1978 280Z EFI Injector wires receiving no power

[Lenbo211]

Hi All, 

I'm brand new to this club/forum, but have found a lot of value in it over the last few months.

My dad, son and I started a project car a few months ago. It is a car we bought from a kid who took it apart and couldn't figure out how to put it back together. I think we're 99% of the way getting it back together and running, but we're struggling with an EFI issue.  This is a very long post, but hopefully that helps rule out some of the initial suggestions guys have and drill into the real issue quick.

 

Just to answer the standard questions:

We have fuel to the rail and can hear the fuel pump running.  

We have verified spark.

We have tested pin 1 on the ECU connector and verified there is a pulse coming from the coil.

While turning over, there is no motion of the tach. (Not sure if that is normal prior to engine start or an indicator of an issue.)

When we spray a little carb cleaner into the air intake, the car tries to run for a second and then dies.

 

When I tested the injector connectors with a standard test light connected to ground there is no signal/light.  I tried with a Noid light as well and no signal/light while in run position on ignition or while turning over.

 

We did the checks for "Engine will not start" on page 22 of the FSM EF section.

The only one that didn't pass continuity was 1-(5), Water Temp Sensor. The others were all at .000 except for AFM which showed the following results:

6-8 = .182

7-8 = .194

8-9 = .102

I'm ordering a new Water Temp Sensor, but I have a hard time believing that would keep the injectors from getting a signal.

I have already replaced the EFI Main Control Relay with a NOS I found.  The original one burned out the Fuse Link wire instantly when we connected power. When I connected the new one (Part number 2523079903 in exchange for the original 2523089970, All of the exchange part numbers I could find said that was the correct one.)

 

What I'm stumped on is when we did the checks on page 25 "Continuity check using Voltmeter" Check 2-(1) and 2-(2) were fine but every check under 2-(3) failed. So zero results on cylinder 1-6.

Any suggestions on what might be causing this?

 

A few forum threads have mentioned the wiring to the alternator could be an issue or possible the oil pressure sensor or wiring could be an issue. It sounds like the Fuel Pump Control relay relies on these.

I'd like to check both of those, but I'm struggling finding the proper test procedure for those in the FSM. (and to be honest, am not sure I need to because the fuel pump is running, but I'll try anything at this point.) Any suggestions where I can find those tests in the FSM?

I'm going to replace the oil pressure sensor just to make sure. I took the alternator in and it is charging, but maybe it isn’t communicating with things correctly even though it is charging?

 

I didn't check the fuel pump relay or fuel pump control relay because I can hear it running and we have pressure to the rail. That's next on my list tomorrow though because I can't tell from the wiring diagram on page 24 if where pin 73 on the EFI relay goes to the fuel pump control relay pins 95 & 97 could be keeping the EFI relay from sending a signal to the Drop Resistor and main harness to send power and signal to cylinders 1-6.

 

A couple other things we've done:

We did an ohm check on the drop resistors as directed in page 34 and it came back fine.

We did a ohm check on the line between pins 43/1 &43/2 on the Drop Resistor and pin 43 <73 edit> on the EFI main relay and it came back fine.  But when we checked for voltage on the drop resistor side of that line there was no signal. Not sure if that is normal though with the Drop Resistor disconnected.

<Edit, As I was looking at the diagram, I may not have put the correct number in the sentence above. I thought I tested the 43 pin on the plug for continuity to 43/1 &43/2 on the Drop Resistor, but I believe I actually tested 73.  Sometimes it's hard to tell which pin in the FSM I'm testing.  If you look at the plug, with the green wire on top middle, I tested continuity from the bottom right plug to 43/1 &43/2 on the Drop Resistor. I need to verify this tomorrow because I don't see how continuity could happen the way I'm remembering testing the plugs in my mind.>

Not sure it matters, but figured I’d notify just in case.  This car is a ’78, but the dash came out of a ’76. The kid had damaged the dash so bad I used a mostly assembled dash from the ‘76. Someone on another forum thread mentioned the tach could be causing an issue for another guy’s EFI problems, but he was getting power to his injector connectors, so I’m less convinced that is an issue for me.

Thanks for any help

 

Edited February 10, 2020 by Lenbo211

[Zed Head]

CO knows the 78 system better than most.  @Captain Obvious  But I would doublecheck both of the fusible links that supply the EFI relay.  That tachometer problem could be many things.  But with the key on you should definitely see battery voltage at the injector connectors.  The system works by grounding that power.  So, no power, no injection.

I like to work from wiring diagrams myself.  You can see that power to the ECU and power to the injectors each has their own fusible link.  They would be the green ones connected directly to the battery positive.  Not in the fusible link block, but separate, hanging, sort of, by the battery.  With a plastic connector that often gets connected backwardly to the negative connector which is identical.  Nissan faux pas...

 

[Lenbo211]

Thanks for the thought on the Fuse Link.  I forgot to mention that I tested those. They are all new and I have power at both sides.

Something else I forgot to mention is that the plug going into the EFI Control relay are all hot across the top and when the ignition is on and/or the engine is turning over the 73 plug is hot, but the other two are not.

[Zed Head]

Looking at the diagram you can see that if there's power on both sides of the fusible link then there should be power on at least one side of the EFI relay.

You can also see that the ignition relay actuates the EFI relay.  Check that power source.

That's the basics of troubleshooting with a meter and a diagram.  Power here?...check...power here?...check...

Might be that the 76 dash transplant brought some 76 wiring with it.  Who knows....

[Lenbo211]

@Zed Head Finally figured it out after 3 days of continuity testing.  The new relay EFI relay I bought was bad.  Was able to figure out how to test it on page EF-33 and identified the problem.  Thankfully the guy on ebay that sells it warrantied it as well and sent me another.

Now I'm dealing with water, fuel gauge and oil pressure gauge aren't working.  As I read through the FSM, it appears that these are symptoms of the Ignition Relay being bad, but for the life of me I can't find anywhere in the FSM instructions on how to test it.  Only thing I can find is the suggestion on BE 43 to test the Ignition relay is check turn signals. Any other suggestions on how to test it?

 

[Zed Head]

I would go to the diagram.  Identify the pins that power the solenoid coils and the pins that are the circuit being made and broken.  Go from there.  The Ignition Relay doesn't have that many pins to figure out.

I found one on EE-5.  You might have to go through a few pages to ID the power sources and circuits, but the relay itself can be tested alone with a diagram.  Notice that it grounds through the mounting bolts so if you have it just hanging from the wires it might not work.  Nissan added a dedicated ground wire terminal in the ZX's.

 

 

[Lenbo211]

On 2/20/2020 at 6:27 PM, Zed Head said:

I would go to the diagram.  Identify the pins that power the solenoid coils and the pins that are the circuit being made and broken.  Go from there.  The Ignition Relay doesn't have that many pins to figure out.

I found one on EE-5.  You might have to go through a few pages to ID the power sources and circuits, but the relay itself can be tested alone with a diagram.  Notice that it grounds through the mounting bolts so if you have it just hanging from the wires it might not work.  Nissan added a dedicated ground wire terminal in the ZX's.

 

 

Update: I tested it and it seemed to work, but the audible click was kind of soft so I replaced the Ignition Relay with two 4 pin relays to replicate the wiring in the FSM.  Resulted in no change.  Car starts and runs, but still no gauges other than volt meter which I had before. also still no turn signal activity which is what the FSM suggests to check in order to see if the Ignition relay is bad. In theory the water temp gauge may work, but I haven't run it long enough to tell since this is a new engine rebuild and I want to break the cam in correctly and want to make sure I have enough oil pressure to do that.

Decided to remove the variable of the dash from the 1976 Z and put the original 1978 dash back in.  Still no change.

I'm stumped at this point what to test next in order to track down what's going on.

Something that caught my eye as I was swapping the dash is that there are a couple single flat spade connectors for the multifunction switch on the steering column that do not plug into the same color wires. coming out of the MFS (actually the back of the ignition cylinder itself) they are both blue with red line, but what they plug into is a solid black and solid red.  When we took this apart originally, I labeled every wire so I put the correct labels back together.  Do you know if this is normal for the steering column wires?

I also have no dash lights, but it sounds like that is likely a different issue so I'll do some separate research on how to resolve that unless you have any suggestions. (I've discovered that my dome light fuse keeps popping so I have a short there. As far as I can tell when I traced the wire in the '76 parts car that fuse blue wire with white stripe, only goes to the dome light and the engine inspection light.  I don't see any fuse in the fuse diagram that indicates dash lights so I'm not sure what the cause there may be.) We tested continuity on the wire from the rheostat to the firewall plug and it is fine.