Engine fires then dies immediately - 986 Forum - The Community for Porsche Boxster & Cayman Owners

tranceatlantic · 02-10-2012, 06:12 PM

I bought a 986 two weeks ago, had no problems until yesterday when it wouldn't start. It turns over, seems to fire but dies immediately. My OBI says there are no problems. I unbolted the hose on the passenger side fuel rail. I think it's the return fuel hose. On start up it flows a steady stream of fuel. So I'm guessing it's not a fuel problem. I noticed the Bosch idle controller is humming but other threads say this may be ok. I honestly didn't notice it before but I wasn't looking forward for a problem .

Now I'm out of ideas. Please help!

JFP in PA · 02-11-2012, 07:10 AM

Take a look at your crank position sensor, when failing they casue the DME to shut off the fuel supply because they don't see the engine turning over. Located on the bellhousing.........

harryrcb · 02-11-2012, 07:14 AM

Quote:

Originally Posted by tranceatlantic

I bought a 986 two weeks ago, had no problems until yesterday when it wouldn't start. It turns over, seems to fire but dies immediately. My OBI says there are no problems. I unbolted the hose on the passenger side fuel rail. I think it's the return fuel hose. On start up it flows a steady stream of fuel. So I'm guessing it's not a fuel problem. I noticed the Bosch idle controller is humming but other threads say this may be ok. I honestly didn't notice it before but I wasn't looking forward for a problem .

Now I'm out of ideas. Please help!

At idle the fuel pressure should be around 50 psi or 3.5 bar so it should do a little more than flow. Yes you unbolted the return line. the only proper way to determine if you have the appropriate fuel pressure required to run the engine is with a gage hooked up to the test port. Please give us more info on which engine you got, I'm assuming a 2.5 ?

tranceatlantic · 02-11-2012, 07:31 AM

Thanks guys. I was also starting to think that my fuel test was not up to much. Im pretty sure now that it is firing although only very briefly. It dies within seconds even with some starter fluid in the air intake. Would either a bad crank position sensor or bad fuel pump/relay throw an error on the OBDI? I'm getting nothing from the DME.

Either way I'll try to find this sensor and look at the fuel system more closely. What's should I do to test this crank position sensor? I have a volt meter if I can use it to test it?

It's a 1999 2.5L. Again thanks for your help!

JFP in PA · 02-11-2012, 08:06 AM

A bad CPS will not throw a code; the DME will simply think that the engine is not rotating and shut everything off like it is supposed to.........

JFP in PA · 02-11-2012, 08:08 AM

The CPS is a simple "Hall Effect" sensor that sends a signal (around 200 mV if memory serves) when a bit of ferrous metal (the shutter on the back of the flywheel) passes within proximity of it. It is like a light bulb, it either works or does not......

Splitpin · 02-11-2012, 09:54 AM

Watch to see if the rev counter moves at all on crank

tranceatlantic · 02-12-2012, 07:04 AM

Yes I see the rev counter moving when it starts. That signal doesn't come from the crank position sensor does it? I spent the best part of yesterday trying to access it from below but progress was happened by rusty screws on the plastic covering.

Splitpin · 02-12-2012, 07:31 AM

Yes it gets it's information from the crank sensor via the ecu as its stopping does the counter drop before the revs?

tranceatlantic · 02-12-2012, 08:10 AM

No the counter seems to match the revs pretty well but it's hard to be sure as the revs only stay up a second. If thats the case what are the chances that's it's actually the crank position sensors? I still haven't checked the pump or relay. Any hints for finding/checking those?

tranceatlantic · 02-12-2012, 10:37 AM

I got a fuel pressure tester. Hits 50psi then maintains 45psi. I guess it's not fuel then. I got some tools to help me remove the plastic on the underside so I'm going to check the crank position sensor if I can get to it.

tranceatlantic · 02-12-2012, 01:36 PM

Hope fully the above image is a crank position sensor. Could someone please confirm this is what it should look like when viewed from under the car? Id also be really interested to know if I can test it. It has 4 terminals but the youtube vids on a generic sensor say it should have 2 and they should produce a small AC voltage when the crank turns.

JFP in PA · 02-12-2012, 02:04 PM

That is not it. The CPS is on the passenger's side of the bell housing.

ppbon · 02-13-2012, 07:02 AM

Quote:

Originally Posted by tranceatlantic

I bought a 986 two weeks ago, had no problems until yesterday when it wouldn't start. It turns over, seems to fire but dies immediately. My OBI says there are no problems. I unbolted the hose on the passenger side fuel rail. I think it's the return fuel hose. On start up it flows a steady stream of fuel. So I'm guessing it's not a fuel problem. I noticed the Bosch idle controller is humming but other threads say this may be ok. I honestly didn't notice it before but I wasn't looking forward for a problem .

Now I'm out of ideas. Please help!

Disconnect the MAF and see if it runs without it.
Happy Boxstering,
Pedro

tranceatlantic · 02-13-2012, 04:23 PM

Thanks for your patience. I found what I'm pretty sure is the crank position sensor. Getting the plug out took some effort as described in "my99 Boxster Crank Position sensor DIY" on the pelican parts forum. Any ideas on how to test it? There are 3 pins on the plug.

tranceatlantic · 02-14-2012, 01:55 PM

The MAF is out - no change.

tranceatlantic · 02-15-2012, 02:53 PM

.....and it's not the crank position sensor.

tranceatlantic · 02-15-2012, 06:19 PM

I took the battery out and after I put it back in in started up no problem! I've heard of clearing fault codes that way but last time I checked I had none.

DenverSteve · 02-15-2012, 06:40 PM

Sometimes you just have to reboot. Hope it stays okay.

tranceatlantic · 01-06-2013, 04:43 AM

Follow up:

The same problem has happened intermittently over the last year. I'd say about 5 times in total. The engine seems to fire but dies immediately. Maybe its not even firing, I'm not sure. But it sounds normal until you get to the point where you would normally let go of the key. It seems more likely to happen if I give the engine a false-start, like when you turn the key and it slips in your hand so it doesn't have enough turn to get up and going. Its not a big problem - I just always need to have a 10mm socket handy to pull the battery connection, then everything is fine.

I was just wondering if anyone has seen this problem? Is it really a case of my DME crashing and needing a reboot? The first rule of IT is 'have you tried turning it off and then on again?'. Is this going to be the first rule of Porsche's?