Help - light load misfire - Miata Turbo Forum - Boost cars, acquire cats.

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Old 08-11-2012, 04:25 AM   #1
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Join Date: Jan 2012
Posts: 15
Total Cats: -3
Default Help - light load misfire

Hey guys and gals, after a little help. im stumped.

I have a mx5 mk 1 1600 stock motor running a gt 28 motor, 550cc rx7 injectors and megasquirt pnp ecu.

The car has some kays on it but good compression, starts first go, and on boost goes like the clappers. the motor is strong and sound. The problem is i have this light load misfire from about 1500-3000 rpm and i cant track down the cause. I have new magnacor leads, tried new plugs, new coil, another good cas, rewired the stiff cracked coil and cas wire harness and still no joy..... im stumped.

cleaned all the grounds on the engine i could find.

there's no noise on the coolant temp sensor (the one at the rear of the engine)

tried either unplugging or making the following items redundant on the megatune.
the VTPS, the front coolant sensor, the wide band 02 and still no luck.

Any suggestions?. anyone had a similar problem before?

and before anyone suggests it i have checked the megasquirt board and it already has the js8 capacitor filter installed.

afr's as the mis happens are at about 13.5 before spiking lean due to the miss.

thanks in advance.

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Old 08-11-2012, 10:28 PM   #2
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Join Date: Jan 2012
Posts: 15
Total Cats: -3

Anyone willing or able to give me a hand?

i've attached a data log of the issue. have a look at just before my second mark at about 488 seconds. you can see pw and duty cyle and spark angle all oscillate but i think thats a sympton not a cause.

any help would be appreciated.
Attached Files
File Type: xls datalog201208120915.xls (532.2 KB, 54 views)
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