00 Boxster sometimes won't strat

[jimwarriner]

Back in late September my beloved 2000 Boxster began an annoying habit.
It would not start.
It would turn over but not start.
The first time it happened it was a warm day and my first thought was vapor lock
but I think that is a thing of the past.
There seems to be no rhyme or reason to when it happens.
here are the attempts at curing the problem.
1. fuel pressure and and capacity tested ok
2. changed fuel pump relay, one other relay and replaced
fuel filter
3. had battery checked after charging all night, all cells were OK and alternator
was OK ( tests done by an Interstate battery store)
4. replaced battery with a new Interstate battery

The guys at the battery store said "short trips" were the reason and that it takes
10 to 20 minutes of engine time to recover from the drain of a start.

Jump starting is not proven to help i.e. it still takes a long time to start the engine.
Just letting the car sit for 5 to 50 minutes and it will start.
Always starts in the morning.
Outside air temp has been from near 100 to low 40's/high 30's
Climate sunny and dry to cold, wet, cloudy, rainy.

I have a battery tender on order to maintain the battery when th car sits for a while.

Any ideas would be appreciated

[soule77]

Does the car start easily when it is cold and gets subsequently harder to start when it is warmer?

[jimwarriner]

Always starts in the morning regardless of ambient air temp. Reluctance to start seems unrelated to engine temp as well. its in the 30's and 40's here in Oregon and yesterday I drove to a client site the car sat for about an hour and a half and wouldn't start. 30-40 minutes later it fired right up.
It seems it either starts or you crank for 30 to 40 seconds and nothing

[racer]

Has the car gotten wet under the drivers seat? maybe its playing with the computer under there..

When you say a "long time to start" do you mean repeated attempts? Do you mean the engine just sits there turning over for multiple start tries?

There are know issues with the ignition switch. Perhaps it is not completing all its connections?

[KevinH1990]

I had a similar problem, but it only occurred after I filled the car with gas. The symptoms were very similar to the "vapor lock" you might have experienced on a hot day with an older car.

I eventually had a check engine light with code P0446. My problem was the evaporation control valve in the fuel filler. I had to replace the entire vent line. The replacement part number was 996-110-129-05. The tech that worked on my car thinks the previous owner car was in the habit of "topping off the tank" and fuel backed up into the vent system.

[jimwarriner]

No known water under drivers seat.
We live in Oregon and can't self serve fuel so "topping off" shouldn't be an issue.
Car always starts first thing in the morning engine temp may be involved since
amount of time car needs to sit varies but this is hard to pin down since outside
air temp has varied a lot.
Attempts to start go like this car for 10 to 20 secs wait 10 to 20 secs
and repeat until cranking speed slows. Now wait 10 to 90 minutes and
repeat attempts to start car suddenly starts.
I am curios about the engine temp idea

[Wayne 962]

Is the car kicking out any fault codes (do you have a reader?)

-Wayne

[jimwarriner]

No CEL and I believe the shop read the codes
when they replaced the fuel filter and a couple of relays.
They did not report any code to me.
it seems to be related to engine temp.
Always starts when cold or if it hasn't been shutdown
for more than a few minutes.
then there seems to be about a 1 1/2 hour window where
it won't start.

[racer]

Originally Posted by jimwarriner

1. fuel pressure and and capacity tested ok

Fuel pressure in the lines, ie a pump issue? Not sure what you mean by capacity either.

My guess is that it is fuel related. Perhaps fuel cap, vent line, tank etc. While you are equating it with a "hot engine", i think what you are having is vacumn type related fuel issues. Once the car cools (ie, once the pressure in the tank stabilizes) the car starts back up.

[targa44]

If 'vacuum' is the cause.... next time it won't start, can you hop out, take off the fuel cap and reinstall and try again? Worth a try?

I got dinged during smog check for a hundred microscopic hairline cracks in the fuel cap gasket. Is yours okay?



kj

[jimwarriner]

Mechanic reported that both fuel pressure and delivery rate were checked and OK.
Removing and reistalling cap occurred to me as soon as I read racer's post.
I'll try that and check the cap.
Our county doesn't require smog checks so the cap hasn't been inspected in years; it was changed
under warranty when we lived in CA
I am appreciative of everyones input. The nearest mechanic I trust is 30 minutes away and the nearest dealer is about 3 to 4 hours

[jimwarriner]

It turns out the problem was a weak CPS (crankshaft position sensor); a mechanic in Phoenix, Oregon had seen the same/similar problem with Mercedes and Bosch CPS.

[Boxster986VWB6]

I am surprised that didn't trigger a code. I am an electrical engineer for diesel engine electronics and software. We always have fault codes for being unable to sense the cam/crank sensors or not being able to lock pattern with the sensors.

But I am glad to hear the problem has been fixed.

[Wayne 962]

Yes, indeed that should have triggered a sensor error and/or a misfire error code. Oh well, the codes aren't 100% foolproof, glad you got it worked out!

-Wayne