advice / help request:backfiring and cutout

Hi everyone,
I have an annoying intermittent problem with my euro 2v I car - Ill be driving along with car seemingly running ok then I notice that the accelerator pedal goes 'dead' ie engine does not pick up when pressed - then loud backfiring followed by cutting out or total loss of power.

The engine does not seem to miss when the pedal goes dead.
I then pull over and leave the car for say 20 minutes where it will usually start and run for another half hour perhaps then backfire and cut again.

from sitting in my cool garage I can usually get a good half hour drive without any problems. the issue seems to happen if the car has sat outside in the sun for a while or when I go for a 1hr plus drive.
I have looked at the spark plugs after experiencing the problem and they were dry and looked ok to me.

to date I have:
fitted birdman fuse box (fuel pump fuse had gotten v hot at some stage)
replaced crank sensors (x3)
removed 'quasi lambda' system fittted in US.
noticed a small amount of oil in the rear bank distributor cap....

next move:
check and clean Digiplex connections.
check resistance on all extenders.
investigate fuel pressure / fuel pump earthing.

my next guess is that its a fuel pump issue - Ive noticed a relay (poss fuel pump) seems to tick at strange times whilst driving - but why would that cause backfire??

just wander if anyone could advise what they think it might be ?? the exhaust on my car is not good - (slight blow) but I wouldnt have thought that would cause this much trouble..

thanks in advance for any opinions / advice

rgds

James.

 

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).

 

thanks adrian Im going to check the digiplexes next.
I just had the 3 crank sensors replaced - Ill look for the cam sensor too
thanks again
rgds
JW

 

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

 

thanks for all of the advice everyone,
I have just had a look at the digiplexes and vac hoses - hoses look to be ok but ill take them out completely and check properly.
there is some black dirt on the digiplex connections - Ill clean that next.

Is there a way to check the coils? or can I look for signs of failure externally ? they are supposed to be new from the last owner.
checking extenders now. leads too.
thanks again - Ill get this car working nice soon!

 

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).

 

hi everyone - Im afraid Im still having problems with my 2v injected euro car cutting out / not running correctly.

to recap the car starts well from cold but suffers from low power / cutting / backfiring after a random time - sometimes 1 hour of driving but sometimes 30 mins.

i took the car out today for about 40 mins without problem.

after leaving the car in the sun for about 2 hours the car started but ran badly.

I checked the ht leads with a voltage test pen and found the front bank leads had no voltage at all.

the rear bank leads had voltage but seemed a bit irregular compared to how they look when the cars running well.

strangely neither coil lead would cause the light on the pen to illuminate - they usually do when the car is running well.

I changed the wires on the coils over and the same thing was seen. still no front bank.

I returned the wiring on the coils and lifted the digiplex panel - I disconnected both digiplexes to check which one was connected to which bank.

upon re connection the car started and ran ok! the coils both triggered the light on the pen and all 8 seemed to fire.

the front bank digiplex is old but the rear bank digiplex is brand new after I discovered the rear bank had previously had the american model digiplex!

the loom from the digiplex's has the separate earthing mod.

anyone know if having one suspect digiplex could cause both coils to run weakly?
or is the fact that both coils seem to go weak a sign of a deeper electrical issue?
do digiplexes 'reset' after being disconnected?

any advice to help me solve my excruciating problem would be greatly appreciated - I want to put some miles on this car!

plugs, extenders, ht leads, rotors, coils are all new.

thanks in advance

james.

 

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

 

cheers guys - yes I am patient! to be honest Ive been trying stuff but the problem with intermittent faults is that you need to spend all day running the car and trying things and i dont really have time for that Im afraid.
my car has had this problem since ive owned it.
I ordered a new digiplex unit today from maranello classic parts so thats next thing to try. Im sure the coils are ok as i swapped over the wiring to the coils and the front bank was still all dead.
does anyone have any experience of replaceing the short loom that goes into the digiplex units? i would imagine those electrical connectors are NLA now...
thanks
rgds

James

 

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

 

new digiplex arrived today! (both new now) car ran ok tonight but need more running to see if its fixed.. hopefully get some more miles in this week / weekend

cheers

james