Fuel System Problems?

[P-51 Mustang]

Hello, my boxster has been running bad (rough idle, stumple through revs, sometimes wont start and a CEL). So ive replaced the fuel pump, then found ALOT of trash in the fuel line, so I replaced the fuel filter. This worked for half a day, then it wouldnt start again so I put a new fuel relay in from another boxster; it started with the new relay, but it is still running awful. I think it could be a bad check valve, which is letting pressure bleed out of the line. Anyone have a suggestion, I would GREATLY appreciate any comments. Thanks!

[juniinc]

The injectors need to be cleaned, if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions. And the other thing is you could also be dealing with malfunctioning fuel pressure regulator.

Hello, my boxster has been running bad (rough idle, stumple through revs, sometimes wont start and a CEL). So ive replaced the fuel pump, then found ALOT of trash in the fuel line, so I replaced the fuel filter. This worked for half a day, then it wouldnt start again so I put a new fuel relay in from another boxster; it started with the new relay, but it is still running awful. I think it could be a bad check valve, which is letting pressure bleed out of the line. Anyone have a suggestion, I would GREATLY appreciate any comments. Thanks!

Edited October 11, 2007 by juniinc

[rsfeller]

and what were the codes from the CEL?

[Chris_in_NH]

Hello, my boxster has been running bad (rough idle, stumple through revs, sometimes wont start and a CEL). So ive replaced the fuel pump, then found ALOT of trash in the fuel line, so I replaced the fuel filter. This worked for half a day, then it wouldnt start again so I put a new fuel relay in from another boxster; it started with the new relay, but it is still running awful. I think it could be a bad check valve, which is letting pressure bleed out of the line. Anyone have a suggestion, I would GREATLY appreciate any comments. Thanks!

sounds like it could be a bad/failing MAF (Mass Air Flow meter) to me. you can test it very easily.

to test your MAF you need to unclip the MAF's wiring harness (but leave the MAF installed), then disconnect the negative battery cable for at least a minute (to reset the DME/ECU), then reconnect the battery, then start the car. if it runs better with the MAF disconnected, then the MAF is probably bad. if you want to make sure the MAF is bad, plug the MAF's wiring harness back into the MAF, disconnect the battery for a minute, reconnect the battery and start the car. if it runs worse, then your MAF is most certainly bad. running the car without the MAF plugged in will not damage the car/engine at all.

when you reconnect the battery, you'll need a radio code for a '97-'02 radio to get it to work again. 03+ radios don't need a code.

if it runs the same with the MAF connected and disconnected, then the problem probably lies elsewhere. but this sounds very much like a bad MAF sending bad info to the DME. the results are instant and the test is free. give it a try.

Edited October 12, 2007 by Chris_in_NH

[Qtwo]

I would also suggest that you check to see when your gasoline source has checked their pump or pumps for the presence of water which can leak into their tank. The gas manufacturer could also be a culprit because they all formulate their additives at some distribution point. these formulations can be problematic at times. We have that trouble where I live and our solution is to change your supply of gas to a major brand such as Shell or Esso. Do not buy from a local, no name, food store. Change your fuel filter again because you have just contaminated your new one then add a can of HEAT (Red can, not Yellow). If water was your problem it should now be gone. Like wise with the gas formulation. I have done this successfully with my Boxster and my wifes turbo Saab.

Bedst of luck,

Qtwo

[P-51 Mustang]

WOW lots of things I havent even thought about checking, Im going to try the MAF then move to the fuel pressure regulator. Thanks so much!!!!!! :-)

[Chris_in_NH]

I would also suggest that you check to see when your gasoline source has checked their pump or pumps for the presence of water which can leak into their tank. The gas manufacturer could also be a culprit because they all formulate their additives at some distribution point. these formulations can be problematic at times. We have that trouble where I live and our solution is to change your supply of gas to a major brand such as Shell or Esso. Do not buy from a local, no name, food store. Change your fuel filter again because you have just contaminated your new one then add a can of HEAT (Red can, not Yellow). If water was your problem it should now be gone. Like wise with the gas formulation. I have done this successfully with my Boxster and my wifes turbo Saab.

Bedst of luck,

Qtwo

how has he 'contaminated' his new fuel filter?

[Qtwo]

I would also suggest that you check to see when your gasoline source has checked their pump or pumps for the presence of water which can leak into their tank. The gas manufacturer could also be a culprit because they all formulate their additives at some distribution point. these formulations can be problematic at times. We have that trouble where I live and our solution is to change your supply of gas to a major brand such as Shell or Esso. Do not buy from a local, no name, food store. Change your fuel filter again because you have just contaminated your new one then add a can of HEAT (Red can, not Yellow). If water was your problem it should now be gone. Like wise with the gas formulation. I have done this successfully with my Boxster and my wifes turbo Saab.

Bedst of luck,

Qtwo

how has he 'contaminated' his new fuel filter?

Good question, it took me a couple years to find out. "If" there has been water contamination, it takes a while to plug up the fuel filter but it doesn't stay plugged completely. Naturally that depends on the amount of contamination. Reading the original post, I could see that the fuel filter was replaced but strange behavior soon resumed. My experience with a partially plugged fuel filter(free water) was that it really caused the car to behave strangely. eg. You could usually start the car ok but after you drove it for a while it may just quit for no reason and then not start. You could leave the car alone for a while and it would again start and even get you home OK. Everything in the electrical system checked out just fine.

Wow, now what can we look for? So we looked for intermittants with components. No luck.

Then, one of my mechanic friends said that I might have water in the gas problems (this includes alcohol which is mostly water and was mandated by my state to be added to gas for emission reduction)and suggested that I try to add a can of Heat to my gas and change the gas filter. It worked like a charm. The next step was to find a new gas source free from water. I did and haven't had any problems since.

I responded to this request because it would be very inexpensive to try to eliminate water contamination first then go on to component replacement if that didn't work. All of the responses though looked good to me. I just like to try the easy, inexpensive things first. Sometimes they work.

Hope this helps answer your questions. There is a lot more to this though and both my Saab and Boxster responded the same and are now free of these problems for the last two years.