eric951turbo

Hey all,
now I have this problem with my 951.
Symptoms:

1. Small back fires noise under the hood when I decompress or press on the clutch in 1st gear to switch in 2nd gear. Sometimes happen also when switching in 3rd

2. Let say that I switch in 4th in low revolution and press on the gas, big lack of power like if the gas wasnt going to the engine (need to switch back in 3rd gear and rev. it)

3. The smell. Man, when I stop and get out of the car, the car smells like gas big time

4. But the back fires doesn't come from the muffler? It's really in the engine. Like a ''pough'' ''pough'' noise

Does anybody know what this could be? Each time I go see my mechanic for a test drive the car is ok. So he can't find the problem.

thanks

JohnKoaWood

Make sure of the following:
1) Your plug wires are correctly connected
2) Your timing marks are lined up properly
3) Check you throttle position sensor via the procedure on Clarks Garage
4) pull the vacuum line off the fuel pressure regulator, check it for gas
5) with the engine running at idle, pull off a vacuum line and see if the idle changes, no change means a vacuum leak

eric951turbo

thanks, but all of the above as been checked by a professional.
Could it be something else?
I'm asking because if not, I'll go back to see him, and ask him to check everthing, again

JohnKoaWood

Major Exhaust leak could also cause it, like if you had an open hole sucking air in at the header! tell him to leak check the exhaust and intake tracts...

only other reason for backfires in the engine bay is timing being WAY off...

Which brings to mind, make sure they check the rotor button!

eric951turbo

Thanks a thousand.

Black51

You know what, I had a similar problem to what you're describing. When giving er' anything more than half throttle, on boost, the car would make like a muffled sound. Misfiring big time! I was haunted by it for over a year. I took it in to my mechanic in Edmonton and they said they checked all the simple things and worked from there. There even was an exhaust leak in my header. Got it welded up and no change. Honestly, just from experience, unless there's a HUGE exhaust leak, you won't even notice a loss in power. And especially, the car won't be backfiring. If anything, fixing an exhaust leak lowers spool time, nothing more.

So anyway, I had my car in for 3 damn months at the shop while they were looking at it after the failed 'welding the header hoping to fix it' attempt, and finally by the end of the summer, they just gave up and gave the car back. So this spring I looked at the spark plugs and noticed a huge gap in them. So I changed them hoping to find a cheap solution to this problem(and let's just say, I had already dropped some big bucks the last summer trying with the mechanic to no avail), and what do ya know? The damn car works PERFECTLY. Just as God intended it! I was absolutely decombobulated finding out that was the problem. Now laugh all you want in hind sight, but I had already checked many other things out before taking the car in, and I still remember to this day, the guy on the phone at the shop (who is no longer there - go figure) telling me they DID "check the spark plugs and that they're good". So I had good faith in them, being a Porsche dealer and mechanic's outfit here in Edmonton, that the plugs were good. Now I'm not in any way bashing my mechanic here; these things happen. Life goes on.

What I'm saying here is make sure you check the simple things (like the plugs/wires) before you start hopelessly throwing money at your car. Cuz I've found with these cars, they're just like a girlfriend; your money WILL vanish into thin air for no reason. Most of the time on these things, it's something simple that lies right under our nose that is the culprit. Unless the car has catastrophically failed in some way, which I don't think it has in your case, don't throw money at it. Personally, I wouldn't even take it to a mechanic - personally.

Funny, this is the short version of the story I went through last year!

black944 turbo

Check your bypass valve as well. This can cause a lack of power between gears and can cause a "Turkey gobble noise" of the turbo slowing and speeding, which you may describe as backfiring.

peanut

sounds like you're engine is over-fuelling. Could be a leaky injector or faulty temperature sensor or maybe the AFM air flow meter . Also check that your FPR is working properly and the fuel system is not over-pressurizing. DO a fuel pressure test.

Lizard944

My bet is on injector(s). Check each exhaust manifold pipe temperature with an infrared thermometer. The one running cooler than the others is the offending cylinder.

eric951turbo

Thanks guys... Just came back from a small day trip and care also sticks like hell. Makes your eyes all itchy.

Smell's a like a bad mix of gasoline and exhaust fumes.

bfffffffffffffffffff.

Black51

sounds like it's running rich.