help needed - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Badboybox · 01-01-2018, 10:40 PM

Was out driving my 1998 boxster drove great .when I got home pulled in my driveway
Got out to open garage the car started to run rough then turned off.tried to restart , it would start
But only run for maybe 3 to 5 seconds then turn off.if I touched the gas pedal it would turn right off.
Had to push it into my garage as it would not stay running long enough or let me hit the gas with out it turning off .it turns over no problem.i have no check engine light on at all and have no codes.i pulled the MAF sensor and cleaned it now the car turns over but will not come on at all.does anyone have any ideas of what it could be.it just seems so random that one second its running great the next its not wanting to run at all.Thanks again for any help.

YellowS2000 · 01-01-2018, 11:19 PM

Hi Badboy
I had a similar problem when I removed the throttle body and cleaned it. It would turn over and fire but turn off straight away.

Has to get it trailer to a garage. The fault was I hadn't attached one of the plenum chamber tubes back on properly so it was drawing air.

Your sound like a very similar fault.

Its definitely nothing serious

Peter

Badboybox · 01-01-2018, 11:22 PM

Quote:

Originally Posted by YellowS2000

Hi Badboy
I had a similar problem when I removed the throttle body and cleaned it. It would turn over and fire but turn off straight away.

Has to get it trailer to a garage. The fault was I hadn't attached one of the plenum chamber tubes back on properly so it was drawing air.

Your sound like a very similar fault.

Its definitely nothing serious

Peter

Hi thanks for the reply.i didn't remove anything on the engine when it started running bad.
Just started out of no were.

husker boxster · 01-02-2018, 04:23 AM

Sounds like it could be the crankshaft position sensor.

Badboybox · 01-02-2018, 05:42 AM

Quote:

Originally Posted by husker boxster

Sounds like it could be the crankshaft position sensor.

Do they go out like that.one second running next not.? What are the symptoms of it going out.how can I tell if it's the crankshaft position sensor or MAF sensor or fuel pump.when I crank it over I can smell fuel like it's getting gas.so I don't think it's the fuel pump.its weird I'm not getting the check engine light.

Jamesp · 01-02-2018, 06:16 AM

Crank it and watch the tachometer. If the tachometer does not move while cranking, change the CPS.

Badboybox · 01-02-2018, 06:23 AM

Quote:

Originally Posted by Jamesp

Crank it and watch the tachometer. If the tachometer does not move while cranking, change the CPS.

Ok im going to change it..I just went out there after the car sat over night.it started for 2 or 3 seconds then turned off.thanks for the help.

mikefocke · 01-02-2018, 09:46 AM

Fault codes read? Don't just go throwing parts at it. Doesn't the fact that it starts for 2-3 seconds point to a CPS working at least during that time. Fuel pressure?

Quadcammer · 01-02-2018, 10:07 AM

when my cps was bad, the car shut right the hell off and would not restart until stone cold.

this seems more like a major vac leak.

Badboybox · 01-02-2018, 10:50 AM

No love..changed the crank position sensor still just turns over with no start.maybe the fuel pump or the relay.any ideas.Thanks.car is bone stock.ran perfect yesterday till I pulled in my driveway and it just turned off.

Quadcammer · 01-02-2018, 11:20 AM

have you looked over the engine for obvious issues or vac leaks?

Geof3 · 01-02-2018, 11:42 AM

Check this article for an easy way to test the fuel pump.

https://www.pelicanparts.com/techarticles/Boxster_Tech/22-FUEL-Fuel_Pump/22-FUEL-Fuel_Pump.htm

Badboybox · 01-02-2018, 12:33 PM

Yes looked over the engine see nothing..i really think it's Electrical because it was running one minute turned off the next like something electrical went out.

Van914 · 01-02-2018, 01:10 PM

Check the MAS. I had a similar problem

Badboybox · 01-02-2018, 01:36 PM

Quote:

Originally Posted by Van914

Check the MAS. I had a similar problem

I took it out and cleaned it.but wont it still start and run with a bad MAS.?or if you disconnect
The MAS wont it run.my car is just cranking over with out much happening. And it was runjing perfect till I turned into my driveway when it just turned off.when I would turn it over it would act like it wanted to start but would just turn off after a second or 2.

thstone · 01-02-2018, 09:18 PM

Disconnect the electrical connector to the MAS (or MAF) and try to start the car. The ECU will use the factory pre-programmed fuel map and the engine should start and be drivable (although it might run kind of rough). This won't harm anything.

If the engine runs and drives (even roughly) with the MAF disconnected, then replace the MAF. If the engine still won't start, then its not the MAF and you'll have to look elsewhere.

And yes, its fairly common for a car to run perfectly until they don't run at all since many components do not suffer a gradual degradation in performance, but instead fail like a light bulb.

Badboybox · 01-02-2018, 09:59 PM

Quote:

Originally Posted by thstone

Disconnect the electrical connector to the MAS (or MAF) and try to start the car. The ECU will use the factory pre-programmed fuel map and the engine should start and be drivable (although it might run kind of rough). This won't harm anything.

If the engine runs and drives (even roughly) with the MAF disconnected, then replace the MAF. If the engine still won't start, then its not the MAF and you'll have to look elsewhere.

And yes, its fairly common for a car to run perfectly until they don't run at all since many components do not suffer a gradual degradation in performance, but instead fail like a light bulb.

I disconnected the MAF sensor still won't start. Im pretty sure I hear the fuel pump from behind
The dash.when I turn over the motor I can spell gas like its getting full but do spark.i changedvthe crank sensor today with no change.

Geof3 · 01-02-2018, 10:19 PM

Have you checked all of your fuses and relays? Mine died due to a failed (burned actually, longish story) wire harness section to the drivers side aft O2 sensor. It was shorting out and blowing the injector bank fuse. Look to see if all of your fuses are intact, if not it may have just been a fluke. But if you find a dead one, and replace it and it pops again you have a short or something somewhere. I would stop throwing parts at it until you check all the electrical pathways first.

I’m pretty sure all of the various sensors can be checked with a Durametric or pst at the dealer. You may have to bite the bullet and get some systemic diagnostics done.

husker boxster · 01-03-2018, 03:10 AM

It may be time to invest in a code reader or find someone who has one. Pulling codes will help you zero in on the issue. A decent / adequate code reader runs $50-70. You will spend way more than that chasing and replacing parts.

Quadcammer · 01-03-2018, 04:50 AM

a $13 obd bluetooth dongle and a $3 obd fusion app will get the job done.

but I'm guessing he doesn't have any codes.

Definitely check fuses.

go back to the basics.

Does the car have spark?

Have you verified fuel pressure at the rail?