1991 GM 3.1L engine running very rich and can't accelerate!

[Scott-Ohio]

(I've also placed this under Buick Regal, but put here too for additional exposure--please allow to stay here for a few days--thanks for considering this request)

Hi, I've read many posts tonight about poor acceleration, but all seem to be about 2000+ year model GM cars with cat problems which are covered under warranty for 8yr/80k miles -or- 10yr/120k miles ... a bit unclear which, but either way won't help him on his 1991 Buick Regal.

OK, my 23 year old son, who recently moved 90+ miles away, gave me the following symptoms earlier tonight and I'm just totally boggled on this one!!!

After driving ~ 7-10 miles after filling up at a mobil gas station, his Regal (3.1) with approx 135k miles on it, began to run very rough--whole car shaking at 45 mph and had to baby the gas pedal--attempts to accelerate made car run worse! No check engine light came on at this point. After pulling car over and getting out, he smelled a very strong odor of gas and looked to see if any was leaking on the ground, but didn't see any leaks. At this point he could only drive very gingerly back to work.

I advised to put in a can or 2 of dry gas as he may have got bad gas (water tainted) so he put in a can of heet which said it treats up to 20 gallons and had only filled 3/4 way up earlier. He then drove home 35 miles and during last 5 miles the check engine light came on, but went off again just before arriving home. My haynes manual said to jumper wire the A and B terminals (last 2 on top row of 6 terminals--12 total), then switch on ignition, then count the check engine light flashes for stored trouble codes. But, the check engine light didn't flash at all and he said the paperclip he used was contacting metal inside both terminals -- did not even give the 1-2 flashes for "12" prior to flashing/revealing the trouble code(s)!!!

He said the performance remained poor all the way home (35 miles) and so he used the cruise control to maintain steady highway speed and avoid the need to accelerate.

I believe he may have a clogged/plugged cat converter, but don't understand how this could happen so quickly -or- what caused the ultra rich condition so quickly either. If the pre-cat O2 sensor was failing, shouldn't he have received a trouble code for that? And I always thought that O2 sensors failed gradually like fuel injectors, not suddenly! And, how in the world could this tie in with getting bad gas? Doesn't bad gas usually mean "water" contaminated? Sure, water might make the engine run rough, but smell ultra rich? Just doesn't make any sense to me ???

He lives near a new, large firestone center and so I told him to see how much they charge to diagnose the problem(s) in the morning and then go from there.

I was thinking of using my sawzall this weekend to cut out the cat and just replace it with flex pipe/clamps. I figure this to be a cheap approach and if I am nothing else, I am CHEAP!! I figure he should get better gas mieage too without the cat! I know that will likely throw a trouble code since the rear O2's purpose, from what I understand, is to alert the driver of a cat that's no longer doing it's job of superheating any remaining gas fumes before spilling out into the air we breathe, but right now he needs a car to get him back and forth ... and, I've come to learn that cat's don't commit suicide, they get murdered, so I don't want to put in a new cat until I'm confident on what caused the cat to get so plugged with gas in the first place! Could an injector be stuck open? I've had injectors go bad, but when resistance reads close to zero, don't they BARELY pass fuel?

Oh yeah, one final symptom was that his gas gauge went from 3/4 to 1/2 tank after only driving those approx 45 miles and he says that his Regal NEVER used that much so fast before!! This makes me think an injector is dumping fuel like crazy, but have never heard of this happening.

ANY advice would be GREATLY appreciated on what folks think might be going on here! I should note that this car has been maintained well and was a solid running car up until late this afternoon!!!

Thanks in advance and take care,
Scott

[rairigh915]

my buddy had an 02 grand prix with similar problems. he took it to a dealer and they replaced cat for free. his car wouldnt even make it up a hill.

[Scott-Ohio]

UPDATE:

I drove out to check on my son's car today and was able to extract the stored trouble code in memory via the ALDL connector via terminals A and B: code 13, which my haynes manual says is an "O2 sensor open circuit" ... also, very rich exhaust vapors coming out of tailpipe during idle -- smells like raw gas alright! Idles very rough obviously due to ultra rich mixture.

Again, the car has an erratic idle, seems to lose power when trying to accelerate and sometimes won't start. This all started up after driving about ~7-10 miles just after filling gas tank up 3/4's of the way.

Any thoughts, anyone?

Couple mechanics I spoke to today both said to first replace the coolant temp sensor that feeds info to the ECM. They said they've seen a bad temp sensor cause these ultra rich conditions before and it's only about $10. With 145k miles, I suppose it's a cheap start and can't hurt to try. One also said the cat should clear itself of gas if I can eliminate the cause of the rich mixture. I thought for sure that my cat was ruined by all this unburnt fuel, but maybe it will survive afterall ??? Any thoughts on this?

I will visually check wires/connection of O2 sensor tomorrow during daylight hours since the only stored trouble code points to an "O2 open circuit," but that could've simply been a symptomatic response to the ultra rich fuel condition, right? I don't think an O2 sensor would go bad suddenly, nor cause the extreme rich condition, but who knows?

Secondary thoughts by mechanics (referred to above) were to check the Throttle Position Sensor, then the MAP sensor next. When I asked them if they've seen injectors get stuck open they said they had, but very rarely.

Not sure how to "check" either TPS or MAP sensors though. Any thoughts on this anyone?

Again, please throw out ideas if you have any.

Final thought for now: were pre-OBD II cars, like this 1991 Regal with 3.1L is, not known to set codes on these emission sensors? Although I value the inputs by these mechanics I spoke to earlier today, shouldn't I expect to get a trouble code from these sensors if they are bad -or- were pre-OBD II cars not reliable with always setting trouble codes maybe?

Please help if you can ... thanks,
Scott

[Blue Bowtie]

There was a local "episode" just a week ago of a particular fuel station having water contaminated fuel. It seems a fuel delivery driver did not get a seal on the tank fill cap, and snow melt had allowed a lot of water into the gasoline. Your story and your described symptoms seem just too coincidental.

A few cans of Dry-Gas aren't going to offset the effects of even as little as a quart of water. You may need to siphon or pump out as much fuel as possible, then refill with about 5G of fresh fuel, preferably with E-10 ethanol blend to help absorb any remaining water (which will separate to the very bottom of the tank by specific gravity differences). If there IS any water in the tank, that's the first thing the fuel pump will pump to the rails and injectors.

As a result, you may also need to remove the fuel line at the rail or regulator (or at the filter) and allow the pump to push out a gallon or so to eliminate any water in the lines and rails. No fuel injector will tolerate water for very long without pintle or valve ball damage (your '91 should have Multec, ball-type injectors).

NOTE: That's why "cleaners" such as SeaFoam should NEVER be added to fuel (despite the seller's claims), since it contains about 10% water. Don't take my word for it, since I'm just a moron. Check with Cruzin' Performance, TPIS, Linder Tech, or any other reputable injector service company.

Get fresh fuel in the tank, lines, regulator, and through the injectors. You may also want to replace the fuel filter if it hasn't been done in the last 20,000 miles.

Regarding your other questions, yes, ECMs (ODB systems) do not monitor inputs as closely as ODB-II systems. The acceptable "reasonable" ranges of various sensor inputs have a lot more broad tolerance before setting an error code. An open circuit for the O² sensor will set a code, and will also cause he ECM to revert to Backup Fuel Mode, a condition which is intentionally rich, and is intended to briefly operate the engine safely until repairs can be performed. This mode usually also invokes a Backup Spark Mode, which eliminates any ESC timing advance. This is intended to prevent potentially damaging preignition and overheating.

Next, the oxygen sensor could have been either a cause, or a victim. If there were indeed water in the fuel the sensor could have been contaminated by unburned fuel, raw water vapor, or other contaminating chemicals. Water in the combustion chamber would suppress ignition, flame propagation, and in sufficient quantities, cause a complete misfire. Coupled with the poor atomization of a water/fuel mixture at the injector, and flooding with the fuel mixture would be very possible. This would not only contribute to oxygen sensor failure, but explain the lack of power and generally poor idle and operation.

Thirdly, you may want to get back under the vehicle and look more closely. There is a very good chance that there is no second O² sensor (post-Cat sensor) since it was not required. Replacing the converter with a "test pipe" should not affect the ECM in that case.

Fourth, as long as you'll be spending some "quality time" under the hood, it will not hurt to verify the operation of the MAP and TPS. Remember that the TPS base position is not adjustable on most 1991 engines, so all you can do is to make sure the closed throttle voltage is below 0.80VDC, and that the voltage change from the sensor is relatively linear as the throttle is opened and closed.

The MAP can be checked with a voltmeter while a vacuum is applied to the sensor. The readings should be similar to this:



You can check both of those, but the MAP is one of those few sensors which is monitored fairly closely by the ECM, and should set an error code if its output is outside the tighter allowable range at any given RPM and TPS level. Since you evidently did not retrieve either a '33' or '34' error code, I doubt that you will find much trouble there.

Additionally, and since the possibility of contamination, misfire, and excessively rich mixtures exists, you might also want to remove and inspect the spark plugs, or at least the three on the front (2, 4, and 6) and test the plug wire resistances while you have your meter handy. Expect about 500-1,500 ohms per foot of length with stock-type wires.

Further, on the off chance that the mixture is clean but excessively rich, you can remove the vacuum pilot line from the fuel pressure regulator and monitor the connection for liquid fuel leakage while the fuel pump is running.

Not to be an alarmist, but several of the vehicles involved in the local fuel contamination episode received a new pump, filter, regulator, and injectors - All at the expense of the station distributing the fuel (or their insurer). Hopefully, your solution will be less involved, but if there is a significant indication of fuel contamination, you may want to save some of the drained fuel, any replacement parts, receipts, and your labor time, and approach the fuel station with questions.

If you DO find that the fuel was contaminated and do not have to replace the pump, don't be afraid to treat a couple of fuel loads with 2-cycle oil at a rate of about 40:1 or higher to help relubricate everything, but only AFTER it is back to running properly.

[Scott-Ohio]

Thanks to all (here and under Buick Regal) for your inputs.

I spent this weekend trying to pump gas out, first through the Schraeder valve, after removing valve, then via the fuel line from tank, just below the master cylinder--I can never get the small semi-rigid plastic tube far enough in the tank via filler neck to syphon out gas. Unfortunately, I can never get the electric fuel pump in the tank to pump for more than a second or two either--a REAL PAIN trying to remove gas without removing the tank--another REAL PAIN!!!

Anyhow, when I asked my son what bottle of Heet he used, he said the yellow bottle--and he just put in one. So, before I started tearing into everything, I went to AZ and looked over what kind of dry gas they had. I noticed the red bottle (Iso-Heet) claimed to absorb up to 5x more water than the average bottles of dry gas and it's warning label said it contained Isopropyl alcohol, whereas others contained a different type, ethanol alcohol I believe.

So before cracking into the fuel system as mentioned above, I first dumped in 2 bottles of the Iso-Heet into the tank which was now down to only 1/4 tank full.

Then, several attempts to remove fuel (using fuel pump at locations mentioned earlier) only removed about a quart of gas and after settling in my clear container, appeared to have water. I presume most of the water was already run through the engine though during the ~45 miles driven and rough idling periods, which ate up ~6 gallons of water equalling ~ 8 MPG during this time!!!

After unsuccessfully removing enough gas via the fuel pump, I reconnected fuel lines and tried to start the engine and see if the few hours of the dry gas I put in the tank had any effect. The first few times I tried to start the engine, it would fire then immediately come to a screeching hault while making an awful, abrupt sound. I figured vapor lock was occuring and causing this. About the 4th/5th time though she finally stayed running and after about 10 seconds of gently revving engine, she was now running smooth again like her old self!!

So, I let her idle for about a solid 30 mins+ occassionally raising the RPMs to ~ 2000 for good oil pressure lub'ing cylinders, etc. and continued checking the vapors coming out of the tailpipe. As time went by it was less and less rich but the dampness on the concrete drive smelled like raw gas. I was attempting to burn out any remaining fuel in the catalytic converter during this process. I continued to get the "13" code, so the next day I replaced the O2 sensor (which was black from excess carbon) and checked the plugs, but they were fine and gapped at .046 -- just slightly down from original .045 so I left them alone. The air filter needing replacing so I put in a new one, but other than adding 8 gallons of 10% ethanol along with a quart of 2-cycle oil (for a 40:1) mix (as suggested for lubing injectors ball valves and fuel pump) I didn't do anything else and 100 miles later she's still running like a champ!

Again, thanks to all who replied and hopefully this experience will prove helpful to others down the road.

I should add, that through this whole thought process I did NOT want to start replacing sensors, regardless of how logical it seemed, because the ultra-rich condition remained the same whether engine was cold or hot, so other than replacing the coolant temp sensor ($10) which I never did do, it just didn't make sense to replace these emission information sensors to me. If the coolant temp sensor kept telling the ECM (computer) that it was still cold, I could see why that MIGHT play into the continued rich condition, or just maybe a bad O2 sensor, but as it is I simply think the ultra rich condition ended up over carbonizing (? a word ?) the O2 sensor beyond recovery ... plus it was the original 147,000 mile O2 sensor which may have been on it's last leg anyway!

Thanks to all again (for a 3rd time!) and take good care,
Scott