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3.8l ITB engine shut off during full acceleration

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Old 09-20-2024, 12:03 PM
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Maxi_z
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Default 3.8l ITB engine shut off during full acceleration

Excuse the double post in both 993 and 964 forums but my particular car is a 964 RS 3.8 replica that is using a 993 modified engine and electronics so I could find some knowledge in both forums

My car is actually a 964 RS 3.8 replica but using a 993 engine gearbox and motronic ecu and ignition and the engine is a built 3.8 engine with high lift cams and individual throttle bodies with a Motronic ecu mapped in alpha-n by RS tuning in Germany
so not only everything is from a 993 but it s also modified so I would like to know if any experts of this kind of set up could give me some suggestions on what to look for

After a few miles on the street on country roads at normal speeds with a few occasional harder accelerations and the car running perfectly fine I then made a full throttle acceleration in second gear and just before

shifting gear at about 6500 rpm full throttle the engine completely shut off as if the ignition was turned off

For a second I tought I hitted the rev limiter so I disengaged the clutch and could slowly get to a space on the road side

Then I tried to restart the car the engine was cranking perfectly no strange mechanical noises battery was powerful but it was not starting and no signs of almost starting at all be it without throttle or with throttle

I disconnected and reconnected the battery and used a replacement DME relay but it wouldn t start so I called road assistance to get the car towed

After about one hour just before the road assistance arrived I tried again to start and the car immediately started ( as if some excessive fuel had wetted the plugs and they had the time to dry out as in a two stroke ) however it was not really runnign perfectly on throttle and I could

make it shut off by applying full throttle

After towing it home and after one day I again disconnected the battery and ecu and reconnected all and started it then I disconnected one of the main ignition coils at the time but in both cases it continued to idle and did not shut off so I think that means that both ignititions coils are working
and that the small ignition belt is not broken

It actually runs quite well but not perfect still but I m especially wondering what can have caused the shut off under full throttle

The engine and most electric parts are recent or new but I was wondering about the crank position sensor , the fuel pump itself , the fuel filter ?

Old 09-20-2024, 01:09 PM
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Spyerx
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Tuning and/or electronics issues. Not sure what sensors you are using. Is this coil on plug / crank fire etc?

1. confirm fueling & pressures - you're not getting vapor lock or other issues
2. confirm your sensors- crank reference, cam reference, etc
3. If you have knock or other sensors ensure they are functioning
4. confirm injector and fueling settings

The motec software with the right logging turned on can figure out what is going on

When we were tuning my full EFI coil on plug ignition system on my 2.8 (motec M130) we had issues with the supplied crank reference sensor. It was picking up noise over 6k and then causing very erratic running. We had to replace it with a Motec sensor. My engine was tested on the dyno to 9k but we have redline around 8200 for street use.
Old 09-21-2024, 04:44 AM
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koenig_roland
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i would check/renew the crank position sensor first...



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