Help please: Car "mysteriously" dies.
 

1999 Base Boxster

Two weeks ago at the track, while in a big sweeper, the car suddenly died. I coasted off the track. The motor would crank, but not fire up. Got towed back in. There were no codes. There was plenty of pressure at the fuel rail. Primed it with some starting fluid, and the car started.

After about three laps, it died again, same exact symptom. I left the car overnight at the track parking lot. The next morning, it started fine. Trailered the car to a friend's house, and he replaced the fuel pump for me. He checked the fuel pump relay too, and it was fine.

So, I drove home today (about 35 miles), but made a few stops along the way. At the last stop, the car again would not start. Same symptom: motor cranked, but didn't catch. After an hour or so, it started up fine. I was talking to my friend, and left the car idling. After about 15 minutes, the motor suddenly died again. Wouldn't start, but would crank. Put in a new relay. Same, no start.

After about an hour again, the car started fine. I drove home, but left it idling in the driveway. After about 15 minutes, the car died again and wouldn't start.

It has been suggested that this could be a bad crankshaft position sensor, and I will replace this tomorrow.

But, there are NO codes at all being thrown. My understanding is that a bad CPS should certainly throw a code.

Suggestions/comments please.

Thanks in advance!

I had a bad CPS, it failed when I was driving down to Sebring. The car would just shut off and wouldn't crank. After sitting for a little bit, it would crank but then shut off a little later. It did this 4 or 5 times, but the check engine line didn't come on until the next day.

When you attempt to crank the car, do you see any activity on the tachometer? My understanding is that it gets the RPM from the CPS and if that is bad, you will/may not get any RPM on the tach.

Hmmm.... I'm not 100% sure, but I don't think the tach moved at all. Did you get a code when the CPS failed? That's what's odd to me... no thrown codes of any type. No CELs either.

Someone help him, he needs to get it fixed today so he can do an AX on Sat
Mike, I would post this on the other forum as well, someone may be able to help, either that or give you a hard time LOL

Best guess is CPS -- not that expensive and completely a DIY.

Just stuff a rag into the whole between the tranny and engine case where the CPS is.
Don't ask me how I know about this.

Mike

Hey Mike/Jay,

I will be picking up a CPS late this afternoon (Jay, Tom at TC's Garage was able to get one on short notice). I'll mess around with it this evening to try and replace it.

$110 for the part from TC and I can get it today. $263 from the stealership, and I can't get it until Monday. There seem to be tons of aftermarket ones on the internet for much less, but I need the part today, so I can autocross Saturday.

Now, if Porsche could just have built these cars with a more accessible engine, like maybe a '69 Beetle, that would should make things easier!

Mike, why the rag? To prevent SKS?

(Skinned Knuckle Syndrome?

I agree that it is likely the CPS. In my experience they tend NOT to throw a code, and fail when heated up, but function once they cool down.

The CPS replacement is simple, but a total PITA to replace. It's one screw and a troublesome clip, but you have to reach around the rear suspension. It took me over an hour to replace, mostly because the bracket the clip was in bent. It is also hard to replace while wearing gloves, so be really careful if you want to avoid SKS.

The rag is recommended because of seningen's misfortune in this thread:
http://986forum.com/forums/performance-technical-chat/57438-read-before-doing-cps-swap.html

I am guessing it is easier if the car is on a lift.
You have that place near you that rents them by the hour

Hopefully changing the CPS will fix it

I've been trying to solve a very similar or basically identical issue with no resolution yet. Checked electrical connections to fuel system (and replaced pump relay), apparently OK. Replaced CPS, without much difficulty, (be careful not to drop the set screw somewhere it can't be reached) no change. Ran the fuel delivery tests which revealed fuel pressure bleeding back into the tank quickly when pump was shut off. (fuel pump checked out strong) and ended up replacing the fuel level sender ass'y. because I cracked the old plastic housing at the nipple when I removed the fuel supply line. Since the regulator is part of the level sender ass'y., I thought maybe that would solve the problem. For 3 or 4 runs it started and ran fine, turn off with key, start back up, no issues. I thought it was fixed, then the same symptoms began happening again. T'he whole time the issue is present the car always starts up 1st time, cold, in the garage and runs fine until it stops. Also, so far anyway, when it craps, if I wait anywhere from 10 minutes to an hour, it has always started back up, and I have been able to make it home. I just cleaned the MAF sensor and throttle body, switched the DME and fuel injector/coil relays (nos.1&2) with the starter and engine compartment blower relays (nos.7&8) All 4 are the same part. It starts and runs, and I'll be taking a test ride later today.

Edit: '03 S, 83,000 mi., Changed out CPS from underneath on jack stands with right rear wheel removed.

Your cause may not be the same as mine, or maybe it is and you'll figure it out before I do. Either way I hope you get it fixed. I'll keep an eye on the post and post any further results I end up with.

OK, CPS was replaced today.

I let the car idle for about 45 minutes or more in the driveway, and it didn't die. Idle seems smoother too, so am keeping fingers crossed that the problem is solved.

That screw holding it in is REALLY hard to get at from the top. Since I couldn't see the head of it, took me awhile to figure out what socket was even needed. It's a T30 Torx. My friend Adam was able to get it out after I spent over an hour trying different sizes of socket handles and extensions. HINT: Get a pivot-head socket wrench and your life will be much easier!

Driving the car at an autocross tomorrow, so will let you know if I still have any issues with it.

P.S. I read that linked thread about the dropped screw. YOWZA!

BTW, this CPS problem is not limited to Porsches. My wife's Saab had the same problem a couple of years ago. Car cold, no problem. Car hot, dies.

A dying Crankshaft Position Sensor is a pretty common problem. Mostly doesn't throw any codes if it dies. Sometimes Camshaft Position Sensors also die, but throw codes more often.

Regards
Markus

Update: Had no issues at all during the autocross.

Then, on the way home, got a CEL. Ran the codes, and there are a pile of 'em!

P1128
P1130
P2811
P1126
P1124
P0130
P0150
P2401
C0701
C1000
P1126
P1124
P2611

Follow-up: I cleaned the MAF sensor and have driven the car about 150 miles since then. So far, no CELs. Keeping fingers crossed....

Still no codes, car is running fine, so cleaning the MAF sensor seems to have worked. Still, keeping fingers crossed.

I had similar symptoms a few months back. Car would drive OK for a few miles and then suddenly die. Cranked OK but wouldn't fire up. After about 5 minutes it would start again. Sometimes it would run for 10 or more miles then stop. Thought it was the CPS at first but noticed that the tach would bounce slightly on cranking. Turned out to be the fuel pump relay which was losing it's ability to generate a strong enough magnetic field when the coil was hot and subsequently letting go of the contact arm breaking the power circuit to the fuel pump. (I took the relay out, removed the casing, fed it 12v and watched it let go of the arm after a few minutes.) This turned out to be a very cheap and easy fix in the end. Now I carry a spare relay just in case. Everyone suggested it might be the CPS at first due to the lack of CELs/codes. The clue was the tach. Guess I was lucky.

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