Fuel Pump vs Crank Position Sensor vs ....

Magic Mike · 08-09-2013, 02:59 AM

Greetings All,

I have been researching the site for guidance on my fuel supply issue. I recently let my 2001 Porsche Boxster
get very close to empty. Then I did something that I've never done before.......I filled the tank while the car was still running (I know, very stupid). When I went to put it in gear, it simply died. From then on, the engine would turn-over, but would not start.

I later thought that I had successfully jumped the fuel pump relay in an attempt to rule-out a defective fuel pump. When I did not hear the fuel pump turn-on on turning the ignition key, I concluded that it must be a bad fuel pump. I then replaced the fuel pump. The engine again only turned-over, but would not start. The battery is fully-charged.

I re-attempted jumping the fuel pump relay and could then hear the fuel pump come-on, but the engine still would not start. I am now thinking that one of the following might be the culprit:

1) Fuel Pump Relay
2) Crank Position Sensor
3) Fuel Filter

I apologize for posting something that has likely already been covered on this site. If someone could either walk me through this or point me toward the appropriate write-up, I would be eternally grateful.

Best,

Mike

paulv · 09:11 AM

If the CPS has failed, then the DME will not signal the fuel pump on (at least this is how it works on other cars) for safety reasons. You can check the fuel pump relay by using a digital multimeter and check to see if you're getting voltage across the relay windings (first) and then the relay contacts (second). Also, you may want to disconnect the battery and wait a couple of minutes and reconnect so things can reset (but this will cause some systems to "re-adapt" after a few drives).

I have doubts about the fuel filter as the engine was running OK prior to the problem happening.

Check out this: http://www.pelicanparts.com/techarticles/Boxster_Tech/26-FUEL-Engine_Sensors/26-FUEL-Engine_Sensors.htm

Regards,
paul...

Magic Mike · 08-10-2013, 10:00 AM

Paul,

Thank you for the input. The pump will come on once I jumper the fuel pump relay. But the engine still will not start. From what I understand, the fuel pump relay also controls the ignition, right?

Mike

Magic Mike · 08-10-2013, 01:54 PM

Paul,

I hooked my 18V battery from my cordless drill to the two coil terminals (86 and 85) and heard the circuit close (i.e. Clicking Sound). While powered, I then measured the resistance between the two relay terminals (30 and 87) and it was zero. It seems then that the relay is operational, leaving something else as the reason for my problem. I am now leaning more toward it being the crank position sensor.

Your thoughts?

Mike

Cajundaddy · Cajundaddy's Garage

Disconnect the battery first. It will clear the DME and your car should start.

Magic Mike · 08-11-2013, 09:18 AM

I disconnected the battery and reinstalled the fuel pump relay. then reconnected the battery. Still only turns over. No start. I read that there's a fuse on the fuel pump circuit somewhere. Should I try to find this and inspect it? I don't know where it lives, though.

Mike

Magic Mike · 08-12-2013, 05:12 AM

Anyone have any additional input on this issue? I'm starting to get "I told you so" comments from the wife. ;-(

Mike

paulv · 08-12-2013, 06:30 AM

Quote:

Originally Posted by Magic Mike

Paul,

Thank you for the input. The pump will come on once I jumper the fuel pump relay. But the engine still will not start. From what I understand, the fuel pump relay also controls the ignition, right?

Mike

Fuel pump relays are typically controlled by the PCM (or DME for us) and doesn't get involved with the ignition system -- the DME controls that also.

What about the CPS? Do you know if it's working?

Regards,
paul...

BTW, wives are good at saying things that don't contribute to the solution of a problem.

Cajundaddy · Cajundaddy's Garage

Disconnect the fuel line and test fuel pressure. Do we have fuel? Is it within spec? If not, why not?
Test for spark. Do we have spark? If not, why not?

Magic Mike · 08-12-2013, 08:14 AM

Paul: How do I test the CPS?

Cajundaddy: Thanks for the advice. I'll definitely test fuel pressure and confirm spark. The fuel was high octane from a Shell Station.

Thanks all,

Mike

paulv · 08-12-2013, 09:35 AM

I have a Durametric scan system so it's easy for me -- but the best way would be an oscilloscope or a graphing multmeter -- try and see if you can borrow the graphing multimeter. You could remove the sensor and then bench test it but then you would need the sensors parameters to verify (I don't know what they are, sorry).

Regards,
paul...

mikefocke · 08-12-2013, 02:13 PM

Use of the search capability provided by this forum using "test fuel pressure" yields
http://forums.pelicanparts.com/boxster-cayman-forum/676690-fuel-pressure-tester.html

and many other threads.

Cajundaddy · Cajundaddy's Garage

Quote:

Originally Posted by Magic Mike

Paul: How do I test the CPS?

Cajundaddy: Thanks for the advice. I'll definitely test fuel pressure and confirm spark. The fuel was high octane from a Shell Station.

Thanks all,

Mike

Sorry, I meant "is your fuel pressure within spec?" I wasn't concerned about fuel quality at this point. If not it is likely the fuel filter or fuel pump.

No spark? CPS is a possible cause.

Magic Mike · 08-14-2013, 05:09 AM

The fuel pressure at rest is around 3.17 BAR (3.17 PSI). On cranking, it goes to around 3.86 BAR (56 PSI).

Does this sound about right?

Thanks,

Mike

paulv · 08-14-2013, 08:18 AM

Quote:

Originally Posted by Magic Mike

The fuel pressure at rest is around 3.17 BAR (3.17 PSI). On cranking, it goes to around 3.86 BAR (56 PSI).

Does this sound about right?

Thanks,

Mike

Stationary engine 3.8 +/- 0.2 bar
Engine at idle 3.3 +/- 0.2 bar

Sounds like you're OK.

Regards,
paul...

Magic Mike · 08-14-2013, 12:55 PM

I meant 3.17 BAR (which was around 46 PSI) at rest.

I'll be checking spark this evening and will take a look at the CPS.

Thanks,

Mike

Magic Mike · 08-19-2013, 04:52 AM

Is there an easy way to access the coil on plug assembly other than having to jack-up the car to access them from below?

Thanks,

Mike

paulv · 08-19-2013, 09:18 AM

Quote:

Originally Posted by Magic Mike

Is there an easy way to access the coil on plug assembly other than having to jack-up the car to access them from below?

Thanks,

Mike

Jacking up the car seems to be the only way. At least the service info shows accessing the coil packs/plugs from under the vehicle.

Regards,
paul...

stealthn · 08-20-2013, 05:00 PM

Sounds like a vapor lock, start simple, undo the gas cap, then put it back on. Try to start