dimmer

Just finished installing new guides and cables for the sunroof and decided to take it for a ride. Tromped on it as I was leaving the house and the engine suddenly cut back to what felt like about 25% power. Engine was vibrating more than usual and sounded rough. I turned around and took it back home and starting inspecting it in the driveway with the engine running. As I'm looking, I start seeing some smoke (not a lot) coming from the back of the engine under the air filter. I cut the engine and waited with a fire extinguisher. The smoke settled and no fire. First thing that I thought was maybe fuel line ... but I don't smell any fuel. Also, the smoke smelt more like oil and not gas.
Once it cooled down, I was able to start it again, but it's running rough and weak on power.
Anybody have any ideas what might cause these symptoms. I'm hoping it's something small, but I have that sinking feeling that it isn't.
The car is an 1988 S4 5-speed with 210,000 km.

Thanks in advance for any help.

davek9

Do u still have CATs on the exhaust, sounds like you are running on 4 cylinders and almost lost the car due to a cat fire

jeff spahn

Swap you ignition amps with spark checker installed and see if the plugs that aren't sparking start sparking.

dimmer

Yes, the car has the original exhaust and cats. Do you think one of the cats suddenly blocked, hence the loss of one side of the engine and subsequent smoke? Regarding the coils ... I replaced them a couple years ago. Also, coils does not explain the smoke.

StratfordShark

The smoke could be from unburnt fuel being ignited in the cat. Jeff Spahn's suggestion relates to possibility that you have lost one ignition bank (not same as one side). A faulty ignition amplifier (mounted front left slam panel) is possible cause, simpler one could be lead from coil to distributor. From MY89 onwards an ignition protection relay was added mounted on ECU bracket, which would indicate by illuminating red or green LED whether fuel injection had been cut off to that bank because of ignition fault

FredR

If you have unburnt fuel going through the system you should be able to see signs of this on the group of cylinders affected. Run the motor for a few minutes and immediately pull the plugs from two cylinders fired by each of the two distributors [ 4 in total] and see if you can see signs of wetting o two of the plugs from one bank. That will also help confirm shutdown of one of the firing circuits.

Rgds

Fred

davek9

Yep, just get your hands on an inductive Timing light and confirm you are getting spark to all 8 plugs.
Note which ones are not working and follow them back to one of the two distributors and fix the problem.
It could any of the following: a Coli wire, a Rotor/Distributor issue, a Coil, the Ignition Pre-Amp, or bad circuit wiring, bad LH.

The Smoke was coming from the bottom of the cars body, the Super Heated CAT (from excessive Fuel burning inside it) was catching the insulation on the floor pan on fire.

Do Not Run the car for any length time.
Edit: until you resolve the ignition issue, if that is what you find the problem is, as it could also be stuck open injectors, however the former is more likely

DaveK9

dimmer

Just wanted to say "thanks" for the diagnostics help and provide feedback.

I used the timing light to identify that there was no spark coming from the right distributor. Swapping the cables to the ignition modules caused the issue to switch to the other side. Fairly simple and easy fix ... really freaked me out when I started seeing smoke coming from the back of the engine ... makes sense now that it was simply overheated cats smoking the undercoating. Maybe this was a warning to finally do something about those old fuel lines and replace them!

dimmer

One more update .... stick with the original Bosch ignition module.
One of the part stores here suggested a compatible, lower priced Beru ignition module. I figured that since Beru was also a German company, that I should not have any quality issues ... Wrong! The Beru module fired up its cylinders and it idled fine; however, when the rpms changed, it would miss-fire. When the engine stabilized at higher rpms, it also seemed fine ... it just seemed to have trouble with the transition.
In any case, I paid a few bucks more and got an original Bosch 124 module and it's running like a charm again.

davek9

This is GREAT to hear a happy ending, yes fuel lines would be on my list

Also if at all possible ditch the CATS and Air pump, these cars run great w/o them if properly tuned. The Scrap guy will give you at least 200 buck for them

Thank you for the update