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928 dies / won't start when hot

 
Old 07-31-2011, 05:20 PM
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RBA84
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Unhappy 928 dies / won't start when hot

Really need assistance. I may have two separate unrelated car dies / won't start problem or one with two sets of related symptoms.

87 auto with only 62k. Owned for 12 year - do most of my own work.

Symptom 1.

Ai live at 7500 ft (Tahoe) when car is in Reno 5000ft. and warm (not overheating) and I drive up the mountain it dies like it is running out of gas. Let the car cool down 30 minutes and it starts and then dies in a few miles. Tow it home and let it stand overnight and it runs just fine.

My theory is vapor lock - heat plus lower air pressure when climbing mountain and fuel vaporizes. Let it stand and fuel condenses and it runs. Let car cool down overnight and all is working well.

My fix. New fuel pump (replaced original) and check valve. Car ran fine for 2 weeks and then on a hot day it refused to start after running for 20 minutes fine (no altiude change)(thought it was the same problem) but when I finally got it to start it idled at 2,000 RPMS exactly and then died when I put it in drive and tried to get the car to move. Tried 3 times. Same each time - high idle speed but no power. After 4 tries batttery seemed dead - would not turn over at all (stanrge) and I parked it. Came back 2 days later, jumped the car, and it ran perfectly. Drove it home.

WHAT IS GOING ON???? Just send my EZK and LH computers to be checked out and they seem fine. Don't know if I fixed the possible vapor lock problem since I have not run the car up and down the mountain.

The 2000 rpm idle never happened when it died with possible vapor lock before. Again - when the car cools down overnight it runs and idles just fine - until the next????time. I [must get this car to run reliably.It has been my daily transporation for the past 12 years - AGHHHHH.

Any advice, suggestions would be greatly appreciated.

Thanks very much for your assistance.

Dr. Bob
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Old 07-31-2011, 05:36 PM
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Dr Bob - There can't be two Dr Bobs can there 8>)

Welcome to Rennlist and you are now in the right hands for the best available advice.

Did you find the crank sensor connector?
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Old 07-31-2011, 05:44 PM
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Does it crank slow when warm?
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Old 07-31-2011, 05:54 PM
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Cranking is normal. I have an optima red top battery and cranking speed seems O.K.
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Old 07-31-2011, 06:03 PM
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If it happens again disconnect the battery ground for a few seconds, re-attach and see if it starts.

This will reset the LH.

I have had this problem and removing the ground has always worked for me.

I changed LH, EZK, Ignition relays, swapped LH/EZK computer out, replaced the old CPS and rear knock sensor (needed to be done anyway) and still had the problem.

Since then I have cleaned the main ground to the engine under the car and it has seemed to help along with cleaning the Temp II sensor connections and various other connections.

Jim Coreman also suggested re-maping the startup fuel map. I may be sending too much fuel at startup. Haven't gotten to that yet.

Hope this helps.
Good luck!
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Old 07-31-2011, 06:05 PM
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How would the crank position sensor connections account for the car dying only when climbing he mountain when hot (problem 1) and the 2000 rpm idle but no power (problem 2)???

Once I start throwing $$$$ at my car w/o knowing the cause of the problem I will go broke in a hurry. Up until now I was always able to diagnose the problem befor spending time and money on the repair.

Thanks very much for your assistance
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Old 07-31-2011, 06:20 PM
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I can't for the life of me see where the wire attached to the crank position sensor goes. I can feel the wire with my finger for about 3-4" and then it disappears into a mass of wires, etc. next to the MAF on the driver's side. I was told to check this conection, but I just can't follow the wire or see the connector at the end of it. How much do I need to remove to get to it?

Do you believe the two won't start problems are, in fact, two separate issues? Do you think I may have fixed the first one with a new fuel pump? I just installed a fuel pressure gauge today and should know if there is fuel if it happens again. I had a spark tester with me when it happended and I verified spark.

Do you think the no start 2000 rpm problem is totally separate from the died when climbing he mountain when hot problem?
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Old 07-31-2011, 06:25 PM
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Chris -

I carefully cleaned the battery ground connection. I have not, however, cleaned the engine ground connection since I would have to take off the underpan, etc. A real pain unless I am reasonably sure it needs to be done.

Do you think the two no start problems - one withot the 2000 rpm idle when climbine the mountain and the other with the 2000 rpm idle - are related or seprate issues.

I definitely will disconnect the ground to re-set the LH compuer if it happens. I was also told to remove the gas cap - do you agree with this?
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Old 07-31-2011, 06:29 PM
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Unfortunately the CPS and knock sensors connectors fall apart with age. The Knock sensors insulation all falls apart which may cause and issue.

The grounds under the fuel dampeners need to be clean as Chris remarked. You can also look at the CPS connecter while down there.

Take the vacuum lines off the fuel dampeners an regulator, make sure you don't have any fuel present?
(diaphragm bad).

A fuel line runs through a cooler attached to the AC metal line (located on the firewall, has black foam around it) to keep the fuel cooler.

Did you have the AC on?

Have you verified the fuel pressure, does the car hold pressure after sitting?

Have you checked you crank end play?
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Old 07-31-2011, 06:39 PM
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All these suggestions don't seem to address the high idle, in my opinion.
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Old 07-31-2011, 06:40 PM
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I wonder if the cold start circuit was operating when it shouldn't have been? And perhaps that may play into the hot start issue?
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Old 07-31-2011, 06:48 PM
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All good info Chris is giving.

You need to remove the air cleaner and MAF to get to the rear dampeners and CPS connector.

Also look at your MAF connector.

This link may help for parts location.

http://members.rennlist.com/v1uhoh/underthe.htm

Search is you friend.

Last edited by Glenn M; 07-31-2011 at 08:12 PM.
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Old 07-31-2011, 06:56 PM
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Are you suggesting I replace the Temp II sensor? Test it? Clean the connectors? Could a faulty TempII sensor create the 2000 rpm idle? Even with the faulty signal why wouldn't the car run when I put it in gear - it died when I gave it some gas - too rish a mixture?

I hate to start the part swap game since I will run out of $$, but what about the Temp II sensor as a probable cause?
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Old 07-31-2011, 06:57 PM
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S4's and up have a start up fuel map which is set pretty rich.

The car would need to be shark tuned to adjust the map or the stock factory chip load could be modified and a new EPROM burned.

This may not be the problem or one fix to multiple problems.
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Old 07-31-2011, 07:17 PM
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Since you have been the owner for 12 years what is the service history since you have owned the car and major work performed before?

Start with cleaning all the grounds, coil connections, tempII connections.

Search the forums for links to where the grounds are located.

When was the last time the caps and rotors were checked/changed?
Can get arcing which could be part of the problem.
If it has been a while they should be removed and checked for carbon and corrosion build up.

Ignition wires original? Make sure all the ends pushed on tight at the caps and plugs and coils.
Run the engine when it is dark and look for blue "fire flies" eminating from the wires (insulatiion breaking down if bad). If bad wires need to be replaced.

Plug condition?

There are many basic items that can be checked but it takes time and a basic knowledge. There are may threads on the various maintenance items.

Many major links are in the New Visitor section.

https://rennlist.com/forums/928-foru...diagnosis.html

Dwayne has done detailed service procedures along with others.

https://rennlist.com/forums/928-134/?pp=40&daysprune=-1

Do you have the maintenance manuals on paper or CD?

Roger at 928srus.com sells a CD with the manuals and other technical data.
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