where does the dme injector pulse come from?

[ischmitz]

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

[crustychief]

I will try that, thanks!


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

[MarKoBrow]

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.

[steely]

Originally Posted by MarKoBrow

I repaired my computer by replacing this transistor and the diode that make up the injection driver circuit.

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

[MarKoBrow]

Originally Posted by steely

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.

[steely]

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.

[MarKoBrow]

Originally Posted by steely

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.

[crustychief]

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

[copbait73]

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.

[Lorenfb]

"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.

[rick-l]

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.

Alternative Fuel Injectors