Hello
I am Murarie from India.
I have a 87 S4 RHD Automatic
My problem:
The Car starts easily,idles OK but if i try to accelerate past 2-3k RPM the ignition cuts off for an instant (the tach dies) and instantly picks up again.
Following this it backfires .This indicates that fuel is not cut off only ignition and so the backfire when it picks up.
This happens only when the car is warm.
I have changed Temp 2 sensor,Coils,Rotors,Caps,Plugs,wires,fuel pump,Fuel filter,T belt,water pump.
I have checked the MAF for resistance, voltage,Speed refrence sensor for sine wave in a scope,Jumpered all the usual troublesome relays.

My cars PO has bypassed the engine oil cooler since it leaked oil into the coolant.The two connections at the Radiator are looped.
Does this do harm to the engine.

 

Congratulations on your new S4 Murarie.

Since you noted the tach dies, I'd suspect an electrical problem. Check your ground and power wires to the brain, starting from the battery. Could also be a short, which might explain the "only when warm". If that checks out, then it might be the brain. Good luck and keep us posted of your progress.

 

Oh. On the oil cooler bypass. I wouldn't worry about that right now. Long term, higher oil temperatures result in more engine wear and more frequent oil changes.

 

Thanks for the reply borland.

I have already checked and cleaned all the suspect ground points.
Also i have changed a new 83C thermostat.

 

Murarie,
When the tach dies momentarily, do any (red) dash liights come on? - or does the dash simply blank out?
It could be as simple as losing switched power (if the dash goes blank): I would take a look at the electrical switch component of the ignition switch. "Play" with the key a bit when the engine is running: this may simulate the effect of engine vibration on a poor electrical contact.
Otherwise,trace the route Borland mentions. It does sound like "switched" power, so any switches/fuses/relays in thes loop, etc are suspect.
BTW, welcome!!

 

Hi Murarie,
Have you checked the flex plate ? I have known the crank to move so much when the crank thrust bearing has been worn, that the flywheel sensor looses the signal.

No tach signal means either the flywheel sensor is faulty, or the EZK unit is faulty.

 

Murarie
My car used to do this sometimes. I never found the reason but after I thrashed it a few times on the drag strip it stopped happening. This is hardly scientific but it was fun.

Welcome

Colin 89GT

 

Check ignition siwtch for internal failure, and.....one of our guys had a 'lights out' when he turned one way....ended up being bad connection at battery, and battery moving in its box!
jp 83 Euro S AT 48k

 

Thanks to all.
My flexplate is OK,i recently released the pinch bolt and it moved back by about 4mm.
Also if my EZK is bad it should cut out even when cold right?
I have cleaned the contacts for my ignition switch with no effect.
The dash does not show any warning lights.

 

Nope... very common on many cars for the electronics to act up only when warm, or especially when warm...

 

I am not in a position to swap the EZK or the LH.
Any other Ideas?

Can a Clogged CAT or a bad O2 sensor cause these problems.
I Plan to bypass the CAT soon as there are no emmision tests in my City.

 

Murarie,
Are we talking about the same set of contacts on the electrical 'half' of the ignition switch? I'm referring to the internal switch contacts - that are usually inaccessable, and do not respond to injection of contact cleaner (if you find, or drill a hole for injection). The external plug-on harness and contacts are rarely a problem.
Just checking to verify that we are on the same wavelength ....

BTY, a clogged CAT stays clogged - and is very unlikely to be linked to any intermittant problem: A faulty O2 sensor will reflect in decreased fuel economy, but no sudden ignition failures.

 

I Changed the 2 ignition control modules in front of the car and now it seems to be running on 4 cyl,
These are new and Plugged in properly, the ground just near it is also cleaned.
I have a few doubts and i will post a few photos with my doubts.
Also can i fit an aftermarket ignition switch only for troubleshooting,if found bad i can order a new one.

 

What is the Blue,Red,Yellow connectors in the first image?

The RED has an adjustment pot on it.

This wire is spliced in to the Pin 1 of connector W and grounded nearby,if i remove the ground the fuel pump does not run.

Also this splice runs the fuel pump as soon as the ignition is switched to the on position.

 

QUOTE "The RED has an adjustment pot on it".

A: The adjustment pot is the idle CO pot, as used with non catalytic convertor/O2 sensor cars.

QUOTE "Also this splice runs the fuel pump as soon as the ignition is switched to the on position"
A: - this suggests that there may be a problem with the pulse from the EZK to the LH that I mentioned previously in my earlier mail.

The fuel pump should only run when the engine is turning