where does the dme injector pulse come from?
 

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.

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

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

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

-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.

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.

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.

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....

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.

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

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.

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

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?

Ingo.... 3.6@cox.net

He be the schizzle....

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!

just a shot - are these grounds connected?
http://forums.pelicanparts.com/uploa...1307210289.jpg

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.

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

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.

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

I resonded to your PM. To be sure it really is the DME you try both sides of the injector pin against +12V with the LED test light. If both sides do not produce a pulse you have a bad DME most likely.

The reason I am mentioning that is that you could have a bad harness where the other side of the injector pin doesn't have the +12V. In that case the LED test light connected to both pins on the injector connector would not produce a pulse.

Cheers,
Ingo

I will try that, thanks!


Another bump for someone in San Diego with a DME to swap for a verification?

The arrows point to the injector driver circuit, I repaired my computer by replacing this transistor and the diode that make up the injection driver circuit.

10. D1 - OF622 diode that's part of the injector driver circuit.

11. T404 - RBDT93 NPN Transistor that's part of the injector driver circuit.
http://forums.pelicanparts.com/uploa...1307273690.jpg

care to share the failure mode?
So the 0127IC was ok?

Hey Steely, I am not sure what you mean by failure mode, I will assume you are referring to how I knew it was broke? I used a led test light to determine I wasn't get a pulse from the DME, then I asked an EE that works for me what he thought was wrong based on a schematic that I had, He then suggested the two parts I pointed out. I wish I had a better answer for you.

Thanks fine, thanks. I'm an EE myself, and was curious. I pick up a very little bit here and there about the DME and this helps. I got distracted by the IC involved (I don't recognize it), and now see all injectors are turned on thru that single path you identified. They probably get warm / hence the heat sink (and propensity for apparent failure).

Sorry to hi-jack.

There was no hi-jacking here? I at times wish I understood more about electronics than I do now. I am sure the originator of this thread appreciates all input.

I do appreciate all input.
A couple of days ago I knew absolutely nothing about the DME. Today I probably know more about it than 70% of the people on the board. When I retired from the Navy I didn't think I would be called upon to troubleshoot another electronic circuit as long as I lived. After 20 years of doing just that, I have developed a pretty decent ability to troubleshoot. After checking all inputs at the plug, and the outputs that could be checked with my limited test equipment, I spoke with Ingo this morning, the "lightbulb" came on and I am confident the DME is bad. I will start another thread to find a local loner as people probably pass this thread up due to the title. Thank you for all your help everyone, I will revive the thread as soon as the issue is resolved. Thanks again.
Regards,
Sandy

Been there, done all those things. My 3.2 ran fine in my '73. I swapped it into my son's '71. No light. Quized the active old school air-cooled mechanics, bought all the probable/suspect sensors. No light.

Went back to basics. Checked the grounds on the sensors from the connector plug back. Found a broken ground wire at the plug. These old engines have hardened copper. Give it a try.

I feel for you. Makes one want a set of PMOs but this engine is really kicking ass now. Any time, just reach in the drivers window and twist the key. Instant start and idle. Try that with carbs. Daurghty cams, bored TB, Steve Wong Chip, custom header exhaust.

"10. D1 - OF622 diode that's part of the injector driver circuit.

11. T404 - RBDT93 NPN Transistor that's part of the injector driver circuit."

Actually, both those parts rarely if ever fail. They're just part of a 'clamp'
and don't dissipate much power.

This is from a long time ago. Do you think this is how the injector circuit works? Current is sensed by R409 until peak is reached and steered around as follows while it pulses.

http://forums.pelicanparts.com/3868545-post194.html