SR20DET Misfire, Hesitation Help!

[balangproject]

Car ran fine for 2 months after i bought it, now it has developed some issues.

It misfires at idle and when pulling away. The amount that it does it varies greatly from day to day, sometimes never.

It drives fine at low and medium throttle even with low boost, but once I go WOT it hesitates and misfires, theres is also a squeaking noise, maybe pinging its hard to tell. It does this from cold also so not a hot spot causing det.

- Ive replaced spark plugs to NGK copper BKR6E and gapped to 0.035 (0.89mm).
- Checked coil packs for cracks and they all have 1ohm resistance and grounds are fine.
- Cleaned MAF which has improved things slightly.
- No error codes (code 55), but O2 was oscillating from 0.2 to 0.8v, ive got a replacement. I'm running without for now.
- -21 vacuum on boost guage

Car is pretty much stock apart from Walbro fuel pump.
Ive yet to do a boost leak test.

Any help?!?!

[ultimateirving]

Drop gap to .030 or .028, really is the best gap on SR's to combat blow out. Boost leak test is you next step, because it causes those issues too.

[Magnoliarichj]

i had this same issue before my walbro died. went to a supra tt pump denso... no more issues.

[balangproject]

Thanks for the feedback. Did your walbro pump still prime as normal when you turned the ignition?

I did a boost leak check and I do have a leak. Got the intake to 4psi by pressurising it after the turbo, it lost all its pressure within 20 seconds. Couldn't pin point where from as I could barely hear anything.

[ultimateirving]

Thanks for the feedback. Did your walbro pump still prime as normal when you turned the ignition?

I did a boost leak check and I do have a leak. Got the intake to 4psi by pressurising it after the turbo, it lost all its pressure within 20 seconds. Couldn't pin point where from as I could barely hear anything.

If u can get it up to 8-10psi, it shud hiss loud enough for you to hear. Sometimes tiny leaks in vac lines can be hard to find. Sometimes you gotta bust out some soapy water and try to find the holes by making them bubble up. But really a boost leak is what points towards your symptoms.

[steve shadows]

Never run gap bigger than .028. We have tested on the dyno an remote tune customers .032 and even sometimes .030 and there can still be some missfiring at higher boost levels. Go with the .028 to make sure to avoid any missfiring.

[balangproject]

I tested my system before the turbo and it does loose pressure slowly, at higher pressure (enough to inflate and extend the main hose) I get a metallic hiss from the turbo area, maybe waste gate. Hard to pin point.

Should it hold pressure completely or even a slow leak will case an issue? Seem to pressurise it more than it would in normal operation.

[balangproject]

Also when I rev it will sometimes idle at over 1000rpm for a bit then settle. Vac leak???

But my boost gauge registers 20 or over vac at idle.

[balangproject]

It's not a boost leak. Had a smoke test done and nothing on the boost side.
The manifold gasket was leaking and has been replaced which has improved but not completely solved the issue.

It's weird because some pulls its fine, others it bogs/low power at certain rpm ranges.

I'm running out of options, I'll check the tps again.

[Magnoliarichj]

Did you check and or regroups the cool pack harness ?

[Kingtal0n]

Never run gap bigger than .028. We have tested on the dyno an remote tune customers .032 and even sometimes .030 and there can still be some missfiring at higher boost levels. Go with the .028 to make sure to avoid any missfiring.

well now hey, be careful with your blatant random disregard for plug gap. You should always run the largest gap you possible can. If the engine breaks up due the gap, THEN lower the gap or get a "better" ignition. Add an MSD box or something.

The larger the gap you can keep the better the performance and fuel economy will be.

[Magnoliarichj]

Do you know who your talkin to? Lol

[balangproject]

I've checked the coil pack grounds and the coil packs, but I still think it may be them. It was worse after I washed my car. I'll check if moisture got into the plug coil pack area.

[balangproject]

Update:
I ran consult again to check on things and MAF and TPS look fine, I'll post some graphs tomorrow so people can maybe spot something I'm not.

The car is fine up until 3k-ish, then often hesitates at WOTuntil 5.5k, then is GREAT until the limiter. WTF?????
I'm thinking the knock sensor could cause this, I'm not sure what th timing is supposed to be when revving. I'll post graphs of that too.

[ultimateirving]

Do you even have a knock sensor. i found out mine was mia.. And if you do try testing its ohm.

[Kingtal0n]

Update:
I ran consult again to check on things and MAF and TPS look fine, I'll post some graphs tomorrow so people can maybe spot something I'm not.

The car is fine up until 3k-ish, then often hesitates at WOTuntil 5.5k, then is GREAT until the limiter. WTF?????
I'm thinking the knock sensor could cause this, I'm not sure what th timing is supposed to be when revving. I'll post graphs of that too.


One line of thought is that the engine's volumetric efficiency is peak between 3k-5,500 and that is the most possible point for breakup due to insufficient spark, as was mentioned already. assuming you have oem camshafts, from 5,500rpm to redline VE is dropping, so is torque, and the mixture is easier to light off, thus the lack of misfire.

Knock sensors, if they are unplugged, will generally give very poor performance from the engine no matter what rpm is. Many computers are set to run full ignition advance only if the knock sensor is "hooked up" (or something that the ecu thinks is a knock sensor)

So, did you check the gap on the brand new spark plugs you installed? I mean, you DID install brand new NGK 7 heat range spark plugs, and used 7psi of boost from the oem turbocharger to help diagnose this, right? Also pressure the plumbing to check for leaks. those are notorious for causing misfires.

[unijabnx2000]

What heat range plug was in there before you put the #6 in there?

[balangproject]

The plugs in before were denso pk20, so same heat range as ngk 6.

They were gapped and have been regapped to 0.030.

A smoke test was performed on intake system, not under pressure. But I'm only getting 7psi in all gears, its all stock.

If I pressure test cold side of turbo, so disconnect vacuum to cam cover and plug it up, then Pressurise the system from the hose after the filter, should it hold 100% pressure??

[OutlawLui]

I have my BKR6E gaped to .032 and they burn perfect, even the color on the spark plug tips show that. Take out your spark plugs and inspect the tips...

maybe this chart can help http://www.mudinmyblood.net/forum/images/reading_spark_plugs.jpg

This way if they are in good condition, at least you can cross that out of your list...

[Kingtal0n]

The plugs in before were denso pk20, so same heat range as ngk 6.

They were gapped and have been regapped to 0.030.

A smoke test was performed on intake system, not under pressure. But I'm only getting 7psi in all gears, its all stock.

If I pressure test cold side of turbo, so disconnect vacuum to cam cover and plug it up, then Pressurise the system from the hose after the filter, should it hold 100% pressure??

Usually, you pressurize everything from the intake to the engine. In other words, stick a poly vinyl chloride cap with a tire valve stem into the INLET PIPE, yes the rubber part that holds the air filter, and from that point fill the entire plumbing with air pressure. This will help you find every leak along the way. Fill it to at least 15psi if you can.
You will want to cap the line that goes from the air inlet to the valve cover for best results.

[balangproject]

Plugs look ok, greyish maybe on the lighter side.

I haven't got a compressor so I've tried with a foot pump but it takes me ages to pressurise and air is leaked out through the valves in about 30 seconds.

But it was smoke tested and no leak was found.

[Kingtal0n]

Plugs look ok, greyish maybe on the lighter side.

I haven't got a compressor so I've tried with a foot pump but it takes me ages to pressurise and air is leaked out through the valves in about 30 seconds.

But it was smoke tested and no leak was found.

some leaks will not show up until some pressure is applied.