Near End of Life. Please Help!

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?

Year?

Check for any codes set?

TBI, multi port, or sequential injection?

Have you done a coil output test at the end of each ignition wire?

How many miles?

Done a compression check?

1992 3.1L V6 TBI with 160K miles.

No codes on the diagnose interface (I have the ALDL software on a laptop but nothing's out of the ordinary).

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

Here is a sample audio file with engine running:

http://pc.cd/v3dctalK

I remember a post from LMP saying something about an Ignition Relay, does anybody knows where that might be located?

Any other ideas?

My 1993 3.8 has an ignition module. ONce dead, that was it: not intermittent. Totally different from your 3.1 that uses a rotating distributor.
The other issue was the ignition switch itself. Started as an intermittent problem..but got worse with time. It is acted on via a long metal link that goes to the ignition key barrel. It is located low on the steering colums and almost out of reach. I have simply added a relay that I turn ON with a separate toggle switch . This relay applies 12V to the fuel pump circuit (common to the ignition circuit). I still need the key to start but the engine, once started, is kept alive by this circuit. But again this is for the 3.8.

Thank you for the pointer - I've seen in the catalog two parts:
- an ignition relay
- an ignition switch

LMP, you said about the ignition switch failing and causing intermittent operation/misfires?

I'm guessing that these parts are common between the 3.1 and 3.8L Pontiac TS.

Do you have an idea where the ignition relay might be located on the TS? I might check/change that also while we're at it.

I would suggest checking fuel pressure also.

The fuel pressure is all right - just changed the fuel pump a few months ago - before that it took 2 keys to get it started, now it starts right away with the new fuel pump.

On a second note this car also has an alternative LPG fuel system that's independent from the original ones, when it misfires it misfires on either fuel system which lead us to think it's an ignition issue.

Another thing to look for is a poor ground for the computer. I believe it is located on a ground stud just above the starter; check the wiring for looseness and corrosion.
Jeff