Mystery Misfires after 1-2 min of running

[Jin356b]

I'm trying to finish up my build, but my engine likes to start misfiring 1-2 minutes after I start it. I can usually find the answer to these things by surfing the forums, but i've been working this issue for 2 months without success. The car went from stock to TD05 20Gs, 660cc injectors, new timing belt/tensioner, e-manage ultimate w/stage 3 wiring. The misfiring isn't so bad that the car will stall, but the idle rpm and A/F ratio likes to hunt around. The car runs great when I first start it, then you notice the engine start misfiring. Using the timing light, I can see that some wires fire more inconsistently that others. I've listed below what I've done so far:

-Fixed boomslang harness (1 ign input/output chan was reversed)
-Fixed fuel injector o-ring leak
-Change plugs from platinum to coppers
-New Accel plug wires
-Regapped coppers to .030
-Installed new OEM coil pack
-Tested PTU - ok
-Verified marks on cam gears still line up properly

Fixing the boomslang harness help steady out the idle, but didn't fix the misfire problem. I'm almost to the point where I'm going to rip off my accessory belts to verify the crankshaft gear is still aligned with the cam gears. However, the spark plugs should still fire regardless of what is or isn't in the cylinder. So, the only other thing I can think of is to replace the PTU anyways, or maybe my wiring harness is bad, and I should rerun the ignition wires.

Thoughts? Ideas?

-JB

[silentbob97]

Are the injectors new or used?

[Jin356b]

The injectors are used. I soaked the pintels in some brake cleaner before I installed them. If the injectors weren't working, wouldn't you still get a spark?

[glimerman]

but the idle rpm and A/F ratio likes to hunt around

Sounds like something else going on.Usually misfire can be isolated pretty easy to particular cylinder.

[silentbob97]

The plugs will fire yes, but maybe one of the injectors is stuck open or not spraying like it should.

[Jin356b]

After sitting for a couple days, I fired up the engine again, and it started misfiring right away. The only thing that changed was the temp outside. It was around freezing the previous time, and ~30 deg F warmer this time. Maybe something the ECU does at cold temps helps fix the problem?

I used the emanage to advance the timing 15 degrees (equal to 1 tooth on the crank sprocket) and it had no effect. So, I don't think its a timing problem.

I pulled all the injectors, and I made a homebrew flow tester. So, I should know soon if any of the injectors are misbehaving.

Random Thoughts: I'm basing my whole misfire theory on the fact that my timing light shows erratic flashing. But, what if the timing light doesn't flash on low voltage sparks? Our engine is a wasted spark system, with 2 cylinders firing at a time. The cylinder filled with air and fuel takes over 40,000v to fire, while the empty cylinder takes ~18,000v to fire. So, if a spark plug fires in an empty cylinder (or a cylinder with a super lean mixture), would the voltage get high enough to trigger the timing light? I guess this could also depend on the sensitivity of the timing light and shielding of the plug wires.

[Jin356b]

All my fuel injectors flowed good. Looks like its back to the drawing board....

[speedy25]

Originally Posted by Jin356b

I'm basing my whole misfire theory on the fact that my timing light shows erratic flashing.

You still have an ignition problem. The timing light should be even and steady. This is the part of the job where you swap parts around and try to isolate which one may be the problem. SO far you have done all the right things byt changing coils/plugs/wires and testing the PTU, but you are still missing something. CAREFULLY check all connectors for tightness and corrosion free. Its easy to have one bent and not connect properly.

You're almost there!

-SP

[Jin356b]

Thanks for the encouragement Speedy. I started to look more at the temperature being the problem, because the car seemed to run well around freezing temps. And then I noticed that the emanage was reporting my coolant temp around 30 below what the ambient outside temp was. So I tested the connection to ensure it was getting the proper voltage, and replaced the sensor. But the temperature was still off. So, maybe the emanage just has a screwed up temp reading. I got to get a hybrid compatible OBDII reader to verify what the ECU sees.

After that, I opened up the ECU and made sure there were no bulging/leaky caps. Everything looked good, but I read a post that bad caps in the ECS controller can affect the ECU. So I unplugged the ECS, and tried starting her up. I forgot my laptop that day, so the AFR was set kinda rich (~11 at idle), but she idled a lot better than before. I still noticed a little misfiring, which was confirmed with my timing light. All cylinders were firing nearly perfectly, except for cylinder 3. He was only firing consistently about 60% of the time. Maybe it was only running so much better, because it was super rich. I gotta remember to take my laptop next time and confirm that.

Either way, I'm done with this troubleshooting crap, and I need to get this car registered in my new state. So, I'm just going to through in some 360cc injectors and rig up the stock MAF somehow. This will allow me to remove the emanage, and hopefully, everything will work right.

If anybody's got a good set of 360cc laying around, let me know what you want for them. I wish I still had the originals, but I left them with the guy who helped me install the turbos.

-JB

[westcott]

What year is this?

Did you check the CAS or does it have a trigger?