patdonahue

kinda weird. I washed the car Sunday evening, dried it off, drove it 20 miles to dry off the brakes and pulled it into the garage. The car is a 2001 986S with 20000 miles, always garaged. This morning I am getting ready to take it down to the dealer (80 miles one way) for of all things its yearly maintenance check and it will not start. Starter wound away but the engine would not fire. I tried about 3 times to start it holding the key in the start position for 5 seconds at a time-no joy.
So I figure I would look at the simple things first, plenty of gas, good battery, healthy starter, so I pull the fuses for the fuel pump, ignition, engine ECU, etc. Fuses were set securely into their receptacles, all are good no blown elements.
I reinsert the fuses and decide it give it one more try before calling the dealer about a tow. The thing starts right up idled rough for maybe 1 second then settles down to a normal idle, no CEL just fine. I drive it to the dealer and leave it with them to do the yearly and find out what is going on with the start problem. The tech meets me when I get back and tells me they are baffled, it is not giving them any codes and they started the thing like 5 times with no problem. I drive home and had a few stops to make and did about 5 restarts-no problem. Big mystery-anyone else in the Rennlist ether have a gremlin like this happen to them?
TIA, Pat D

Stephen Tinker

I guess the (only) clue is that after replacing the fuses, the car starts right up and you don't mention if the dealer has found any codes to help them diagnose the problem.
Having an electrical background I would suspect something like the fuel pump fuse being loose, though my engineering thought process "should" rule that out as you haven't said if you have worked on or close to the fuse box recently....
The cps (crank position sensor) might also be suspect, though they usually fail when hot.
You may never know - just be prepared for it to happen again.....

Macster

A dead -- even if only temporarily -- fuel pump can account for that behavior.

I think a dead spot is the cause. The pump can be resume working -- the car being jostled or the doors being closed can do it -- but it will manifest this behavior again and at some point will have to be replaced.

The above is not a recommendation to replace the fuel pump only offering up what has proved to be a rather common scenario for a number of owners.

(My 2002 Boxster fuel pump working well enough and let the engine start then the engine died. Cranking afterwards was unsuccessful. The engine didn't start again. The fuel pump proved to be dead. In my car's case the fuel pump just up and quit.)

Another explanation is a marginal crankshaft position sensor. The engine will crank just fine but because of no CPS signal the DME doesn't know when to trigger the fuel injectors or spark. Since emissions are not affected there is no CEL and no OBD2 errors. There might be one or more Porsche proprietary error codes logged that a Porsche diagnostics computer can retrieve.

Not sure if there any proprietary codes if they remain if the engine is started successfully. Did the tech check for any errors, Porsche proprietary errors *before* he attempted to start the engine?

Again the above is not a recommendation to replace the CPS. However, this is not a very expensive item -- less than the cost of a new fuel pump -- and I don't think it costs that much in labor to replace.

Up to you if you want to throw parts at the behavior or wait until something concrete develops the intermittent failure becomes a solid failure. Trouble is this can take a while and then you are playing Russian Roulette with the car every time you shut off the engine not knowing if it will start again or not.

So you can check with your tech and get a quote to have a new CPS installed and if the cost is acceptable consider having this done.

If the no start behavior returns then consult with your tech about the idea of just replacing the fuel pump. But ask him what else could account for this behavior?

patdonahue

Macster thanks for the input. When I got it to the dealer I shut it down and figured if it would not start I was in the perfect place. When it came time to move it in the service bay it just started up fine. The car was not giving any codes at all, it just kept restarting with no problem. They spent quite an amount of time trying to find the gremlin, but no joy. He even asked me if there was a possibility since I live in a very rural country area if a mouse or what ever could have taken up residence (!), but the car is always garaged on a clean concrete floor. The tech and I had a talk about possible problems but we are drawing a blank as of now. IIRC the 2001 cars probably do not store as much information as the newer cars for the read outs.
The car ids due a major next year and your fuel pump/CPS merits consideration.
Granted the car is 15 years old so that is a possible problem although it only has 20000 miles. I do not believe that this is a one time offbeat occurrence, although that would be nice were it true.
Thank you again for your thoughts on this matter.
Pat D

Macster

Mice can't be ruled out.

Mice can be anywhere. The only thing you can do it give the car a close inspection for any signs of mice infestation. I've seen them leave bare spots on the carpet -- they collect the fuzz for nesting -- and of course chew/gnaw anything, but hard plastic and rubber are the preferred materials. One chewed through the plastic gasoline vapor line that runs down the center of the car (this in a Cayman) until it broke through and got a snoot full of gasoline vapor.

Give the top of the underside plastic panels a look with a flashlight. The critter drop litter on these surfaces and use them from moving around under the car while remaining off the floor of the garage.

Look on top of the engine for any signs of trash/droppings.

My Boxster would not start. Would not even crank. But a retry would have the engine fire right up.

I ignored this behavior for some time, became accustomed to it, and then late one night I took a cab nearly 40 miles to pick up the Boxster I had left at the dealer when I bought the Turbo. The cab left and I was at the dealer late at night. Dealer of course closed and nothing open for blocks in either direction. The engine didn't even crank. Not a noise. The dash lights came on just fine but that was about it.

I tried and tried to no avail. To make matters worse I was sicker than a dog. I thought I was going to die there at the dealer. Finally I gave the engine one more chance before making my peace with God before accepting my fate and the engine fired right up. I didn't wait around but drove the car away at lightning speed.

Of course the next day I had the car in at the dealer and the most senior tech taking a look at the car. He tried a number of times to replicate the behavior and the engine started every time. (Unfortunately I forget what was done to address the behavior. I had a new clutch interlock switch installed but I think the problem continued after this. I had a new ignition switch installed at some point, too. Don't remember the order of what was done and even what was done. All I know is whatever I had done the symptom has only appeared just a few times and due to me not fully depressing the clutch pedal.)

My point is it never fails. The car can manifest a problem all the time and then when one has it at the shop the car is the most well behaved piece of machinery ever.

20K miles is not many miles. But a fuel pump can quit at any time. The one my Boxster was fine every time the entire 172K miles and then just like that it was dead. No warning.

I've never had a CPS go bad, but had at least one O2 sensor go bad. This in my Turbo.

(The ones in the Boxster have needed replacement once or twice over the years but I recall the Turbo's sensor problems as it was more recent.)

My Turbo was fine even drove it 2K miles to MO and back, or nearly back with just under 132K miles on the car when at a Barstow CA gas station the CEL came on and the car logged an O2 sensor error code. The CEL came on after every gas stop all the way from Barstow to Livermore. Booked the car in as soon as I could to have all 4 O2 sensors replaced.

My point is that like a fuel pump a CPS (or O2) sensor can go bad at any time.

patdonahue

My dad had a Fiero that a mouse got into. he would be sitting at a stop light and the wipers would start, all kinds of crazy stuff like it was possessed. IIRC they had to replace the harness in the engine bay.
Your last point is well made sometimes even new stuff out of the box doesn't work. I think we as a whole have become spoiled by the solid state technology and its reliability-until it isn't

"My point is it never fails. The car can manifest a problem all the time and then when one has it at the shop the car is the most well behaved piece of machinery ever."

An aircraft I used to fly had an autopilot problem that would NEVER manifest itself when we took it to the avionics shop. Yet if you got in the thing took off and engaged the autopilot you got an "interesting" ride.
Thank you again for the time you took to explore this problem.
Best,
Pat D

Schnell Gelb

"the symptom has only appeared just a few times and due to me not fully depressing the clutch pedal."
= dead spot in the clutch interlock switch ?
very interesting fault.
When you are tired/sick/distracted, you don't press the clutch pedal all the way to the floor or some other 'magic' position ?Did the switch gt damp/corroded internally
So for the O.P. - just bypass this switch temporarily for diagnosis?

Macster

Some times I get a bit sloppy with the clutch. That night while I was very sick I certainly was concentrating on pushing the clutch down all the way.

It was not a factor that night but at other times it can be factor and that is I may be distracted thinking of something else and not thinking about the car. Also, once in a while, thankfully not too often, but once in a while pain in my foot/ankle can cause me to be a bit tentative with the clutch.

Also, it doesn't take much for the clutch to not be fully depressed for the switch to not be closed and if it is not closed this prevents the engine from cranking.

There can be another issue: The tech told me what can happen is the clutch hardware -- the pedal linkage hardware -- can wear and the part that pushes down on the clutch switch may be offset a bit -- from the wear -- and thus not contact the switch plunger squarely. In this case then the switch plunger doesn't get pushed down/in as far as it might otherwise. Remember in my car's case the clutch hardware is original and the car has now covered almost 305K miles.

The clutch interlock switch didn't suffer from corrosion or moisture. It just wore out. (Other things have worn out over the years: Brake light switch; Oil filler tube cap (2 times now); gas tank filler tube cap (and tether); window regulators; front and rear trunk struts; 3 AOS's; O2 sensors (several sets now); Also the aforementioned fuel pump; The water pump; And the coolant tank cap and even the coolant tank.)

Really I only mentioned my experience with the clutch interlock switch to emphasize how something that can be bad enough to create a real problem can then seemingly work just fine when a tech is in the car trying to reproduce the problem.

Anyhow, the problem the OP is reporting is the engine cranks but doesn't start.

If the clutch interlock switch is bad the engine would not crank.

Two possible explanations that can fit with this behavior -- crank but no start -- is an intermittent problem with the fuel pump or an intermittent problem with the crankshaft position sensor.

I can't be sure enough to outright recommend/advise a replacement of either item. Apparently the OP is going to take a wait and see course of action.