause there is not enough tension to seal the pipe.

 

[cotjones 10+ year member]

Potentially awesome update...

Took it to a freind who repairs all the ground equipment here at the airport, and he opened the aircleaner and said the same thing i did, "Looks like its dumping way to much fuel." then he wanted to test fuel pressure. Low and behold, we could never get the fuel pressure above 5 psi. in fact very often, it appeared to lack pressure completely. Apparently, it looks like it's dumping too much fuel because its not atomizing enough and it's basically dripping out, causing the misfiring and spotty performance.

The only thing i'm confused about, it that it runs at all... seems like such a lack of pressure would have it not running at all, but i'm looking for someone to get a second opinion. Trying to keep it cheap, i'm low on the monies. autozone doesn't do Pressure tests free do they?

 

[audioatg 10+ year member]

O god. I wish it was always that simple. 

---------- Post added at 05:54 PM ---------- Previous post was at 05:53 PM ----------

 

Not sure. But have you checked fuel pressure yet.

Sooo you didnt check fuel pressure. JK.

You can buy your own kit from harbor freight. Im sure that is a hard line into the TBI there. So you will have to T into it. Its not that hard.

 

[VWBobby 10+ year member]

Good tip on the HF pressure gauge. I have the kit and its good for the money.

Carbureted engines only use 2-8 PSI for delivery, having less than 5 PSI is plenty to dribble-drop-run the engine using the injector as a main jet. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

GM failure problems.... Ignition pack/coil or trigger depending on year. Fuel pumps, regulators, and related sensors. MAF and MAP sensors, depending on application. ALL other sensors. Cooling system, mostly water pumps and drive couplers. I can't stand GM cars. My parents have owned close to 50 of them and I'm tired of working on them. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif