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Old 12-09-2014, 12:37 PM   #1
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987 Cuts out Briefly Under Acceleration.

Hey Guys,
2005 987 S 178,000 miles.
I'm having an issue during acceleration from stops and on the highway. This occurs at any engine temperature. Usually occurs after a stop sign or light. I will accelerate moderatly, like you would to pull into the street, and as the RPMs build and I accelerate I will lose engine power for a brief moment. Maybe 2 or 3 seconds, and then the power jumps back like nothing happened. When I lose power, the RPMs drop slightly, but never below idle, and there is a distinctive jerk every time it happens, like the power gets reversed for a second. This happens usually on main streets but also on the highway while cruising, albeit while crusing its just brief second or so. It happens more since it's colder.

It's been going on a few months and I figured it's the fuel pump, since I've been having trouble starting the car a lot for several months. It always started but took several revs. Now, I've replaced the fuel pump, and it starts like a champ, but I still get these moments of lost power. I figured the pump was the cause for both problems since cutting out is a symptom of a bad pump, but I'm not sure now. It happens after I hit sizeable bumps on the highway too.

I think it may be the fuel pump relay or throttle body needing cleaning. Ive run thru fuel system cleaner a while ago, and I lost the AOS almost a year ago, which required some cleaning and replacement if that makes a difference.

If anyone has an opinion it would be appreciated before I goto the dealership. No CELs. No weird smoke or sounds. Spark plugs mostly new, around a year and a half old. Thx.
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Old 12-09-2014, 04:22 PM   #2
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Has it ever been hit from behind? I mean "ever" like before you owned it? Any signs?
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Old 12-09-2014, 05:08 PM   #3
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Sounds like it could be related to the e-Gas pedal. Maybe there's a dead spot in the sweep of the pedal that's causing the loss of power?
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Old 12-09-2014, 05:28 PM   #4
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+1 and I wonder if it could be a loose ground?
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Old 12-10-2014, 07:36 AM   #5
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The ground is solid since I made sure after putting in the new fuel pump and reconnecting the battery. When I said losing power I mean a loss of just engine power. Electronics are fine the entire time.

This cutting out doesn't happen every time I take off, but more often right after a stop. If the pedal has a dead spot wouldn't it happen every time? I think it's happened at various throttle inputs, especially when taking off and needing quick power, when you need to merge quickly, I'll just start off and lose it then it goes back to normal.

I've been bumped from behind but nothing major, just a scratch at stoplight. I've owned the entire time.
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Last edited by darkstormvx; 12-10-2014 at 07:42 AM.
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Old 12-10-2014, 02:27 PM   #6
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I think you can test the e-pedal with a Durametric. Fuel pressure regulator? Any codes?
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Last edited by woodsman; 12-10-2014 at 02:33 PM.
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Old 12-15-2014, 01:22 PM   #7
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No codes. Got one for a solenoid, but that was over a year ago and hasn't come up since. Most recent one was for a catalytic converter. Don't think these are related.

I haven't had the fuel pressure checked yet. Would I be able to acquire a durametric cheap or will i need the dealership for that?
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Old 12-16-2014, 10:44 AM   #8
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With a Durametric you can check for codes. Durametric is a private company not affiliated with Porsche . A dealer has an even more complicated tool for diagnostics. A check engine light illuminates for emission- related codes ONLY so you may in fact have a code(s) and not know it. Goggle Durametric and you will see the 'enthusiast's' package costs $287. You need a laptop and once you plug in the durametric you have access to the whole array of diagnostics on the car. You can test run some systems to see if they're functioning and any codes will lead you in the right direction. It gets complicated and may not interest you but it can save you a small fortune.
Testing fuel pressure requires a common fuel pressure tester and can be found for $30-50.
It could also be spark related, especially since the new fuel pump cured the starting problem but not the other. Also the fact that it happens after you hit a bump is significant- would seem to indicate something is loose...

Last edited by woodsman; 12-16-2014 at 11:00 AM.
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