3.2 Carrera Race Car Miss. Need help.

[regnihe]

I'm also posting this in the racing forum.

Help;
Chasing a miss in the race car. 87 3.2 Carrera. PCA Club Race prepared. Extremely well developed car. Very competent crew. Multiple head scratching trying to diagnose this issue.

Symptoms;
-Slight stumble/miss fire.

When does it happen?
-After 2-3 laps, on track. 12-15 minutes of run time. Does not happen before 10 minute mark.
-Around 4200-6200 RPM, but at WOT.
-Happens in left and right corners. Also happens on straights.
-Seems to appear soon after a shift, or after getting off the throttle.
-Driver reports via radio to crew. Driver describes it as “stumble”.

Thing check, replaced up until now.
Fuel:
-Checked for bad gas.
-Pulled all mechanicals out of fuel cell. Check pick up, lines etc.
-Inspected fuel line to look for crimps or collapse.
-Metered fuel injectors.

Computer & Engine
-Swapped complete engine.
-Swapped ECU.
-Swapped engine wire harness.
-Replaced all plugs
-Metered plug wires
-Connected MSD box. Disconnected MSD box.
-Replaced coil. Twice.
-Steve Wong Chip. Checked twice.

-Replaced ignition switch.
-Replaced air box with rebuilt. Twice.
-Metered all reference sensors.
-Checked TPS.
-Replaced fuel pump.
-Check all wiring/grounds for shorts.
-When engine was swapped, wire loom came with second engine.

Update 5/20. Installed new/used wire harness. We metered the harness before installing and all was good. Same exact problem. We ran the car today. First two 15 minute sessions the car was fine. After lunch, 45 minute session and it starts to miss and gets progressively worse. It is certainly heat related. Changing out all the injectors tonight again.

Car is equipped with AFM and exhaust temp sensor. When miss happens, exhaust temp pegs. We are running out of things to check/replace. Any suggestions welcome and highly appreciated. If you find the cause beer at the WGI club race is on

[rsscotty]

What is your spark plug part number, and gap?

[ClickClickBoom]

Coil

[regnihe]

Replaced coil. Twice.

[ZOA NOM]

Peel back each plug wire end to verify the integrity of each metal "elbow" inside. I had one (from the coil) that cracked at the bend inside, and it would meter fine when I pressed a probe in there, but it would open up on the track.

edit: I see no mention of the DME Relay... did you swap it?

edit: also check the flywheel sensor gaps

[snbush67]

Detonation? Pull some timing out and see if it goes away.

[Tippy]

Detonation? Pull some timing out and see if it goes away.

Missing and rising EGT's sounds like detonation to me. Sure the WOT switch is working?

[rick-l]

Another long shot do the weights in the distributor move freely?

[Texel]

Had a suggestion for finding the cause of a miss in an old 2.25 landrover I once owned, I couldn't decide whether it was fuel or electrical.

In the end I didn't have to do it, but I thought the theory was interesting.

Clip a timing light pick up on each low tension lead individually (on a long extension) and put the timing gun on the dash and take it for a drive, at whatever rev range you are experiencing the miss you can see the timing light falter if it involves that lead, point, electrickerythingy whatever.

If all 6 behave, then you start looking at fuel delivery.

Like I said, I never tried it, but the concept looked like it had potential.

Might be worth a try

[911quest]

Check and adjust the valves also check the ground wires on the intake manifold to make sure they are tight.

[Joe Bob]

Fused power to the DME cutting out?

[rsscotty]

There are a lot of helpful comments regarding this issue, but not much feedback from the OP.

[porterdog]

Originally Posted by regnihe

Replaced coil. Twice.

With what? The Bosch Silvers from Brazil have a well known rep for complete suckage.