Thanks SoCal!

Which pin is the IAT or VAT sensor connected ?
Or is the temp sensor the resistor that is connected to pin 1?

Hmmm, not sure if you combined the blow-up picture with the schematic, but it'll make more sense if you do. Electricity has to flow from point A to point B, so for every component, there's two wires. The air-temp sensor is hooked up to both #1 and #4 on the AFM connector. One side provides a reference voltage and one side is the return signal after it's gonne through the resistor. Internally in the DME, this is hooked up to a resistor-ladder/voltage-divider circuit to compare it.

Do someone know the spec for a replacement air temp sensor? Can I use a IAT sensor from example splitsecond(www.splitsec.com) ?

This is a section of the factory manuals. The wires going out the right go directly to the block symbolizing the DME. The block (rectangle) has pin numbers only. Most likely the DME Testing Plan booklet that the dealer sells will have the values for each pin.

Danno, the MegaSquirt'n'Spark has 12x12 tables, also MegaSquirt2 is out which has 12x12 suport also. Im still trying to figure out where to mount the wheel, a guy at a machine shop at work is going to make me a custom pulley because supercharger is using a 6 rib belt and stock is 4, Ill just need him to make me a small one for the alternator too. Im also considering putting a 72-2 wheel on cam where the distributer used to be, it would be easier to get to and to make a wheel for. Any way like I said I already have the MS system so Im gona use it and I like it a lot better the stock, why? because I know the schematic, I can retrofit anything I want to it, if any thing fails, I know how to fix it. Stock computer is ok, but I the freedom MSnS gives me blows the stock system away.

On the subject of the DME pinout, does anyone know what the signal should look like at pin 11?
This appears to be an input to the DME from the MPG gauge in the tach.

Thanks

What model and year.

Early '85 944.

Guess: A buffered injector pulse signal. FR would know for sure. If you are into reading schematics FR does have the schematic for the 911 DME's. Supposedly "almost" identical to the 944 DME's.

Well, it looks like it ties in to a chip in the dme that affects the spark. At least according to the 911 dme schematic. I'm wondering whether it's tied in with my weak spark issues. I've sent an email to FR.

Hmm, SoCal man, I just noticed how many posts you have, you must live on this forum :) hehe. Btw, can some one post a link to the schematics for the 911 DME, the link's on FR's page are broken....all though I guess I should inform him of that.....but if some one has them and doesnt mind emailing them to me at rdulgarov@hotmail.com that would be great. Thanks. Ohh umm I think Im under a falce presumption that 944 throttle body already has variable possition sensor? I haven't checked it yet but i looked at the connector and its a 3pin connector so I assumed it had a POT there. If not Ill need to look for another throttle body to use, and go with a larger one while im at it. Man all this "ill just get that later" is turning into "i'll need it now" hehe....later.

Wow! Over 5,000. Guess I should look at it once in a while.

As to the signal tying into the spark; this would not give a fuel usage value that can be used against the forward speed. So I don't think so.

Spark can be compromized via the reference sensor not being set right, bad ignition switch, bad HV cable between the coil and dist cap, worn rotor and cap, old sparking bolt wires (cracked and arcing to the engine or hood if a 944S or ends corroded inside the weather boots where they screw into the connectors), and last the carbon filled spark plug connectors.

In some cases the triggers (transistors) in the DME can be faulty or a bad connection somewhere between them and the coil.

Is the ignition on the engine stock? Coil and wires.

Barbie Twins?

FR Wilk,

Thank you Sir! Great page btw, I remember it from way back... :)

Gaah! You're right, SoCal. Pin 11 on the DME is an output; a square wave signal to the MPG gauge.
I'm off on another tack now.
There is a heavy braided ground cable running from the block to the firewall, and two brown ground wires from the dme to the block.
There are two bolts on the firewall, right in front of the blower fan. They hold brackets for some hoses, and run into a plastic enclosure. One of these measures isolated from ground, and I have the braided cable run to the other one. Is this the correct tie point for the engine ground?

Any point on the chassis is good as long as the connection is clean and the open braded cable is not crusty.

One thing you wana do with grounds is keep all of them comming to same point, otherwise if you have 2 grounds some distance away from each other the differences in resistance in between them can create a ground loop.

Thought only poorly designed landing gear caused ground loops???

There is a point here; if the ground between the engine and the chassis is bad to non existant the DME becomes the ground path and will burn the PCB traces like a wet bathroom heater.

OK, new question regarding my no-start issue.
Should the reference sensor trigger when the #1 cylinder is at TDC?
I'm turning over the engine with a breaker bar, and the reference sensor triggers when the rotor points to #4, or 180 degrees off.
I've verified that the rotor points to #1 when cylinder #1 is at TDC on its compression stroke.

Is it even possible that I got the flywheel in 180 degrees off? Is it possible to move the stud that triggers the sensor to another (pre-drilled) hole? Or do I need to grit my teeth, curse the gods of luck, and pull the engine back out?

Edit: Never mind. After thinking about it, I realized that the DME doesn't care which cylinder is firing, that's determined by the rotor position. And the sensor-triggering pin could point to either #1 or #4 TDC, depending how the cam is synced to the crank.

Do you have 1 sensor or 2? make sure you didnt accedently swapped them around if you have the old 2 sensor setup. Also it might just be bad, if you have a voltmeter with a friquency counter on it you might be able to see if there is a signal comming out of the sensors. If you need one I have one good one still left, or you can use bmw one like some one suggested earlier.