D-Jet Fuel injection electricity path?

bobswei · bobswei's Garage

On our '74 2.0L, the car sat for a few months and now wont start. I traced it to the fuel injectors not squirting. So, I started tracing the wiring and found that I have, what I belueve, is 12 volts (pulsing), coming out of the dizzy (green wire) and nothing coming out of the 3 plug connector on the side of the dizzy (three white wires). I'm thinking my trigger point are the fault but uncertain if power would be coming from somewhere else or the pig tail needs to be plugged in (grounded) to have voltage?
Unless a wiring expert tells me otherwise, I will pull the dizzy out tomorrow and inspect the trigger points. Here's a photo of what I'm refering to.
Thanks for any suggestions.

930cabman · 11-25-2021, 02:38 PM

Looks like you are on the right track, keep us posted with your progress. It could be one connection. Try "Deoxit", it's a contact cleaner

Dave at Pelican Parts · Dave at Pelican Parts's Garage

The trigger points work by closing one side or the other to the middle contact. The middle is permanently grounded (through the ECU).

You can read through Brad Anders' thorough description of how D-jet works: https://members.rennlist.com/pbanders/

--DD

bowlsby · 11-26-2021, 06:35 AM

No squirtum?

Could be the trigger points, maybe not. The trigger points initiate the injection pulse, the sensors combined allow the ECU to determine when to end the pulse. No real voltage goes through the trigger points they are just an on-off circuit continuity switch.

Firstly, check that your injector grounds are attached at the top rear of the engine case.

bobswei · bobswei's Garage

OK, today I removed the dizzy and took it apart. Here are the triggers (not cleaned yet). I check continuity before and after cleaning and work perfectly. I also checked continuity on ground wires to rear of engine case, and sprayed electrical contact cleaner on them. Not the brand mentioned but I had it at home. Dave, I looked at the link you sent. Most of it looked like a word blender to me. But didn't see anything related to where the 12 volts comes from to run the ECU.
But, a new question. Could it be a "relay"? I have a relay missing that the car has never had. But, when I got the car, it didn't run. I got it running fairly well but got put aside for a few years before finishing the resto. So, can the car run without the relay for FI?
Thanks for the previous responses

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Yes, you need that relay to send power to the FI system.

As a temporary measure, you can swap the heater blower relay (the rear one on that relay board) or the defroster relay (the front one, if it is there) into the position for this relay and see if it works.

If those are also missing, you can even swap in a relay from the headlight motors up in the front trunk.

--DD

bobswei · bobswei's Garage

OK, it runs now. Yes Dave. I swapped the relay from the front connector and it started and kept running. Still runs rough, like in the past but that's fine for now. I'll deal with that later. I'm not sure if my memory is bad but, I drove this car into my portable garage, in the backyard about 3 months ago to do some work on another car. Never touched it till I installed a thermal time sensor (trying to make it run better), a few days ago and it wouldn't start unless I poured a little fuel in the intake. Then, ran for a second or two.
Well, the injectors are squirtin" again so one problem solved. Thanks again for all the responses.
Bob

djpateman · 11-27-2021, 03:10 PM

You may need to get the tool to adjust your trigger points:
914World.com - The largest online 914 community!

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Dave, how often do you find trigger points to be out of adjustment? They don't pass much current, unlike ignition points, so the only wear I can think of is the rubbing blocks. Or possibly the spring tension.

I've seen pics of the tool a number of times, and I haven't really worked out what wear it compensates for.

--DD

djpateman · 11-28-2021, 02:51 AM

It is the rubbing blocks that wear. Like the OP found out, without the relay you have nothing. Then without the trigger points there is no wave train for the computer to massage into shape with the help of the various sensors. If the dwell time of the signal from the trigger points is not correct, then the computer will never have a chance to provide the correct output.