DME relay - No can jump.

[A horse with no name]

Where I am at the moment...

I have 13 V on the #30 female pin of the DME. I have tried both; the one I took off and the new spare that I have. (both covers are of). I can get the pump to run if I manually hold the points for the pump, but I cannot get it to run when jumping #87 -#87b and #30.

When grounding #20 on the harness the fuel pump should run but it doesn't.

There is 12+ volts at#18 on the ECU harness, but not on#35 as stated in Bentley's.

At the speed sensor harness there is .9877 ohms ( should be from .6 - 1.6 ohms )
When testing the ohms on pins #8 and 27 on the harness, the reading is the same, so the new speed sensor is working.

When I manually let the fuel pump run, there was no smell of gas anywhere. When I loosened the fuel plug on the left injection rail there was pressure.

Any idea's?...

[ischmitz]

Let's try to get some clarifications on record here:

DME: Is the large box with silver metal cover under the driver's seat and is also called ECU or control module or similar. It is the electronic brain that "listens" to the sensors and delivers fuel and spark signals.

DME relay: is the black small box. It's a double-stage relay (or two relays with some common connections) that serves two purposes.

DME relay stage 1 is where a portion of Term#15 is controlled. This is the branch that is powered when the ignition is in RUN or START. This stage turns on and then powers the injectors and the ICV and the DME itself when you turn the key. It also provides power to the positive side of the coil of relay's 2nd stage.

DME relay stage 2 of the DME relay could also be called fuel pump relay since it serves exactly that function. It is controlled by the DME and when it is turned on it powers the fuel pump and the O2 sensor heater.

Term#30 on the DME relay socket is a direct connection to the battery positive terminal without fuse. So this should always be +12V.

Pin 20 of the DME harness needs turn the 2nd stage of the DME relay on only when the key is in RUN position. If that doesn't work the DME relay or the harness is damaged or the ignition switch isn't working. Could also be an alarm issue if equipped.

Pin 18 and pin 35 are connected internally inside the DME harness. The wires are spliced together inside. If you are absolutely sure you have counted the pins correctly this would suggest the DME harness is damaged. A very unlikely but not impossible scenario.

The resistance readings are 800 - 1600 Ohm or 0.8 - 1.6kOhm. Same difference but let's keep the units correct if someone else reads this in the future.

Let me ask you this: When you turn the key to RUN you should see (if the cover is off) and hear the DME relay click. This is the first stage turning on. At the same time you should confirm that the ICV on the back on the engine is vibrating. That tells you that the DME is getting power and the first stage of the DME relay is working. If not check the ignition switch or any factory-alarm or after-market alarm unit.

And last but not least why are you starting this new thread instead of continuing the previous version here input needed for no start. Maybe more efficient to keep everything in the same.

Good luck,
Ingo

[A horse with no name]

Hi ...I just read your post on my new thread.

I understand what who are stating in how the replay works in conjunction with the ECU aka DME. Thanks for the info. For clarification, there is no power on #35. I should then open up the wiring harness that enters the 'box' - Correct?

Should I delete this info and move it over to the original thread? Thanks!

[A horse with no name]

No, there is no ' click' at the relay when I turn the key on. I have the covers off both of the DME's and the points do not move. I also took the ICV off and cleaned it with carb cleaner. It did rattle when I shook it before I did so. It appears though to rattle a little easier now. I assume that there is no vibration due to having no power.

BTW, the alarm was disconnected many years ago and the ignition switch is about two years old. There are no other aftermarket items running off of the ignition switch. I do have an aftermarket amp which runs through original the radio head. I use my iphone for my tunes and it is plugged directly into the amp. I do have a separate on-off switch for the amp which is for the iPhone.

Again, any thoughts on why the DME relay won't work when jumped?

In the morning I'll open up the harness to the ECU to see if a wire is broken or whatever. Would you happen to no the colour of the wires for both #35 and #20? On the ECU that I have, #35 is the last pin.

[A horse with no name]

input needed for no start

Sorry for the double thread.

Thanks!

[Lake Guy]

Hello Horse, wish I could help you out with this but I've never had to trouble shoot any electrical issues yet. I'm sure my time will come. Good luck with this one. Come on Pelicans, I'm sure someone has some helpful info on this issue so please jump in and help out.

[T77911S]

you really cant say more than what ingo said.

I hope he copies and saves his comment. it will reduce his typing in the future

[86 911 Targa]

Do you have the factory alarm?

[86 911 Targa]

^^^^^
DME test harness

Good luck,

Gerry

[A horse with no name]

Thanks guys for the great info...

I have, unfortunately an older thread on this- about 4 days ago. I'll repost the info here so as to let you know where i am at. Thanks.

1 Post:

Update...When grounding #20 on the harness the fuel pump should run but it doesn't.

There is though 12+ volts at #1 on the ECU harness. No power on any other pins.

At the speed sensor harness there is .9877 ohms ( should be from .600 - 1.600 ohms )
On pins #8 and 27, on the harness, the reading is the same so the new speed sensor is working.

When I manually let the fuel pump run, there was no smell of gas anywhere. When I loosened the fuel plug on the left injection rail there was pressure.
______________

[A horse with no name]

2. Post

Unfortunately I still have no power on pin #86 on the relay. From what I understand is that pin #86 on the relay is controlled by the alarm unit which is output pin 87a.

Just making an edit.. re 87b being part of the alarm. I have read that it is the black wire that connects directly to bus 15 at the unfused side of the turn signal/back up light fuse. In the 'Run' position it has 12 V.

Now 'IF' the relay has a malfunctioning factory alarm, how do I check to see if is 'malfunctioning?

There is still no power on fuse #7 but there is 12 V on #8...I understand that these two are the 'Run + Start' positions which is also #15 on the ignition switch...Is this correct?

What is new, is that by jumping #30 and #86 it will power the fuel pump. #86 is a thicker red wire with a green stripe. On the fuse block it is #7.... I ran a continuity test on it and was OK.
Why I cannot get power to the 'cornerstone pin' - # 86 continues to evade me.


Question: How can I check if the fault is in the ignition switch? I said that it was two years old but I see that it is now four years old, but with very few starts, relative to a daily driver.

The switch or the alarm seems to be the only things that I can narrow it down to.

Input please...Thanks

[A horse with no name]

I have had some great help from '86 911 Targa' this afternoon!

He not only sent me 'many pages' from his OEM Porsche Electrical manual, but he also guided me through numerous tests. I still have a 'no start', but at the moment, at least the alarm is now correctly disconnected with the proper jumpers. I'll keep on trying to resolve it...Whatever it is, it continues to be very elusive.

I plan on taking the electrical section of the ignition switch off to see whats happing within. At the moment, the current 'run' position, does power everything that I know of.

The first 'turn' powers pin #86 on the relay which is the cornerstone of everything else to turn on and off in the DME relay.

Has anyone ever had only 'one position' fail on their ignition switch?: