[Cloud9...68]

In my continuing quest to troubleshoot my car's hesitation under load (see thread), I'd like to test Flash's theory that it might be caused by insufficient fuel flow (volume). In principle this should be very easy to test (disconnect fuel line, have wife turn key to ON position, measure number of cc's of gas that flow into a graduated container per unit time). I just have one question: which is the right fuel line to disconnect? I assumed it was the one connected to the fuel pressure regulator (which is connected to the fuel rail), but when I disconnected it, I didn't get the expected gush of fuel; nothing came out. Did I disconnect the wrong line? Thanks.

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[rustech]

Yes, wrong line. You have to disconnect the line that feeds directly to the rail. The pressure regulator limits flow to hold pressure in the rail. You disconnected the return line.

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[Cloud9...68]

[quote name='rustech' date='Jun 22 2005, 10:48 PM']Yes, wrong line.  You have to disconnect the line that feeds directly to the rail.  The pressure regulator limits flow to hold pressure in the rail.  You disconnected the return line.

[right][post="6231"]<{POST_SNAPBACK}>[/post][/right][/quote]



Thanks, that's what I figured, but I wanted to be sure. Any idea how much flow I should see?

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[Greimann]

[quote name='Cloud9...68' date='Jun 23 2005, 05:01 PM']Thanks, that's what I figured, but I wanted to be sure.  Any idea how much flow I should see?

[right][post="6272"]<{POST_SNAPBACK}>[/post][/right][/quote]

According to the service manual - 850cc in 30 sec.



You will probably have to jumper the DME relay to get the fuel pump to run as it will only run when the engine is turning, as during the start cycle.

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[Cloud9...68]

[quote name='Greimann' date='Jun 24 2005, 06:45 PM']According to the service manual - 850cc in 30 sec.



You will probably have to jumper the DME relay to get the fuel pump to run as it will only run when the engine is turning, as during the start cycle.

[right][post="6300"]<{POST_SNAPBACK}>[/post][/right][/quote]



Hmmm... How exactly do I do that? Thanks.

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[Greimann]

You pulll the realy out, and bridge terminal 30 and 87B in the socket where the relay is installed. See attached PDF. The terminals are identified on the relay itself.

fuel_volume_check.pdf Size: 73.38 KB  Downloads: 28

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[Cloud9...68]

Thanks! I really appreciate the info. Where do you find this stuff?! <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



As a somewhat related aside, I downloaded the repair manual from the DIY section a few weeks ago, but my search feature isn't working, which renders the 819 page less than useful (unless I wanted to print the whole thing). Any ideas? I have Adobe Acrobat Reader 7.0. Thanks.

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[Greimann]

The fuel volume check procedure is actually from the 944 manual. There are a few procedures that are not in the 968 manual. The 968 manual refreences the 944 manual in the table of contents.



For searching the PDF, I mainly use the index tabs that appear on the left column. It will get you close. It is a lot of scrolling and paging, but you discover interesting things along the way.

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[Cloud9...68]

OK, I ran the fuel flow rate test. It came out perfect; better than spec, if fact. I measured a flow of about 450 ml in 15 sec at the return line, which exceeds the 850 ml in 30 sec as specified in the manual. So this rules out fuel pump, blockage in the lines, cripmed lines, etc. Between this and the cleaned/blueprinted injectors, I can now be 100% certain the car is getting plenty of fuel. So, unless there's a problem with the fuel pressure regulator, something non-fuel related is causing my hesitation. I'll check the manifold vacuum next...

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[Greimann]

[quote name='Cloud9...68' date='Jun 25 2005, 10:34 AM']... So, unless there's a problem with the fuel pressure regulator,..

[right][post="6326"]<{POST_SNAPBACK}>[/post][/right][/quote]

That was going to be my next speculation. I know that my adjustable fuel pressure regulator took out all of what I call "holes" in the throttle response and slight hesitations. Nothing as dramatic as what you apparently have, but these cars are mapped lean to begin with and adding some fuel pressure makes it run the way you think it should run.



The trick is finding a fure pressure gauge that will fit the nipple on the fuel rail. Very odd fitting and and you need a special connector. I fabricated my adapter, but I saw a relatively cheap gauge kit somewhere that had the right fitting. I'll try to dig that up.

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[Cloud9...68]

I followed your thread on the adjustable fuel pressure regulator fabrication, and it sounds like a very sound upgrade. But does my symptom of severe hesitation under sudden load fit the symptom of insufficient fuel pressure? It's almost, but not quite, reminiscent of an old car with a faulty vacuum advance. But it differs in that it never really smooths out much, whereas a car with an old vacuum/centrifugal advance configuration should in theory achieve the correct ignition timing once the revs got high enough for the mechanical advance to take over.



While an adjustable regulator would be nice, I would think that a stock, properly working regulator would provide relatively smooth acceleration under varying load conditions. Maybe I should start by rigging up your fuel pressure gauge to see if I have a fuel pressure issue.

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[Greimann]

Considering that your symptoms come on after 20 minutes of running, it is sounding more like a sensor or something. The DME temperature sensor or something like that. These things can be so aggravating sometimes. One little stream of electrons is not flowing and you are supposed to figure that out!

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[Cloud9...68]

[quote name='Greimann' date='Jun 25 2005, 08:36 PM']... it is sounding more like a sensor or something. The DME temperature sensor or something like that. These things can be so aggravating sometimes. One little stream of electrons is not flowing and you are supposed to figure that out!

[right][post="6337"]<{POST_SNAPBACK}>[/post][/right][/quote]



I have by no means ruled out a sensor, but considering the flash code test came out perfect, I'm wondering if it isn't maybe something else. If a sensor were performing sub-par, but not quite bad enough to trip a flash code, I don't see how it could cause the car to run as badly as mine is. I hate the idea of just replacing them one by one; sloppy technique, and costly too!



I'm going to hook up a vacuum gauge tomorrow and start looking for leaks. By the way, what was the source into which you tapped the vacuum gauge you have in your console gauge assembly?

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[Greimann]

I tapped the vacuum for the gauge from the tee on the fuel pressure regulator.



Speaking of vacuum - one fortunate thing is most of the vacuum lines on this car are the tiny rigid style. A loose or broken one will probably not cause major problems because they are so small.



One line that that isn't so small is the tank venting valve line. It is about 1/2" in diameter and it is located just behind the throttle body on the lower part of the manifold. The tank venting valve is controlled by the computer, or perhaps the troll that lives under the brake booster, not sure which. It operates intermittently to purge the fuel fumes from the charcoal cannister that traps fuel tank fumes. If this thing is not operating properly, then a severe vacuum leak could occur. Try plugging it for a quick test to diagnose your problem, but certainly don't leave it plugged!

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[Cloud9...68]

Thanks, I'll give that a try. Are you saying that the tank venting valve line is large enough that if it springs a leak, it could cause a lean running condition under load? Or do you think that insufficient venting of the charcoal cannister, resulting in the build-up of fumes in it, could somehow cause the hesitation I'm experiencing?

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[Greimann]

The issue would be a vacuum leak. That line would be a remote possibility, but I'm sure you are taking all suggestions at this point.

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[flash]

i don't think it's vacuum related at this point - vacuum leaks always show abrubt and severe reading changes - this is not like that

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[Cloud9...68]

[quote name='Greimann' date='Jun 26 2005, 03:49 PM']The issue would be a vacuum leak. That line would be a remote possibility, but I'm sure you are taking all suggestions at this point.

[right][post="6369"]<{POST_SNAPBACK}>[/post][/right][/quote]

You hit it on the head - I'm most definitely looking for any suggestions, however remote. I'm up to about 15 things tried, replaced, or ruled out, with not a dent in the problem so far. This is why I'm peppering both forums with posts. "Desperate" is such an ugly word, but I'm beginning to run out of euphemisms <img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" />

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