legacycentral bbs

I'm not sure if this belongs here or in the electrical section, so mods, feel free to move this if needed.

I have been troubleshooting this problem off and on for about a year now, and I am at a loss of what could be causing my car to not fire or miss on cylinder 4.

I have tried swapping the coil pack between 3 different coils, new spark plugs and new spark plug wires. I've also smoke tested the intake track, done a compression test which came back really good, and a leak down test as well that was good. I have tested all the wiring for the injectors between the plugs to the ECU. The last thing I tried was swapping the rocker/lifter assembly from a known good head to mine, and it still misfires. Examining the spark plug on cylinder 4, the plug is very fuel fouled. All other cylinders spark plugs look normal. If I pull the spark plug wire from the coil to #4, I see spark jumping the gap, but there is no change in how it runs. If I pull the injector plug to #4, there is no change in how it runs. WB AFR is between 14.5-17 at cruise, and almost always dead lean while accelerating (only light acceleration, no boost). I think this is skewed though because of this problem. Sometimes under acceleration, there is backfire in what sounds like the intake. Timing is also correct.

Now the kicker here is the miss is almost always there. It's there 100% on cold start, and regularly there on warm start. Sometimes (I'd say 1/20 times) when I am driving it and cruising at around 3000rpm, the misfire stops, and the car runs awesome, like nothing has ever been wrong. AFRs when running correctly are in the 14's when cruising, and 11-14 while accelerating. EBC is set at 12psi.

Does anyone have any idea(s) about what is going on here? I am now starting to wonder if something is wrong with the Robtune ECU. My supporting mods are in my signature. Thank you for any help.

Have you checked the resistance of each injector? They should be between 11-12 ohms.

http://main.experiencetherave.com/subar ... iagram.pdf

If the resistance checks out I would try swapping the number 4 injector with another cylinder to see if the miss stays with cylinder 4 or moves to the cylinder with the previous number 4 injector. If the miss moves, then you have a bad injector and need to replace it.

I knew I forgot some important info in my OP.

I have also had the injectors rebuilt once and cleaned/flow tested twice by WitchHunter. Both times they have come back good. I have also done what you suggested: all the injectors are between 11 - 11.4 ohms. I've also tried swapping injectors between cylinders 1 and 4, but the miss didn't follow the injector, the miss stayed on #4.

Now that's very interesting....how does the compression of that cylinder compare to the others?

Any chance you have access to a boroscope to see if there more carbon build up on the piston top compared to the others?

Like you, I'm kind of at a loss if all the components that could affect that cylinder have been swapped and the issue still remains. The only long shot I could see is something related to timing; crank gear, belt, sensors, etc.

The compression test is within 5 psi on each cylinder. Compression was great - ~150ish psi on each cylinder warm.

I unfortunately don't have a boroscope to see if something is going on in the cylinder. Maybe I should try to find someone with one.

Is there any chance this could be the Robtune ECU? Do you know if he is still around?

Thank you for your help and ideas.

It's possible it could be related to the Robtune. I guess one thing to note or question, are you using the 4-to-2 ignition converter with the robtune ECU? There could be something bad with the converter or wiring related to that or the ECU.

Rob is still around, I think your best chance of getting a hold of him is by email. I am pretty sure his email is on his website.

Yes, I'm running the 4-to-2 ignition converter. I'm not sure how to diagnose it though. I've given the wiring a once over real quick, but I will go through it again more thoroughly to see if I have any mistakes or loose connections.

I think I'll try reaching out to Rob as well and see if he has any ideas. I'll post back here with any helpful info.

The only thorough way to check the wiring is a point-to-point check with a multi-meter to check resistance.