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Old 09-27-2015, 05:40 PM   #1
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testing 2002-2004 non-return fuel supply?

I've been trying to educate myself on non return fuel supply systems generally and the Boxster system specifically. Found a lot of general info but only a smattering of specific info searching the Forum and Google.

I have an '03 S with 83K miles. I believe all models from 2002-2004 have the same non-return fuel system in common.

The Bentley manual states that "fuel delivery tests for non-return models (2002-2004) require the Porsche System Tester 2 (PST2) and are beyond the scope of this manual." Is this correct?

Answer: No this is not correct. The Bentley manual is wrong. Part of my objective in this post was to clarify this for myself and future DIYers.

As Timco stated in next post, there is in fact a port on the passenger side fuel rail, towards the front, which allows attachment of a fuel pressure gauge. The port consists of a Schrader valve so that when the cap (which is essentially just a dust cap) is removed, no fuel is released. For anyone buying a pressure gauge to test the '02-'04 system, this (Schrader) is the connection you will want.

The Bentley manual also states that the parts comprising the "maintenance free" non return fuel system, namely the pump, level sender, fuel filter, and pressure regulator are not available separately, but I noticed that the level sender ass'y. and the pump ass'y. are indeed apparently available separately from Pelican and other sources. So the Bentley seems to be in error here also.

I will elaborate on my objective and give some of my initial test results on a subsequent post.


Last edited by luckyed7711; 11-02-2015 at 02:19 PM. Reason: simplification, clarification
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Old 09-27-2015, 06:38 PM   #2
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Pressure is a port for a gauge on the fuel rail. You can bypass the fuel pump relay and turn the pump on. Don't know about rate.
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Old 11-02-2015, 02:55 PM   #3
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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.
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Old 11-02-2015, 04:32 PM   #4
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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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Old 11-09-2015, 04:38 PM   #5
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faulty regulator? fuel line connector O ring?

"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?"

Further results: So I checked the volume/flow rate by removing the fuel line at the top of the tank, attaching a length of hose to the nipple and running the fuel pump for 30 seconds into a container. This is another test that the Bentley manual claims, in error, cannot be made for 2002-2004 systems without a diagnostic tool. (note to future DIYers)

In 30 seconds the pump put out about 1.2 litres, well over the 850ml minimum given as passable. Unfortunately when I reconnected the fuel line it now leaks at the connection. I'm hoping there's an O ring in there that I can replace. Anyone know?

However, although the fuel pressure while running seems to be in spec, and the flow rate seems to be more than adequate, I've still got pressure lower while not running than running, instead of the other way around. Also, after checking the volume, I was able to, fairly easily, blow the fuel in my test line back into the tank the wrong way through the pump.

Should that be possible? Can this mean a faulty regulator? If the regulator is failing and my pump runs fine I presume that I'd have to by a new fuel pump ass'y. anyway as the 2 components are apparently integrated?

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