Author Topic: Intermittent `Bad´ Starting  (Read 2468 times)

Offline Super fx

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Intermittent `Bad´ Starting
« on: January 06, 2022, 10:21:40 pm »
Happy New Year to everyone,
I´m hoping someone can help me with some inside knowledge of vems.
I have a V3.3 (bought from Peep as a pnp as i really didn´t want to be going into the nittygritty diy of ecu´s at the mo) installed on a Porsche 944 turbo. It starts, idles and runs great on a good start BUT on about 50% of starts it is BAD and has a light misfire (like a vac leak or weak spark), almost dies on accel (like a carb accel pump not working) and has `hard´ backfires on rapid decels (like a bad vac leak).
Once started in this state it will not recover unless restarted (ecu reset ?) and is immediately obvious by the popping sounds at idle in the exhaust.
At idle (800rpm) The 02 is approx .05 higher than a good start (i presume unburnt fuel?) and very unstable as are the rpms & 02 with tps held at 4%.
Turn it off & on again and it will run perfect - 02 @ 99 or wherever it is set, no misfire, backfire etc.
I´ve tried all external troubleshooting i can find & think of, and am now wondering if its possible for Vems to initialise and latch in a state that can cause these issues until the power is cycled.
I was running WS with new leads, but have put the stock coil n cap/leads back in, tried 3 new ws coils, deactivated and plugged the IAC, 2 new sets of plugs (resistor & non), checked for vac leaks, swapped inj, ign Channels & pins, jiggled harness´s conned out connectors, checked tps sweep, disabled inj cha´s during idle but cant find anything wrong.
Trigger logs look good, timing strobe looks good steady n solid also.
Cylinder head recon & turbo were replaced at the same time as installing vems.
Next thing i´m going to try is reinstalling the Motronic ecu but i was hoping for some ideas before doing that.
I´m not sure how to add a logfile...
Any advice appreciated,
Thanks !

« Last Edit: January 06, 2022, 10:32:11 pm by Super fx »