Random misfiring, need input/help.

[HaLo]

Hey guys!

I've got a problem. My SR randomly misfires at boost over 9 psi. It gets worse when boostin' more. My idle is a tiny bit erratic too. I am currently running a retuned ecu for 550cc and Z32 mafs.

I have changed the plugs twice, gapping them differently. I have also changed the fuel filter and cleaned up the air filter. I'm getting good fuel pressure.

Now I never had this problem for 5000km or so. It's been a major pain in the last 800km. I suspect the coilpacks or the ignitor chip. How can you check these?

Any other idea what's wrong with the car.

[HaLo]

Forgot to mention that I also checked the timing and it's set at the stock 15 degrees.

[sil80phobia]

how do you know it's misfiring? Can you describe it? Is it only under light/moderate throttle, or WOT?

[HaLo]

Mostly WOT on everything over 9.5-10 psi.

the feeling is like stumbling or hitting some sort of fuel cut. It jerks, and it sounds horrible. Just like continuous backfiring.

[sil80phobia]

I've experienced that in the last 2 turbo cars I've owned.

If it feels like fuel cut, it could possibly be a boost leak. Did you just notice this after turning up the boost? Essentially turbo is boosting 9.5 psi worth of air. MAF has metered a certain volume of air indicative of 9.5 psi. Boost leak before the throttle body has bled off some of the air, so less than what the MAF has metered is entering the engine.

I made a simple boost leak tester. got a bit of intercooler hose, and hoseclamped it to a PVC endcap. drilled a hole in the middle of the cap and put a tire stem and sealed it with epoxy.

Remove the air intake pipe going to the turbine inlet and clamp onto the inlet. Hook up an air compressor (in a pinch, the tire compressors that hook up to your cigarette lighter will work), and pressurize everything.

I was able to get this tester to hold 20psi on my turbo eclipse. If there is a leak (usually a loose/faulty IC hose clamp) you can usually hear it. For the small and subtle leaks you can spray soapy water on different areas to see if any air leaks out.

[HaLo]

Thanks!! That's very helpful. I'll try that.

I had no problems with the car before. I was running 18 psi. One day, the mafs shorted out the ECU and I had to replace both and redo a part of my harness. Since then, I've been getting misfiring at around 10 psi and more. More boost equals more misfiring. A boost leak might be it.

[HaLo]

I found the problem. My coilpacks seems to be the problem. A friend lent me his and I can now boost at 16 psi without any problems. I had some carbon deposit on my coilpacks. I cleaned them and I'll test them one by one to see if they are still good.

[B-rob]

How do you clean coil packs