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skytrooper
Joined: 29 Aug 2007
Posts: 461
Location: Canandaigua, NY
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 Posted: Wed Apr 30, 2008 6:17 am Post subject: DME relay getting hot while driving |
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A friend of mine asked me about this as his '83 944 is having this problem. He has replaced the DME relay once due to this and asked me if I knew anything about it. Since I haven't a clue....I figured that someone here would more than likely have a possible answer
Thanks
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Matt
1987 - 924S "Black Pearl"
1982 - BMW 633CSi
1984 - BMW 528e
1983 - 944 N/A "Blue Max" (Gone)
1981 - 931 "Scarlet Harlot" (Gone)
1976 911S Targa (Gone) |
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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| Posted: Wed Apr 30, 2008 6:22 am Post subject: |
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Something is drawing excessive current through the relay. Fuel pump?
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Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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skytrooper
Joined: 29 Aug 2007
Posts: 461
Location: Canandaigua, NY
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| Posted: Wed Apr 30, 2008 9:08 am Post subject: |
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I passed this info on to him
Thanks Rasta
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Matt
1987 - 924S "Black Pearl"
1982 - BMW 633CSi
1984 - BMW 528e
1983 - 944 N/A "Blue Max" (Gone)
1981 - 931 "Scarlet Harlot" (Gone)
1976 911S Targa (Gone) |
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John Brown
Joined: 07 Nov 2002
Posts: 903
Location: Leesburg VA
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| Posted: Wed Apr 30, 2008 10:19 pm Post subject: Re: DME relay getting hot while driving |
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| skytrooper wrote: | A friend of mine asked me about this as his '83 944 is having this problem. He has replaced the DME relay once due to this and asked me if I knew anything about it. Since I haven't a clue....I figured that someone here would more than likely have a possible answer
Thanks |
If a new relay is also running extra hot it can be as already answered something drawing excess current. However ...
It can also be corrosion at the relay socket and the connections on the back of the relay socket which are creating a 'high' resistance connection. The 'Eye squared R' (current x resistance = power) drop across that connection is the heat source. This is common with the VW type electrics and is a double whammy as the heat thus generated then goes to work on the inside of the relay and those connections are not overly robust to begin with either.
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82 |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Wed Apr 30, 2008 10:52 pm Post subject: |
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Might be time to get out the emory boards and needle file and go to work on that fuse block...
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erstwhile owner of just about every 924 variant ever made |
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!tom
Joined: 28 Aug 2006
Posts: 1941
Location: Victoria, BC Canada
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| Posted: Thu May 01, 2008 2:20 am Post subject: Re: DME relay getting hot while driving |
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| John Brown wrote: | | The 'Eye squared R' (current x resistance = power) drop across that connection is the heat source. |
Yes, and this is actually (current * current * resistance = power) -- remember it's I^2.
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78 924 NA
5-lug |
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John Brown
Joined: 07 Nov 2002
Posts: 903
Location: Leesburg VA
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| Posted: Thu May 01, 2008 2:59 am Post subject: Re: DME relay getting hot while driving |
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| !tom wrote: | | John Brown wrote: | | The 'Eye squared R' (current x resistance = power) drop across that connection is the heat source. |
Yes, and this is actually (current * current * resistance = power) -- remember it's I^2. |
Beg your pardon. I stand corrected. Electrical and electronic engineers, in my experience, would have understood with just 'eye squared r loss'. Next time I'll leave it at that.
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82 |
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gohim
Joined: 02 Nov 2002
Posts: 4459
Location: Rialto, CA
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| Posted: Thu May 01, 2008 4:25 am Post subject: |
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It should be noted that the fuel pump/DME relay, runs warm/hot to begin with. The problem is that it is difficult to quantify HOT, WARM, and OKAY. Everyone has a different threshold and opinion of what is hot or warm, so okay is impossible to judge.
Now, as far as I can tell. On my cars the fuel pump relay runs HOT. So hot that it is uncomfortable for me to grasp and continuously hold one. But they have run that way in my cars for years without ill effect. |
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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| Posted: Thu May 01, 2008 4:28 am Post subject: |
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Perhaps pop the cover off and look for obvious signs of overheating, like melted/discolored components?
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Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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