prescott

Hi guys.

My 88 S4 Manual ran great yesterday AM. Tried to start it to come home in the evening 91 degrees F, shaded, not run in 9 hours, would turn over, occasionally try to fire once (1 out of 7 crank attempts) but would never start. I replaced the XX and XXV relays with new ones to see it that would work, but got the same result. Waited for the tow for 3 hours....not a great night.

Had the TB, WP, AC rebuild done 3 months ago. New battery 1 month ago.

Any ideas on where to start looking?

Thanks
Brian

John Speake

XVI completes the set of three vital relay (EZK). If it is the fuse tester relay, it's perfectly Ok to use a 53 relay for testing.

Does the car have spark ? Does the rev counter flicker when cranking on a good battery ?

You may find this helpful; http://www.jdsporsche.com/fault%20find.html

RAPIDFIRE1

Brian. I had the same thing with my 87 s4 a few weeks ago. Follow Johns link on the previous post. Turned out it was my LH ECU unit. Sent it to Louie Ott . Turn around was a few days. Started right up after I installed it. Just follow the steps in the diagonistics that John sent. Good luck Dave

prescott

OK. Relays 20, 25 and 16 replaced with new.

Fuel pump jumped and works.

Only getting spark on one bank of cylinders.

Now I'm stuck. Any ideas or is this an ECU unit failure?

Thanks

depami

There are two final stage amplifiers, two coils and two distributors to verify good or bad before condemning an ECU. Not sure of the most likely component or quickest route but you at least have parts to swap back and forth for process of elimination.

I'm sure someone S4 savvy will chime in with a precise next step.

Kevin in Atlanta

Mounted on the front of the car in front of your headlight motor there are a pair of ignition modules under a plastic cover. If one fails you will not have spark to 4 cylinders. You can swap the connectors to see if the cylinders that fire changes. If so, you have found the culprit.

Glenn M

Make sure your coil and coil wires are good on the bank that isn't firing.

John Speake

/\ /\ Start at the King lead and check for spark, if spark there then check out the distributor.

If no spark then swap the output amps over and see if one is faulty. However I wuld have expected the car to start and run on 4 cylinders.

prescott

Thanks for the tip. I will work on it and let you know! Its amazing how many relays and fuses are in this car!

dr bob

My 'new' Honda dd makes the 928 look primitive electrically. There are four major fuse-and-relay panels distributed around the car. CAN bus meams run a single power lead plus data, and do LOTS of fusing and switching locally.

FWIW, my LH failure symptoms same as yours.

depami

LH will kill spark on one bank? I thought LH was just fuel?

John Speake

On digi dash cars, they have the igntion protection relay that can cut out 4 injectors from firing. Totally independant system to the LH.

So this possibility is not applicable to the OP.

prescott

Got it up and running.

Turns out one of the ignition modules fell apart in my hand when trying to remove it. Replaced the pair. Still no ignition.

Replaced the crank position sensor (expensive bugger!) and VROOOOOM!

Hope this thread helps! Thank you for all your advice!

Mrmerlin

have you done an intake refresh?
how many miles on your car

depami

Must have been a compound failure because the CPS can't kill spark on just one bank.