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Another fuel pump question

 
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rod30  



Joined: 05 Aug 2018
Posts: 18
Location: Carrolltom Mo

PostPosted: Sat Aug 18, 2018 8:21 am    Post subject: Another fuel pump question Reply with quote

I am working on a 1987 924S. This car did not run when I got it and I have made good progress toward getting it back on the road. My question is about the fuel pump. I have looked at many old posts and am still unclear about what starts the pump. My car will start the pump when the car is cranking and after pressure comes up it will start. The problem is it takes to long for it to start. I expected the pump to come on with the key and prime the system for a quick start. The DME relay is working as I find voltage on the back side of 87 with the key on. It seems to me this should send voltage to the pump for priming. Please set me off in the right direction toward a fix.
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Sat Aug 18, 2018 12:43 pm    Post subject: Reply with quote

http://www.clarks-garage.com/shop-manual/fuel-05.htm
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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rod30  



Joined: 05 Aug 2018
Posts: 18
Location: Carrolltom Mo

PostPosted: Sun Aug 19, 2018 10:43 am    Post subject: Another fuel pump question Reply with quote

Thank you. I have read this information before and I believe the pump should start when the key set to on. As I said before the only time mine comes on is when the engine is cranking. I do see power on the back side of terminal 87 when the key is on. Since the pump is not running the power must not be getting to the black/green wire going to the pump. Where does this connection happen? Under the dash? It's hard to follow when it leaves the relay.
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Sun Aug 19, 2018 11:17 am    Post subject: Reply with quote

Did you look at the diagram that's included in the link?

The pump is powered from 87b not 87.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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KDJones2000  



Joined: 14 Sep 2010
Posts: 298
Location: Phoenix, AZ

PostPosted: Sun Aug 19, 2018 1:43 pm    Post subject: Reply with quote

The green/black wire has a connection in the driver's footwell. You should be able to find it up in the dash or if you remove the side carpet.

The wire goes along the DS running board up to behind the rear seat backrest.

That being said, make sure you are testing the correct pins in the relay socket...
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1987 924S SPEC car
Team Toofah Racing
1988 944 Turbo S
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rod30  



Joined: 05 Aug 2018
Posts: 18
Location: Carrolltom Mo

PostPosted: Mon Aug 20, 2018 12:22 am    Post subject: Another fuel pump question Reply with quote

Thank you for making me look again at the drawing. I do have power on terminal 87 but not 87b. When I test for ground at 85b, there is none. So either the DME is not providing the ground or it is not making it to the relay. When I provide my own ground at 85b the pump does turn on. Is this something you have run into before?
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rod30  



Joined: 05 Aug 2018
Posts: 18
Location: Carrolltom Mo

PostPosted: Mon Aug 20, 2018 3:43 am    Post subject: Another fuel pump question Reply with quote

Now I have checked and do have continuity from pin 20 in the DME connector to terminal 85b at the relay. So it seems as if the DME is not providing the ground.
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KDJones2000  



Joined: 14 Sep 2010
Posts: 298
Location: Phoenix, AZ

PostPosted: Mon Aug 20, 2018 3:59 am    Post subject: Reply with quote

GET A NEW DME RELAY!!!

They are a known weak point on these cars...
_________________
1987 924S SPEC car
Team Toofah Racing
1988 944 Turbo S
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Mon Aug 20, 2018 4:16 am    Post subject: Reply with quote

It is a good idea to have a spare relay, but based on the testing done so far the relay is working.

The fuel pump only runs when the engine is rotating. For one reason it prevents the pump from running in the event of a crash.

I'm guessing your problem is the check valve in the fuel system that's allowing fuel pressure to bleed down. Check this with a fuel pressure gauge attached to the end of the fuel rail. If it bleeds down too fast the remaining fuel in the rail vaporizes causing a slow restart later. This can also be caused by a leaky injector, a bad pressure regulator, or a fuel leak. The regulator's diaphragm can rupture, this can be checked by observing fuel at the vacuum port of the regulator and a rough idle.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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rod30  



Joined: 05 Aug 2018
Posts: 18
Location: Carrolltom Mo

PostPosted: Mon Aug 20, 2018 5:13 am    Post subject: Another fuel pump question Reply with quote

Pressure does drop to zero in a very short time and I wondered about a check valve. I timed it and it get close to zero in just two or three minutes. The injectors are new so I think I will look elsewhere first. Is there a check valve other than what is in the pressure regulator? What about the pressure damper? It does have a rough idle.
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Mon Aug 20, 2018 5:21 am    Post subject: Reply with quote

You should have about 15 psi after 20 minutes. The check valve is on the pump. The damper can be checked by seeing if it holds vacuum at the vacuum port.

http://www.clarks-garage.com/shop-manual/fuel-01.htm
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Mon Aug 20, 2018 5:30 am    Post subject: Reply with quote

https://www.fcpeuro.com/products/vw-fuel-pump-check-valve-jetta-1587010536
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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rod30  



Joined: 05 Aug 2018
Posts: 18
Location: Carrolltom Mo

PostPosted: Mon Aug 20, 2018 5:32 am    Post subject: Another fuel pump question Reply with quote

When I got the car the fuel pump was not working and I replaced it. I tried to get by with the least expense one I could find. Sounds like I should have got the better one. You get what you pay for.
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Paul  



Joined: 02 Nov 2002
Posts: 9344
Location: Southeast Wisconsin

PostPosted: Mon Aug 20, 2018 5:43 am    Post subject: Reply with quote

https://www.fcpeuro.com/products/electric-fuel-pump-94460810204

But you may only need the $16 check valve in my previous post.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
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rod30  



Joined: 05 Aug 2018
Posts: 18
Location: Carrolltom Mo

PostPosted: Mon Aug 20, 2018 7:55 am    Post subject: Another fuel pump question Reply with quote

Yes. I did order the check valve in your post. Thanks
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