1999 996 won't start when hot (cranks)

[whatnot]

A few days ago my car started not starting when hot. It seems somewhat random when it will happen. I think it is heat related because it starts fine after sitting and today it was much hotter outside and I had to wait over an hour before it would start.

From reading the forums I thought it sounded like the fuel pump. I put a gauge on it when it wouldn't start last Friday and jumpered the fuel pump relay and it was only making 15 psi. I ordered a new fuel pump and installed it yesterday. Put the 5 gallons of gas back in and drove to station and filled tank full last night and everything seemed fine.

Today the problem was back. I put the pressure gauge on and there was no pressure. Cranked the engine and no pressure. Jumpered the relay and went up to about 60 psi. Cranked engine and still no start. Let cool for an hour or so and started.

Now I am at a loss where to look. This is the first problem that I have had with this car so not real familiar with what to look for.

Thanks in advance for any help.

[ltusler]

Try a new coolant sensor. That fixed mine with the same problem.

[rb101]

Impulse sensor on the flywheel going bad.

[white99c2]

Same thing happened to my '99. It took a year to get really bad, new starter and never happened again. The starter gets hot and after years it dies.
Only a problem with a hot engine, trying to restart after a short 5 min stop and would slowly crank and not start until it cooled off. Is this what is happening?

[whatnot]

Originally Posted by white99c2

Same thing happened to my '99. It took a year to get really bad, new starter and never happened again. The starter gets hot and after years it dies.
Only a problem with a hot engine, trying to restart after a short 5 min stop and would slowly crank and not start until it cooled off. Is this what is happening?

It is usually longer trips, some have been over 30 minutes when it happened. Some shorter but not the first one of the day so the engine probably hadn't cooled down fully.
It sounds like it is spinning the engine as fast as normal. Did yours sound weak?

[whatnot]

Is there any way to test the impulse sensor and the coolant sensor or should I just replace them?

[white99c2]

Yes mine was spinning very slowly until it cooled off.

[whatnot]

I didn't have a lot of time to play with it today but I drove around for a while and parked it and let it sit. It wouldn't start when I tried.
While I was driving around I had torque running on my phone and was watching the coolant temperature and nothing out of the ordinary happened with the readings. When I can back to try starting it the coolant was reading 127 degrees.

Looking through the other sensors I found that the IAT is reading -40 degrees. I didn't look at it earlier when the car was running so I don't know if Torque can read it properly. I will see tomorrow if it will start.

Does anyone uses Torque for Android and know if it can read the IAT properly?

Would a bad reading for the intake temp keep the engine from starting?

[whatnot]

It looks like Torque just wasn't working right. This morning it showed -40 on the IAT but then after I started the engine went to 50 degrees.

[whatnot]

Is this the correct part number for the Impulse sensor?
986-606-112-02-M14
Porsche 996 Ignition - Page 2

[rb101]

yes, I'm showing 986-606-112-01 in the pet, the -02 is the updated part

[whatnot]

I replaced the impulse sensor yesterday and I think it fixed it. It was getting worse and I had to wait over 3 hours yesterday before it would start. Today after changing the sensor it started every time.

I had to give up trying to get the connector back in the place it was mounted. Even with a lift I don't see how anyone could possibly get at that location.
Is it just the cabriolet models that are impossible to get at?

Next job is to replace the fuel filter. That looks like it will be just as fun.

[jwgn777]

It is a pain on a coupe too. You should try to mount it correctly instead of having the connector flopping around. I am use to working blind so it could be very difficult if you don't do that type of work all the time. Remove the wheel and try again.

[whatnot]

I probably spend over an hour trying. I don't think I can possibly get it back no matter how long I keep at it. I zip tied it to the other wires it was near so it couldn't flop around.

I am 99% sure the problem is gone now. Drove to several places today and no trouble starting what so ever. It also seems to idle smoother.

[MrMorninwood]

I think I may be having the same issue. I've attached a video.



Did the impulse sensor fix this issue for good?
This only happens after its parked at work all day, in the desert...

[whatnot]

Yes, never had a problem with starting since.

[FPB111]

Two different issues. One didn't start when the engine was hot the other has a hard time starting when it is hot out.

[jwetering]

Mine wouldn't start and replaced the impulse sender but ended up being the fuel pump relay. Clue was wether or not the tachometer shows engine speed while cranking. If the impulse sender is bad then the tacho won't show anything (since the tacho gets it's signal from that sensor).

The fuel pump relay is a dead easy fix. Not that the impulse sensor is hard or anything, but the relay is reach under the dash level easy.

[FPB111]

Fuel "tank" pressure sensor?
https://rennlist.com/forums/996-forum/931081-fuel-pressure-sensor-replacement-guide-with-pics.html

[jcsjcs]

Bringing back this thread - as I am having a starting problem while hot. Car starts fine when cold - I have been topping up the battery, but it is a new battery and I don't think it is the problem.

My car is a 2002 C4S (with a 2005 engine).

Yesterday after stalling out at a light (purely my fault), it would not start up. It cranked but very very slowly and then slowed down even more as I tried again in a few minutes.

I called for a jump - but then after 30 minutes, I was able to get it to start. Cranking was a bit slow but fast enough to start up.

I am tempted to change the Starter, but have also heard that wiring can be less conductive when hot, or it could be one of the many above suggestions, fuel pump relay, impulse sensor, etc.

Any suggestions on how to narrow it down without buying a lot of parts???