`91 Buick Regal (3.1L) probs accelerating!

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!

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!!

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

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

The O2 sensor can cause the over rich condition that you spoke of and if you got a code I would change the sensor and see if the car runs better. If you are dumping raw fuel into the engine then it can damage the cat and cause the car to run badly. I would check the cat to see if it is damaged by looking removing it and see if the car runs better. If you need a replacement purchase a magnaflow one for less than $100 and have it installed.

The throttle position sensor is a rheostat and you will need a digital volt meter to test is. A repair manual will tell you the values as you move from closed to open. If it is out of spec then replace it.

You may also want to check the gasoline he bought for water. This can cause major performance issues and if he got a lot of water then the can account for the poor performance and since this issue starter right after getting gas that would be the first place I would start.

Finally, before doing anything else pull the spark plugs and see what they look like. If the plugs are wet then fuel is the issue. If they are very white then fuel starvation could be an issue too. A blocked fuel filter can cause this and can account for the lack of performance just like too much fuel.

I hope these ideas help you find the problem. Please post once you check things out and let us know how it turned out.

Hi GTP Dad, and thanks for the reply.

Regarding bad gas, I want to link the problem directly to that too, but I don't think either water in the gas or sediment would cause the engine run rich, let alone ultra-rich.

Instead, I would think that a clogged fuel filter would make it run lean as it starves to deliver enough fuel due to restriction in fuel filter. Would/could water in fuel lines cause such a rich condition? I wouldn't think so, but maybe I'm overlooking something. Any thoughts, anyone?

Thanks for the tip on the magnaflow cats--I'll probably go with that brand if I've ruined the cat with gas, but not until after I correct whatever is causing the high delivery of fuel--don't want to burn out another cat! I may try a length of 2" flex pipe until I get this excessive fuel issue resolved. This is not your ordinary rich fuel mixture as the fuel is just pouring through the exhaust and gas mileage has dropped at least in half. If you place your hand near tailpipe during idle it immediately becomes dampened with fuel from the heavy gas vapors!

Thanks again, I'll pass on more as the diagnosis/repair attempts progresses.

Take care, Scott

You are correct in your assumptions that a rich condition would not be caused by what I suggested however they are all problems that can cause the issues of poor acceleration. Water in the gas can cause a rich condition since it will not allow the fuel to burn properly and therefore fuel can accumulate in the cylinders. The O2 sensor will certainly cause more fuel to go to the cylinders since it will send wrong signals to the computer. I hope you get this resolved.

:rolleyes:

Keep in mind the VIN "T" 3.1L engine has throttle body injection (TBI) and not multi-point EFI. Used up until the 1993 model year.

Regardless, the 02 sensor is what the ECU/ECM module uses to control the fuel injection system and help keep it at that ideal 14.7:1 air/fuel mixture ratio, otherwise you'll get either a rich or lean conditon.

It would make sense if the 02 sensor circuit is open. That would probably cause the excessively rich conditon and in a TBI system it would be more noticeable. If the 02 sensor DTC is valid checkout the 02 sensor circuit or replace the 02 sensor, if necessary.

I Just went through this exact same thing, last week on my 350 TBI Chevy truck, that I loaned to my son some time ago. He called and said that it was running extremely rich, (10 mpg) loading up at idle and poor acceleration in about all ranges. BTW, no codes! He replaced the CTS, TPS and 02 sensor and put a bypass pipe in place of the cat, to no avail. I suspected that if none of these things were giving a code or reading out of range on the scanner, that it might be a waste of time/money, however, it was time to replace some parts anyway. After some additional thought, (while sipping a cold Bud), I told him to drop by and we would replace the fuel pressure regulator. Once we got everything off the top of the TBI, I noticed the return line (braided stainless) was somewhat twisted and may have been restricting fuel return. After correcting the return line and replacing the regulator & spring, “BAM”, she runs like a new one. Of course, the plugs will need to be changed next! Oh, he called yesterday and said that it was running great (even with the old plugs) and he got 18.5 mpg city/hwy driving. That is better than it got new!

Now with all that said, what would cause this extremely rich condition in your case. This would not be the 02 sensor, because if it were completely non-functional, it would not cause the engine to load up with raw fuel. (The 02 only controls a small percentage of the total fuel curve). You may have to replace the 02 & cat, after you fix the problem, since they were flooded with unburned fuel. I think, you have either a fuel pressure regulator stuck, or a restriction in the return line. Check both possibilities and replace the regulator at a minimum! :grinyes:

Thanks to all (here and under Chevy non-specific) 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

Thanks for the feedback. I'm not a gambling man but I were I would place my bet on the 02 sensor in your case, especially with 147K miles on the car. They do degrade over time and the recovery rate when they get old leaves alot to be desired. First sign is normally a unexplained loss of fuel economy. Now unless your ECM module was just pulling your leg and the DTC code generated was a fluke which I highly doubt.

BTW - Also, it would be a good idea not to get gas at that same Mobil station again. Good luck.

Thanks for the feedback. I'm not a gambling man but I were I would place my bet on the 02 sensor in your case, especially with 147K miles on the car. They do degrade over time and the recovery rate when they get old leaves alot to be desired. First sign is normally a unexplained loss of fuel economy. Now unless your ECM module was just pulling your leg and the DTC code generated was a fluke which I highly doubt.

BTW - Also, it would be a good idea not to get gas at that same Mobil station again. Good luck.

With everything said and done, I'd say the best explanation to this entire nightmare is the water in the fuel caused incomplete combustion allowing raw gas to continue through the exhaust partially plugging the cat then remaining raw gas sprayed out the tailpipe and dripped onto pavement. The incomplete combustion likely created excess carbon buildup or something thereby damaging the O2 sensor. Then after water in tank was removed, the damage had already been done to the O2 sensor. My son had gotten great gas mileage out of this 3.1L V-6 up to this point and hasn't noticed any improvement from what he used to get before the water in fuel factor even though I replaced the O2 sensor with a new one. Also, never got the "13" before this bad gas attack occurred.

With regard to the bad gas from Mobil, I've sent an e-mail to the station owner who has now passed it on to their insurance company. I explained I had receipts for all and I hope to be reimbursed for my labor time too. I'll follow up on this post after we see what they offer to reimburse us for all of our trouble brought about by this bad gas!