No Start
 

88 S4 Auto

Been having this intermittent start issue for some time now. When running the motor seems fine. However, it will sometimes stop cold in its tracks... and nothing obvious will get it to re-start. Needless to say I have not driven out of my neighborhood since this started. Seems to have spark and the fuel pump is working. It will kick over on starting fluid. I believe it's in the injector wiring and have a noid light to test with. Is there a specific sequence for testing the injectors? Also, just today it would turn over fine but not start. The battery was at 80%. Charged it to 100% and she fired right up. Any indication of something else?

Thanks,
Steve

I’m not familiar with your particular model year but sounds like an intermittent electrical issue. I’d start with cleaning grounds and checking the battery ground strap, if you haven’t already.

Thanks... that was one of the first things I tried. I've also replaced the engine wiring harness, refreshed the fuse box and replaced all fuses and most relays, and replaced the crankshaft position sensor.

please post a picture of your engine bay close ups are better

Are there any clues offered by the gauge cluster or any other behavior peculiarities before complete shutdown occurs?

Steve,

Whereas there are a number of things that can cause starting issues there are not that many that cause the motor to suddenly stop running.

Friend of mine had such an issue- it would start up, run for a while and then mysteriously stop. Fitting my spare LH stopped the problem and when JDS got the unit back in England sure enough it was an LH issue.. Not saying for sure this is your issue but you need to eliminate such from the list of possibilities. Best way is to pop your LH unit in a running 928. If the LH in your car is the original item and has not been replaced or refurbed previously it is long past its sell by date.

The fuel injection is batch fired- i.e. all at the same time.

Thanks Stan... I'll take a few pics later today

In reply to the other comments, when the car stops it is sudden with no lead up indications. I have a spare LH and EZK. Swapping them when the car is in a stop/no start state makes zero difference.

Any symptoms of your ignition switch going bad, like occasional lack of dash lights or other odd behavior?

Hi Stan... attached are a few pics. If there's anything specific you want to see please advise. Note the injector covers and air filter housing are off in anticipation of doing the noid light assessment. However it's running at the moment so that will have to wait. I know I need a top end refresh and I intend to do that as soon as I determine what is causing the short to the injectors. For what it's worth I also replaced all the electrical leads to the injectors within the past year. If one were available I'd buy a new harness just to eliminate that as a potential cause. As always appreciate your knowledge and recommendations.

Steve
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Nothing that seems like it is ignition switch related.

I agree that it sounds like an intermittent electrical issue, and that there are not a whole lot of things that will simply stop you dead in your tracks while driving--most of which are electrical related, not fuel pressure related.
Make sure your battery is good (will hold a charge) and fully charged.
Using the same multimeter, car off, battery hooked up. Don't remove/move anything:
Measure voltage at the (+) and (-) battery posts.
Measure voltage between (+) battery post and (-) the bolt/nut that holds your battery ground strap to the body in the hatch.
Measure (+) voltage between jump post at front of car and good (-) ground in engine bay. (Scrape away the corrosion on one of bolt heads on your engine brace until you see a shiny metal contact.)
Leaving the CE Panel in place, pull the fuel pump relay (XX) and measure (+) voltage at socket #30 and good (-) ground nearby. (The multiple ground point top/behind the CE if you can reach it with your probe. Otherwise the allen head ECU unit bracket bolt to the right of the CE panel is usually clean.)
Record and report results.

Just to clarify, when it dies and you pull the key out and re-insert the key and try to start it, the starter will engage (crank), but no start? Or when you turn the key nothing happens?
Jason

Hi Jason,

Thanks... I'll test the voltages as described. The engine will always crank. Just sometimes doesn't start.

Steve

This makes me wonder what condition the batt has been in? How old?
Has it been load tested? Is there a maintainer on it? Check for drain issues? Grounds? Ground strap. I would check these before looking deeper.

It would be a good idea to follow Jasons testing protocol to narrow down the possibilities,

Based on the engine bay pictures you need to do the intake refresh first,
Beyond the peeling paint you might find a bad ground at the back of the V,or any other number of fouled up electrical connections
the ignition wires look newish but the engine harness looks like its ready to be swapped,
Once the intake is refreshed then you will have an easier time of trouble shooting as many possible culprits will be repaired

Hi Jason

Battery was 100% charged. Showing 16.1 volts at all locations.

Steve