Took out the 914 and it just stopped cold during the drive. It appears the fuel pump is not running. I did tow it back and ran some rudimentary electrical tests (I'm not good at wiring). I get no power to the fuel pump. I then pulled the dme relay and I do get 12v on 30, 12v on 86, no voltage on 87 or 87b.

This is an 84 3.2l

thoughts?

The infamous dme relay. I was happily driving along last month when the engine simply stopped. Had a spare relay, swapped it in and off I went. I bought a solid state relay as a replacement, and have an OEM relay strapped to it as a spare.

Two things I did after towing home my 84 911
I bought two dme relays, one for the car, one for tge glove box.
Second thing is I built a three wire (wire but three wires together on one end) jumper with flat spade connectors on the ends.

Google the relay
Power comes in on one line, goes out to two lines.
This is my ultra spare, get me home thing.

Rich

Thanks all….looked up the relay pinouts and will try that bypass this evening.

+1 for the DME relay.

I always carry a spare with me. Well, not me, but the car.

DME relays have suckdilliuckucked since their invention. They were the evolution of the L-Jet double relay that was on the 914 and other VW cars.

After fixing lots of them over the years, on conversions I take the wiring out of the DME relay socket and put in sockets for two Bosch square relays. The bosch square relay is available at FLAPS, and are far cheaper than a DME relay. And way more reliable.

I did this on the 964 harness that I had in my 914-6 conversion. It works fine. The double relay is just two relays and one diode in a box. It gives the manufacturer a way to charge you more money for something simple.

Thanks Clay. Apparently more is actually more.

I read there are two sensors on the flywheel. One is the speed sensor for the ignition and the other turns the fuel pump off if the motor isn’t running. Mine were original so I replaced them both as well as the head sensor and idle control valve. I also moved the board in the air flow meter.

Timely post as I had the same thing happen last week, luckily a mile from home. Swapped using two separate DME relays so guessing the sensors may be bad.

both my 944's and my bmw 2,7 e28 crapped out with these relays...rubbish but can't say any were new ?.

For those of you that want to get rid of the problematic DME relay, here is how to do it.

This is the diagram for the DME relay in a 3.2 Carrera.

Click to view attachment


I took this diagram, and edited it to show the changes necessary to use two Bosch square relays.

Click to view attachment


You can see in a side by side view that the DME relay is just two Bosch relays linked together. The only addition is a diode, and that is just for voltage spike suppression.

Hope that helps someone in the future.

Why I stick with carbs... . No in all seriousness I am working on switching to EFI but the extra electrical makes me nervous.

Carbs never left me stranded, but the DME fuel injection is awesome. With a Steve Wong Chip and aftermarket cone air cleaner, it sounds and throttle response is similar to carbs, but better gas mileage, no cold start issues, clogged jets, etc. However I would purchase the bentley manual that matches your motor (3.2 or 3.6). The manual has a great troubleshooting section.

Ok, I jumpered 30 (always hot), to 87 and 87b and the fuel pump runs. Not sure if the car should start or not (it didn’t) but at least I know the fuel pump is good, the relay is bad. Ordering up 2 tonight.

Thanks Clay for the diagrams.

I’m not certain this proves that the relay is the problem. The DME relay only powers the fuel pump when the DME senses the engine rotating; you could still have a sensor issue.

I was testing if my fuel pump was any good (only 2 years old) and if the dme relay was passing on voltage.. The dme relay is original and probably should be replaced anyhow. I have the dme pinout so I have a feel for which ones are from the speed sensors….anybody know what I could test with my ohm meter while cranking at the sensor pins to see if they are working?

Would think if you could do the "Y" jumper wire trick and the fuel pump doesn't run, it's the pump or wiring to the pump. Can you supply power directly to the pump, see if it runs?

The Bentley manual has all the test points for the sensors as well as readings on the DME computer and info on how to test the fuel pressure. I also bought an aftermarket fuel pressure gauge. I connected it with a hose to the special port on the fuel rail to check the pressure on the fuel injection. You have to take out the metal ball when you test it. When I first installed my 3.2 it would not start and the fuel pressure was twice as high as it should of been. It was a pinched fuel line under the tank.

Root…when I did the Y jumper the fuel pump did run.

With DME, if the ECU sees the engine turning from the sensors, it turns on the ignition, the fuel injectors and the fuel pump. If you have spark, then It is probably the fuel pump side of the DME relay.

Plug the DME relay back in, and see if you have spark.

Finally got back to this. Found reference video on testing ohms and voltage. Reference sensor reads fine, speed sensor appears dead. I also get no tach bounce when cranking.

That is a common failure for the 3.2 911 engine. The sensor is not hard to replace, but you will have to do it from underneath.



I would also suggest that you replace both sensors. That way you don't have to go back next week to replace the other one.

You should be able to just pull the sensors out of the mount and replace them. The sensor gap should be OK after the replacement.

Otherwise you have to pull the transmission to set the sensor gap.

Good Luck!

Thanks Clay!

I had the speed sensor fail after engine swap from 2.5 to 2.7 944,danced around doing when it first ran real nice , long night so off to bed ,next day no start and no tach bounce so had a fair idea as I did have issues when the car had the 2.5,chucked in a spare and happy camper ran nice .
If one craps out the engine has no input on flywheel position or no input for when to fire so both need to be ok, shop around for these as the prices vary a lot .
Good luck .

Sorry 2 x post

Success! I replaced both reference sensors and it fired up immediately. Also got a new dme relay…old one still worked so I’ll use the old one as a spare. These were a pain to replace. One was frozen in (speed) so I had to remove the entire assembly and re-gap. Also tight on top to get everything unplugged, had to remove heater blower etc. in all, it took me about 8 hours from start to finish.

Just got back from a long spirited drive! Thanks all for your help!

Said the electrical engineer!