Olds Cutlass Supreme 3.1 Stalling/Idling Problems

[13btJim]

For a little bit of some background history on the car, I have replaced quite a bit on the vehicle and am still having problems with it. The car is a 1991 Olds Cutlass Supreme with a 3.1 engine with around 120k on the odometer. I have replaced the idle control valve, spark plugs, spark plug wires, fuel filter, TPS, air filter, and fuel injectors and the car still runs like absolute crap. The injectors were purchased new as well as all of the other parts. The car has just progressively gotton worse with the idling, stalling, and surging when driving. It particularly has problems when cruising and the rpms are between 1500 and 2500. It will surge and buck quite badly. I actually just replaced the fuel injectors last night with facotry ones and it drove pretty good. The idle was off slightly but most of the hesitation no longer existed. This morning I went back out to the car and was going to do the idle learn procedure and by the time I was done the car ran like shit, didnt idle, died when I come to a stop sign, and is running pig rich. The exhaust stinks of unburnt gas. I am really getting sick of throwing money into it and working on it. What could the problem be?

[heavymtl]

if i were you...i wouild look at a couple things...1..vacum leaks (hoses...intake)....also if you have a mass air flow sensor take it out and look close for broken wires...or just plain dirty....another thing...check your fuel filter....and hows your fuel pressure regulator?....hope some of this helps you

[pocket-rocket]

I would think fuel pressure regulator too. Pull the vac hose to it and see if there is gas in the line. If there is, replace the FPR. If not, put a vacuum pump on it and pump it up just to make sure.

[13btJim]

When I had changed the injectors I looked for a vaccum leak but didn't find any. Surprisingly, there arn't many vaccum lines under the upper intake manifold. I was starting to think it was the FPR but was unable to check it this weekend and now I am back at school. I was going to check the rail pressure. I did however pull the vaccum line off of the FPR while the car was running to check if it would die or stay running and this would indicate a leaking fuel pressure regulator. The car did die at that point. I do know the original injectors in the car were part of the problem because when I pulled them out several let fuel go right through them without being hooked up, they were stuck open. Also, when the upper intake was off I did clean the inside up pretty good as well as the butterfly in the throttle body. I will be running out of things to change here pretty soon.

[sil]

i would def. check the FPR, also check the vacuum with a gauge and get your repair manual out to see what the vacuum gauge is telling you.

also maybe clean the EGR, stuff gets cruddy and makes it stick open

[bszopi]

Suprised no one mentioned the O2 sensor. Since it is what tells the ECM what fueling requirements are, if it is bad, it could easily tell the ECM to spray more fuel. Might also look at the catalytic converter, as it could possibly be clogged. I personally would start with the O2 sensor though.

[13btJim]

I was thinking the O2 sensor as well but it has been replaced in the past 15k miles. This weekend I am going to tear the ignition apart and maybe see if that is the problem.

[bszopi]

Well, you never mentioned the O2 sensor being replaced, so... It still might be the culprit, as you stated that there were bad injectors that were stuck open. If it was run for an extended amount of time at such a rich condition, the O2 sensor could very well have gotten fouled.

[13btJim]

I will probably end up replacing the O2 sensor in the car and I am going to take a better look at the fuel pressure regulator. I have been trying to diagnose the problem and I have done some searching on the net and have found many people have had problems with their FPR. Apparently the diaphram inside splits causing the engine vaccum to suck gas into the intake as well as not providing enough fuel pressure to create a nice jet from the injectors but rather more of a stream causing it to run rich. I had this same problem with my Rx7 before I got my Aeromotive pump put into my car. The car would not hold a high enough fuel pressure to create a nice spray pattern but instead a stream from the injectors. The car ran really rich.

[pocket-rocket]

Slapping a fuel pressure gauge on there along with hooking a vacuum pump to the FPR wouldn't be a bad idea. I had to change a FPR in a 3.1 this past summer in a cherry Cavy RS, but I don't remember if I had access to the vacuum port on the FPR with the UIM in the way... I wish I could be more help with that.

[13btJim]

Yeah I can hook up a fuel pressure tester and have pretty easy access to the vacuum port of the FPR. Is this a pretty common failure with these cars, the FPR?

[bszopi]

Not sure I would call it common, but I have heard of it happening many times.

[13btJim]

Changed the FPR and the idle of the car drastically improved, however there are still several problems. The first is a shuddering or a bucking between 1500 and 2000 rpm when at cruising highway speeds. The other is hard starting. The car is still starting pretty hard. I am thinking that I may change the plugs again on the car. I changed them roughly 10k miles ago but I believe they may be fouled out because with the leaking FPR the engine was pulling raw gas into the intake and flooding the car out pretty bad, bad enough to where I pulled the plug on cylinder 6 and it was full of fuel, probably 4oz or so. It was unreal how much gas was in that engine. I will be changing the oil because of it.

[1988GTU]

You could still need coils / icm if they are original. ICM and coils going bad are a common concern due to location.

[13btJim]

I was thinking about changing the coils. I think I am having troubles with cylinder 6 coil. Even after changing plugs it is this cylinder that keeps fouling plugs out. It isnt getting enough spark, I believe. Also when cruising at highway speeds yet, the cars will shudder and missfire between 1500-2000 rpm. The hard starting issue is still there as well. I am certain it is now an ignition problem.