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Old 02-19-2009, 03:26 AM   #1
Capt Squid
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Default Will not start when hot

Friend has a 76 928 that starts fine when cold and will not start when hot. He has had it towed twice. Any ideas? I am a 944 guy and do not have a clue.

Jim Richmond
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Old 02-19-2009, 03:38 AM   #2
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never heard of a '76 928. Check the temp 2 sensor maybe?
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Old 02-19-2009, 08:53 AM   #3
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Several possible reasons, which vary with model year. We need to know what model the car actually is.
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Old 02-19-2009, 10:03 AM   #4
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Squid, can you get him to come here for help? We would be happy to assist him. BTW, 1978 was the first year for the 928.
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Old 02-19-2009, 10:19 AM   #5
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Jim, need the real year. My '78 wouldn't start when hot. Started right up when cold. Spent $$$$'s at dealerships and garages for mechanics that didn't know what they were doing.

I traced my problem to some common and simple to fix things that I tracked down with this indispensible book by Ben Watson:
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Old 02-19-2009, 04:56 PM   #6
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Mine (83 k-jet) did similar recently. Wait 5-10 mins, would fire up, but in a small time window, nothing. In the end it seemed to be the warm start solenoid temp switch, which is either NLA or silly money. Adapted a 944 part in, and seemed to fix it, but the failure occurred again recently....waited 5mins, ok again, but thats first time in several months now. This is a temp sensor screwed into the hot water outlet fitting that feeds the heater. To test, remove, check open circuit cold, then heat to over 50C, check closed circuit, near zero ohms. Mine was showing 20 ohms, which is enough to stop the solenoid firing.
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Old 02-19-2009, 05:56 PM   #7
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What does 'will not start' mean?

Does the starter turn over but the engine does not run?

More details, including the correct model year, please.
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Old 02-19-2009, 07:07 PM   #8
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Fuel pump check valve,
Leaking fuel accumulator,
Those are the two most commmon sources for CIS hot start problems
With those 2 things not working system pressure drops extremely fast and creates a vapor lock in the cis dizzy.
Purchase a CIS system tester to confirm this is the problem, they are around $60.
Accumulator are about $130 give or take a bit.

Or another check is with car hot and not wanting to start jumper the fp relay and run the pump for around a min. As well you can put a momentary switch with 12v to the cold start valve and hold the switch when you start.

Hth
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Old 02-20-2009, 03:26 AM   #9
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Sorry guys,

It is a 1978 928. When he shuts it off when hot it will crank but not fire. He can get it to fire with a squirt of starter fluid but it will not stay running. After it cools down and it is cold then it fires right up.

I will relay the info you supplied.

Thanks.........

Jim
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Old 02-20-2009, 09:53 AM   #10
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I had similair symptoms, cold start fine. Hot start immediately after shut off, fine. Hot start after it sat for over 5 minutes - impossible.

Using fuel pressure gauges, I was able to determine mine was not holding rest fuel pressure. This allowed vapor lock and seems to be a common occurance with CIS.

I replaced the check valve (cheap) at the fuel pump and it cured it.

It can also lose rest pressure from a faulty fuel distributor or warm up regulator (expensive, expensive).

The book taught me how to trouble shoot the problem.
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Old 09-26-2009, 11:38 PM   #11
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Default Hot Start Problem

Occasionally my 1985 928 S won't start when it's hot. After reading the threads, I guess I have to start by replacing the fuel pump check valve. In the meantime, does anyone know if there is a way to get the car started when it won't start hot? It cranks but won't fire. I know I'm going to get stuck somewhere and end up waiting a hour or two for it to cool off.

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Old 09-27-2009, 01:58 AM   #12
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Check the battery terminals, clean and the ground. Mine did the same thing and the ground strap was no good. Car started great cold, not hot, not at all. it would crank for ever. Worth a shot, easy to get at and re do...
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Old 09-27-2009, 10:28 AM   #13
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Thanks Wag. I'll give that a try.

Sam
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Old 09-27-2009, 10:34 AM   #14
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My 84 had a failing fuel pump relay. It sits basically over top of the header on the passenger side and was getting warm. When the car was hot the relay couldn't latch and the fuel pump wouldn't come on. Exactly the same result you have.
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Old 09-27-2009, 10:59 AM   #15
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Quote:
Originally Posted by Capt Squid View Post
I am a 944 guy and do not have a clue.

Jim Richmond
What no one said it yet?

An honest 944 owner. Surely an endangered species!
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Old 09-27-2009, 10:59 AM
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