DME Swapping

89911 · 05-23-2003, 05:13 AM

I am trying to diagnose a potential problem with my dme. Which boxes can swap with a 89's? All 84-89's? 87-89's? And if I need a new one, which is the best source for these. I imagine these are rebuilt units. Thanks.

BGCarrera32 · 05-23-2003, 05:32 AM

I think 84-86 is the same pinout, and then it changed in 87, but I am not positive. Hopefully others will set it straight.

If you need a DME checked out, I've heard these guys mentioned a few times... www.programainc.com

What's going on with your car?

-BG

RickM · RickM's Garage

The link that BG has provided is an auto electronic component rebuild company. They have a very good reputation with the BMW crowd.

89911 · 05-23-2003, 05:47 AM

Quote:

Originally posted by BGCarrera32
I think 84-86 is the same pinout, and then it changed in 87, but I am not positive. Hopefully others will set it straight.

If you need a DME checked out, I've heard these guys mentioned a few times... www.programainc.com

What's going on with your car?

-BG

I wish I knew!!! This is the original problem and it is not with the MAF (They installed the stock intake and the problem is still there. Cuts out and floods when you attempt to acclerate from idle.)

Help me get my car out of the garage!

Jim Richards · 05-23-2003, 06:02 AM

Hey 89, I don't know if this is going to be an issue for you but I seem to remember hearing about bad grounds leading to damaged DME boxes. You might do a quick search on this. If my recollection is correct, swapping DMEs may lead to damaging another DME. Hopefully that's not the case here.

BGCarrera32 · 05-23-2003, 06:22 AM

Well, this could be *not* the problem, but I have had a similar situation here that I'll relay...

There are 2 sensors in your car that relate engine speed and crank position back to the ECU. Both are called impulse senders- one of them is the "speed sensor" labeled "DG" and the other is the reference sensor labeled "BG". Both of these sensors generate an AC voltage when the engine is turning. Their connections can be found on the same bracket as the head temp sensor. The speed sensor looks at the teeth on your flywheel and the ref sensor (which tells the engine where tdc is) looks at a small socket head cap screw fixed into the side of the flywheel. Both sensors are found at the bellhousing, drivers side-back side of the engine.

When the engine is cranking (and running for that matter) the speed sensor should be kicking out an AC voltage of around 2.5v.
The ref sensor is tough to check without and oscilliscope, but does put out I believe a 2.0v sine (this won't show up on even a Fluke digital meter, but the speed sensor will). There are 3 pins on the sensor connector, the top one is a shield and the bottom 2 pins should read around 1k ohms I think in a resistance check.

The speed sensor is *very* finicky about its placement in relation between its own face and the flywheel teeth. The spec is 0.8mm from the face of the sensor to the flywheel teeth. It is possible that the bracket holding the sensor in position is loose (you can pvot the bracket to adjust), or the insulation on the sensor is failing, or it is getting hairy when the sensor gets warm (it is located right near the exhaust crossover pipe). I swear mine passed all the tests and then gets goofy when it gets warm.

1st off, a Bentley manual will tell you that only the ref sensor is needed to start the car. Well, disconnect your speed sensor and try to start your car...you'll prove the manual wrong.

2nd, you might try finding an ecu pinout diagram, and hooking a digital AC meter inline with the two sensor connections to your speed sensor. Then drive around with it hooked up in real time (you'l have to improvise your connections), and see if the voltage drops or gets goofy when the car gets warm.

I don't know if this is all making sense, but take a look at this area. These sensors are some of the most reliable on the car I'm told, but they can fail. They are $125 a piece so it pays to check them carefully.

Arrow left is where .8mm gap should be (you can see mine is misadjusted) arrow right points to speed sensor. Either of these sensors going goofy *might* cause the problems you describe.

-BG

Tim Polzin · 05-23-2003, 06:46 AM

You should be able to test your DME by subsituting any 911 DME from year 84 to 89. If you use an earlier DME, you may need to re-adjust your idle bypass.

Tim

Lorenfb · 05-23-2003, 08:11 AM

Do didn't state a problem!

Check out this website for possible info.
Systemsc.com

Good luck
Lorenfb@aol.com

eion · 05-23-2003, 08:18 AM

Changes happened in '87, so you'll need one from an '87-'89. The DME you need depends on where the car came from, whether or not it's high compression, and on a couple of other options - M240, the "version for countries with inferior fuel", and M637, the "sport group". In other words, you need to check the one you've got at the moment. There is some crossover between Porsche part numbers, though:
911.618.111.18 and 911.618.111.19 are both Bosch 0 261 200 078
911.618.111.15 and 911.618.111.17 are both Bosch 0 261 200 084

Chances are that your DME will be either 911.618.111.20 (Bosch 0 261 200 082) - for normal US cars - or 911.618.111.16 (Bosch 0 261 200 085) - for US cars with the aforementioned sport group option.

The speed sensor and reference mark sensor both require an oscilloscope to test them - if you've got access to one, PM me and I'll find the info. There are a whole bunch of other 'possibles': I'd check the idle positioner and the throttle switch contacts first (given that the problem is when you're accelerating from idle), fuel pressure (you've tested the idle, but there're a couple of other conditions to test), and the engine temperature sensor (in that order). If you've got a scope then you should check the fuel injection timing, but if the timing *is* wonky, then that's just confirming what you already know.

Peter Kelly · 08:33 AM

If you have not yet checked the operation of the idle and WOT switches, do so now. Instructions are in Bently.

Check connections on coil, (plus all other connections especially grounds) Make sure the connectors for the speed and reference sensor are clean.

Next, if it were me, I would replace both the reference and speed sensors. It is next to impossible to eliinate these as the cause by trying to test them, so just put new ones in. they can be gotten for $ 80 each. Replacing these can be done with engine in car, but it is easiest if you remove the left rear shock... ask me how I know.

I have the same year car as you with many similar upgrades plus I have modified my motronic to make it PC-programmable.

Tim Polzin · 05-23-2003, 08:58 AM

Eion is right about the differences between boxes, but functionality between 911.618.111.05, 16 and 20 are all close enough use interchangeably for tests. Shoot, even a stock BMW box 0-261-200-059 will fire up a 84 to 89 Carrera.

Tim

Lorenfb · 05-23-2003, 11:34 AM

Call Programa in Florida. They have a tech support guy that can help.
Also, call Pelican Parts direct. They have a tech guy for these problems.

Good luck
Lorenfb@aol.com

BGCarrera32 · 05-23-2003, 12:10 PM

Peter Kelly check your Pelican mail...

Bill Verburg · Bill Verburg's Garage

This site has a breakdown of the various DME's

ATP Electronics

Lorenfb · 05-23-2003, 02:46 PM

Thanks for the good website (ATP) for DME's.

I just learned that Porsche made a 924 in 1988 & 89.

Anyone know where to find a good '89 924.

Lorenfb@aol.com

Tim Polzin · 05-23-2003, 05:01 PM

Here is another reference.

84-89 DME Chart

Peter Kelly · 05-27-2003, 05:09 AM

Hey 89911, any update on solving your problem?

ChrisBennet · ChrisBennet's Garage

If you aren't sure whether your DME is working, try your DME in another car. Your DME won't hurt anything, but your car could hurt the DME you are using for testing. Like Tim said, the '84 to 89 DME's are functionally about the same. The idle speed changed in '87 so it may hunt a bit at idle if you have a '87-89 DME in a '84-86 car (and visa versa) but other than that you can swap them for testing purposes.
-Chris