where does the dme injector pulse come from?

[crustychief]

1984 3.2.
It appears as though everything is working as it should.
The DME energizes, fuel pump activates, idle controller hums, engine cranks normally and will run if fuel is added to the intake, spark happens but no fuel delivery from the injectors. CHT ohms out within specs. I am running out of ideas. Thanks in advance.

[steely]

Maybe the speed and/or reference sensors are kaput?
I think they're supposed to read 1000 Kohm.

[redx999]

Maybe the speed and/or reference sensors are kaput?
I think they're supposed to read 1000 Kohm.
________________________________________
+1 for Steely

But, mine have always had a resistance of 950-1000 Ohms (not 1000 Kohm).

-Redx999

[crustychief]

I will check those tonight. I am new to the DME stuff so there is a learning curve here. I did a search and it mentioned the CHT sensor. Does the DME use the CHT as a ground path for the injector pulses? Right now I am trying to pick my way through the Bentley in section 240. Thanks for the tip

[steely]

Originally Posted by redx999

But, mine have always had a resistance of 950-1000 Ohms (not 1000 Kohm).

-Redx999

-1 for Steely - I meant to say about 1Kohm.
I have to stop posting at night

I think if the ref sensor is bad, it just plain won't start.
Not sure about the speed sensor.
I think the DME will start with a bad CHT, but won't run well (too rich or lean).

If you can confirm the ref sensor is bad (and it could give an intermittent good reading), then you should consider replacing the speed sensor next to it. The insulation get exposed to heat and dries out, so if yours crumble just by your touch, that's another sign they're due. And look the the BMW flavor since they're compatible to Porsche (both Bosch) and less expensive.

[kidrock]

Crusty,

Have you checked fuel delivery from the pump? You say that the car will start when fuel is introduced into the intake, and that you have spark....that is a sure sign that your car is starved for fuel. You may want to disconnect one of the hoses from your fuel filter and put it in a coffee can or some other receptacle, and have someone turn the car over quickly to do a fuel check.

I had a similar problem once, and I jumpered the DME relay block and sure enough, the pump hummed away but alas, there was no fuel at the other end. I replaced the pump and that solved the problem.

[fastfredracing]

Easiest test for you to do right now would be to get a " noid light" , or just use a plain old 12v test light at the injector harness. You should have 12 v+ on one side of the connector, and the other side should "pulse ground as the car is cranking" this will tell you if you have a DME related issue.

[Joe Bob]

Usually , air, fuel, spark,,,

Tossing Quik Start down the throat would suggest a fuel issue,,,,,

But in light of abby normally stuff, a new fuel pump, and a working FI....

[crustychief]

There is fuel circulating through the fuel rails, I did the 9v battery "wake up" to two of the injectors and residual pressure allowed fuel to the cylinders I did that to.
fastfredracing, I thought you couldn't use a regular test light at the injectors? I do not have an LED test light ( noid ). I have 12V at both sides of the injectors. I will try the test light if it won't harm the system.

[crustychief]

speed sensor = 1034 Ohms. reference = 1104 Ohms....... still looking

[crustychief]

I made a noid light from some L.E.D.s I had laying around. I get one pulse at ignition on then nothing while cranking. Cycling the key several times without cranking then cranking gives me a brief start. Back to square "what inputs does the DME use to generate the pulse?" one. Is there anyone in the San Diego area with a spare DME to help me isolate this further? I do not have an oscilloscope or a breakout box so my troubleshooting is running into a box canyon pretty quickly.

[steely]

Originally Posted by crustychief

Back to square "what inputs does the DME use to generate the pulse?" one.

Hope this helps, just trying to answer the above question.

From Bentley, DME inputs are:
Air flow sensor (Pins 2 – 3 of the volume air flow sensor connector should read a varying resistance with change in position of the door flap, and +5v present at pin 3 to gnd.)
Intake Air temp sensor (IAT) pins 1 and 4 of the volume air flow sensor connector (1.4 to 3.6K ohm @ ambient temp)
CHT (1.4 to 3.6K ohm @ ambient temp)
Ref pos sensor (TDC) (~1K ohm)
Crankshaft speed (RPM) sensor (~1K)
Throttle position sensor
O2 sensor
Altitude correction sensor

hth

[rick-l]

If you have a spark all the sensors for the DME are working.

Time to find INGO.

If he dosen't find this thread look for member ischmitz Pelican Parts Technical BBS - View Profile: ischmitz

Edit: out of curiosity you haven't had a alternator regulator issue lately have you?

[Joe Bob]

Ingo.... 3.6@cox.net

He be the schizzle....

[crustychief]

Originally Posted by rick-l

If you have a spark all the sensors for the DME are working.

Time to find INGO.

If he dosen't find this thread look for member ischmitz Pelican Parts Technical BBS - View Profile: ischmitz

Edit: out of curiosity you haven't had a alternator regulator issue lately have you?

There hasn't been an alternator / regulator issue but there was a wiring issue. Maybe there still is a wiring issue.

Thanks for the help so far!

[steely]

just a shot - are these grounds connected?

[crustychief]

The grounds on the engine are connected, that was one of my original thoughts. I am going to pull the ECU connector and do some cold checks, maybe I missed something. This system is totally new to me. Thanks for the suggestion.

[ischmitz]

What others said is correct:

1. If you have spark and all that is missing is the fuel your sensors are good. Period.
2. The injectors need permanent +12V on one side and the pulse (GND) from the DME on the other and fuel pressure of course.

Here is what to check:

Check you have fuel pressure (pump running, no clogged fuel filter, fuel pressure regulator). Then, if the car sat for extended periods of time (several month) the fuel injectors could be stuck shut, tap them with a screwdriver handle to "wake'em up". Else, get an LED test light and check for injector pulses. At that point it is very likely there is none: your DME needs repair.

Regards,
Ingo

[crustychief]

Thanks Ingo, after checking all the inputs, verifying fuel at the rails, and hooking a led to the injectors and seeing no pulse I am thinking the DME needs looked at. I am sending a PM to you now.

[crustychief]

Bump for anyone with a spare DME in San Diego area?