advice / help request:backfiring and cutout

Sounds like a dropout of the ignition. Have a look at the ground connection of the Digiplexes, they tend to corrode. Might also be a failure of the cam sensor, that would be typical if the failure is only apparent with a hot engine.

Does the tacho drop down from the current RPMs when the engine cuts out? That would be an indicator of an ignition failure (at least on the bank where the tach is wired to the coil).

 

Maybe a sensor got loose , check everything you replaced too.

 

Almost certainly losing 1 bank of the ignition per Adrian's thought (the F V8 architecture runs perfectly smoothly when this happens, but at 1/2 power -- and the unburned fuel from the dead bank entering the exhaust system causes backfires). The "takes some time to failure and heals after cooling off" might indicate a thermal-related issue in either the DigiPlex or coil of a bank.

(Unlikely a fuel issue -- your model's fuel system architecture can't affect only one bank completely while working perfectly on the other bank.)

 

Agree with Adrian's and Steve's inclination ---- ignition dropout / failure to advance on at least one bank is most likely the problem.

While you are checking the DigiPlexes, also thoroughly inspect the vacuum hose and all its connections going from the intake plenum to the units. If the hose is cracked / leaking / bad seal, the ignition will not advance sufficiently = big hesitation during acceleration.

Pay particular attention to the (2) short pieces of vacuum tubing that feed each DigiPlex module independently (right after the T-fitting in the supply line). These are located right at the modules, they are exposed to a lot of heat and jostling around back there --- not uncommon for one or both of them to split or lose their tight sealing at either the T-fitting nipple or the port on the DigiPlex itself.

 

Have the simple things like ignition leads been checked or replaced?

 

Agree with all of above. If that's not it, could possibly be a clogged catalytic convertor (if, of course, you have one).

 

Jim,
if you have exchanged the three sensors (1x Speed, 2x TDC) already, then it's most likely one of the Digiplex units or coils failing when they warm up, as Steve already posted.

good luck,
Adrian

 

http://maben.homeip.net/static/auto/ferrari/

Maybe some manuals can help.

I have the same problem on the turbo i purchased one month ago: misfiring is getting worse (i drove the car just two times), just today it became quite big so i stopped the car. It looks that now just one bank is working, so i'm trying to find where the problem is. I'm looking to one of the two ignition coils, the distributor cap or the spark plug wires. But who knows which of them gives the problem: the diagnostic plug could help?

That will be an headache...

ciao

 

probably a leaking coil, which fails when it gets too hot, resulting in one bank cutting off. happened on my carb'd car exactly this way.

 

My problem is Always the same from the the Engine start so i think it's the dustributor cap

 

problem found on my car: two spark plug wires gone.

Hope tomorrow it will be fixed

ciao

 

Please exchange all of them including the king wire while you're at it Also a good time to check and clean the inside of the distributor cap.

 

Thank you very much for the tip you gave me: yes, i will change them all and will install new seals to the distributor caps too. Maybe also new carbon stones (i do not know the english name) into the distributors.

ciao

 

Checking the coils without proper tools (an LCR meter or a AC power supply and a scope) is a bit difficult, especially if they only fail at a high temperature.
If you want to have a go at a simple test with a multimeter, the primary resistance should be around 0.5-1Ω +-20% and the secondary around 3.5K-4K Ohm +-20% based on my notes.

 

all done: i just tested the car this morning and it perfecly works and perfectly starts. I had all high voltage wires changed, distributor caps cleaned, high voltage coils sealed, new spark plugs, new air filter.

The turbo is very sensible to misfiring: a misfiring causes a gas flow decrease so the turbo won't pump well well anymore, increasing the misfiring effect more than than on the 3x8 engines.

ciao
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If you can determine which bank has the trouble, you can then swap coils (and/or DigiPlex ECUs) and see if you can identify a bad player of the four that the problem follows (or not).

 

To check the coils you need the engine cold- start up drive, as soon as you get the first sign of an issue like a backfire stop the car and put your hands on both coils. They should both be warm but if 1 is hotter than the other, the hotter one is breaking down and hence the poping and banking.
You say the engine dies but normally with a coil break down the engine will keep running but will pop and bang so i am not convinced

 

So it's been doing this for two years now? (last post in 2014) Wow, you are a really patient guy!

Did you check all the things that were previously suggested? It seems obviously electrical - ignition/sensor related. You mentioned you had replaced the sensors in one of your initial posts. Did the engine exhibit the same problem BEFORE you replaced the sensors or made any other modifications? IOW, if the problem started after some mod was made, that mod, or related work (wiring/bad connections, etc) would be the likely culprit

 

Thank you. I have a similar condition on my car. Now I've got something new to try and diagnose.