Hot start problem on 99 Boxster

[egress91506]

Having some trouble with hot starts on my 99 Boxster. Car has been converted to a BSR. Past 2 weekends, I'd go out on the track, run a session (20-30 min), come off track, let it cool down and park it. Come back to the car later (15 minutes to an hour later) and it won't start. Engine cranks over, but no start. Eventually, after being left alone for a while (another 30 min, 1 hour), starts right up. Weather over the 2 weekends was high of mid-70s, low of 50s.

Tried troubleshooting a number of different things:

(1) engine cover off to let it cool down more, no impact. Vapor lock seems unlikely to me because have run the car in far hotter conditions without the problem. Also, vapor lock doesn't seem likely (in my uninformed opinion) because fuel returns to tank from fuel rails.

(2) swapped various relays (1 at a time) with working BSR. Fuel pump relay, DME relay, other related relays in back trunk of car. No impact, car wouldn't start with my switching in relays that were working in another car.

(3) pulled a coil pack off and confirmed the engine is getting spark. I think that eliminates the crank position sensor in this problem.

(4) plugged in the Porsche tester (PWIS?). No codes that would explain the non-starting. Code related to secondary air injection, but I always have that code on this car.

(5) key in first position, can hear the fuel pump running.

(6) opened up a fuel rail and fuel coming out. Porsche tech who was involved in troubleshooting didn't think the volume was what it should have been, so replaced the fuel pump. Didn't start after that until the waiting period was over. Following weekend, even with new fuel pump, still had the problem.

(7) no codes associated with the alarm box. My alarm box has been moved from the floor, so no chance of water damage. (Once the car was back to starting, I turned it off, unplugged the alarm box and turning the key would not engage the starter. Plugged it back in and it started. Since when I'm having the hot start problem, my car will engage the starter, but won't start, I concluded that the alarm box was not the problem. Flaw in that logic?)

(8) one other issue, which I noticed last Saturday was the fuel filler neck was filling with gas and slowly gurgling into tank. Don't think it's related, but don't want to leave out anything. By the way, used fuel from different places over the weekends, all real gas stations.

So, any ideas? Sorry for the long post and kudos to anyone who's read this far into it.

[eric523]

I had the same issue with my BSR in Vegas last year. I was convinced it was a fuel problem and went through the same checks that you did. Relays, check pressure, even changed out the fuel pump and nothing changed.
It didn't want to start when hot, and the idle was inconsistent at times. But when it got running I didn't notice any problems out on track.
Eventually I found an air leak at the oil filler neck, and had a mass air sensor going bad. I changed the neck and the airflow sensor and none of the symptoms have returned.
Wish I could help you further...Good luck!

[Wayne 962]

Some comments:

1) I think it might be a vapor lock, or let's call it a "hot fuel" issue. Vapor lock can occur with recirculating systems all the time - just ask 914 owners.

2) agree

3) agree, coil packs are good, although just because you have spark, doesn't necessarily mean you have spark at the right time (timing). This is a common mistake in diagnosing older cars, but I don't think it's very applicable to the Boxster

4) Fuel supply problems don't show up on the PST-2 I've found (from experience trying to figure something similar out). All your sensors are probably okay.

5) This is odd though - as the pump shouldn't be running when it's in the first position, unless as a conversion to Boxster Spec, you wired up the pump to run continuously?

6) Low volume indeed could be related to the hot issue. I would have recommended changing the pump, but you did this already indeed

7) Right - the alarm will stop the starter from turning - it doesn't affect fuel. So, if your starter is turning over, it's not an alarm issue (good thing for people to remember for troubleshooting in the future).

8) YES - I was going to ask about this! I think it has something possibly to do with your vent system. If the system is closed with no vent (sometimes this equipment is removed or altered on these spec cars), then the fuel will try to pull vacuum on the tank. You can collapse your tank (if you still had a stock plastic tank) if the venting is not setup properly.

My suggestions:

- Get a fuel pressure gauge and install it permanently into the engine compartment. Check it when cold and when hot - that should give you some good clues

- Check out the gas filler - try removing the gas cap and stuffing a long screwdriver down there when the car won't start. There are several valves in there that seem to fail all the time.

- When hot, check the fuel pressure, and then shut it off, and then check the pressure again when you're trying to start it. See if they are the same.

- Check out why the pump is continuously running - I'm pretty sure that's not supposed to be the case.

- You might want to try to pull an injector side rail off and see what the injectors are actually spraying. I've done this with other cars, but I haven't tried it with one of these M96 engines. I'm not sure it would be too easy.

Hope this helps,

Wayne

[randy_k]

Hmmmmmmmm, I had the very same problem. But all the info I read about it on renntech, pointed to the CPS. (it doesn't throw codes as a side note).So I replaced that and it seems to have cured that problem. Although, now a new problem has arrisen. (another story for another thread. I'm not saying the CPS is necessarly your problem.
Just a thought.
Randy

[Wayne 962]

I would think that the CPS would indicate and show up as a problem when it's running hot - not just when it's trying to start hot. If the CPS wasn't triggering properly, then I would imagine that it would trigger a code?

-Wayne

[randy_k]

Ignition turns over, engine won't start - RennTech.org Forums

post #8

[egress91506]

First, thanks for weighing in on my problem. The problem is annoying and I'm trying to work through the logic of it all.

As for CPS, I've read through a number of those posts and it sounded promising, but I've been assuming that the fact that I have spark from a coilpack means that the CPS is working. Assumption (right or wrong) is that if the CPS can't figure out the crank position, it is not sending a signal to trigger a spark. Since I have a spark, the CPS is working. Flawed thinking on my part?

As for Wayne's comments, the theory of a vacuum in the tank has been suggested and seems consistent with the observation that the old fuel pump didn't seem to be putting out enough volume. When we replaced the fuel pump, the car didn't start. Opening the tank would have equalizied the pressure? As for the fuel pump running, there wasn't any modification to the pump to make it always run. From what I understand, there's a sound that can heard when the ignition is on that indicates the pump is running and it will shut off when it reaches a certain pressure. The tech with the Porsche tester was able to trigger the pump on and off with the tester.

Eric, I'll check for leaks. I did replace the MAF before the event, but can't think of how I would have screwed that up.

[Wayne 962]

Originally Posted by egress91506

When we replaced the fuel pump, the car didn't start. Opening the tank would have equalizied the pressure?

Wait a sec. Unless you replaced the pump lightning quick, then the car did not start when it was cold? So this isn't just a hot start problem?

-Wayne

[egress91506]

Originally Posted by Wayne at Pelican Parts

Wait a sec. Unless you replaced the pump lightning quick, then the car did not start when it was cold? So this isn't just a hot start problem?

-Wayne

It was a pretty speedy replacement (under 45 minutes). What's the book rate -- 2.2 hours? More to your point, when the car refires, temp gauge is about the 10-11 o'clock position.

[Wayne 962]

I still think it's probably a fuel issue. If it was a sensor or wire harness issue, then the car would have issues running hot, which you didn't seem to indicate that it did. Also, when you're changing stuff to convert to a Boxster Spec car, people tend to remove anything for weight savings - even odd panels and plastic stuff that doesn't look like it does anything, but might actually act as a heat shield.

One more thing - you can try getting one of those air-in-a-can blower things, hold it upside down, and let the cold (liquid-nitrogen type fluid) drip on the fuel lines to cool them down quickly when it's hot. This way, you can test to see if the lines are what are causing the problem. You can also try that with the crank position sensor, just for giggles too.

-Wayne

[egress91506]

Originally Posted by Wayne at Pelican Parts

I still think it's probably a fuel issue. If it was a sensor or wire harness issue, then the car would have issues running hot, which you didn't seem to indicate that it did. Also, when you're changing stuff to convert to a Boxster Spec car, people tend to remove anything for weight savings - even odd panels and plastic stuff that doesn't look like it does anything, but might actually act as a heat shield.

One more thing - you can try getting one of those air-in-a-can blower things, hold it upside down, and let the cold (liquid-nitrogen type fluid) drip on the fuel lines to cool them down quickly when it's hot. This way, you can test to see if the lines are what are causing the problem. You can also try that with the crank position sensor, just for giggles too.

-Wayne

Thanks, I'll carry one of those air blower cans and try cooling off some parts and see if it makes a difference.

[stuttgart1]

egress91506, any update on this issue?

I am having this problem on my '99 Boxster, I've replaced fuel pump and fuel pump relay and no luck. Next thing I will try is the CPS. Just wanted to see is there anything I can do to further narrow down the problem before I order a new CPS.

Thanks!

[egress91506]

Had the problem again at a track weekend in May. Ended up replacing the CPS and it seems to have solved the problem. I say "seems" because I haven't had a track weekend since replacement, but the shop that worked on it was able to duplicate the non-start, replaced the CPS and got the car hot without the return of the non-start. Bottom line is I'm pretty confident that the CPS was the problem. Hope it solves your problem and helps others out (before they replace the fuel pump first).

By the way, do you have a lightweight flywheel on your car? From my reading of others with the problem and discussions with the shop that worked on my car, when the CPS is ageing and getting out of spec, it's more of a problem with cars with the LW flywheel.

Finally, hat tip to Randy k for the right answer. I was hung up on the idea that I confirmed spark and assuming that the failure on the CPS would be not providing info (rather than providing wrong info) to the ignition.

[randy_k]

Glad it worked for ya. And thanks for the tip o the hat.
Randy

[stuttgart1]

Thank you for the info! Just ordered a new CPS. =)
I have OEM flywheel on my car, no lighten flywheel.