Engine quits and won't restart .... until later

Hi folks, I have a 1999 996 coupe and have an issue that has me stumped. For the last two nights in a row now. Driving home from work at reasonable speeds for summertime traffic on the Cape (35-50mph) and the 'check engine' light comes on and a couple of seconds later the engine quits. Everything else still working (headlights, stereo, etc.). Pull over to the side of the road, and try to restart engine. It cranks, all gages look good but it won't start. Call for tow, get the car home, try starting, it starts fine. This is the 3rd actual occurrence of this. the first time was at the tire store a couple of months back. They brought the car around, I paid, went out to leave and it wouldn't start. Towed home. Started right up. Checked car for OBDII codes, none. Both days I have driven the same route to work with no issues. The car has also been to Vermont, New York and to and from work many times. Any ideas? Thanks in advance, Jeff PS: A little more info. Over the winter I replaced the IMS and RMS, clutch, flywheel etc. Just recently installed (last week) a short shift kit and aftermarket stereo. The first time this happened was before the stereo and short shift kit.

Have you pulled the engine codes? If not, I would suggest getting the codes to assist with troubleshooting the issue.

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My WAG is the crankshaft position sensor quits working due to heat or because it is loose and gets out of position and delivers an implausible signal and the DME kills the engine. Before you try starting the engine again, even before you attempt to move the car any at all, it would be nice if you could arrange to connect an OBD2 code reader to the car's OBD2 port and read the code (or codes) that is associated with the check engine light before you attempt to restart the engine. After the car sits the sensor cools down and works again or after the car is jostled the sensor returns to some good enough position to resume working again. Or the sensor might have a mounting or connection problem with the sensor. It might have gotten disturbed during the IMS, RMS and flywheel/clutch work. Especially the flywheel. The crankshaft sensor mounts very close to the flywheel and the tabs on the flywheel. If the sensor is loose or not mounted the right distance from the flywheel and those tabs... Yet another possible cause is the fuel pump or the fuel pump relay quits, for awhile. You can buy or rig up or even borrow (a tech at a local dealer loaned me his for a few hours) a fuel pump relay bypass and the next time use that to see if bypassing the fuel pump relay you can hear the pump come on. Sincerely, Macster.

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Tonight when it happened again, I read the OBD2 codes before trying to restart. There were not any codes listed. As mentioned by Kazul99 are there other codes that can be looked at with something other than an OBD2 reader? Thanks for your insight. Jeff Oh, I should try the fuel pump relay. My 944 cars always had a spare relay available.

Well, with proper test equipment (PST2 or PIWIS -- Porsche specific diagnostics computer systems) and maybe Durametric you might be able to get to the Porsche internal error codes and other low level info that might provide you a clue as to what's going on. I do not have any experience with any of those systems but have watched techs use them and they can pull out some interesting info. If there is no OBD2 code the error condition clears and the DME erases the code and I guess turns off the light unless you tell the light is on and there are no codes. In which case a Porsche specific diagnostics computer system might be of some value if you had access to one. Sincerely, Macster.

It sounds heat related. I would guess ignition or fuel pump. Does is stutter any (like running out of gas), or just die like you turned off the key? I'm just guessing, but I had a 76 Cutlass back in the day that did the exact same thing. One of the first cars with a solid state distributor. It turned out to be a short in the distributor that only appeared with heat expansion.

I'm with Macster on this one. Try the pulse sender, they can be erratic and don't always show up on an OBD even with the Durametric. When one goes everything seems to be OK but the car will not start. If the DME does not get a signal from the pulse sender then the fuel pump cuts off and the engine who't start.

What's the volts showing when cranking hot and cold? I've seen some other varieties of car have the starter suck all the amps not leaving much for the ignition but eh probably not that. I've heard September is possibly the end of the world so maybe this probablem is part of it. I hope not

could be some junk in the fuel system but I have to admit it is weird that it works then stops after a bit of driving. anyways I'd suggest buying some fuel additive like 'techron'. it doens't cost much to try it. I had an intermittent engine start problem in the past and it was because of a bad gas fill. After techron and a new fillup from a reputable gas station I was all good to go.

If there are no OBDII codes, I'd suggest looking at the following: 1) crank position sensor (like Macster said) 2) Fuel filter 2) Fuel pump relay and/or pump itself Symptoms of the CPS shows when the engine cranks when everything eventually cools down. (Macster may have typed this symptom, I didn't read his post).

Well, I have decided, based on your advice, to replace the crank sensor. I have the car up on stands and the connector disconnected, but am having trouble with the bolt that holds the sensor. I can't quite figure out if it is a star or hex bolt. Does anyone know or remember the type of head on this bolt? It looks like it may have been removed previously and damaged. The car has almost 130Kmiles on it so it is possible the sensor has been changed before. Thanks for all the advice, Jeff

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I looked through my engine pics -- for instance I have some pics of a new X51 engine -- but I don't have good pic of the crankshaft position sensor face on to the bolt head. But other views of the engine find the other bolts bolts are either star bolts or star cap screws. That is the bolts either take a star socket or a star bit. From a pretty bad pic I have of the crankshaft position sensor the bolt head looks to be one that takes a star bit. But do *not* take my word for it and don't guess at it either. From feeling the bolt head with your fingers you should at least be able to determine the style. Or better yet get a mirror on a sliding extension with a swivel at the mirror end (find these at a good automotive parts/tools store) and you can view the bolt head using the mirror and confirm the style of the bolt and confirm you have the right tool. Or visit your local Porsche dealer parts deparment and buy a crankshaft position sensor bolt (be sure you supply a VIN). However, there's a chance the bolt in the engine may not be the same, or if the engine was been worked on in the past the bolt may be a non-standard bolt. You do not want to strip that bolt's head because that's almost certainly an engine out job to get at the bolt and drill it out. My preference I think would be to use the mirror and a bright light to be sure, as sure as you can be. It would not be a bad idea to get a new proper sized bolt from your local Porsche dealer just in case the old bolt is rusty, corroded, or has been damaged from someone wrenching on it before you. Sincerely, Macster.

Pet describes it a an M6x16 pan head screw. As I remember it is a hex head but I don't remember the size.

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Yah I agree there. Had an Accord 20 years ago that loved to have the fuel pump fail if I'd play let the fuel get below a 1/4 or 1/8th plugging the fuel filter and over working the fuel pump. Life sucks when you want to play only top off at the end of the work week. When running low fuel levels if the pump picks up air it probably wont be recognized as fuel starvation but the air reduces cooling that the new modern electrnic fuel pumps in the fuel tank depend on. Less cooling means the fuel pump motor is prone to burn out progressively loosing fuel pressure during degradation. The lower fuel levels around 1/4 gets gunk on the bottom of the tank stirred up putting more trash in the fuel filter. I know the old fuel line filters when plugging up would starve the engine then after sitting a while with amount I time needed to get lucky for a restart varying all the time. The packed in gunk in the filter would need to sit in the fuel filter till it slowly loosens up and allows fuel to flow again till fuel flow slowly plugs it again. Lots of possibilties.

It's been a month since I got the crank position sensor placed and everything seems fine now. It even starts quicker and doesn't rev as high on startup as it used to. Thank you all for your help. Jeff

That's good news.

..

Perhaps yes, that is where the AOS bellows is, and perhaps they damaged that when they replaced the sensor. There is also the AOS tube to the 4-6 bank. Although if done right, replacing the crank position sensor does not require touching either of those things. CAM position sensor on the other hand, which is also up there, might require removing the AOS boot and/or tube to 4-6, which would easily explain a leak. Or perhaps the leak was already there and you are hypersensitive to the issue since it just had work done on it.

You're a funny guy. No, it was bone dry before that. Its too much of a coincidence. Soooo, based on what you've told me, if they did damage one of those things, then it won't cost me too much to fix when I take it to a better shop for diagnosis and repair on the leak. Thanks. Anyone else have any ideas?

unplug the fuel evap rejuv valve in the back. It located just above the oil filler. It supplies vaccume to the charcole canister. This will give you a CEL but report back if it fixed the issue Valve sticks open.. Puts a vaccume on fuel tank, pump cant pump, no fuel, no CEL. just a dead car for about an hour till vacc leaks from fuel tank. Been there...

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+1 It appears that we have several guys on this board that are possibly suffering from the same issue. Kyle, I was trying to find the write-up on this issue and can't remember if it is on Rennlist or Renntech... any thoughts? BTW, the fuel evap valve is only about $40 and is 5 mins to change. One of my Indy friends keeps an extra valve in his tool box at all times.

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Dont know... Didnt use a write up. Just searched this forum. I also had a clue, my charcole canister was "farting" everytime i shut off the car for a few days before