TS Misfire in a 3.1 TBI Chevy engine

[Meridivs]

On our 200+ miles trip for Easter holidays the Pontiac TS 3.1L TBI engine started to miss under acceleration and lose power uphill.

After a few minutes everything came back to normal and we made it ok to our destination but some misfire can still be heard at idle.

I have attached the audio recording of it at http://vocaroo.com/i/s1qbeh6OVmFX

If you have encoutered this problem or you have an idea on where we should start troubleshooting this issue you are most welcome!

Thank you!

[Blue Bowtie]

Begin by checking the common causes. Spark plug gap, ignition wire condition, and coil pack condition. It is possible that the problem is also fuel related, involving injectors or fuel pressure, but given the random nature of the miss ignition is the more likely cause.

[Meridivs]

I have checked the obvious things so far - distributor cap, rotor, spark plugs and wires were changed recently and look OK, not touching ground or anything hot on the engine.

Vacuum lines are also ok, not loose, cracked or disconnected.

The only thing we can rule out so far is the fuel system - this van has dual gas and LPG fuel systems, problem is the same on both.

I wonder what we could try next beside pulling plugs to check for spark/fouling.

[Blue Bowtie]

Inspect the plug condition and gaps. The 3.1 uses a wasted spark system which is more sensitive to plug gap since the firing occurs across two plugs in series. If one is "dead" the adjacent cylinder in the firing order is also dead.

[Tech II]

Blue, he has a distributor......HEI system......

I would be checking spark output with a spark tester........

Look for vac leak around throttle body base.....

Also aim a timing light(remember those?) at the spray out of the injectors, and see if you see large droplets......could be a bad injector.....

Have had to replace a few ECM's on TBI setups.....

What year?

[Meridivs]

1992

Fuel System is out of the question - I also have an alternative LPG fuel system, independent of the gas system and the problem manifests on both.

[Meridivs]

We just changed spark plug wires (Delphi) and spark plugs. Cap and Rotor were changed less than 20K miles back and are looking good.

Old plugs (ACDelco) were good, with no strange *deposits/carbon build-up.*Unfortunately car is running even worse now - very rough idle with frequent intake backfires and spitting sounds on the exhaust. Mechanic believes it's an electrical issue more than anything else.

We have a Code 22 on the diagnose interface - TPS sensor low - just ordered the TPS and will post after we replace it.

[StumpedGMowner1]

Did you test the old tps sensor and harness before ordering new sensor?? Common place for harness damage.

[maltondhc]

I am basing the information I have on my manual for my 1995 TS, which indicates code 22 that an open or short to ground in circuits 416 (5V ref),grey wire from A term on TPS, or circuit 417 ( TP sensor circuit, blue wire, terminal C).
I have had similar issues with my 3.8 TS, where wires have broken internally, most often within about 15 cm of the engine side of the body connector harness.
Circuit 416 in cavity J2 in Connector 110 (30 pin connector)
Circuit 417 in cavity J4 in connector 111 ( also 30 pin connector
Connector 110 located forward passenger side of engine compartment
Connector 111 located closer to firewall, passengers side
Turn ignition on, disconnect TPS wiring and measure for 5 V. Squeeze, bend, push, pull harness to see if you lose the voltage when you encounter the break in the wire.
Similarly, check for continuity in circuit 417.
Good luck