AO

Greg's being too cautious. A little won't hurt anything. Have a helper crank the car while you spay SPARINGLY a little starting fluid. If the car tries to catch, you have your answer.

John Speake

An alternative to the fuel pressure test is to carry out the fuel flow volume test.

Run the return line at the top of the fuel tank (under that round rubber bung uder the carpet on the RHS in the boot (trunk US) into a suitable container. Bridge the fuel pump relay for 30 seconds. You should collect 1350cc of fuel.

Usual precautions apply when dealing with fuel and sparks !

guess21dan

Thanks John, I will give that a try too. Sorry forgot to mention before that I had the car running for a few seconds on WD40 sprayed directly in to the air inlet.

SeanR

Have you tried to start it with your foot planted on the pedal?

Verified that the fuel pumps are running?

blown 87

You are willing to take risks I am not willing to take, but I knew that the first time I tried to keep up with you.

AO

I dunno... i've never chased a guy down at gunpoint.

uncre8tv

Sorry for reviving old thread, but I have similar symptoms and am starting to suspect Temp2 sensor. Mine is a 1989 S4 5spd.

What would starting with the pedal to the floor tell you? Mine will roar-die, if I hold my foot on the floor it will do this three or four times (roar stumble, roar stumble, roar stumble, die) whereas without the foot to the floor it only does it once.

Strong fuel smell while doing this, too. If that adds anything. Car has an exhaust leak already so when it did start I was only smelling rich exhaust.

dr bob

You have rather classic symptoms of LH failure. A fairly typical failure mode has the injectors firing continously after key is on and before you even crank the starter. Pop the hood and listen for that clicking-buzzing when key is in engine-run position.

After that there are checks to do around the fuel pressure regulators and dampers. Then check fuel pressure.


If your conditions included a hard backfire as the OP reported, you should verify that the cam timing is correct before you try and start the car again. There are lots of possible causes, one of which is cam timing jumped, so valves open at the wrong times. Takes an hour or two to get the covers off and rotate the engine carefully by hand, after looking at current crank position vs cam positions, belt condition, etc.

uncre8tv

Thanks DrBob. I'll dig into it later this week. I am reading a lot about checking grounds for everything too, but not finding a succinct list. Any pointers to typical ground spots to check? Does the LH ground from its frame/mounting bolts/screws, or is there a bolt point I should be looking for?

MainePorsche

LH grounds at MP VIII deep at the back of the engine to the bolt that holds the throttle wheel bracket to the block on the driver's side. Need to clear airbox and FPR to really access it. MP IX is the ground point on the other side of the same bracket on the passenger side.
The MAF, EZK, O2 sensor loop, TPS, and some tester/code plugs ground to these points too. If you're having ignition issues, I think these are mission critical to verify these grounds are OK in order to exclude them as a cause.
Make 'em shiny before you put 'em back.

Bertrand Daoust

Here's a good diagram of the ground points.

https://rennlist.com/forums/928-foru...nd-points.html

MainePorsche

A pic is worth a thousand words.

uncre8tv

Thank you! I was fiddling with an interior fuse issue tonight (fuse 24 dome light issue) and turned the key for fun. Fired right up. All the ductwork was off the inake, so I didn't do anything but (gently) rev it a few times and let it idle for a minute. I still need to dig in this weekend and see if i can't either make it repeat or make it not come back.

When I took the intake plumbing off last night I did stare at it for a good 20 min trying to puzzle out which was the right bolt to be fussing with. This pic will help immensely when I dive back in!

I also talked to Rich at ERI this morning. SUPER nice dude, he also recommended checking the FPR in addition to the above.