It's not an F body, but I'm told this is THE place for TBI help.

92 Chevy pickup, 203K on the clock.
I bought not running, new fuel pump and it was good to go... or so I thought.

It began randomly stalling when driving around at light throttle for extended periods. The transmission went out the next day, so it was out of commission for about a month.
Last week I got a used tranny put in.

I had been told to check 2 things- EGR and MAP sensor.
Unplugged and blocked EGR vac hose, ran fine 2 days then began dying on me. I swapped MAP with a known good one, again seemed fine, even idled better, sure enough she began dying the other day.

It's been down for a few days because of a broken CV axle, hoping to get that wrapped up tomorrow.

-What it does-
Besides burning a LOT of oil (I'm going to replace PVC and see what it does), exhaust smells VERY rich and faint black smoke at idle and fairly decent black smoke under throttle. I was noticing a slight surging the other day, then when taking off from a stop at around 1200 RPM it cuts out, not just a miss, but totally dying, sometimes coughs, comes back up to 1K ish, then either finally running for a few seconds or completely dying.

I also replaced 1 injector, and verified the other does not leak. Truck has no cat.
The SES comes and goes, it was on most of the day, but went off about 10 min before the truck started dying.

I kind of thing it's the fuel pressure regulator, but its only a guess. It really acts as though there is no gas. The issue doesnt seem to show up until its been warmed up and ran at least 20-30 minutes.

The temp sender is also a suspected culprit of running rich, but wouldn't cause the stalling.

 

check your O2 sensor

 

If I unplug the O2 would the computer default to the point where it *should* run good (not rich)
I know that cant be causing my stalling though, I noticed today (got front end finished) it has a slight miss from 3200ish up then at about 4100 coughs really bad and doesn't make any more power. Lower RPMs it seemed to run ok, might be lacking a little power though.

Does this sound like a fuel pressure regulator issue?

I ran codes, the only one I get is 32 (EGR). I'm assuming that's because I unplugged it, suspecting that as the problem before.

 

I replaced fuel pressure regulator (old 1 was rusty). My high RPM coughing is now gone.
Thought everything was all good.

Drove it to school (40 miles). About halfway home, what do you know, it starts surging and dying just like it has since the day I bought it.

A local mechanic told me to change the distributor with a different one. I did so, and now it has a slight miss most of the time, and lacks power below 2500 (but I just set timing by ear). I drove it around for a long time that night, seemed fine.

I drove it to school next day, and about halfway home, the problem came back
Starts bucking and gradually losing power until it wont hold overdrive any more.
After coasting through town and back on the highway press the gas, RPMs go up by about 500, coughs, almost dies, left off throttle, comes back, and repeat. If I flat out floor it it coughs then goes like hell, coughing a few times but catching itself after 1-200RPM.

I finally made it home, would sit and idle just fine. If I held the throttle open a little bit (maybe around 1200RPM) it would run for a few seconds then start coughing and die. The injector spray pattern stayed good throughout the time while it was dying.
I unplugged these sensors 1 at a time, and none fixed the problem
EGR
MAP
TPS
IAC
O2
Coolant Temp

It still runs rich, smoking black when its coughing.

The only other possibility I could think of was ECM. I swapped it with another one last night, exact same issue, I didn't even make it out of the driveway before it died.

I'm totally lost. At this point, I'm ready to buy another truck and junk this one. I found one that needs a tranny and just so happens mine is good.

I put a lot of work and money into this truck, what a waste

Any insight would be appreciated.

 

You'll have to establish a known baseline.

1) Verify that you are not loosing fuel pressure. Even though you have a new fuel pump it is common for low cost China made pumps to poop out after a short service period.

2) Reconnect EGR. Disconnecting EGR sets DTC code which may affect drivability.

3) Set timing Correctly - setting timing without a timing light is meaningless. On your truck timing should be 0 deg with EST connector open. If you give it couple degrees more it may run a touch better.

4) If you are not getting any codes (A+B of ALDL shorted and SES only blinks 12 12 12) swapping sensors is somewhat pointless.

5) If your truck is really burning oil O2 Sensor maybe coated too heavily with oil. O2 sensors are finicky creatures and do function well when exposed to oil, antifreeze or silicon fumes! A new heated O2 may provide a temporary relief, but long term you need to get oil out of exhaust stream. Sorry - can not help you there.

//RF

 

1) At the moment I don't have a fuel pressure gauge, but the injectors never seem to cut out and since its smoking black, I'm fairly certain it's not losing fuel pressure.
2) EGR has been reconnected for a while
3) I'll look into it, but I might pull a dist out of a running engine and swap it
4) I haven't swapped any sensors, just unplugged individually.
5) Seeing as how my oil consumption is so severe (about a quart every 100 miles) the engine is probly a lost cause anyway.

 

I dont know for sure if the truck I want to replace this one is coming up for sale, so I was messing with this the other day.

It has a steady miss, you can't hear it as good as you can see the engine shake.
It doesn't seem very responsive when you blip the throttle as compared to another TBI 350 we have. Driving seems like its lacking a little power.
The SES came on when it started running like **** so I got a paper clip and checked it out.
33- MAP out of range, high
34- MAP out of range, low
45- O2 rich exhaust (finally the computer realizes whats going on)

Although it hasn't made it run any better, this is still the ECM out of an 89 parts truck.

I have swapped the MAP before and it didn't make a bit of difference. What else could it be?

 

Hmmmm - it is strange for both 33 and 34 to be present. I would check base timing, with EST connector open just to make sure that timing is not way off. On a truck LO5 base timing is spec'd at 0 deg BTDC, bumping to 1-3 deg may help with throttle response.

The other possibility is a flaky vacuum hose between the MAP sensor and back side of TB.

//RF

 

I am having about the same issue you are having. Seems like I have checked EVERYTHING! I haven't replaced my distributor yet, or the EGR Valve, but I am going to pull the EGR this weekend and clean it up a bit to see if it helps.

I've replaced about everything, including new injectors and FPR, fuel pump and filter,
exhaust from the manifolds back, plugs, wires, cap, rotor, MAP, IAC, tested my TPS, replaced 02 sensor and CTS, reset my timing, checked the vacuum....
Let me know if you find a solution!

 

You guys have missed everything that you're looking for and you're making it too hard, but not your fault. I had an 87 GMC with a tbi 350. Same problem, same symtoms. REPLACE

 

You guys have missed everything that you're looking for and you're making it too hard, but not your fault. I had an 87 GMC with a tbi 350. Same problem, same symtoms. REPLACE THE DISTRIBUTOR!!!!! My original dizzy lasted 18 years, then the pick up coil failed, pretty good run. Two years go by, pick up coil dies again, every time bad miss, no power, dies after warm. I finally got mad, bought a new dizzy, and no problems since. If you have any more questions, PM me and I'll go more in depth.

 

Is the est the larger plug on the dist base?
I swapped vac hose to MAP because sometimes, the truck sounds like a has a huge vac leak, but I think it's just it sucking air through the TB because I can't find any vac leaks.

I'm going to switch the distributor again, since I don't remember the steady miss before. This time I'm taking one out of a known running truck.
I also am going to check the grounds going to thermostat housing.

If I unplug the MAP, it dies. It will restart but runs really bad and idles much better when plugged back in.

 

i just bought a 91 rs tbi 305 convertible,

i am having a very similar problem and i am pretty sure i know what is causing it.
problem: sudden full throttle kills the car, wheezes down to 300 rpm and dies.
also very sloppy idle, surging between 800rpm and 1500 rpm, i have adjusted the throttle to get it down but when it's warm it doesn't want to run below 1200
car runs better in cold air. also idling sends black smoke out the exhaust, smells like gas, and a romp on the pedal causes major black smoke, if you ease on the throttle it responds much better. also i'm pretty sure my timing is off which i will deal with later this week.

i found a vacuum line between the air check valve (2" circle behind left side of throttle body) and the throttle body that is broken and taped with electrical tape. i took off the old tape and put on new tape (don't hate me) problem is not as bad, i'm going to go get a new vacuum line today and replace it.
i am told that this air check valve is a major component for acceleration, is this accurate? this does sound very similar, however i'll admit i'm no pro so please advise if there is a more relevant thread somewhere

also, there is a sticker under the hood for crane cams, how can i tell if this actually has a cam?
also, the previous owners claimed it had been rebuilt 20k ago and that it is now a 350, how can i check this?

 

I switched the distributor again, seemed to run better. Then started chugging and stalling out after driving around a little. I pulled TB off and vac port to PCV was plugged, cleaned all TB ports and new gasket.

Reinstalled TB, started engine, chugging and smoking black. Then it cleared up and was running smoother than it ever had.

Test drive- after about 4 miles I stopped and floored it taking off, at around 3500 RPM the tach dropped back to 1000. it was still running- but barely. I kept my foot light into the throttle and it came back and ran normally, although I thought it was lacking a little power, but maybe not.

After a few more miles of driving around, I passed a tractor, it downshifted, and at around 35-3700RPM she dropped to 1000, I was feathering the throttle, but it died. I hit the key it cranked about 5 seconds then slowed to a stop. battery is weak but it still shouldve started.

Pulled it home, swapped batteries. First crank it started then died. Started right back up and ran very smooth. I let it run for a minute or so, it was doing fine. I shut it off and went to restart but it would just crank and crank. I have spark but the injectors barely drip while it cranks. fuel pump is priming. I need to get a fuel pressure gage, but pump, filter, regulator, and 1 injector are new so you would assume they would all be fine.

I'm out of ideas, and starting to think it'd make more sense to but a truck that isnt flippin jinxed.

 

The temp sender is also a suspected culprit of running rich, but wouldn't cause the stalling.[/quote]

so i replaced that vac line, and still 100% the same... i noticed when i get below 1/4 tank it runs like $%!#, so i also noticed that the fan doesn't always automatically kick on so i wired the fan directly to the motor... at least i can cool it down... could this all be caused by this "temp sender" but still doesn't explain my stalling problem, i have yet to disconnect my o2 sensor and play with that... (also havn't messed with other sensors)
i noticed that the sensor (don't know what it is) that the air check valve goes through is not mounted to anything so it may not be grounded, could this have any relevance?

 

oh yea 92 chevy, check to see if while cranking you floor it (really floor it) if it starts mine has this problem, it just won't start sometimes unless i well, floor it...

 

Don't you hate simple things that get overlooked? I was out of gas, but gage showed nearly 1/4. Dumped a few gallons in, fired right up. I still dont think its running quite right, but doesn't seem as rich. Will post back when I find out more. Either tomorrow or wed I plan on setting the timing with the light and doing some test driving close to home, LOL.

A few weeks ago when it would load up and flood itself out, it would restart fairly quick if I floored while cranking.

 

huh thats funny, mine was doing the same thing, i was on 1/4 tank and it acted empty...

 

i am tranferring all of my stuff to a new thread
https://www.thirdgen.org/forums/tbi/590743-91-tbi-sputter-backfire.html

 

So today- put more gas in and head out to drive around the section (~4 miles). Seems to run good, has the slight miss as usual but nothing horrible.

I went to pass a slow moving vehicle, kicked it down, all was well. I stopped at the next corner (~1/2 mile)turned and right as I hit the gas (reached maybe 1000 RPM) it coughed and died. Hit the starter- it cranked a few seconds, I floored it and it came to life but it would barely idle and died instantly when throttle was opened. Floor it and would restart fairly quick. I finally got it to keep running in gear and romped on it, all the way to 80 MPH when I let off she was running fine.

Turned onto my road, stepped on the throttle a little, it died. Floor, crank, restarts. After a few times once again I was able to get on it and away she went.

At home, I notice the gas coming out of the vac canister, I had this happen on my S10 a few years ago, it would randomly die and canister would be overflowing with gas.
I opened the gas cap and the tank had a lot of pressure in it. Truck started to run better. I revved lightly a few times, seemed fine but that steady miss was still there. Not really bad, but enough to really bother me.

I back out of the driveway, shift to D, step on the gas and IT DIED. Floor, crank, restarts, I parked it back in the driveway.

I've had enough

Out of 40 or so vehicles, this is the most unreliable thing I've had yet.
What gets me is you can't ever tell if the problem is fixed because it's so spontaneous. And EVERY time I have replaced something, it will run really good for a few days, then die on me without warning. Fuel pump, injector, fuel pressure regulator, distributor. Each of those seemed to fix it, then the SAME issue comes back.

Sorry but I REALLY needed to vent

 

hey, this is definately worth a try!
as i said i was having basically the same problem as you,
i would strongly suggest replacing the cts sensor, its the coolant temp sensor, there are two, one located in intake manifold near the thermostat; this one controls ecm (replace this one) the other controls your temp gauge and is located on the cylinder head between spark plug 1 and 3 i think, that one doesnt matter though. anyways i replaced it and poof, omg my car runs so much better, i am so happy!
my throttle response is so much better
its a $11 part and only takes 2 min to replace, if it fixes it you'll probably be a little pissed because of how much you've gone through... but it just might do the trick

EDIT:
before it:
poured black smoke out the exhaust, now gone
sounded like a shop vac in my intake, now gone
steady miss, now gone
backfiring, now gone
wouldn't start without slamming gas (sometimes), now gone
after started when hit gas too fast it bogged out and died, now gone
now, throttle response is better than i have ever seen, immediate, i still have alot of work to do but boy that engine runs so much better!!
also don't let the parts guy try to sell you an IAT sensor, it looks almost the same iat has a black plastic end with holes in the sides, it reads the air temp, our tbis dont have this sensor in the intake, oreilly insists they do but they dont. ours is located in the air cleaner (the only wired sensor in the air cleaner) and doesn't effect our mixture that much. i was told this is important as well yet less common of a problem as the cts, from what ASE doc told me
he went through 4 iats
and like 12 cts in 10 years or so
reference this page for my fix
https://www.thirdgen.org/forums/tbi/...-pressure.html

 

Chevy 92, It may be worth replacing your CTS just to eliminate it as a possible intermittent problem. This part has such a significant effect on fuel delivery. It should almost be a maintenance item, like spark plugs. You might check the connector for loose terminals and make sure the wiring looks good. One thing Im really wondering about though is your fuel filter. Have you replaced it? Also, when you swapped fuel pumps, did you check the tank for debri, and did you replace the filter sock?

Another issue is the MAP codes. Generally having both 33 and 34 means the sensor is bad. However, while MAP failure causes severely bad engine performance, severely bad engine performance can also cause MAP codes. Nonetheless, you really should perform the test sequence for one of the codes. Either test set will reveal the cause of both codes.

 

One thing that just occurred to me, your engine uses alot of oil. You might want to check the vacuum port that supplies vacuum to the MAP sensor. You may find it plugged or badly restricted.

 

Already had the TBI off, cleaned it out, the port to PCV was totally plugged. It seemed to run REALLY smooth after that, but it does that every time I do something to the truck, then it runs like s*** a few days later. Always works like that, never fails.
I could replace the CTS, but it still surges with it unplugged so I really don't think it would help. Fuel filter, pump, sock, and tank were brand new less than 100 miles ago.
It could be the MAP, but wouldn't unplugging it default the computer? I did try a different sensor and it didn't make any difference.

It seems like its gradually running better, yesterday I drove around about 10 miles, did 2 really long burnouts (hard on things, I know, but if its gonna start cutting out it does it after that). It was running good, power is quite a bit better with timing set but after it surges a little the power comes and goes.

Now it seems to only surge when the transmission shifts. And its worse if you stop while you've been driving and take off, getting heavy on the throttle usually makes it run better and it doesn't *usually* chug horribly while cruising.

EGR, MAP, and CTS are the big 3 I would think, but unplugging them doesn't make the problem go away.

Also I had a spark tester on #1 a few days ago when it was cutting out and running rich and it's definitley not losing spark.

I thought about swapping TB just for the hell of it, but I can't see what else it could be.

This thing is really frustrating me.

 

Had a local guy check it out, and it wouldn't act up for him (go figure). But the ses came on with a TPS code so I went home and swapped TPS and it hasn't skipped a beat since. Except when you start it and leave the driveway (engine cold) it seems like it has a small miss but its really hard to notice.

I haven't taken it on more than a 30 mile trip yet, maybe later this week.
It still smells a little rich, I was thinking O2 but I unplugged it and no change. Is that good or bad?
I planned on checking my MPG to see where I'm at for sure.

 

If your engine and management system are working okay, you shouldnt expect to see much effect from disconnecting the O2 sensor. Disconnecting the O2 neutralizes the secondary fuel correction system(BLM and Integrator). This test is mostly to point out gaps in the base fuel map and primary fuel correction system caused by unmetered air, bad injector(s), or any other fault in the primary fuel management system. Your problem may very well have been caused by a TPS issue. A faulty TPS can also cause false MAP codes since the ECM compares TPS and MAP values to determine MAP failure. Your type of symptom isnt what I generally expect to see from a bad TPS, but I have seen it atleast once before.

As for unplugging the CTS, that tells us nothing. The CTS unfortunately, due to its particular function of measuring tempurature, does not have a fault mode or limp in default in Memcal. In other words, when you unplug it the ECM will go full cold(-43f) and, unless its very very cold out, the engine will run like dog meat. The only way to check CTS is either by reading data or by measuring resistance of the sensor.

 

Well, thanks for clearing that up. I didn't know unplugging CTS and O2 won't do anything, I think I'll just replace them. I will check resistance of CTS first though

 

Did I say that unplugging the O2 does nothing? I didnt mean to. Unplugging the O2 will disable secondary fuel correction and is a quck test for a faulty O2 sensor. The O2 controls the ECM's secondary fuel correction, otherwise known as "post combustion" fuel correction(Block Learn & Integrator). These fuel correction maps can have a great effect on fuel mixture by adding or subtracting up to 25% to/from the base fuel map and primary fuel correction maps.

By using a scan tool we can monitor these secondary maps and see a lean or rich condition. By unplugging the O2 and disabling this system, we can see what the engine and primary fuel managenent system are doing. If the engine runs better with the O2 unplugged, you have a faulty O2. If it runs more lean, you have a lean condition. If it runs more rich, you have a rich condition.

 

Unplugging the O2 doesn't seem to make any difference. It could be full of carbon (engine burns oil). I'm going to pull it out and look at it.

 

Sounds good. However, if there is a severe issue in ignition or fuel management, the O2 will not make much difference. No one's mentioned ignition up to this point. The issue at 4,100 could very well be the ign module taking a dump. You may want to use an inline spark tester to look for ignition drop out and intermittent misfires.

 

I had a spark tester on it the last time it was acting up and it wasn't losing spark.
I'm fairly sure my cutting out / surging is gone since I switched TPS.

The CTS ohm'ed out ok. I pulled O2 out and blew some compressed air thru it, didn't seem too plugged up, put it back in and it seems to be more responsive now (compared to having it unplugged).

I can't afford the gas at the moment to take it on a very long trip, so I will report back when I am able to do that.

 

Doc, it needs shot (engine rebuild I suspect), he has already been told by RF.

Nice of you to help but these pickup kids mostly make monkeys out of us.
I hammer them pretty hard on their own forum & they don't listen.
If I can figure out who sent 'em I'll get them too.
The last thing you need is them showing up over here wasting your time.

It burns a quart of oil in 100mi.
Just sayin..
JR

 

Today when I started the truck it sounded like it was idling rough and when I gave it gas it was coughing and missing like it was flooding out and smelled really rich.
This is not the same coughing and stalling issue I had previously.

I drove the truck 1/2 mile and came back home. It was running perfectly fine, smooth and didn't seem rich.

My haynes manual isn't very clear on testing O2, otherwise I would, just to see where I'm at.

Seems as the truck runs very rich on cold start, then comes somewhat back to normal.

 

I suspect that there's a discrepancy in your CTS at cold temps, or that theres a mechanical rich condition that your secondary(BLM and Integrator) fuel correction is covering once the system goes closed loop. I would not be suprised at all if the engine is so worn and sloppy that its pulling weak vacuum and skewing the MAP value. I must admit, I completely overlooked the engine's mileage. I think that before we waste anymore time trying to diag this issue, you need to perform a proper overhaul on this motor or replace it. Damn it sucks getting old.

 

I was hoping to limp this engine along through the winter (that's what I bought the truck for).
Maybe a compression test is in order. I could hook up a vac gage and see what it pulls for vacuum as well.

 

Vac test would be good. Should idle at about 19". Ohm test the CTS should read 3,400f at 70 degrees.