Vorsicht

Need Help. Sometimes, generally on a warm start, there will be a loud pop - backfire up thru the intake manifold. It's strong enough to pop off the entire manifold from the engine and the throttle body. This has happened several times.

First time I checked the wires and found 2 in the wrong position on distributor cap. I fixed this and the car ran great. Fast forward two weeks. The same thing happened again. I triple checked the wires again - they are fine.
I recently changed all the wires, plugs, but not the caps/rotor. The caps/rotor have 30K on them. MAF has been cleaned and working. Fuel injectors were recently checked and cleaned.

This seems to be a timing issue but I am at a loss for what to check next. Any ideas? Flywheel sensor? Other timing issue?

Perplexed!

Steve Weiner-Rennsport Systems

Peter,

How old are the ignition wires??????

Vincent C.

make sure the belt is good inside the distributor.....vinnie

Vorsicht

The wires are three months old. I will take a look at the dist. belt. Also, This is happening on the left side only (1,2,3).

chris walrod

Double check the firing order with relation to the wires.

Vorsicht

Checked Distributor belt. It is fine. But, Take a look at the rotor and caps. Does this look like it could have caused the timing issue? I'm gonna replace because they look black and corroded. Is this evidence of arcing? Opinions Please!

leonardo72

Hi Vorsicht, did you manage to solve the problem of the intake popping off? I recently rebuild a 964 engine and had the same problem. I've replaced the belt in the distributor including its caps, cleaned injectors, replaced all intake rubbers and fuel pump, replaced air mass meter, flywheel sensor.... Im reaching an end here.
Does anyone has an idea what else it could be?

jeanhules

Have you checked the fuel pressure regulator?

Vorsicht

I did two things one of which solved the issue. I replaced caps and rotors and re-adjusted the flywheel sensor gap( it's should be 1 mm plus/minus .2 mm). You might want to check for fuel smell b4 starting. Leaking injector can cause this ss well. Good luck.

leonardo72

caps are new. I haven't checked the gap of the flywheel sensor yet, my mate replaced it but im not too sure if he's checked the gap. I'll do that and hope it helps :-)

_snowbird_

This was my first thought, based on a similar experience with a VW.

993Porsche

EDoyle

Another thing to check would be the cylinder head temperature sensor. Measure the resistance at a given temperature and see if it correlates to what it is supposed to. The head temp sensor plays a big role in fuel injection mixture on these cars as I have learned in the past chasing down a similar problem.

leonardo72

UPDATE: I've measured the fuel pressure, 4.5 bar. far too hight. after switching off, pressure drops to 0.5 and holds there. Not enough to restart.
I've ordered the fuel regulator and I'll keep you posted on the outcome.