Starting Problem

[rogerjohnsen]

The other day I drove my car approx. 20 miles and stopped at my destination.  When I went to leave, the car would turn over and initially "almost" catch and then just turn over but not start.  I have about a half tank of gas and there's no error codes showing - it just won't start.  I searched around a bit and thought it could be the fuel pump hose issue that's somewhat common on these cars but removed the fuel pump and inspected the hoses.  Any thoughts or suggestions on what to check?  I'm sorry I don't have a lot of information at this point since the car is stranded at my in-laws and I don't have tools readily available.

 

As far as before I parked it - the car was running fine and I had nothing out of the ordinary going on.

[wvicary]

How did you check for fault codes? Do you have good spark from both distributor caps? What is the fuel pressure/volume? Could be many many things at fault so we need to verify a few basics first. If you don't have tools and aren't near the car I suggest towing to a dealer or good independent garage.

[JFP in PA]

The other day I drove my car approx. 20 miles and stopped at my destination.  When I went to leave, the car would turn over and initially "almost" catch and then just turn over but not start.  I have about a half tank of gas and there's no error codes showing - it just won't start.  I searched around a bit and thought it could be the fuel pump hose issue that's somewhat common on these cars but removed the fuel pump and inspected the hoses.  Any thoughts or suggestions on what to check?  I'm sorry I don't have a lot of information at this point since the car is stranded at my in-laws and I don't have tools readily available.

 

As far as before I parked it - the car was running fine and I had nothing out of the ordinary going on.

 

You should always include the year and model when asking these type of questions as the diagnostic's can differ.

 

Several possibles: Low fuel pressure or delivery volume, possible pump or fuel line issue.  Early cars also had a fuel pressure regulator on the fuel rail that could cause issues, as well as an external fuel filter that can clog.  Another would be a failing crank position sensor; when they go off, the DME does not see the engine turning and shuts off the fuel pump.  You are going to need to dig in and do some testing.

[rogerjohnsen]

I was afraid on the digging part given that won't be too feasible here but hoping there was something obvious I was missing. No codes according to the obd or faults causing check engine. Just seems really weird the car would run perfect, sit for a few hours and then not start. Assuming no quick things to check I'll have it towed to the shop.

Sorry about the lack of car details but for some reason thought they showed up automatically from my profile. It's been a while since I've signed on here so my recollection was off.

Here's the car info...

2004 996 TT Cabriolet All stock. Approx. 40k miles

Fueled at chevron over a week ago and drove a few times on that gas with no issues. Seems like I might smell faint gas smell trying to start for a while. Seems like ignition problem. Read about the fuel pump house issue so inspected the fuel pump and hoses are fine.

[rogerjohnsen]

Sorry- make that fuel pump hose issue... typing these from my phone.

[JFP in PA]

I was afraid on the digging part given that won't be too feasible here but hoping there was something obvious I was missing. No codes according to the obd or faults causing check engine. Just seems really weird the car would run perfect, sit for a few hours and then not start. Assuming no quick things to check I'll have it towed to the shop.

Sorry about the lack of car details but for some reason thought they showed up automatically from my profile. It's been a while since I've signed on here so my recollection was off.

Here's the car info...

2004 996 TT Cabriolet All stock. Approx. 40k miles

Fueled at chevron over a week ago and drove a few times on that gas with no issues. Seems like I might smell faint gas smell trying to start for a while. Seems like ignition problem. Read about the fuel pump house issue so inspected the fuel pump and hoses are fine.

 

I would still look the CPS as when they go bad the often do not throw any codes, but will not let the car start, particularly when warm.

[rogerjohnsen]

Okay - I read about the CPS in other posts but remember it said something about error codes being present when this is the case.  Can the CPS have gone bad without any error codes?  I guess the fact there aren't any error codes is very concerning in general - makes me feel like I'm hunting for a needle in a haystack.

[JFP in PA]

Okay - I read about the CPS in other posts but remember it said something about error codes being present when this is the case.  Can the CPS have gone bad without any error codes?  I guess the fact there aren't any error codes is very concerning in general - makes me feel like I'm hunting for a needle in a haystack.

 

Decidedly yes.  The CPS is a simple Hall Effect type sensor that generates a very weak electrical signal when ferrous metal moves past it.  If it shorts, it will throw a specific codes, but if the signal is just weak, or even non existent, the DME just thinks the engine is not turning and shuts off the fuel and ignition without a code being thrown as the DME sees nothing unusual.  It is a quirk of how crank position sensors work.

[rogerjohnsen]

I'm heading back down to my car today in an effort to check the CPS as recommended.  I think I've pieced together enough posts to find the PCS and how to test it with the ohmmeter. Should be fun...  Nothing like being broken down in Tucson, AZ.  I have no clue about shops in the area although I did find a Porsche dealership here so I'm assuming I can at least get the part if it turns out to be the CPS.

 

Thanks for your help and I'll post an update once I have it.

[rogerjohnsen]

Whew - took me longer to get this sorted out than I anticipated...

 

 So I wasn't able to confirm the sensor was bad since I couldn't get to it given the limited amount of tools / resources.  Ultimately I ended-up having the car towed and found a great little independent shop in the area.  They were able to confirm the CPS was indeed the problem, replaced it and we're off & running.  JFP in PA is a rockstar and nailed it as to what was causing the problem.  I'm still a little shocked this is what it turned out to be but glad it was something minor and only wish I could have fixed it myself.  Porsche of Tucson wanted almost $300 for the part alone but I was able to find a place online (RM European) that had it delivered the next day for $87.52 including shipping.  It's a standard Bosch part so nothing really fancy there - just searched on the part number.

 

Thanks you so much JFP in PA sir for your help and advice!!!

[JFP in PA]

Whew - took me longer to get this sorted out than I anticipated...

 

 So I wasn't able to confirm the sensor was bad since I couldn't get to it given the limited amount of tools / resources.  Ultimately I ended-up having the car towed and found a great little independent shop in the area.  They were able to confirm the CPS was indeed the problem, replaced it and we're off & running.  JFP in PA is a rockstar and nailed it as to what was causing the problem.  I'm still a little shocked this is what it turned out to be but glad it was something minor and only wish I could have fixed it myself.  Porsche of Tucson wanted almost $300 for the part alone but I was able to find a place online (RM European) that had it delivered the next day for $87.52 including shipping.  It's a standard Bosch part so nothing really fancy there - just searched on the part number.

 

Thanks you so much JFP in PA sir for your help and advice!!!

 

Any time, glad you got it sorted.  We have seen more than our share of failed or failing CPS in these cars, and it is one sensor that can act up, or even fail totally, shutting off an otherwise perfectly running engine, or prevent one from starting, all without throwing a code.

[jpflip]

Another happy customer!!! Great job JFP!!!

[rogerjohnsen]

It's happened again! I don't believe it but I'm having the exact same problem. I picked up the car and drove it approximately 15 miles and parked it. Just tried to start it this morning and I have the exact same problem. The engine initially started and then died. Subsequent attempts to start and the engine won't start but simply cranks over.

Is it possible something upstream is causing this part to fail? This is a brand new CPS so I'm not sure why it would fail after 2 short rides.

[JFP in PA]

It's happened again! I don't believe it but I'm having the exact same problem. I picked up the car and drove it approximately 15 miles and parked it. Just tried to start it this morning and I have the exact same problem. The engine initially started and then died. Subsequent attempts to start and the engine won't start but simply cranks over.

Is it possible something upstream is causing this part to fail? This is a brand new CPS so I'm not sure why it would fail after 2 short rides.

 

I seriously doubt the new CPS is at fault, it is a simple Hall Effect sensor with no moving parts.  Do you have a fuel pressure test unit for the car?  That would be the next thing that I would look at

[rogerjohnsen]

I don't have a fuel pressure test unit. Is it worth buying or better to have it towed back to the shop? What is the bigger picture of what we're trying to accomplish by testing fuel pressure? Once again the car shows no sign of trouble and everything works flawlessly prior to this problem popping up.

Side note:

At least I have a significant number of tools and a lift now.

[Ahsai]

Not sure how easy it is on your car but maybe at least check the new CPS connector to see if it's fully plugged in? Does the tach needle bounce while you're cranking the engine?

[JFP in PA]

A decent fuel test unit (Actron) is going to be about $60 or so, and has adaptors to work on just about anything.

 

With a test unit, you can test for fuel pressure and delivery rates to determine if the fuel pump is working correctly.  You can also check for pressure bleed down while the engine is off, a sign the regulator is on the way out.

[rogerjohnsen]

I see- Thank you for that explanation. Seems like will be worthwhile purchase the test kit. Is there any other tool that would be able see what's going on from a debugging perspective? I'm a computer science grad so thinking if I could see logs or messages from the computer this would give the most insight- at least in theory. Would a durametric reader accomplish this?

As for the tachometer needle question- I will check and post back with the results. I can't imagine the CPS connector would be loose but will check that as well. I'll also check the output of the CPS on the ohm meter.

Thanks again for your help. Super frustrating but I can't tell you how much I appreciate the knowledge on this site.

[JFP in PA]

I see- Thank you for that explanation. Seems like will be worthwhile purchase the test kit. Is there any other tool that would be able see what's going on from a debugging perspective? I'm a computer science grad so thinking if I could see logs or messages from the computer this would give the most insight- at least in theory. Would a durametric reader accomplish this?

As for the tachometer needle question- I will check and post back with the results. I can't imagine the CPS connector would be loose but will check that as well. I'll also check the output of the CPS on the ohm meter.

Thanks again for your help. Super frustrating but I can't tell you how much I appreciate the knowledge on this site.

 

Unfortunately, while the Durametric can see many things, fuel pressure is not one of them; that requires a mechanical gauge hooked up to the test port on the fuel rail.  The Durametric would still be an excellent addition to any Porsche owners tool kit however.

[rogerjohnsen]

Ahsai - In response to your post about the tachometer needle:  The tachometer needle went from just below zero (key off) to zero (key on) to 1 notch above zero (cranking). I'm not sure that constitutes bouncing but it definitely moves.  Will check the connector next.

[Ahsai]

I think that constitues bouncing. Have you checked the fuses to the fuel pump and the DME? Just thinking for you what easy things to check before the fuel pressure test...

[Ahsai]

Looks like fuses C1 to C4, same as 996 n/a.

[rogerjohnsen]

Should be easy enough - I'll check them tonight and report back.  Thanks!!!

[rogerjohnsen]

All fuses check out fine.

[Ahsai]

I think the next steps will be verifying sparks and fuel pressure then.