DME relay, easy fix?

[Alex599]

Hi guys,

I just tested a spare DME I received with the car when I bought it. It failed. Now, I fixed my fog light relay quite easily a few months ago. It was a connection clearance issue, fairly easy fix. I thought I'd check with my fellow Pelicans before I drop $100 on a new one. Is there an easy fix? What should I be looking for?

Thanks,

Alex

[JackkTheMackk]

http://www.ftech9.com/new-products/911-ss

Purchase that DME relay. I have one of theirs in my 944 turbo with the pump prime. SSD relay will last forever.

[Lyle O]

Originally Posted by JackkTheMackk

http://www.ftech9.com/new-products/911-ss

Purchase that DME relay. I have one of theirs in my 944 turbo with the pump prime. SSD relay will last forever.

^^^^Same for me...works great in my '87 911. I love the pump-prime feature.

[MrBonus]

Originally Posted by JackkTheMackk

http://www.ftech9.com/new-products/911-ss

Purchase that DME relay. I have one of theirs in my 944 turbo with the pump prime. SSD relay will last forever.

Do you mean this one?

911 Solid-State Relay (Pump-Prime) — Focus 9 Technology, LLC

[SpyderMike]

it was an easy fix for me - bad solder joints. I reflowed them and it came back to life.

[86 911 Targa]

Originally Posted by SpyderMike

it was an easy fix for me - bad solder joints. I reflowed them and it came back to life.

^^^^^
The very usual suspect......

Gerry

[adias]

Originally Posted by JackkTheMackk

http://www.ftech9.com/new-products/911-ss

Purchase that DME relay. I have one of theirs in my 944 turbo with the pump prime. SSD relay will last forever.

That is interesting I have 2 questions though: How long does the fuel pump run when the ignition is turned on? Can the ignition be on for a while without burning the fuel pump?

[Alex599]

Thanks all,

I'll definitely go the ftech9 route if I can't fix mine. In the picture below, should the solder be bridged at the pen tip?

Thanks,

Alex

[SpyderMike]

Buzz that sucker out - pretty much it is two relays. Find that open. Here is a nice thread on the workings of the dual relay unit.

https://dorkiphus.net/porsche/showthread.php?t=16859

and yes, I believe that is bridged. Flip it over and look at the width of the metal landing there...

[SpyderMike]

by the way, this contact looks suspect (could be the photo though). I would reflow all solder joints and see how it works.

[JackkTheMackk]

Originally Posted by adias

That is interesting I have 2 questions though: How long does the fuel pump run when the ignition is turned on? Can the ignition be on for a while without burning the fuel pump?

The prime only runs the pump for three seconds and then shuts off. It will not burn your pump up.

[adias]

Originally Posted by JackkTheMackk

The prime only runs the pump for three seconds and then shuts off. It will not burn your pump up.

That is good but follow-up question: if for some reason, while doing car maintenance, the ignition is turned on and off several times, minutes apart is there any chance that pump priming will stress something?

[gtc]

Originally Posted by adias

That is good but follow-up question: if for some reason, while doing car maintenance, the ignition is turned on and off several times, minutes apart is there any chance that pump priming will stress something?

No

[adias]

Great! Thanks for posting the link to the FTech9 device, and the pump primer in particular.

[Jack Stands]

Would it make sense to fuse the power to the DME? Supposedly Porsche does not have the power to the DME fused.

[86 911 Targa]

Originally Posted by Jack Stands

Would it make sense to fuse the power to the DME? Supposedly Porsche does not have the power to the DME fused.

According to my 1986 3.2 factory manual, the DME relay is not fused.

Don't know why?

Gerry

[DanielDudley]

It's a primary wire from the battery. It would have a fusible link if it was in a modern car. The fuel pump wire goes from the DME relay to the fuse box, and from there to the fuel pump.

I fixed my old DME, and then replaced it with the solid state unit. Because I can always hear the fuel pump run before I start the car, I know that both the relay and the pump are working. I like that.

Also, since it is considered a pretty good idea to have a spare relay, I use the old relay as my spare.

[MrBonus]

I just ordered one of the prime-pump relays. I've never had the DME relay fail but I have noticed that it takes a few seconds of the engine turning over to fire up the engine and I'm wondering if this will reduce the strain on the starter.

[SpyderMike]

I have read that the circuit needs to see a certain minimum rpm of the engine before turning on the fuel pump relay (I have read 200)...could be why you have to crank for a bit to get it started. The idea being they didn't want the fuel pump running without the engine running.

[86 911 Targa]

Originally Posted by SpyderMike

I have read that the circuit needs to see a certain minimum rpm of the engine before turning on the fuel pump relay (I have read 200)...could be why you have to crank for a bit to get it started. The idea being they didn't want the fuel pump running without the engine running.

^^^^^
Thus, the reason for the flywheel sensors....

Gerry