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Old 11-02-2015, 04:32 PM   #4
BYprodriver
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Join Date: Oct 2008
Location: O.C. CA
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Garage
Quote:
Originally Posted by luckyed7711 View Post
OK. Here is my issue. I have one of those pesky intermittent problems that end up being tough to diagnose. The car starts up fine every time when cold and runs perfectly while it's running. However, almost every time I drive it at some point it either stutters in and out, the engine cutting out completely for a fraction of a second, then cutting back in a few times, finally running fine as usual;

Or, other times the engine dies completely without warning, not at any particular time in the driving cycle. So far, when it has stopped completely, if I wait long enough, anywhere from 10 minutes to half an hour, it'll start up and I've been able to drive home without issue.

One or the other (or both) of these issues have happened the last 7 or 8 times I've taken the car out.

There is no CEL. I've ruled out the crank position sensor, the fuel pump relay, and any wiring issues, so I'm checking the fuel supply system.

My results so far: Fuel pressure at the rail after the fuel pump runs for a few seconds with the engine off is 50 psi. When the pump's no longer running the pressure starts to slowly, but steadily bleed off, until a day or two later there's no pressure at the rail.

Start up the car, engine at idle, the fuel pressure is steady at 57-58 psi, and as I said the car runs fine until it stutters and/or stops.

I believe the fact that the pressure is higher with the engine running than when it's not running is the opposite of what is supposed to happen, no?

Can anyone suggest what my results indicate? Could the fuel be bleeding back into the tank and suggest an issue with the regulator? (I suppose I might have one or more leaking injectors. It doesn't seem to be running rich.) Could a failing fuel level sensor ass'y. be causing my problems? Might the tank pressure sensor or any other part of the venting system have anything to do with it?

Any suggestions on how to proceed would be welcome. Thanks.
Due to the age of 986's I would be surprised if any of them didn't have clogged/leaking injectors. I tested mine @ 80K miles & had 2 leaking.
Good news is I would guess your main issue is your fuel pump. When they get hot &/or battery is low, output is reduced. Gas cools the pump so if the tank is below 1/4 full it could cause hotter fuel pump. Check your in tank filter while the tank is low on fuel, but beware if the battery is disconnected while below 1/4 the fuel gauge may lose it's level calibration. To recalibrate requires a PST2 or PIWIS diagnostic tool.
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OE engine rebuilt,3.6 litre LN Engineering billet sleeves,triple row IMSB,LN rods. Deep sump oil pan with DT40 oil.
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