[ds968]

And it happened again this morning ! This time the car sat for three whole weeks without being driven which is probably its longest rest period ever. The moment it enaged, it started shaking and sputtering so badly I did not know if I should let it run for one more second thinking I'm going to do some damage to the engine if I did not turn it off. So I did, and then a couple of seconds later tried to start it again but it kept turning over without engaging this time. I waited half a minute and started it again. Still very rough although bit less so than the first time so I let it run for about one minute until it smoothed out to normal idle . Took it for a drive and no problem whatsoever, running perfectly , smooth acceleration, no sputtering, no hesitation, nothing. Went into a store for about 15 minutes, started and idled smoothly right away. I usually drive it every weekend, once in a while even two weeks might go buy, but this never happens in those cases, however three weeks seems to be the magic threshold .

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[Rap]

Your car is speaking to you grasshopper. Listen!

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[ds968]

It's incredible you would say that, my very first thought was to start a new thread with the title : " my car is speaking to me " but then quickly remembered this thread so I posted here. Brilliant minds think alike , lol. Setting aside the car's loud and clear " drive me more often " message, still not sure why it is the symptom does not happen after a week or even two, but three weeks or more and it's shake, rattle and roll , baby !

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[flash]

when was your fuel filter last changed?

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[Rap]

Indeed!

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[ds968]

[quote name='flash' timestamp='1345944463' post='131610']when was your fuel filter last changed?[/quote]



Don't recall. I'll look it up. ( but If the fuel filter is clogged why in the world would it then be perfectly fine after the car warms up for a minute , and why does it not act up when the car sits for a week ? )

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[flash]

why does your toilet back up for no reason, and then be fine under "high load" conditions?



the filter, the check valve, and even gummy injectors can cause this problem. i asked about the filter, because it is the likeliest culprit.

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[vliegwielolaf1234]

I think leaky injectors .

No pressure in the system after sitting for a while .

Then you try to start , air gets trapped in the injector .

After a couple start attemps . air gone pressure in the rail and all looks fine .

I would get them cleaned and tested .

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[flash]

injectors don't leak like that. they open and close too fast.



but the "air in the system" theory is sound



the check valve in the rear is supposed to keep pressure in the system. when that gets sticky, it bleeds off. it gets sticky because gunk was introduced due to a clogged filter no longer doing its job.

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[ds968]

Filter has only 10k miles on it. What's a check valve and where exactly " in the rear " is it located ( just wondering if it's something easily accessible and simple enough to replace where I can do it myself ) .

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[flash]

lol - it's right next to the fuel filter - pain in the butt to change, due to the fuel spill that will definitely occur

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[ds968]

Crap. Oh well, more money for my mechanic. I'll have to ask him though if he also changed the valve when he replaced the fliter and if that was done, I guess I have to look for other causes to this ...?

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[968Syncro]

I just went through this part of the car, not because of rough running, but because the fuel pump broke. The check valve is between the pump and the filter; which is a somewhat odd design because the check valve is therefore exposed to any potential gunk from the fuel in the tank. Would have been better to put the check valve after the filter.



25 - connection to tank and the screen

20 - pump

6 - check valve

13- filter.





   



This stuff is located under the car, directly behind and above the right rear wheel. Jack it up, remove the wheel, remove the cover (just one bolt that holds a retaining strap), and you'll see it all. The fuel pump is attached to the cover, so you kind have to undo the fuel pump retaining clamp as the cover drops (another odd design since in my car the cover seems to act like a drum that amplifies the fuel pump drone). The filter is above the right rear axle, really hard to get at. I am embarrassed I couldn't get the fittings undone, really self annoyed, just couldn't get the correct wrenches up in those tight spaces and then be able to apply the needed force. The check valve was only $20.25 from Pelican Parts, my mechanic replaced all 3 for $160.00. Filter was $29.25. So if that is the cause of the problem it shouldn't cost too much.



Since studying the fuel system for this repair, I also learned about the fuel pressure regulator, and now I keep my mind open to problems that may result from this part failing. But I can't say your symptoms suggest this part is the cause.

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[ds968]

Thanks Roland, that's very comprehensive info which further goes to support the reasoning of having my mechanic take care of this. :-).

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[vliegwielolaf1234]

[quote name='flash' timestamp='1345990878' post='131625']

injectors don't leak like that. they open and close too fast.



but the "air in the system" theory is sound



the check valve in the rear is supposed to keep pressure in the system. when that gets sticky, it bleeds off. it gets sticky because gunk was introduced due to a clogged filter no longer doing its job.

[/quote]

Don't agree i saw it with my own eyes they can leak .

Expert told me and actually showed me , it was a bosch injector similair to the 968 but different car .

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[flash]

when they leak, it's because the o-ring has gone bad. the injector itself does not "leak". when that happens though, it does not cause a "bleed off" problem, as the fuel is still in the fuel rail, and stopped by the injector itself. the leak just squirts fuel out of the hole.



it's sort of like your main water valve at your house, and the faucet. regardless of leaks at the faucet, if you shut off the main valve you stop the leak. similarly, the check valve keeps fuel in the rail on the back side, and the injectors stop that fuel from exiting into the engine. during operation, they open and close many times per second. if they had an internal failure, they would not work, and you would flood your engine. unlike most devices, they are "always on" whenever the key is on, and shut off each cycle.

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[tamathumper]

The injectors on my 944S did leak just like that - they would dribble gas after I shut the car off, which would reduce pressure in the fuel rail, and pool gas in the cylinders. The symptoms were that it would start rough because of all the liquid gas in the cylinders, and it also ran down past the piston and put quite a bit of gas into my oil, which I could smell on the dipstick.

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[flash]

yup - the issue though when they are leaking internally is that the don't stop doing that when the engine is running. they will continually be pouring gas into your cylinders when they are not supposed to. this is pretty easy to diagnose though, as a quick sniff of the dipstick will tell you, and you will have black soot on the tailpipe from the unburnt fuel. normally the tailpipe should NOT have any black soot on it.



the fuel evaporates pretty quickly though, and/or seeps down into the crank case, so trouble starting is usually not the issue, with the exception being a few minutes after shutting down the engine. basically trying to start it right after it has pissed itself. the symptom here usually is accompanied by a fuel smell, and/or black soot on the tailpipe.



when the check valve fails, the fuel goes back to the tank, causing the fuel rail to need to fill before the engine will fire properly. the symptom here is an uneven firing, but no fuel smell, and no black soot.

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[Cloud9...68]

[quote name='ds968' timestamp='1346000664' post='131639']

Thanks Roland, that's very comprehensive info which further goes to support the reasoning of having my mechanic take care of this. :-).

[/quote]

+1 Thanks for posting the diagram, Roland. I'd never given the fuel delivery system much thought, as it's never given me any problems (that I've known of, anyway), other than replacing the fuel filter as part of general maintenance soon after I bought the car, but your diagram really clarifies things. It does sound like a faulty check valve could possibly give some of the symptoms some people in this thread have been experiencing. Fool (and cheapskate) that I am, I'd probably tackle it myself if mine failed...

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[flash]

it's not all that hard, it's just messy. i hate dealing with fuel leaking all over me.

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