1975 280z Electrical Issue

[Barefootdan]

Alright, did some testing. Got through the manual you linked until step 6.b where i need to test the ECU. From there I got until test #2 - 3(a): #4 Injector Circuit. I have no volts to this (or any) of my injectors at the ECU. Going to my injector, I do see 12v at one pin, the other does not have power. I moved to the FSM. Drop resistors checked out. Main relay and fuel pump relay click when moved to ON and START. I moved to the injector test. "Check continuity between the two terminals. Continuity should exists. If not, injectors are faulty". Am I checking for continuity of the injector itself? I receive none across all 6 injectors. I then picked up a NOID light test kit. But these are not lighting up either. 

Misc tests:

NOID light showed no power when cranking. 

I have 12v at ECU pin 1, but not continuity from ECU pin 1 to (-) coil pack (jumper ran from (-) to inside the car to reach). 

Manually grounding the (-) pole of the coil results in no injector pulse.

Manually grounding injector pins from the ECU results in no injector pulse.

Confirmed i do get spark by pulling a plug and laying on valve cover. Strong and blue. Coil is new, plugs and wires as well.

Edited March 17, 2021 by Barefootdan

[Barefootdan]

After all this cranking I think my starter also went out 😞 I get spinning of the starter but not the engine. Going to swap it out in the mean time.

[Barefootdan]

@Zed HeadAnother update today. I was able to get continuity from the (-) coil pole to the ECU pin #1. Progress!

My next tackle is to why I am getting 12v at one pin of the injector, but not at the ECU pins for the injectors. This may also explain why the manual grounding of the (-) pole of the coil results in no injector pulse. It appears it is a straight shot from the connector to the ECU and I see no visible breaks. I may need to remove the sheathing. 

[Zed Head]

Are you testing with all of the injectors unplugged?  That would make sense then.  The ECU only grounds the voltage to activate the solenoid.  One pin is power, one pin is ground.  People often see voltage on both sides because the injectors are wired in parallel.  CO elucidated this in past posts.  So, on the ECU side, it's only a ground circuit when the ECU says it is.

Anyway, if all injectors are unplugged then seeing voltage on only one pin makes sense.  If you have continuity to Pin 1 now then you should get injector clicking every three sparks.

Any chance you can borrow an ECU?  Any ECU from 75 through 78 should work.

[Barefootdan]

Actually I am seeing power at 1 pin with only 1 injector unplugged. I'll need to go back and verify with all injectors unplugged what is happening.

Also, ran out to test a manual zap of the injectors with a 12v battery. No go either. Could faulty injectors kill the pathway between the 12V pin and the ECU as power needs to flow through the injector? I.E. a faulty injector not a stuck one.

[Zed Head]

Have you measured resistance through the injector circuits from the ECU connector?  Page 63 and on in the book.

You can test an individual injectors pretty easily just by putting a quick 12 volts across the pins.  I used to use an old injector plug to make the wires easier to get to.  You can also put the power through the pins at the ECU connector.  I smash a piece of solid copper wire down to a flat shape than I can stick in the connector then use alligator clips to apply power.  You should hear a distinct click each time.  Maybe your injectors are stuck.  How long has the car been sitting?

The resistance test will confirm the solenoid electrical path.  If that's good and they don't open with a quick 12 volt tap on the terminals, you might ry tapping them with a screwdriver or wrench.  I have unstuck injectors that way before.  Old dried up fuel will gum up the insides.

Edited March 18, 2021 by Zed Head

[Zed Head]

Last weird thing - there was a time when if the resistor fell out of the tachometer circuit on my car the ECU would not open the injectors.  I never really understood why since it's a branched circuit.  But it was real. The ECU seems sensitive to the quality of the pulse from the coil.

But measuring resistance and applying power through the circuit will at least confirm that the injectors should work.

[Barefootdan]

2 hours ago, Zed Head said:

Have you measured resistance through the injector circuits from the ECU connector?  Page 63 and on in the book.

I did, i have no voltage on any of the injector pins. 

2 hours ago, Zed Head said:

You can test an individual injectors pretty easily just by putting a quick 12 volts across the pins.  I used to use an old injector plug to make the wires easier to get to.  You can also put the power through the pins at the ECU connector.  I smash a piece of solid copper wire down to a flat shape than I can stick in the connector then use alligator clips to apply power.  You should hear a distinct click each time.  Maybe your injectors are stuck.  How long has the car been sitting?

I tested injector #6 so far (ran out of time) and had no clicks even after tapping the injector. I wouldn't be surprised if they are bad...registration shows it last in 1993!

2 hours ago, Zed Head said:

The resistance test will confirm the solenoid electrical path.  If that's good and they don't open with a quick 12 volt tap on the terminals, you might ry tapping them with a screwdriver or wrench.  I have unstuck injectors that way before.  Old dried up fuel will gum up the insides.

My big concern now is finding out why I am seeing power at 1 injector pin with only 1 injector unplugged and no power at any injector pins at the ecu harness. I will hop back out to the garage tonight. If I recall correctly, I had power at 1 pin, the other pin had power but I could see it dropping in my multimeter. Started at 12 and ends up at 0 after maybe 10 seconds?

[Zed Head]

4 minutes ago, Barefootdan said:

I did, i have no voltage on any of the injector pins. 

I was thinking of a different test, I said resistance, but that one still shows you something.  I was thinking of testing resistance through the EFI relay connection, or the dropping resistors, to the ECU connector.  You can see the circuit on the diagram, of how things are supposed to happen.  You'd have to get to the dropping resistors or the EFI relay.

I wonder if you have an EFI relay problem.  You might be measuring voltage of a very high resistance circuit.  The EFI relay is above the hood release lever in the cabin.  Two screws and it drops out.  The FSM has a procedure for testing the relay.  It's a fairly common failure point, my car came with an extra one becuase the one in it was failing.  You can take them apart and look inside if they don't work right.  Might have dirty contacts or a failing solenoid coil.  The EFI relay is combined with the fuel pump relay.  Silver box about 1 x 1 2 inches.  The pin numbers are stamped in to the board, you can barely see them but they are there.  It's the "RELAY' just under the battery in the schematic.

 

[Barefootdan]

2 minutes ago, Zed Head said:

I was thinking of a different test, I said resistance, but that one still shows you something.  I was thinking of testing resistance through the EFI relay connection, or the dropping resistors, to the ECU connector.

Ah! I will need to test this. I was following page 63 asking for battery voltage. I did test the dropping resistors yesterday. Unplugged them and tested the resistor directly. Spec for all 6 injectors was 6 ohms and I was hovering between 7 and 8 for all. I am using a cheapy multimeter though so I'd assume we are in a margin of error?

I'll redo the EFI relay test. Since I heard a click going to the START position (or rather felt it) I moved on. Looking at that diagram, it doesn't seem that the EFI relay would be the cause of no volts to the ecu though? Unless I am misunderstanding. I will say that the fuel pump does run when my AFM flap is moved and it looks to run through that relay.

[Barefootdan]

@Zed HeadRe-ran the EFI relay test. Clicked over at 12v and had continuity between the two test pins. 

I tested each injector, all failed the 9v battery test. Also, all failed the continuity test from page EF-57:

Continuity check <• "; 1. Disconnect ground cable from battery. 2. Disconnect, electric connectors from injectors. 3. Check continuity between the two. terminals. Continuity should exist. If not, injector(s) are faulty.

 

My thoughts now...Since all 6 injectors are bad (and they sure look the part with some nasty corrosion) and they are wired in a series(?) that the current is not able to flow through them to the ECU. The ECU then never has a chance to ground or fire them. This would explain my failed NOID light test. Thoughts?

[Zed Head]

I don't know about the NOID light test, that should be testing the harness and ECU, but the injector solenoid windings are exposed to the fuel so if moisture got in they could corrode and open.  

If you look at the schematic you can see that each injector is supplied with power through the dropping resistors.  Parallel circuits, so each should work independently.

You might check the circuit, continuity, from each injector plug to the ECU connector.  14, 15, 30, 31, 32, 33.  You might use the NOID lights in place of injectors to complete the circuit, for testing.

You're certainly making progress, but it seems like you have multiple issues.  Well done.  You'll find something and things will start working.  The EFI systems are all about check, check, check, check......