Near End of Life, Please Help!

[Meridivs]

Our trusty Pontiac TS 3.1L SE has developed a bad case of misses while hot. It's like the engine cuts-out for a second then recovers and so on until it eventually stops. In higher revs it's usually ok but sometimes the rpm just drops.

Nothing we've tried so far had any effect:
- changed the whole distributor assembly with ignition-control chip and new pick-up coil
- changed the ignition coil
- tried another engine computer/ECU
- spark plugs are original ACDelcos and new
- spark plug wires are new
- Idle Air Control valve is new
- every other sensor checked-out ok

We're at the ropes-end with this one.

Any ideas on what we could try before throwing in the towel?

[jacobi22]

i'm not a specialist for the 3.1 engine, but it look's for me like a problem with the fuel pressure or with the electric

fuel pressure: fuel pump inside of the tank & electrical wire or connector nearly to the filter, fuel filter, tank ventilation (open the tank, if the problem's come - better?

[schnezi]

When the problem only appear when the engine gets warm it can maybe problem with the egr, unplug the vacuumline from the egr and close the line
schnezi

[heavyhinkel]

Check the o2 Sensor for he should work on the entire range from 0,00 to appr. 1,00 Volt.

Did you checked the fuel system? (pressure regulator, fuel pump)

Even the vacuum lines are allways a hot spot for hesitation.

regards

Thomas

[Meridivs]

Thank you for your ideas!

Just changed the EGR valve with a new Delphi unit, no effect - engine maintains idle for a while then just starts to misfire until it dies.

O2 sensor was changed recently & is working as it should.

Here is a sample audio file with engine running (here it recovers after the idle drops):

https://my.pcloud.com/publink/show?code=...oChyVyKOI7

Any other ideas?

[jacobi22]

the audio is nearly to my problem with the harmonic balancer on the 3.8-engine (broken rubber in the center), but i'm not sure, how it work's on the 3.1-engine

[yogibaer]

I listen to the audio file.

You have a hart noise that is not normal, thats the Problem.

May be a crack in the Distributer cap.

regards

Gerhard

[schnezi]

The 3.1 works only ober the Ditriputer and the picup coil so the could be no Problem with the harmonic ballancer, what can be is an broken house in the fueltank between fuelpump and Fueltankcap, maybe the fiel pressure regulator get stuck
schnezi

[heavyhinkel]

Did you any works on the vacuum lines or their connections to the throttle body?

The vapor canister shall be connected on the the only ported vacuum connector. That will ensure that vapors are consumed when throttle valves ar opened.
Ported connectors are closed as long as the throttle valves are closed.
Consuming vapors during idling can cause instability while idling.

Thomas

[Meridivs]

Thank you for your ideas!

To take one at  time:
- the distributor assembly is all new (with brass contacts cap, rotor, pickup coil and ignition module) and of highest quality. Ignition coil is also new along with the wires and new ACDelco spark plugs. I would rule this out for now since the idle issue stayed after changing all this.

- this car has a new fuel pump which really does its job (it starts much easier now than it started with the old fuel pump) and also have an alternative fuel system - LPG. Idle issue/misfires are the same regardless of the fuel system we use. If it was a problem with the pump it would have been different on LPG.

- the vapor canister is something I can look into but it feels like there's no spark or at the wrong time in some cylinders. I can only describe this as something stealing the spark/air from the engine when it gets hot. It can be an electrical issue or a vacuum one (we have already checked all the vacuum lines going to the Throttle body).

Wonder if this ever happened to any of you that have the 3.1L TBI engine?

[schnezi]

Cant remember to hear this Form an 3.1, one possibility is to check the connecrors if there are broken whires vor mad pins,
schnezi

[Meridivs]

Problem sorted finally.

After more than 2 years looking for all kinds of mechanics and electricians we found one that did it.

He nearly took apart the whole wiring and found a wire to the Ignition Control Module that was not doing its job as it should have. Cost us dearly but now the engine idles & runs like new.

Damn electrics... this could nearly become the end of our dustbuster.