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Mahorelee's Avatar
 
Join Date: Mar 2017
Location: Louisville, KY
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Unhappy 1986 Porsche 928 turns but will not start

I've been driving my 1986 Porsche 928s for about 6 months now. But if I let it sit for longer than 2 days the car will not start and I have to jump it. Sometimes it takes about 15 minutes on the jumper cables before it will turn over, always if it sits for several days.

However recently it just will not turn over. Here's what I've done:
  1. Made sure there was gas
  2. Replaced spark plugs
  3. Replaced air filter
  4. Checked for spark on spark plugs. I'm getting an infrequent yellow spark
  5. Replaced EZF replay with Horn relay, still same thing.
  6. Seems like the following relays are replacements (I could be wrong):
    • LH fuel injection
    • Fuel pump O2 sensor
    • EZF Ignition System

It's been a pain so far to check anything as to get it to turn with enough juice I have to jump it for 10+ minutes.

I've attached a picture of my relays and here's a video of the car trying to start so you can hear what it sounds like: https://youtu.be/GCkCGm0oeHo

Any recommendations are greatly appreciated but I am very new to this so keep that in mind.
Old 03-18-2017, 10:31 AM
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Crank position sensor? Battery to low.
Old 03-21-2017, 02:54 AM
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Quote:
Originally Posted by fast928tt View Post
Crank position sensor? Battery to low.
Battery cables? Battery ground cable? Old battery. Battery static voltage should be about 12.46V, on charge, motor running 13.8V.
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1986 928S
32 valve engine
All stock, automatic, 539 Weissgold Metallic, 70K original miles, Hankook Ventus 2 tires.
Previously owned: 67 Vette, 427 L88 Stingray, 74 De Tomaso Pantera L
Old 03-21-2017, 04:40 AM
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Quote:
Originally Posted by harborman View Post
Battery cables? Battery ground cable? Old battery. Battery static voltage should be about 12.46V, on charge, motor running 13.8V.
The engine is turning over. The EZK has to see that the engine is turning over to turn on the LH. He has no spark in his video. CPS . Had car same year same problem . We replaced CPS with a Porsche one from the dealer and car stated right up. CPS

Last edited by fast928tt; 03-21-2017 at 03:03 PM..
Old 03-21-2017, 02:59 PM
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Quote:
Originally Posted by fast928tt View Post
The engine is turning over. The EZK has to see that the engine is turning over to turn on the LH. He has no spark in his video. CPS . Had car same year same problem . We replaced CPS with a Porsche one from the dealer and car stated right up. CPS
"Sometimes it takes about 15 minutes on the jumper cables before it will turn over, always if it sits for several days."

I saw that video and it is not turning over very fast and sure sounds like a weak battery to me. Also I had a problem with my ground cable. The inside of the cable was all corroded inside the braided connection.
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1986 928S
32 valve engine
All stock, automatic, 539 Weissgold Metallic, 70K original miles, Hankook Ventus 2 tires.
Previously owned: 67 Vette, 427 L88 Stingray, 74 De Tomaso Pantera L
Old 03-22-2017, 05:07 AM
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How is the timing belt?
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1981 928 Euro "Babied and Pampered"
Old 03-25-2017, 01:03 AM
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Finding the drain on the battery the right thing to do, quick and easy fix is to use a battery tender or disconnect switch when parked.
Old 03-28-2017, 07:02 AM
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Your video is indicative of a low battery.

Get a cheap meter if you don't have one.

If you have an discount auto type parts store bring the battery in and load test it. To me this is the first thing I would do.

Basic check:
I would check your battery voltage before you start the car should be around 12.2-12.7 D.C. Volts
If you can get someone to start it and read the voltage 11.8 is acceptable on a good battery.
If it won't start charge it get it running and measure your voltage 13.8-14.2 indicates a good alternator.

If the alternator is charging go for a ride, disconnect your battery and charge it for an hour measure the voltage after 15 min then leaving it disconnected measure it in the morning. The voltage should be a min of 12.2 volts.

It is possible your have a drain and you depleted your battery too many times or you have a large drain which is whole other conversation.
Old 03-31-2017, 05:14 PM
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928 , relays , spark plugs , start , won't start


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