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Sudden Power Loss at Speed


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I'm looking for some help. I have a '99 Boxster w/ 30K miles on it. I've recently started getting a sudden, temporary power loss at highway speeds (as if I turned the car off and then on again). Electrical seems fine, CE light comes on for duration of loss and then goes out again. I brought the car to the dealer but they were not able to reproduce problem. In an hour drive the problem typically will demonstrate itself anywhere from 0 to 6 times (usually at least a couple). The dealer stated that vacuum leaks, MAF among other things could cause this. Their suggestion, they could start replacing things until they fix it (at my expense). I'm looking for a better/ less costly solution. After some discussion, they felt it was the MAF and I did allow them to replace it but it didn't solve the problem.

Any guidance would be appreciated!

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No I'm not hitting the rev limiter at all, It happens while crusing at 70 - 75 on the highway. About a week before the power problem I had the CE light come on and stay on. At first I didn't panic, I checked the gas cap, etc. but it didn't go out. Then the power loss thing happened and it freaked me out a bit. I didn't hesitaite to bring it to the dealer.

The dealer found the following codes: 35 & 27 indicating O2 sensors. They checked the O2 sensors and said they were fine which led them to the MAF as a suggested fault (maybe because I have High Flow Intake with K&N filter). The MAF didn't fix the problem. I don't know if any codes are being recorded now since the CE light is only on for the second the that the power drops.

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  • Moderators

You have a K&N oiled filter. ;) http://www.renntech.org/forums/index.php?showtopic=659

Having the light come on and then immediately go out is a new one for me. I will look at my OBDII manual when I get a chance. There are other people here with the manual and maybe they have some suggestions. Otherwise, this is a Peter question.

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Craig - Thanks, you guys are great!. The codes that were stored in the DME were P1125 & P1123. I guess the codes they printed on my invoice refer to something else. What the dealer told me they referred to was the O2 sensors. They said that a simultaneous failure of both was unlikely and that they would cause the car to run poorly but not the rapid loss of power I've experienced. Who knows?

Anyway, I look forward to you thoughts.

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P1123-O2 sensing adaptation range 1(cyl 1-3) lean limit

P1125- same as above but (cyl 4-6)

Fault areas- fuel presure too high, fuel injector leaking

Check:

-fuel pressure, fuel regulator, vacuum, fuel injector leaks.

I would probably put the factory filtering system back in. Aftermarkets are known to cause problems. The rapid loss of power is probably one of the above mentioned. You may want to check and see if any old codes are stored in the ECU.

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Thanks Craig. The cold air intake has been on for a while now. Unfortunately, I had all of the old parts in a box and threw them out when cleaning out the garage around xmas (no going back).

I'd be surprised if it where the intake system. I think you've pointed me in the right direction (fuel pressure, fuel regulator, vacuum, fuel injector leaks). Is there an easy way for me to check any of these things or is it back to the dealer?

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Vacuum: remove vacuum line at fuel pressure regulator:

-start engine: 0.4-0.6 bar

Fuel pressure:

-stationary engine: 3.8 +or- 0.2 bar

-engine idling: 3.3 +or- 0.2 bar

The early PO software did not take well to variances to intake volume beyond that which it was designed for. Good luck with it, hope this helps.

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  • 2 weeks later...

:thumbup: Board Members: FYI, It appears that the problem is resolved. I started thinking about the power loss. It was like the fuel was shut off, causing the sudden 2000 RPM drop in power at highway speeds. I thought that maybe an obstruction in the fuel filter could intermittently position itself in a way to obstruct flow, when the loss of power is experienced, it shifted again and power was restored (purely speculating). Anyway I looked my recent maintenance record to see if the fuel filter was replaced at 30K and saw that it wasn't. I ordered a replacement fuel filter but in the meantime added a fuel injector cleaner to see if that did anything (it had been 10K miles or so since done last). Believe it or not, I have not experienced the problem since adding the cleaner. I'm going to change the filter anyway. Whether the problem was located in the filter or somewhere else in the fuel system, I'm happy I didn't have the dealer go on a part swapping spree.

BTW, where is the fuel filter located? Is this something I can easily get access to and replace?

Thanks to all

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BTW, where is the fuel filter located? Is this something I can easily get access to and replace?
You will need to remove the plastic belly pan as it is under this and looking towards the front of the car. Here it is on a Boxster (996 is the same location). Gas will run down your arm... :(

Jeff's pic

fuel_filter.jpg

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