hard to start when warm

Porscheke · 07-01-2010, 11:28 PM

Hello

I have a Porsche 3.2 from 87.
When engine is cold, it starts immediately.

When I drive the car for some 30 min, so when engine is hot, and I turn off the engine wait for some 15min. the engine won't start from the first attempt.

I have to turn of the contact try again, and most of the time it starts up the second time after some 10 seconds?

I have done a search but didn't find an answer for this problem?
Does anyone have had the same problem?

How to fix it?

Hope someone can help me

Regards
Porscheke

twistoffat · 07-01-2010, 11:43 PM

Sounds like an MSD box ignition problem.
I´ve read similar threads here in the past with hot starting problems and most diagnosed a CDI or MSD problem. Have a look at this thread
No Hot Start

http://forums.pelicanparts.com/uploads/MSD.gif

Porscheke · 07-01-2010, 11:53 PM

Hello

Thanks for the fast reply.
But my engine is a 3.2 from 87.

I don't think I have such a MSD box??

Strange thing is the car runs fine but when warm and turn off the engine.... problems starts :-(

start first time: engine turns over strong but won't start
Start second time : after some hesitation the engine starts (some 10 seconds)

Regards
Porscheke

twistoffat · 07-02-2010, 12:20 AM

Okay I talked to a friend who said he had a similar problem.His mechanic thought it may be the fuel pump but it turned out to be a defective fuel pressure regulator which sits next to the fuel filter. Pressure was dying and difficult to start warm.

Porscheke · 07-02-2010, 02:25 AM

Hello twistoffat

I'm hoping it will be something like that.

I just checked but on my engine there is no fuel pressure regulator which sits next to the fuel filter. This is only on cars till 3.0.

My fuel line goes directly to the fuel filter and then to the engine??

twistoffat · 07-02-2010, 02:38 AM

this is the part Pelican Parts - Product Information: 928-110-198-01-M14

and this thread will show you the location

Fuel Pressure Regulator - Access ? (3.2)

Porscheke · 07-02-2010, 02:54 AM

Ok

I will order this part,hopefully this is the problem.

Thanks for the feedback

I will keep you informed

regards
Bart

twistoffat · 07-02-2010, 02:57 AM

You could ask you local friendly dealer to check it before you go to any expense. With a guage is should be a quicky

johnsjmc · 07-02-2010, 04:27 AM

If a fuel pressure drop happens in 15 min ask yourself why doesn,t the same thing happen when parked overnight? Has the engine temp sender been changed to the updated one? Does it smell rich when it starts hot? The fuel injection uses an input from a temp sensor in the foreward end drivers side head to determine if the engine is warm or cold If defective the engine goes very rich when starting. Like a choke is on.This can cause hard hot starts but allow normal cold starts. There is an updated sensor so there have been premature failure issues with the original ones. That would be my guess not a pressure reg. There are tests for either. It is not a good idea to just throw parts at a problem.

Albuquerque · Albuquerque's Garage

Quote:

Originally Posted by johnsjmc

If a fuel pressure drop happens in 15 min ask yourself why doesn,t the same thing happen when parked overnight? Has the engine temp sender been changed to the updated one? Does it smell rich when it starts hot? The fuel injection uses an input from a temp sensor in the foreward end drivers side head to determine if the engine is warm or cold If defective the engine goes very rich when starting. Like a choke is on.This can cause hard hot starts but allow normal cold starts. There is an updated sensor so there have been premature failure issues with the original ones. That would be my guess not a pressure reg. There are tests for either. It is not a good idea to just throw parts at a problem.

What is the part number for that updated sensor? I'm having the same symptoms: after a run it is very difficult to start and after start smells very rich.

Thank you

José

twistoffat · 07-02-2010, 05:17 AM

Quote:

Originally Posted by johnsjmc

If a fuel pressure drop happens in 15 min ask yourself why doesn,t the same thing happen when parked overnight? Has the engine temp sender been changed to the updated one? Does it smell rich when it starts hot? The fuel injection uses an input from a temp sensor in the foreward end drivers side head to determine if the engine is warm or cold If defective the engine goes very rich when starting. Like a choke is on.This can cause hard hot starts but allow normal cold starts. There is an updated sensor so there have been premature failure issues with the original ones. That would be my guess not a pressure reg. There are tests for either. It is not a good idea to just throw parts at a problem.

The reason it wont happen overnight is that with a defective regulator the heat from the hot engine vapourizes the fuel in the line causing vapour lock. It takes a few turn for the fuel pump to clear the line and restore pressure. As we both mentioned though better to test both before chucking money at it.

Porscheke · 07-02-2010, 05:22 AM

Ok, I've read some more articles now here on this forum...

As far as I understand the problem, the root cause for this hard warm start could be several things:

1. Bad fuel pump (car drives good ones it's started->so don't think this is it)
2. fuel pressure regulator (has to be checked)
3. Bad fuel injectors (leaking)
4. Temperature sensor (any sugestions how to check this one?)

Think number 2 & 4 could be my problem....starting with changing the temp sensor

Regards
Porscheke

johnsjmc · 07-02-2010, 05:28 AM

There is a technical article on this site about upgrading the cylinder head temperature sensor.I found it easily but don,t know how to link to it. Look up the part and you should find it

dentist90 · dentist90's Garage

Loss of fuel pressure while sitting is due to i) leaking injector(s) or ii) failing fuel pump check valve. The fuel pressure regulator's function is to maintain ~40psi of fuel pressure while the pump is operating, as the fuel pump is capable of producing much more than this. The excess fuel is routed back to the fuel tank. Inadequate fuel pressure once started doesn't sound like your problem. Easy to test that with a basic fuel pressure gauge.
The difference between hot and cold starts with inadequate residual fuel pressure may be vapour lock, or "boiling" of the fuel in the fuel rail/lines due to the heat of the engine. Maintaining 15psi residual pressure in the fuel system at all times makes for quick starts.
If you have a loss of fuel pressure while sitting there should be a cold start symptom: initial stumbling on start up. ie, it starts right away but takes a few seconds to get into a smooth fast idle. This is due to the delay while the fuel pump restores adequate fuel pressure.
If you have a leaking injector it will dump fuel into the intake causing a very rich restart. This is worse in a warm engine (flooded) but not as noticable after the engine has cooled and needs a richer start mixture. Black sootyy smoke on warm restart is a symptom of too much fuel and possibly a leaking injector.
I would start by checking residual fuel pressure. Run the car with the fuel pressure gauge hooked up. Should read 38 psi. Then shut it off and check again in 1/2 hour. If pressure has dropped below 15 psi one of the above causes is most likely. Hope this helps.