3.1 driveability issues..

[mikey67]

Car is '91 GP w/ 3.1. I was traveling about 40 mph. and went to accelerate and out of the blue it falls on it's face. I had to feather the gas to get it home. In park it idles very rough and smells very rich. If i tach it up and hold, as an example, to 2500rpm it will hold it for a couple seconds and then it falls off, misses and then stalls. It also starts hard on occasion. I'm guessing it is a fuel pressure/injector issue since the coil packs and module are good, and I was unable to find any vacuum leaks. I know a bad CPS usually results in a no-start, but could an intermittent CPS cause a condition like this? One more thing, I had filled the gas tank earlier in the day, bad gas possibly? Thanks for reading!

[GPRacer]

It sounds like it could be stuck (dirty) injectors.
Kinda hard to tell though...i'd more have to be driving it

[SappySE107]

Intermittent CPS would throw a code, or at least it should. Bad fuel injectors will do this, but I would get a pressure reading at the rail, and also check the flow since you can have a bad pump that has pressure but no real flow. Are you sure the coils, wires, and plugs are good?

Do a vacuum test on the regulator, as it could be shot.

[eliteweapons]

I know this one is stupid but no one mentioned it. When is the last time you changed the fuel filter? It doesn't explain it smelling rich thou.

[geoffinbc]

My first question to you is... What kind of spark plugs?

[mikey67]

I am going to pick up a fuel pressure guage tomorrow. My fuel pump is functioning but it sounds a bit different to me... As far as ignition, the packs tested to spec but for good measure I swapped the packs and Ig. module with new Delcos I had that were to be installed on a car I sold... Today it idled fine but still has the stumble/stalling. I'll have some more daylight tomorrow to play with it. Thanks for your replies, I'll keep ya posted!

[Juglenaut]

A fuel pump can either stop like a light or fail slowly.

[mikey67]

I had a few minutes to test the fuel pressure, key on it is at 8 psi, at idle the guage flutters between 10-12 psi. I'm surprised it still starts! Tomorrow I'll change the filter and see what happens, although it seems like a weak pump to me.

[eliteweapons]

The fuel filter is a cheap fix. It sounds like it could be the pump but the filter won't hurt for about $10.00. Even if its not it it can't hurt to change it.

[roxieshotrod]

same symptoms

hey did you happen to figure out what your problem was? My '95 started the exact same thing Saturday. My husband has been working on it all week, replaced the computer, the fuel pump, had the alt. and batt. tested, both ok, and its not throwing any codes. Any other ideas would be appreciated!

[mikey67]

RE: same symptoms

Have you ruled out an ignition problem? i.e. coil packs, ign. module etc....I haven't had time to work on my car, although the filter didn't help. I am pretty sure my car needs a fuel pump. Before I drop the tank, could it be the fuel pressure regulator? Am I correct to assume that a faulty pressure reg. would cause very high psi readings? Can anyone confirm this?

[MasterJacko96]

RE: same symptoms

my car does the same thing my 2.8 cutlass supreme it smells rich and eats gas way to fast and at about 40 mph is the time it falls on its face the most. it runs good in spirts but other times u can have your foot to the floor hear the engine working and reving all the way up and it barely moves. i went through about 4.5 gallons of gas in 40 or so miles u do the math thats horrible milage

[Juglenaut]

RE: same symptoms

If you had a bad pump the engine wouldn't run rich.

The thing about the regulator, the regulator regulates PSI and usually at 30 pounds or so. If overall pressure is not above 30 psi then it can't regulate it. You said about 12psi, then that is what is behind the regulator before the rail. However a regulator can stick partially closed, try and tap it to see if the engine flutters, remove the vac line, try and use lung power to open the regulator with a long piece of vac tube. You should see changes in pressure as you apply vac or pressure. If you don't see any changes after a physical test then it is very possible the regulator is bad.

You definitly should see more then 8psi with the key on test.

Bad enough injectors will throw a ICM code. Stuck open or floating injectors will cause flooding and possibly with vapor lock,..

[mikey67]

3.1 driveability issues.. *update*

Finally had the chance to get going on this and it turns out it was a weak fuel pump. This doesn't explain why it smelled rich initially, maybe due to such weak pressure the fuel wasn't atomizing properly when attempting to start? Not sure, but it runs now... Well, at least 'til the next problem arises!Thanks for everyones input! mikey67

[Juglenaut]

RE: 3.1 driveability issues.. *update*

There are several reasons the engine appeared to run rich, one is the knock sensor, the o2, and the map, and more reasons why.

I'd say that if the engine is starving for fuel the spark gets severly retarded, so to speak, instead of advanced, however it can over advance. So what fuel does make its way into the engine doesn't get burned, becasue the spark is either to advanced or retarded.

Basically the ECM is compensating according to recorded data to find the correct A/F ratio, spark advance and fuel advance.