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Old 04-19-2011, 05:13 PM   #1
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Default Running fault during dyno tune

Hello from across the pond

Okay I've got a strange problem that I need help with. Basically the car is a race car and has just had a full engine rebuild, little bit of head work, fitted with a T28 Garrett turbo, MiataLink ECU, 600cc Deatchwerks Injectors, Large intercooler. ETc ETc.

Now the car was on the dyno being tuned and all is well, apart from after a high rpm run when the clutch is dipped and engine idle's it drops to 3 cylinders (sometimes 2 cylinders) and then slowly picks back up to 4 cylinders. If the car is loaded back up on boost on 3 cylinders it clears and pulls like a train on 4 cylinders. It sometimes drops cylinder 1 and sometimes cylinder 2? But not 3 or 4?

Can anyone point me in the right direction of the problem.

Cheers.
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Old 04-19-2011, 05:16 PM   #2
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Is it always cylinder 1 and 2? What ignition system, which car year and what engine?
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Old 04-19-2011, 05:20 PM   #3
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Is it always cylinder 1 and 2? What ignition system, which car year and what engine?
Yes always 1 or 2, sometimes both. Running standard ignition system. The car is a 1990 1600cc.
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Old 04-19-2011, 05:23 PM   #4
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Does it pick up instantly if you unplug and immediately replug the spark plug wire for that cylinder?
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Old 04-19-2011, 05:26 PM   #5
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Does it pick up instantly if you unplug and immediately replug the spark plug wire for that cylinder?
No pulling the lead off and replacing makes no differance the clyinder remains dead. The HT lead can be heard arcing when pulled off.
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Old 04-19-2011, 05:30 PM   #6
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Sounds like an injection problem then - try to pull one injector connector off (cyl 1 or 2 - whichever one is not firing) and see if that changes behaviour. Either something is faulty inside the ECU (injector drivers) or the injectors themselves are whacked out. For starters you can swap injectors between cylinders to see if that changes the pattern (move 1+2 in place of 3+4). If the cylinders affected are now 3 and 4, you need to check your injectors.
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Old 04-19-2011, 05:40 PM   #7
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Sounds like an injection problem then - try to pull one injector connector off (cyl 1 or 2 - whichever one is not firing) and see if that changes behaviour. Either something is faulty inside the ECU (injector drivers) or the injectors themselves are whacked out. For starters you can swap injectors between cylinders to see if that changes the pattern (move 1+2 in place of 3+4). If the cylinders affected are now 3 and 4, you need to check your injectors.
I'll try switching the injectors around tomorrow, however they are brand new Deatchwerks 600cc injectors. I'd be pretty pissed if they weren't 100%. The ECU on the other hand is pretty old.

It just seems odd that it sorts itself out after idling for little while and has no effect when load/boost is applied.

It also seems to get progressively worse, ie the first run it would be fine, second run it would drop a cylinder but come back quickly, third run maybe take longer to come back and then maybe drop two cylinders the next time.
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Old 04-19-2011, 05:48 PM   #8
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Sounds more like injector drivers then. You can confirm this if you have an oscilloscope - if you probe the two pins on the injectors while idling, on the faulty cylinder, you won't see injection events.
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Old 04-19-2011, 05:55 PM   #9
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Didn't probe them with an oscilloscope, but when the cylinder was missing we felt the injector and it seemed to be pulsing. But will check with a stethoscope tomorrow to see if I can here the injector clicking, don't have a working oscilloscope at the garage.
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