turbo toic

Hello all,

Would like to say hi to everyone. I am new to this site. i am trying to help my father out with his car. He has a 1988 928 s4. The sitution he/we are having is the car wont start. Just want to rewind a little bit and tell you guys some history about it. For the past 3-4 yrs the car would have a hard time starting once the car was warmed up. Never an issue with cold start. So now it wont start. The things we checked were spark and fuel pressure, which their is. The one thing my father notice was a "clicking" noise in the engine bay when the key was in the ACC position. The noise was coming from under the intake manifold. We did a little research but didnt find anything we can relate this issue. The only thing i can think of is a faulty idle stabilizer valve, which could mean to replace the throttle body.

thank you in advance.

worf928

Remove the LH ECU and send it to Rich Andrade at Electronik Repair or Louis Ott at Ott's Performance Engineering for testing.

Based upon your description, the obvious failure mode is that of the LH ECU. They ALL fail eventually due to a design flaw.

In the future post the transaxle type as well as the model year; that can be critical information for diagnosis.

turbo toic

the car is a 1988 s4 automatic. it has 65k on odm.

Can you be more specfic on the " design flaw". Is there a electronic compontant i can check inside the ecu if i were to take it apart.

DR

Hi Turbo (and Dave),

Dave is dead on with his diagnosis and recommendation. IF you want to know more about what to look for you can visit this webpage http://home.kpn.nl/mirjam_paul/928_lh_repair.html .

As you will see mentioned there, it would take a microscope etc to be able to see the issue. Myself and the guys at Autothority discovered this flaw first hand back in the mid to late 90s. To my knowledge this was the first confirmed LH failure, which just happened to be on my 89S4 as I was driving up the the 928 Frenzy from Atlanta. After flat bedding my S4 up to Autothority in the DC area for Frenzy 2 IIRC we discovered this after a few hours of diagnosing the problem..

The clicking you hear under the hood is from the fuel injectors firing at a static rate due to this specific LH failure. Since my original failure issue the "clicking under the hood" has been the dead ringer for suspected LH failure. Other symptoms can be that if you manually jump the Fuel Pump relay (fuel pump trigger can also be lost with this specific LH damage) the 928 will most likely start and run at a low rpm and die as soon as you attempt to move the gas pedal. Basically what is happening is the fuel injectors are firing at a specific and static RPM rate and when you try to add more air it dies because the injectors do not speed up to match the increased RPM demands.

Don't waste your time taking it apart because there really is nothing to be seen, or repaired. Just send it off to one of the guys that Dave mentioned.

Best of luck and kudos for helping out your Dad with his 928!

Cheers and Happy Holidays!,

Dave

StratfordShark

Can’t add to main diagnosis, as this does sound like classic case of LH failure.

But when it’s running again, one possible explanation for warm start problems is leaky fuel injectors (they flood cylinders, but cold start ok as fuel has chance to evaporate).

You can make definite diagnosis with pressure gauge attached to test point at front of right hand fuel rail. With engine off you can bridge pump relay to build pressure, then if injectors are leaking you’ll see substantial drop over 20-30 minutes. The workshop manual has full test procedure including specifications for pressure drop.

Mrmerlin

Where are you located?

walfreyydo

Posted in wrong thread

mj1pate

I’ve had my LH and EZK rebuilt by Rich and he’s a good source.
Rough starts, bad starts, poor running can’t be ignored in the future. The damage to the expensive/maybe NLA cats is cumulative.
Best of luck!