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Another stupid question, this time about DME relays


Another stupid question, this time about DME relays

Old 01-21-2019, 02:02 AM
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Default Another stupid question, this time about DME relays

I understand that it is prudent to keep a spare DME relay in the car. No fuel pump, no go.

Have any of you tried these?

Are they worth the premium? Is the one that "primes" the fuel pump for 3 seconds the one to get? For cold start situations, I can see an advantage. For hot starts, not so much.

AKA 968 Virgin
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Old 01-21-2019, 11:46 AM
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You could also keep a jumper wire, invest the money or pay down debt with what the spare relay would have cost.
The F9tech products are interesting but:
1 - In 20 years I have had zero problems with the 993 part number DME relays from reputable manufacturers
2 - We do not know how the F9tech products will last, until they have lasted

Also I think the pump prime is not desirable and possibly dangerous as I have read they do not really affect cranking time (and maybe a few cranks is better to circulate oil before firing) and that they can decide to "prime" unexpectedly. You might find them "priming" after a crash and feeding a fire. Cost extra, maybe dangerous, and no benefit. This is my opinion based on reading the experiences of others. I'm all for improvements and have fitted some updated, newer, better technology parts to most of my cars but not if the old part works fine, costs less, lasts the same, etc.
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Old 01-21-2019, 04:20 PM
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Iĺm running both of the F9T Solid-State Relays in my 944 / 968.
My 944 is VEMSed, so the Pump-Prime Relay was not needed. In VEMS I set up Fuel Pump On after Powerup 3.0s, Pump Off after inactivity 0.52s. This works fine. Cold start after long sitting seems to have improved.
My 968 got the F9T, Pump-Prime Relay, because of the well tried and tested VEMS setting. No issues so far. 08-31-2018 -->
And a further benefit, the huge difference in weight. ;-)

Stock vs. F9T solid-state relay
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Old 01-21-2019, 07:21 PM
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I bought and use an F9 relay. You can hear the pump priming very briefly when you turn the key.
I noticed little or no difference in starting immediacy when cold (It’s never had a problem starting), but I did notice that the car started more quickly when warm with the F9. I carry my old DME unit in my glovebox carefully wrapped and sealed just in case......
I like the unit, but as Joel said it might have been money I didn’t really need to spend.
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Old 01-28-2019, 09:29 AM
Nathan J.
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I have used the F9 relay for a year and a half now, and these are my comments / conclusions:

1) No difference in starting, it fired up with one second of cranking both before and after the switch in relays.
2) I like the priming of the fuel pump for the auditory feedback that the pump is actually on ( the sound is too faint to hear during engine cranking or engine running, so before cranking is the only time I can here it ).
3) The first unit I got did not work, but was told that it was probably damaged by ESD, and it was promptly replaced with a working unit, which has worked flawlessly ever since.
4) Like others here, I keep the mechanical unit in the glove-box as a spare.
5) Overall happy with the purchase, but as others have stated, maybe wasted money to solve a problem I did not really have??
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Old 01-28-2019, 08:33 PM
Daniel S
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I have used the F9 relay with the prime feature for about 2 years now. My comments echo Nathan's pretty much point by point. I do think that a solid state relay should be more reliable over the long term compared to a mechanical one which will wear out, but who knows. The one I replaced, which did die right after my 968 arrived (literally after it arrived, I pulled it into the garage and it would not start the next time I tried) was from 1993 and had a 993 part number on it, so I can only suspect that it was original or close to original.

As with all reviews, YMMV.
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