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Old 12-30-2014, 08:26 PM   #1
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Default Crazy misfire/hard start, car won't run

First off I apologize for posting this without a video and I should have one up soon.
I have a 94 block/96 head with Megasquirt and gm wastespark coil setup. Recently I got dyno tuned after redoing my intercooler setup. While on the dyno my voltage regulator started failing and my voltage shot to around 27 or 28 volts if I recall correctly. I proceeded to get home, swap the alt out, and drive the car with no issues for about 4 days.
After getting used to the new tune and going easy on the turbo I figured I'd take the car out and beat on it. The car ran great while I took it through it's paces and I parked it shortly afterwards.
Well fast forward about two hours and I leave my friend's house to get gas and go home. The car drives fine all the way to the gas station (about 15 minute) and starts up fine when I leave. 30 seconds after I pull out of the gas station I take a right hand corner at about 25mph, just cruising, go back into gear and apply throttle and the car starts bucking really hard and missing. I pull over and shut the car off and start it back up with no issue, start driving it again and it starts randomly missing with anything over a feather press of the throttle. I get home, park the car, start it up again and it sounds like a tractor and backfires randomly.
I shut the engine off again, start it back up, and it starts "binding" while turning over. It'll try to crank and then it seems to get a lot of resistance and just falls on it's face. If I do get the car to start it idles like **** and backfires out the exhaust.
Also unplugging the injectors from cylinders 3 or 4 will cause the hard crank to go away and the car turns right over

I've changed my CAS, ICM base for the coils, coils, spark plugs, injectors, had continuity checked throughout my harness and even ran a compression test (130,130,140,120 rounded numbers obviously but very close). I also had my tuner/MS builder check my Megasquirt to see if something was misbehaving with no luck. I'm at my wits end for what could be wrong and I'm about to just call it quits and tear the engine out.

-edit- The car made 250whp/260tq at 17-18psi, stock internals. Just posting that in case I bent a valve? I was told a compression test would show a bent valve though....

Last edited by KipCantDrift; 12-30-2014 at 08:40 PM.
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Old 01-05-2015, 12:14 PM   #2
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Old 01-05-2015, 12:43 PM   #3
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are the voltages still in check?

backfires suggest too much fuel, system flooding, then BOOOOOOOOOM.
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Old 01-24-2015, 09:43 AM   #4
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I have a very similar problem on my megasquirt 1.6 turbo. I have changed coils plugs igniter ect. But when it warms she back fires and losses 2 cylinders very random my Afr gauge shows full lean though , could be a bad cam signal I guess . I have a 255lp pump and 550cc injectors with a stock regulator I was thinking possibly the fuel pressure is to high with stock fpr locking the injectors. new regulator is on the way hopefully this fixes it I will let you know. I am also tearing my hair out.
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