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Discussion Starter #1 (Edited)
Alright, help me out if you can please, i have a 97 240SX with a non-vvti 1JZ swap, just finishing it up.

So from the very beginning, when I first started my new engine, it ran rough, and had a random misfire at idle. I figured it was the 20 years old oem coil packs with small hairline cracks, so I replaced them with replacement coils from Autozone. The car ran 100% better at idle, and driving around town, no miss, no stutter, just that smooth JZ growl, however they developed cracks and missed under WOT at full boost(cheap chinese coils). So then I bought brand new OEM Denso coil packs (see below), and now the car runs like total dick again. Random misfire at idle, runs on 4-5 cylinders when cruising around town etc...So heres what I did tonight:

* Tested my NEW Denso coils, on a known-good 1JZ with exact same build, car ran its ass off, confirming that the coils themselves are not bad.
* Tested ANOTHER set of used cracked AutoZone coils on my engine, random misfire at idle went away, and drives around town flawlessly, but still misses under WOT full boost.
* Tried a new ignitor...no change
* Went through each brand new OEM connector, and resqueezed the pins to ensure a full connection...no change.
* Unplugged each coil one at a time while the car was running, each time it changed the idle, and you could hear it make a difference
* Unplugged each injector one at a time while it was running, each time it changed the idle, and you could hear/feel it make a difference
* So both those tests show that its not a specific cylinder that has a problem.

Its a random, constant misfire at any load above 10% throttle. All the way home from the shop it ran on 4-5 cylinders, with a very rare and occasional clearing of its throat and ran normal for split seconds at a time...

What in the fuck could cause it to run rough on 4-5 cylindrs with 2 different sets of OEM Denso coils and a constant random misfire, but run 95% better with the 2 different sets of Chinese Autozone coils?

Car:






Engine Spec:
*1JZGTE (low mileage in great shape)
*HE351CW turbo
*440cc injectors
*Stock ECU+SAFC+FCD (very mild adjustments made)
*Plugs are new (~300 miles) NGK BKR7E gapped at .028
*Denso Coils (brand new in box, OEM Denso, with brand new OEM connectors)
*Aeromotive AFPR @ 44psi
*Aeromotive 340lph fuel pump
 

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have u pulled the connectors(injectors) at 10+% throttle to find the dead hole? ...u don't want to pull coil wires to check for misfire. sounds like ur testing idle, when off idle is the issue. (sounds to me like a stuck injector dumping fuel off idle). check resistance of the fuel injectors cold and warm. they should be with in .2 ohms of resistance (field test, not by the manual)
 

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Discussion Starter #5
have u pulled the connectors(injectors) at 10+% throttle to find the dead hole? ...u don't want to pull coil wires to check for misfire. sounds like ur testing idle, when off idle is the issue. (sounds to me like a stuck injector dumping fuel off idle). check resistance of the fuel injectors cold and warm. they should be with in .2 ohms of resistance (field test, not by the manual)
It misses at idle also, sounds like its running on 5 cylinders constantly, but no specific cylinder showed signs of dead.

AFR at idle is 14.4-15.2
 

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Discussion Starter #6
Ok, here's a bit more info, maybe we can see if this makes sense to anyone.

The Chinese Autozone coils all ohm out at .8-.9, where as all of the OEM Denso Coils ohm out at 1.0-1.1 Does that make sense to anyone else?
 

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Ok, here's a bit more info, maybe we can see if this makes sense to anyone.

The Chinese Autozone coils all ohm out at .8-.9, where as all of the OEM Denso Coils ohm out at 1.0-1.1 Does that make sense to anyone else?
Did you check the resistance hot or cold? Your numbers are alittle high if you checked them cold. But nothing that should cause any issues
 

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Unlimited Time Attack A70
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Have not, I will be planning on checking that this weekend. But why would it run good with one set of coils, and bad with another set?
yea i was thinking this aswell. Not to sure, was more jsut throwing out a possible cause for bad runablility
 

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Discussion Starter #11
Ok, now whats the relation between the 2? What part of the ignition system would have a hard time firing the 1.0 resistance coils while being able to fire the .8 resistance coils? If its not the ignitor, because we tested a different ignitor.
 

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Crank trigger wheel could have separated and re-adjusted itself, slightly?
 

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Discussion Starter #13
I appreciate the idea, But I dont think that's possibly it at all. Because it went from running shitty, to running pretty good, to running shitty, to running pretty good. All with trying different sets of coils, there have been 4 sets of coils on this car in the past 2 days. Both sets of Denso run the same, both sets of Autozone run the same.
 

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Unlimited Time Attack A70
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This sounds very much like a worn cylinder bore. If your oil level is low at all, fill it to just above full. If you do have cylinder scoring, the oil will help seal the piston rings. Also, try a compression test as well, hot or cold. Your bad cylinder will reach a low compression and will take more cranks to get there.
 

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Discussion Starter #17
This sounds very much like a worn cylinder bore. If your oil level is low at all, fill it to just above full. If you do have cylinder scoring, the oil will help seal the piston rings. Also, try a compression test as well, hot or cold. Your bad cylinder will reach a low compression and will take more cranks to get there.
Just curious how you came to a "worn cylinder bore" from a weird ignition misfire lol
 

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Unlimited Time Attack A70
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This sounds very much like a worn cylinder bore. If your oil level is low at all, fill it to just above full. If you do have cylinder scoring, the oil will help seal the piston rings. Also, try a compression test as well, hot or cold. Your bad cylinder will reach a low compression and will take more cranks to get there.
:scratch::wtf:
 

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Discussion Starter #19
Well, looked at the ECU, looks like at least 4 of my capacitors shit themselves and need to be replaced...that's encouraging, I'll get it done this weekend. What plugs does everyone run on these engines?





 
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