I am resurrecting a '74 2.0 with D-Jetronic FI with my mechanic buddy, and we have hit a block wall. The injectors won't fire, but we have spark, air, and fuel. We have installed a newly rebuilt MPS, new air pressure sensor, new head temp sensor, new injector seals, have good ground, replaced most fuel lines, blown out the remaining fuel lines, cleaned and blown out the injectors, reset fuel pressure to 35 psi, tested the injectors with 12 volts direct to the injectors to see if they activate (which they do), but they don't activate when we attempt to start. The engine does crank. Is my next step to test/repair/rebuild the ECU? Is there anything we are missing that we can do before sending out the ECU? I'm not the mechanic, so I hope the above makes sense. I figured the vast experience of the guys here might get us across the finish line to getting this car started. Thanks in advance for any advice you might have for us. Happy driving!

This one is going to be hard to troubleshoot over the Internet...

Can you get it to fire using some kind of spray (starter fluid, brake cleaner, etc). Reason I ask, there's two modes for firing the D-Jet.

The first is a wire from the starter solenoid circuit to the "ECU" (I chuckle when I type that) that tells the "ECU" (har de har) to fire the injectors.

The secomd mode is a signal from the tach/coil to the "ECU" (I kill myself) that the engine is running so it can fire the injectors.

A spray test will demonstrate the engine can run, if it gets fuel. Plus, if the RPM gets high enough using that method and it keeps running then that demonstrates the "ECU" (ok, I'll stop) is seeing the tach signal and firing the injectors.

If that works, then it implies a disconnect in the signal to the ECU* from the start circuit.

Good luck! - GA

*See? I told you I'd stop.

Greg has some good info here,

@JMTaxter

the last time i had this happen the issue was that the injectors were not firing due to a short in the relay board that is in the back engine compartment on the left side behind driver.

So also i ahve had a relay going bad once too but i would bet that your ECU is ok, but the board is getting a signal but its not getting to the ECU so the injectors wont fire.
there is a procedure to follow to sort thru the board and test the circuits, however, i did this and it tested with good continuity but when the board was in the car as i drove i think due to shifting and vibration then the contact was intermittent and sometimes then not run or start and eventually stranding me. SO now i carry a spare board and spare relays.

Sort thru the board, Jeff Bowlsby has instructions in a document on his website , a step by step to check it- or also get a newly rebuilt board. Have you looked at the board? the underside potting material will crack out and expose the tracers and joints and they will corrode.
the other issue is just corrosion or lack of contact by the pins or connectors on the board so clean all the contacts and pins and make sure they are all tight.

Good luck , i bet that if you look to this board you will find your issue.

Phil

The MPS is the air pressure sensor but you mentioned both. Are you talking about something else?

Did you confirm that the 3 pairs of ground wires at the top-rear of the engine case are connected to the 3 spade ground lug? Those are your injector grounds.

PS the injectors only need less than 3 volts to activate. 12V will burn them out.

Did you check trigger points?

I'm the poor soul that has to get this car running for my best friend JMTAXTER !
* all the grounds at the upper engine case are good
* removed the trigger points cleaned and lubed and plugged them back in while out of the distributor and operated them with key on, still no injector "click"
* tach wire to ECU is connected
* engine will fire when fuel is offered to the throttle body
I will check connection to starter starter connection, 12V to injectors as a momentary test will not burn out injector, continuous , YES

I'm the poor soul that has to get this car running for my best friend JMTAXTER !
* all the grounds at the upper engine case are good
* removed the trigger points cleaned and lubed and plugged them back in while out of the distributor and operated them with key on, still no injector "click"
* tach wire to ECU is connected
* engine will fire when fuel is offered to the throttle body
I will check connection to starter starter connection, 12V to the injector as a momentary test will not burn them out, continuous.... yes it will.

I guess it's the air temp sensor, not the air pressure sensor. 12V to injectors was only momentary. Ground is correct. Thanks, Jeff!

@jftrailoff1 - check the wiring schematic and verify the relay board in the engine compartment doesnt have a short , i am betting either it or a relay is bad- see my previous post- a short on the board will not allow the inejctors to fire- thats your smoking gun.....

Engine will fire with spray test but does not continue to run. Shuts down after a few seconds. We'll look for disconnect in signal to ECU from the start circuit. Thanks, GA!

Does the fuel pump run for about 5 seconds when the key is turned to the on position and then stop ‘whirring’? By “offered” do you mean squirting fuel directly in to the TB?

We'll work on that. Thanks, DrPhil914!

Yes, checked em. Will continue to check other stuff. Thanks, BeatNavy!

Yes, "offered" is squirted directly into the TB. Fuel pump is temporarily set up to run continuously with a bridge in the relay board.

You are welcome. When i first bought my car, i had similar issue, would run with spray of carb cleaner into throttle body, but found we had a dirty tank and bad fuel filter, once all that was cleaned out i found a failed MPS , as others also have suggested a bad MPS will not let it run but that usually defaults to a super rich issue not a zero fuel issue, and a bad CHT will not let it start either. So if the fuel flow is verified but no fuel flowing due to the injectors not triggered pretty sure its got to be that board or relay.

https://members.rennlist.com/pbanders/DJetParts.htm

The injectors fire off of the closing of the contacts in the dizzy. If they don't close, you won't have any injector turn on.

Also, do you have injectors firing as you open the throttle? The injectors fire as you open the throttle.

With key on but engine not running, rotate the throttle linkage. You should hear the injectors fire 20 times or so. If not, could be a TPS board issue.

The car will run without the TPS hooked up, so I'm not sure the TPS circuitry is a suspect for why the injectors won't fire.

I think it's: grounds, trigger points (not connected or way out of adjustment), ECU, or some other wiring harness fault.

Do read the link I posted above.
It’s the djet bible we all grew up with

You can find these at harbor freight. These will tell you if you’re getting power to the injectors.



Click to view attachment


Click to view attachment

If there isn’t any power going to the injectors you will need to check each device for power, TPS MPS TEMP I and TEMP II.

Check for power with a VOM at the relay plate, also check the relays for correct orientation, I’ve seen people tear their entire FI system apart because they installed the FI relays incorrectly.

I got nothin - removed what I wrote since it was said already......how come we cannot delete?

I just went through this....I believe it is the wiring harness so get started on checking that....brand new ones are spendy from Jeff Bosley but at this point I would say worth every penny and even though I patched my wiring harness up to run again I can wait to buy one of Jeff's....can't wait!!
gg

Update on JMTAXTERS 74 914 issue, I did the 24 test as outlined in the documentation and found no 12V to 16 and 24, did a quick jumper and WALA (SP) the engine fired up and ran ...and surprisingly well ! Bad relay plate !!

The bane of these cars' existence.

Glad you got it whipped!

Congradulations!
---Well, see Post #3 a few days ago... "Good luck , i bet that if you look to this board you will find your issue."

it just sounded too familiar, it literally stranded me on the road a couple years ago.
i now carry a spare board along with other parts, added to the travel bag, along with spare MPS, cables, etc etc. Its a great feeling to work thru the process and figure it out!.

Phil