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1988 924s DME relay/fuel pump question

 
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chumwon  



Joined: 07 Sep 2017
Posts: 9
Location: Greenville mi

PostPosted: Fri Sep 15, 2017 3:06 am    Post subject: 1988 924s DME relay/fuel pump question Reply with quote

Hello again folks, been slowly tinkering away at little things from the ole boy sitting so long but now I decided to try an figure out why this thing quit running and was parked for it 18 years ago.

Now I noticed with the key in the on position I don't hear my fuel pump running or even quickly price it. I found the fuel pump relay under the dash and it appears an smells very burnt! I tried to make a jumper to just hear the fuel pump run but nothing...

After doing some research on here I noticed some people saying they have a pre prime setting in the on position and others don't an rely on the motor turning to activate the pump. Is mine suppose to prime? I only have the one fuel pump relay and one fuse. I've also learned that this relay has something to do with the computers DME aswell. Just trying to trouble shoot my issue but I'm unfortunately running into a problem I can't quite grasp. My next step was going to be putting 12v right to the pump to rule that out but I wanted to see what some of you more educated souls thought of my situation.

Thanks again everyone!
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Paul  



Joined: 02 Nov 2002
Posts: 9295
Location: Southeast Wisconsin

PostPosted: Fri Sep 15, 2017 7:59 am    Post subject: Reply with quote

The pump doesn't get power until the car is being cranked. Drain the gas. Most likely the pump is toast from sitting so long.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
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chumwon  



Joined: 07 Sep 2017
Posts: 9
Location: Greenville mi

PostPosted: Sat Sep 16, 2017 1:07 am    Post subject: Reply with quote

Thanks Paul! Yes draining the fuel is a must!! And I was thinking the same thing about the pump sitting for that long with nasty fuel. I'll start pricing pumps and DME relays.
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curtisr  



Joined: 07 Apr 2012
Posts: 79
Location: Kingston, Ontario, Canada

PostPosted: Mon Jan 08, 2018 2:28 am    Post subject: Reply with quote

You can get a priming solid-state DME relay here: http://www.ftech9.com/new-products/993-ssr-pp (No affiliation.)
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Eric P  



Joined: 21 Jun 2017
Posts: 122
Location: NY, USA

PostPosted: Tue Jan 09, 2018 12:41 am    Post subject: Reply with quote

This thread is about 4 months old so hopefully you found your solution already however:

There are a few different DME relays from what I've read. The original DME relay from Porsche supposedly has a self prime function and primes 2-3 seconds with key on. I've never seen one in person so I can't verify this claim, however I have seen circuit diagrams and that appears to be how they're wired. The commonly available aftermarket relays (Kaehler) does not have a self prime function and the engine must be cranking to run the pump.

That being said, start with the fuse. Replace it with a new 16A fuse. Clean the terminals while you're in there. Try to start the car with a friend listening to the pump. If that doesn't work, pull the DME and jumper it with a 3 way jumper to puns 30, 87, and 87B. Listen for the pump to kick on. If you have nothing, check the voltage across the pump with a multi-meter. If you have no/low voltage, the fault is in the wiring. If you have good voltage at the pump, you need a new pump.

If the car has been sitting 18 years, I would just replace the pump. Even if it is working, chances are that it will get noisy and die soon. Replacing the pump also gives you a chance to clean out the fuel tank and replace the fuel filter. On my 924S I used a Walbro GCL-606 pump. It was way cheaper than a Bosch and fits/works flawlessly. It's nice and quiet too.

If you need a new relay, start by figuring out why the relay burned out before you drop a bunch of money and burn out a solid state relay. I found that the circuit board on the KAE relay tends to burn out before the contacts in the relay do, so I doubt a solid state relay would fix any issues. It might increase reliability due to corrosion though.

On a side note, I wonder if it's better to crank the engine for a couple seconds before starting it to get the oil flowing anyway? Just something to think about.
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