GM 350 TBI Help

[64osby]

I have had a check engine light on my 1992 Caprice pop on every couple weeks for several months. It would only come on when driving about 60 for more than 5 miles. Finally decided to see what might be going on. It has high a high idle for months and the mpg is lower than it should be averages about 18.

Read the codes with a paper clip. Code 32 - Haynes says check vacuum source and lines, check EGR and PMC.

Pulled off the air intake and saw the vacuum line to the EGR was off. Slipped it back on, the EGR valve opened (diaphragm pulls away from motor) and the engine began to stumble and either barely runs or it stalls. Pulled hose back off and engine smooths out and goes to a high idle.

The existing EGR vacuum solenoid is allowing full vacuum at idle. I have an old solenoid and used it to replace the one on the engine. No vacuum is noticed at idle and the engine idles down and runs smooth. It also looks like the EGR valve doesn't move at any speed with this replacement solenoid. Both solenoids test zero ohms.

Did a 2 mile test drive with the old solenoid and all seemed good. Ran some errands drove about 40 miles. About half way during the trip the engine started to stumble when letting off the gas at low speeds but would then recover. Between 50mph and 75mph I notice a small amount of surging. No codes popped up.

I checked the codes that were stored from when I was messing with the motor yesterday, 23 low Intake air temp, 32 EGR Failure and 43 ECS module not receiving a knock signal.

Looking to see if anyone might be able to help this hack of a shadetree figure out how the EGR is supposed to function (vac or no vac at idle) Which solenoid should be used, existing or the replacement old one and/or where to go next.

I have a spare vehicle and lots of duplicate parts, PCM, and many sensors that may or may not be good. I'm willing to exchange them in an attempt to get this running smooth just don't know what direction I should go from here.

 

[matt167]

Re: GM 350 TBI Help

I would use a known good part as a test. Plenty of aftermarkets produce out of spec readings.. As far as the EGR Vac/ no vac at idle. I don't know, but you should be able to check the vac routing diagram and just make sure it's right. No vac at idle sounds right.. Just change the knock/ IAT sensors also, and reset your codes.

 

[DECK SWABBER 58]

Re: GM 350 TBI Help

NO egr vacumn at idle.

 

[stackz]

Re: GM 350 TBI Help

pull the spare tbi manifold off your other car and get in there with a couple long skinny screwdrivers and get all the built up carbon out, use brake parts cleaner liberally as well. blow it out with air (I believe I remember the egr passages on the intakes on these engines?) if its somewhere else...clean those passages out instead.

swap over to your car and see how it does. sounds like the egr passages themselves are clogged up so even if the valve/solenoid is good, its not able to pass air properly causing the ecu to freak out.

also, low intake air temp is most likely your ACT (if equipped) or IAT sensor.

 

[64osby]

Re: GM 350 TBI Help

I messed with a few things and have done lots of reading online.

I changed the IAT and cleaned the IAC value. Switched back to the original EGR solenoid, disconnected the line to the EGR and plugged it. Engine idles down and runs without stumbling.

Haven't seen an ACT in all the forums or my Haynes. ???

Ordered a new EGR solenoid and will wait to see what if any good comes from changing it out.

Can't find any vacuum leaks, hoses, TBI or manifold. and don't want to pop off the manifold until I look at a few other options.

Looking at the Chevy forums there is a ton of info out there, it's just a matter of wading through the info and testing asI go.

Thanks for the input so far.

 

[RogersJetboat454]

Re: GM 350 TBI Help

I messed with a few things and have done lots of reading online.

I changed the IAT and cleaned the IAC value. Switched back to the original EGR solenoid, disconnected the line to the EGR and plugged it. Engine idles down and runs without stumbling.

Haven't seen an ACT in all the forums or my Haynes. ???

Ordered a new EGR solenoid and will wait to see what if any good comes from changing it out.

Can't find any vacuum leaks, hoses, TBI or manifold. and don't want to pop off the manifold until I look at a few other options.

Looking at the Chevy forums there is a ton of info out there, it's just a matter of wading through the info and testing asI go.

Thanks for the input so far.

See what replacing the solenoid does for you...
With the engine stumbling/stalling when vacuum is applied to the valve, you know the EGR passages are clear.

Another thing to keep in mind, GM EGR valves from that era get weak. The springs that hold the diaphragm closed will soften up, and allow exhaust gas pressure to push the valve open. If the solenoid does not do the trick, that may be another avenue to look into.

If you determine you need a valve, get the correct valve for the vehicle. The valve should have a number on it that you match. If your new valve comes with little washers with various sized openings to match to that number, that valve is a joke, and should be returned. You should be using one thats a direct-fit out of the box.

One other thing to keep in mind is how the vehicle determines EGR opening. It's done through the MAP sensor detecting a drop in manifold vacuum when the valve opens. If the MAP sensor is coked up with carbon, it may not be sensitive enough to detect valve opening, and would also not be doing so great determining fuel mixture.

Good luck!

 

[64osby]

Re: GM 350 TBI Help

RJ - Thanks for looking in.

I've read plenty on the EGR and getting the exact match. Mine seems pretty good as it takes a lot of pressure to move it with my fingers and it moves if I hook up the vac line to it.

I did exchange my PCM but there was no change in anything.

Just waiting on the solenoid at this point.:bored:

 

[coreybv]

Re: GM 350 TBI Help

These symptoms, including the codes you're getting, sound almost identical to a problem I had with a similar era GM vehicle. Turned out to be the mass airflow sensor. Cleaning it with carb cleaner would get it going for a month or so. At the time it was an $80 part and took less than 5 minutes to replace.

If the solenoid doesn't solve your problem, that's the next thing I'd look into.

 

[64osby]

Re: GM 350 TBI Help

Well I had a box with a smile on it come to the house today.

Took a few minutes from cutting, splitting and stacking wood to install the new ERG solenoid.

Now I'm smiling.

Seems to have done the trick, so far. I'll probably recheck the timing but it ran great with all the hoses hooked up, no codes popping up... yet. I'd like to say I'm smart getting this fixed on the first shot, but I think lucky is a better call.:bounce:

 

[DECK SWABBER 58]

Re: GM 350 TBI Help

Isn't it a great feeling to actually fix something rather then break it ?

Don't ask me how I know. :facepalm: :lol:

 

[64osby]

Re: GM 350 TBI Help

Yes it is, done the other many, many, many times.

It's getting better though, now i'm fixing the same stuff over again, because I've owned it sooooooo long

 

[RogersJetboat454]

Re: GM 350 TBI Help

These symptoms, including the codes you're getting, sound almost identical to a problem I had with a similar era GM vehicle. Turned out to be the mass airflow sensor. Cleaning it with carb cleaner would get it going for a month or so. At the time it was an $80 part and took less than 5 minutes to replace.

If the solenoid doesn't solve your problem, that's the next thing I'd look into.

No MAF on a TBI vehicle. TBI uses speed density VIA feedback from the MAP and O2 sensor.
Also, should refrain from using carb clean on a MAF sensor. Carb cleaner leaves a film behind to lubricate the moving parts of carbs and throttle bodies. Any kind of contamination on the hot wires of a MAF is a bad thing. Best thing for cleaning a MAF is; MAF cleaner. No residue, and dries instantly.

 

[RogersJetboat454]

Re: GM 350 TBI Help

Well I had a box with a smile on it come to the house today.

Took a few minutes from cutting, splitting and stacking wood to install the new ERG solenoid.

Now I'm smiling.

Seems to have done the trick, so far. I'll probably recheck the timing but it ran great with all the hoses hooked up, no codes popping up... yet. I'd like to say I'm smart getting this fixed on the first shot, but I think lucky is a better call.:bounce:

Sounds good... Cross your fingers.

 

[64osby]

Re: GM 350 TBI Help

Update... while taking the old Caprice on a 200 mile drive it started acting up. A CEL flashed on for a couple minutes and then went off. Threw a code 32. About half way on the trip it started to surge or hesitate at just above idle and at 50 to 60 mph.

Did a bunch more reading and decided to trade out the ERG valve. I don't know if the valve itself is bad but the gasket sure was weak, replaced it with a new one.

Test run today and all seems good, so far. No hesitation just above idle or surging while cruising.

Time will tell and also looking to see if the MPG picks up where it should be.

 

[RogersJetboat454]

Re: GM 350 TBI Help

Update... while taking the old Caprice on a 200 mile drive it started acting up. A CEL flashed on for a couple minutes and then went off. Threw a code 32. About half way on the trip it started to surge or hesitate at just above idle and at 50 to 60 mph.

Did a bunch more reading and decided to trade out the ERG valve. I don't know if the valve itself is bad but the gasket sure was weak, replaced it with a new one.

Test run today and all seems good, so far. No hesitation just above idle or surging while cruising.

Time will tell and also looking to see if the MPG picks up where it should be.

See what it does...
If things are still acting funny, remember what I told ya. The MAP sensor is critical for both fuel trim calculation, and measuring EGR performance.

Might be worth it for you to at least pop it off, and look in the vacuum tube (on the sensor). Sometimes you find them nice and packed with oily carbon.