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Problems Starting Car After Warmed Up

I am posting this for my cousing, he has a 4 cylinder 87' 944. He will take the car for a drive, it will start up fine the first time. after drilets say he parks the car and goes into a store or something, then when he comes back out the car will crank but wont start. After 20-30 mins of the car sitting there, it will eventually start back up. He has already changed the DME Module, the alternator, fuel pump and the security module. Any ideas what could be causing this problem? Thanks in advance.

Old 12-05-2003, 11:20 AM
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Just keep changing out things till it starts.

Try the sensors next.
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Old 12-05-2003, 01:00 PM
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Quote:
Originally posted by SoCal Driver
Just keep changing out things till it starts.

Try the sensors next.
That is the most vague response i have ever gotten. Nobody on here has had this problem, or has any idea what would cause a problem like this. Maybe something that warms up and is not letting the car start when it's warm and needs to cool down before starting. Are there any tech guys on here?
Old 12-05-2003, 01:08 PM
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Unless you use a set plan of testing the DME elements of the car you are just shooting in the dark -- replacing components.

Doing a search of this forum will give you dozens of threads where hot no-start has been discussed in depth.

Now if you want to get serious and discuss what to check and why I'll continue. Please note that there are 15 test points in the Porsche factory DME testing plan. Twelve of these are for no start.

And yes many of use have problems with the 944 or we would not have come here hundreds if not thousands of messages ago.

Check the sensors. These will age crack at the electrical fittings breaking the wires. You should get 2K ohms between the center pin and one of the outer pins. The other is a floating shield. Flex the wires as you check.
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Hugh - So Cal 83 944 Driver Person
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Old 12-05-2003, 02:32 PM
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Thats more of the answer i was looking for. I am a VW person, i build and race vw's, everything from fully programmable engine management to custom fabrication. But, I am not too familiar with porsche electronice, let alone 1987 porsche electronics. Can you give me examples of where to start with checking the sensors to possible narrow my search down a bit? Thank you, i appreciate the help.
Old 12-05-2003, 02:58 PM
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Went to the Culver City VW-Porsche training center a few times in 1969 and 1970. One was for the beginnings of the Bosch fuel injection that VW was starting to use. Worked part way through college at independent shops and dealers.

I strongly suggest you find someone locally that has the factory manuals. In the back of the engine sections you will find the DME Testing Plan I mentioned.

There are two sensors mounted on the back of the engine block that look through the bell housing at the flywheel. One is for engine speed, it looks at the teeth of the starter gear, and the other is for TDC reference, looks at a pin on the flywheel. You can see their connectors one above the other and the back of the block. Many non hot start problems can be these sensor electrical connections expanding when hot breaking the central wire. If you put a volt meter to the center and correct side pin and crank the car you should see two volts or better coming off of the speed and a two volt spike coming off of the reference when the pin passes under it.

There is also concerns with the fuel pressure regulator, FPR, and the fuel dampener closing off when hot. The fuel recirculates back to the tank and gets pretty darn hot. The fuel pump also exhibits some possible temp lock ups.

All of these and more can be tested before you start throwing parts at it.
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Hugh - So Cal 83 944 Driver Person
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Old 12-05-2003, 03:21 PM
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Thanks! great info, i will see what diagnosis i can do and see if i can get my hands on a factory manual. I will update here as i find things out.
Old 12-05-2003, 04:31 PM
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There is some online info at www.frwilk.com and www.clarks-garge.com

Also www.pelicanparts.com has electrical diagrams.
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Hugh - So Cal 83 944 Driver Person
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Never break more than you fix!
Old 12-05-2003, 06:49 PM
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...Welcome to the board....

by the way you are in good hands with Socal....

In troubleshooting. I always try and keep it simple. You need four key things to start an engine. Compression, timing, fuel, spark. With those 4 things an engine will start, maybe it will not run well, but that is another story.... SO

Compression and timing are obviously not affected in this case.

1. Check for spark. DME relay, Corroded grounds etc...

2. Do we have fuel. FPR,Dampner, Fuel Pump, Injectors, Fuel Pump Relay, Vaporlock.....etc

So now start trouble shooting each of these.

Have fun.
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Old 12-05-2003, 07:45 PM
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Quote:
Originally posted by SoCal Driver




And yes many of use have problems with the 944 or we would not have come here hundreds if not thousands of messages ago.

What, did you move to Jersey?? Use two guys are right about Socal. He may be a bit short or gruff when he gets weary, but he's sharp as a tack, has all the manuals, and very quick to help a brother out!

I would check and see if your reference sensor is sending a pulse to your DME, and hence your coil. If your set screw fell out of your flywheel, would you know and how many other things would you replace before you figured it out. I had a coil wire break inside the insulation! I pulled in at a Food4less and went inside. came out and started the car, reversed for about 3' and it just died. Dead dead dead. starter would crank like crazy, but no start. I called AAA and had it towed home. took me two days to figure out that my coil wire was seperated, but looked good!

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Old 12-05-2003, 09:35 PM
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If the car start OK from cold but does not when warm I reacon is a fueling/mixture problem. Three things come to my mind.
1. Faulty coolant temperature sensor or faulty connection to the sensor or faulty air flow temperature sensor or connection. If this is the problem you should also notice that the car is not running properly with either rich or weak mixture. Check spark plugs.
2. The other posibility which I think is more likely is leaking fuel injectors. When you stop the engine the fuel pours out of the injectors and flooding the engine. As a result the engine cannot be started straight away and you have to wait.
3. Another possibility is clogged air filter and perhaps faulty air flow meter. If one of these is at fault the car will also not run properly. Again check spark plugs.
Old 12-06-2003, 12:07 AM
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Also - if your ground is corroded you will get a hot start problem.

the ground is opn the back side of the engine, drivers side, right under the heater control valve. Big black or copper wire bolted to the bell housing.

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Old 12-06-2003, 06:23 AM
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Quote:
Originally posted by Makis
If the car start OK from cold but does not when warm I reacon is a fueling/mixture problem. Three things come to my mind.
1. Faulty coolant temperature sensor or faulty connection to the sensor or faulty air flow temperature sensor or connection. If this is the problem you should also notice that the car is not running properly with either rich or weak mixture. Check spark plugs.
2. The other posibility which I think is more likely is leaking fuel injectors. When you stop the engine the fuel pours out of the injectors and flooding the engine. As a result the engine cannot be started straight away and you have to wait.
3. Another possibility is clogged air filter and perhaps faulty air flow meter. If one of these is at fault the car will also not run properly. Again check spark plugs.
See the issue with a fewof the things you mentioned which i have already thought about like the coolant temp sensor and the MAF, is that the car wouldnt run well, the car starts fine when cold and runs fine. Also about flooding the engine, it wouldnt leak bad enough to flood an engine where it takes 20-30 mins to start the car. Ive flooded my race car with the 700cc injectors before and after 5 mins of cranking it will start. Im going to look into all these suggestions regardless as i am new to porsches. Great help all of you. Keep any info coming. Thanks
Old 12-06-2003, 10:09 AM
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Nothing really trick with the 944's. Just "simple" Bosch injection.

The temp sensor on the engine could be bad. This is the one that has the same type of connector as the injectors. Front of the block below the #1 cylinder intake runner.

A hot or over heated fuel system can vapor lock in it's own way.

Sometimes it's just as simple as replacing the $20 DME/fuel pump relay.

You need the DME testing plan from the manuals. Send me a PM with your address.

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Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 12-06-2003, 12:14 PM
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