HELP: 4age 20v bt stuttering and missing

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HELP: 4age 20v bt stuttering and missing

Postby sja4ag » Fri Mar 17, 2017 11:11 am

So i have a complete 20v bt swapped into my ae86. when the car is cold most of the time it will rev all the way to 8200. What I mean by that is that I will get 2-3 pulls to redline before it starts studdering and missing at 6500 (after letting it warm up a bit at first). Then once it has reached operating temp or if I have done 2-3 pulls, it will pop and studder at 6500 almost as if it is hitting a limiter. If I apply less than half throttle it will rev all the way up without issue.

The car has SQ Engineering coils with a Tweak'd Performance harness. After taking out the plugs, it seems that the motor is running a bit lean. I changed plugs, fuel filter, checked my injectors (all seem good), and my fuel pressure is good (fuel pump is a replacement OEM GTS pump that works great). I can't figure out what is wrong for the life of me. Sometimes it will not happen as bad, or it will studder and get past it and rev up to 8200, but other times it gets worse and it will studder and miss all the way from 3500ish until 5k then miss and not rev any higher. After the car is at operating temp however, it is almost 100% that it will miss and do this. When it hits 6500 it will studder pop and crack out of the exhaust (backfires). I would assume that it was spark cutting because of the backfiring which is really loud, but when I checked the plugs it seems that it's running lean. I tried disconnecting the o2 sensor as well but that had no effect. If anyone has run into an issue like this or can help me out that would greatly appreciated. thanks.
1985 hatch, 20v silvertop -- drift car (soon to be f20c swapped!)
1986 coupe, 20v blacktop -- daily

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Re: HELP: 4age 20v bt stuttering and missing

Postby jondee86 » Sat Mar 18, 2017 2:07 pm

At a guess I'd say you are probably running open throttles without the factory airbox
and filter. So its likely your engine is running a bit on the lean side. The engine gets
a bit of extra fuel (enrichment) when cold, so that will let it run cleanly until it warms
up and the cold enrichment tapers to zero.

I don't know of any good solutions, but you could research the coolant sensor kludge :)
This involves inserting a variable resistance potentiometer into the cooling sensor
wiring. Then you can adjust the signal to fool the ECU into believing that the engine
is colder than it really is, and the ECU continues to run a richer mixture.

This kludge was popular back in the early silvertop days and with modified 16V's, and
maybe it will work with the blacktop.

Cheers... jondee86
Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

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