95 Tahoe sooty plugs wont start now many new parts

[borninabarn]

I have a 95 tahoe 350 TBI 240,000 miles started running like it was being choked out bogging down no power black smoke from exaust.Had a fuel pump installed last year still has correct fuel pressure,new plugs,new wires.new temp sensor,new tps sensor,new iac valve,new dist module,o2 sensor,good egr valve was tested,have switched out distributors with a know good one,also switched coil with a good one.have good spark.new plugs are all sooted up after only running 15 minutes when it was running.Has 120 plus compression on all cylinders.any ideas on this mind boggler guys?maybe a timing chain?What would you check next?Thanks born

[borninabarn]

not the timing chain either any of you heard of problems with the ecms on these there are no codes help thanks

[2000CAYukon]

How is the injector spray pattern? Has the TBI been rebuilt? The fuel pressure regulator diaphram may be worn causing extra fuel to be dumped into the intake.

I know you replaced the temp sensor (the one in the intake) but does the engine get up to operating temp (195). If you installed a lower temp tstat, it can cause the ECM to stay in open loop and it will use too much fuel.

Check the vacuum at the MAP sensor. If the port is clogged, the MAP will think the engine is under load and add more fuel. At idle, you should have 18-20 HG.

Before you swap out the ecm, you should really hook up a scan tool (or winaldl) and see what it is doing.

//2000CAYukon

[borninabarn]

95 Tahoe running better, but still too rich or seems to be. Seems to idle ok but then PCM starts taking fuel away and when the integreter gets to 109 it starts surging and will shut down injectors. Thats when its warm - it really loads up cold. Have tried different O2 sensor,dist,pcm,coolant sensor,egr valve,pressure reg,coil, have taken off timing cover and checked cam gears.
I'm out of ideas,please help!

[maxwedge]

Originally Posted by borninabarn

95 Tahoe running better, but still too rich or seems to be. Seems to idle ok but then PCM starts taking fuel away and when the integreter gets to 109 it starts surging and will shut down injectors. Thats when its warm - it really loads up cold. Have tried different O2 sensor,dist,pcm,coolant sensor,egr valve,pressure reg,coil, have taken off timing cover and checked cam gears.
I'm out of ideas,please help!

Parts replacement won't fix this, diagnostics will, check fuel pressure, get a full function scanner on it and check coolant temp reading cold and hot, look at sensor inputs, obviously the pcm is trying to pull fuel out as the it senses the rich mixture. Check engine vacuum, a restricted cat can cause low vacuum and a rich mixture. TBI engine? if so look for an injector dumping fuel.

[MT-2500]

Originally Posted by borninabarn

95 Tahoe running better, but still too rich or seems to be. Seems to idle ok but then PCM starts taking fuel away and when the integreter gets to 109 it starts surging and will shut down injectors. Thats when its warm - it really loads up cold. Have tried different O2 sensor,dist,pcm,coolant sensor,egr valve,pressure reg,coil, have taken off timing cover and checked cam gears.
I'm out of ideas,please help!

Also one little overlooked thing is the ground wires on the thermostat housing.
Make sure they are hooked up and making good ground.
MT

[borninabarn]

I've been a ASE master tech with L1 for 20 years. I don't need the lecture on parts replacement. I've worn out a scan tool on this thing. Everything looks good on scan but the O2 sensor rich. Good fuel pressure and back pressure. I've cleaned every ground. I've changed parts off a known good truck to try to find something that may be checking good but isn't. Just looking for something odd that might have happened to someone else doing the same thing.

[MT-2500]

Originally Posted by borninabarn

I've been a ASE master tech with L1 for 20 years. I don't need the lecture on parts replacement. I've worn out a scan tool on this thing. Everything looks good on scan but the O2 sensor rich. Good fuel pressure and back pressure. I've cleaned every ground. I've changed parts off a known good truck to try to find something that may be checking good but isn't. Just looking for something odd that might have happened to someone else doing the same thing.

So You have been a ASE master tech with L1 for 20 years
That puts you still in diapers when Maxwedge and me was fixing cars.
Better listen to the old pros most of them have been there and done that.
Good luck
MT

[horse482]

Like 2000CAYukon said, it is probably either the fuel pressure regulator or the injectors causing problems.

[borninabarn]

Hello friends this is borninabarn.Im logged in to this forum at the the shop.I have been letting our tech here use this site to figure out this tahoe.It is just a brainteaser.He did put a new gm fuel pressure regulator on this thing.Seems to keep running the same.Throttle body all cleaned out(was pretty gunky but still is acting up)something is telling the computor to cut the fuel down when it hits 125 runs fine for a few minutes then down hill from there.Could the exaust being plugged cause this thing to react like it is?Will try that next i guess?no offense to any of you techs out there i use this site alot at work to help me fix some of these odd ball problems!Thanks Kurt

[MT-2500]

Originally Posted by borninabarn

Hello friends this is borninabarn.Im logged in to this forum at the the shop.I have been letting our tech here use this site to figure out this tahoe.It is just a brainteaser.He did put a new gm fuel pressure regulator on this thing.Seems to keep running the same.Throttle body all cleaned out(was pretty gunky but still is acting up)something is telling the computor to cut the fuel down when it hits 125 runs fine for a few minutes then down hill from there.Could the exaust being plugged cause this thing to react like it is?Will try that next i guess?no offense to any of you techs out there i use this site alot at work to help me fix some of these odd ball problems!Thanks Kurt

That would be one thing to check. A good vacume gauge will show a pluged exhaust system check vacume at idle and at about 2500 rpm
Here is some things I sure you and your tech are aware of but needs to be double check.
Also Maxwedge may know of some more things to help.
And as 2000CAYukon suggested check the vacume to the map sensor.
One thing to watch for is if a sensor goes bad the pcm will substitute a fixed value.
Double check and watch the engine tempt and air intake tempt sensor readings.
The charcoal canister is another thing to check out if it is flooded it will cause a rich run.
A bad wire or ground in the dist/ign system can throw off the rpm readings and throw it in a rich mode.
Make sure all 02 sensors have good up and down readings.
And check the prom in the pcm and pcm application. Sometimes they get switched/changed. And the old tap or twist on the pcm may show something.
Good luck and let us know how it goes.
MT

[borninabarn]

Thanks for your help on this one its fixed!Ended up being the ecm.Thanks again born!

[MT-2500]

Originally Posted by borninabarn

Thanks for your help on this one its fixed!Ended up being the ecm.Thanks again born!

You are welcome and.
Thanks for posting back with the fix.
Just wondering? How you found it?
Did the old twist or tap show it bad or did you just have to change it to find it?
Glad you got it going and all is well.
MT

[borninabarn]

Tapping on it didnt change much.Just switching them out solved the problem.Thanks again guys!!!!