Can I generate fuel injector signals? Do I have a bad DME?
 

I have a 1984 944 NA I received from my brother which has been sitting for six years in a garage. I’ve been scouring this site and other sites online for a couple of days now, and performed the following:

-I got past the dead battery and bad starter.
-It will start with starting fluid through the air intake and dies when the fluid runs out.
-I have fuel at the rail cap; about ½ liter cranking the engine for 15 seconds.
-I used the fuel from the fuel rail and sprayed it in the air intake, and it will run until the fuel is used up, so fuel is ok. I also added about 5 gals to the tank. I will change the fuel filter and screen after I get it running.
-I took off the fuel rail and injectors, and cleaned them up.
-I checked the resistance on the injectors and I get 2.4-2.6 ohms on each one.
-I checked voltages on the injector connectors, and I get 12 volts on both pins for each injector.
-I applied 12v to the injectors and I hear the clicking sound each time I do it.

-I checked the speed and reference sensors in accordance with:
-----Speed and Reference Sensors - Checking, Replacement, and Adjustment
-----I get the proper resistance readings on both sensors
-----I get varying voltages from the DME connector when cranking the engine over (from the sensors).
-----(I do not have an oscilloscope).
-----I did not adjust the sensor clearance.

In summary, fuel to the injectors is good, but the injectors are not receiving the grounding signal to open up. Is there a way for me to generate those signals?

I’m guessing the speed and reference sensors are good since the DME is receiving signals (but can’t verify the magnitude of the voltage). Is this a result of a bad DME? I do not have a source for a good DME without purchasing one.

Also, there is absolutely no tach bounce. Does the sensor go through the DME then to the tach? Could I have a bad tach and bad DME? Or could the sensor voltages be inadequate going to the DME? Is there a way to simulate the sensor signals to the DME?

Thanks in advance for your help.

Yes you can generate the signals by grounding the other wire (not +12) periodically since this is what the dme does to get signals. If you do it & get running it stiff tells you nothing but that the injectors work.

Did you use a noid light at the injector connector? If you get a consistent bright light at the injector you have good signal, but anything else you don't. You say you have varying voltages at the DME connector, do you mean the injector connectors? Make sure your DME grounds are intact and good, without a good ground at the DME you wont have a way to ground the injectors properly.
You will want to check AC voltage at the reference sensors. If you have it you have processor problems.

Dave

Dave, I don't have a noid light, but I'm almost certain the injectors are working, so that's why I want to replicate the grounding signals to verify.

The varying voltages are at the DME connector coming between pins 8 and 27 for the speed sensor, and pins 25 and 26 for the reference sensor. I don't have an oscilloscope to check the waveforms.

I'll check the DME ground.
Thanks,
Joe

Does it matter which wire, because they both get 12v?

Joe, a noid light does NOT check injectors, it tells you if you have a good signal to the injectors. Having 12 volts at both sides of the injector tells you nothing about the DME because you don't know if the DME is ever grounding the injectors, or if the ground is good. You don't need a scope to measure voltage at the reference sensors, you can measure AC voltage with a DVOM that has a hold function. make sure to measure AC voltage, not DC. Harbor freight sells a cheap noid light set, they are a big help, or you can wire up a 12V light bulb with 2 wires.
Honestly if your grounds are good, then an educated guess is a DME, but to be sure you need to do what I stated above, and to be absolutely certain get a waveform from the reference sensors also.

Yes it matters, you want the wire that gets constant 12v. should be a fused circuit independant of the DME.

Dave, I understood what the noid light does, but I ruled out bad injectors because I got good resistances, and I can hear the clicking when applying a voltage to the injectors. Assuming good injectors and ok fuel, I figured the injectors were not getting the grounding signal from the DME, and a noid light would just confirm that. I will use a 12v light bulb to confirm the DME is not sending a signal though.

I just don’t know if the DME is not sending the grounding signals because the DME is bad, or if it is not getting the signals from the speed and reference sensors. I am measuring AC voltage, but I do not have a hold function. I did check for ground at the DME, and it is grounded.

Are there any other signals the DME is looking for besides the speed and reference signal before it sends the ground signal to the DME? I’m thinking a bad DME as well, but I’m just trying to rule everything else out before I fork out a chunk of change since I don’t have a DME to borrow.

Thanks again for your help.

I will get some service info tomorrow at work, and will be able to tell you what else could be in the circuit. If the DME relay is good and your grounds are good, you should be ok. If you have a dvom at all check the ac voltage at the sensors. you should have voltage, doesn't matter right now what that is. I'll PM you my number , give me a call tomorrow, Im on central time.

Dave

Dave, I was about to call you while I was at the car today, but the conditions have taken some steps backwards.

Now, I am not getting any spark at all. I'll go through the troubleshooting steps to figure it out. It used to run with the starting fluid, but not anymore.

I used a light bulb at the fuel injector connector, and there is no light when cranking. I still get 12v at each pin (the light works between each pin and ground).

Just to see if anything else got worse, I checked, and there's still fuel at the rail.

"Are there any other signals the DME is looking for besides the speed and reference signal before it sends the ground signal to the DME? I’m thinking a bad DME as well, but I’m just trying to rule everything else out before I fork out a chunk of change since I don’t have a DME to borrow."

Do you know someone in your area with another early 944? If so, plug your DME into that car. I had a somewhat similar problem, went through all the checks and still no start...the only spark I could get was from the initial charge when the key was turn to the start position. I plugged my dme into a friends car and found it to be dead, exibited the same problem in his car...initial spark when the coil energized, but no spark when cranking.

Darn, still can figure out how to quote just a portion of someones else's post. :(

Ignition System Troubleshooting
 

Unfortunately no for know someone else with a 944 . . . for partial quotes, just delete stuff you don't want, but nothing in between the two sets of brackets

a few questions from running the Ignition System Troubleshooting
----- Ignition System Troubleshooting
-----I get a weak, weak spark during the coil test when grounding the negative
-----I get all the voltages I'm supposed to where it says I should
-----I get good resistances as it says
-----Doing it another time, I forgot to take the green wire off the negative terminal, and the spark plug got really good spark, and did it again with out the green wire, and weak spark. Resistances were still good. Did I mess anything up?

If the results of the resistance checks are good, does that mean it's definitely a good coil, or it should be good?

Pins 18 and 35 of the DME plug are supposed to be for ground. Should those have a good ground when the plug is disconnected or only when connected? The case ground is good.

why not unbolt the fuel rail and slide some paper under it, crank it over a couple times and look at the paper afterwards. if they sprayed then itll be obvious if not then you have bad signals and need to check wiring/dme.

Thanks, but I'm actually past the injectors not getting signals, and I was trying to determine if it was bad sensors or DME, but got sidetracked by now not getting spark as well. I'm waiting for parts to come in which will hopefully give me spark.

Update
 

So, I decided to throw a bunch of parts at the car.

I ordered the tune-up pack and vacuum tubing kit from Lindsey Racing, and I received a used set of sensors, and a DME off of ebay.

Just by ordering the tune-up kit, I have spark back, lol.

I've installed the other set of sensors, and the DME, and still exhibit all the same symptoms.

I disconnected the wiring for all the injectors, and connected each injector to ground and 12v through a momentary switch to open up the injectors manually. The car will run, and I can keep it idling by depressing the switch to open the injectors.

I've tried switching the connectors for the sensors to see if I had them backwards, but the car won't even spark if they're flip-flopped. Actually, I think when I lost spark, it was because I switched it a few times and left it on the wrong ones. I've tried the different combinations with the used and old sensors and DMEs, but none of it works.

By manually opening up the injectors and running the car, it tells me fuel pump, fuel/dme relay and fuel pressure is good.

The issue is the injectors are not getting the grounding signal from the DME to open up. The difficulty I'm having is determining what's not getting processed to deliver the appropriate signals.

Also, I am getting absolutely no tach bounce, so I'm going to attempt to bench test the tach when I get a chance to trace the wires.

Wow, somewhere I read pins 18 an 35 are for ground which is why I asked my question on post #13.

According to FR Wilks, pin 18 and 35 is 12v coming from the relay.
http://www.the944.com/connector.htm

I have a couple of things to check.