78 280Z - no injector pulse

[Virto]

I sure hope it doesn't come down to a bad ECU. Those things are too much money, even if you have a rebuildable core!

Hopefully I find a loose connection or something and it's a fast fix - I don't want to risk getting the garage owner in trouble by poking around under the hood in the parking lot.

[FastWoman]

Kelly, I only know of one bad ECU that cropped up on this list. It was a cold solder joint, and it was fixed by re-flowing. So these things are pretty robust. If you do end up needing one, they sometimes show up on ebay relatively cheaply.

[Virto]

280ZX computers look to be dime a dozen. Hopefully it's a non-issue. We'll see what I can come up with while I'm with the car.

Do I need to pull the ECU from its mounting location to remove the cable? I've never tried before - I've never even had that trim panel off.

[FastWoman]

No, you leave the ECU in place. If I recall correctly, the big connector is held down with a screw on one end (??). Free up that one end, and the connector hinges away from the box. It's very quick/easy to get into the thing.

[Zed Head]

The connector is under the black plastic kick panel left of the driver's feet. Three screws hold the panel. Then the connector actually has a spring clip that is pressed up (I think), allowing the top, cable, end of the connector to swing out (you have to tug on the wires, they'll be okay), far enough to pull the other end of the connector off of it's little pin pivot/hinge. Then it's free. You need to pull the top end out a ways before the bottom will release. This part might require having the door open. Once you get it free you should be able to get to the pins with your meter while inside. Might be cramped though.

[Captain Obvious]

In addition to pulling off the cover over the ECU, I think you'll want to remove the small trim strip that runs horizontal above the driver's knees. I don't think there's enough room to swing the big ECU connector off it's bottom hook if you don't take out that trim panel as well.

Before you start poking around at the ECU connector... Have you checked the big fusible link(s) that feeds the whole fuel injection system? Goes right from the battery to the FI harness? Spade connectors on both ends to facilitate replacement if necessary. You should have 12V on both sides of that link at all times.

[Captain Obvious]

Make sure that there is 12 volts on each pin of the injector connectors, removed from the injector, with the key On. It will seem weird from an Electricity 101 perspective, but one side is power and the other side is the transistor circuit. Probably a pull-up circuit of some kind (unresolved in other threads). Both pins in each connector will show voltage if the ECU has power and things are correct.

There's no pull ups on the injector outputs inside the ECU. However, unless you pull all the injector connectors off at the same time (at least all the ones that share the same transistor) you'll read 12 back feeding through the other injectors and their dropping resistors.

In other words, for example... If you pull the connector off injector #2 and probe the contacts for voltage WRT ground:

One side will read 12V because it's pulled up to Vbatt through it's dropping resistor.

The other side will ALSO read 12 volts because it's pulled up through the solenoid coils of injectors #1 and #3 through THIER dropping resistors to Vbatt.

If you pull all the injector connectors at the same time, you should be able to determine which side is hot and which side is pulled to ground by the ECU.

Does that make sense? Did I say that right? :bulb:

[Virto]

I haven't checked any of the links yet. I did replace all the links on the fender before I dropped the car off last year. I haven't checked any other links but those four.

[Zed Head]

I haven't checked any of the links yet. I did replace all the links on the fender before I dropped the car off last year. I haven't checked any other links but those four.

CO is right, the links could be a factor. No power to the ECU. On your 78 car, there are two green fusible links in line in a small power wire directly from the positive post of the battery. If they haven't been messed with they'll be attached to the metal framework that holds all of the relays in the engine bay. Right in front of the battery. It's possible also that the links just came unplugged, they're held in place by plastic connectors that get old and break. So, overall, you have 6 fusible links. Even if the links look good, the power checks at the ECU connector will tell you if they're working.

The EFI relay is also a possibility although they really don't go bad often. It's described in the Guidebook also.

Edited August 30, 2014 by Zed Head

[Zed Head]

There's no pull ups on the injector outputs inside the ECU. However, unless you pull all the injector connectors off at the same time (at least all the ones that share the same transistor) you'll read 12 back feeding through the other injectors and their dropping resistors.

In other words, for example... If you pull the connector off injector #2 and probe the contacts for voltage WRT ground:

One side will read 12V because it's pulled up to Vbatt through it's dropping resistor.

The other side will ALSO read 12 volts because it's pulled up through the solenoid coils of injectors #1 and #3 through THIER dropping resistors to Vbatt.

If you pull all the injector connectors at the same time, you should be able to determine which side is hot and which side is pulled to ground by the ECU.

Does that make sense? Did I say that right? :bulb:

I can't say myself, because I generally describe the 12 volts on each side as "transistor weirdness". Not an authority. Sounds reasonable though, I think that you're saying the 12 volts is "backfeeding" through the transistor that controls those injectors. So it should be groups of three then. Added a diagram just for ambience. Of course, it doesn't show the transistor circuits but it does show how all injectors are powered and feed back the ECU.

Added another diagram. I had a 78 that had the combined EFI/Fuel Pump relay, like 1976. Just for reference. Virto will probably not need to go that deep.

Edited August 30, 2014 by Zed Head

[Captain Obvious]

You don't backfeed through the transistor. You backfeed through the other injector(s). Maybe these sketches will help with the weirdness.

Here's why you would see +12 on both sides of the injector connector if you pull just one:

And here's why you should be able to determine which side is which if you pull all of them (or at least the ones that share a transistor):

[Virto]

Well, no joy at the moment. The shop is closed, at least for the morning - one man operations have random hours, I've noticed.

It's also raining, which isn't conductive to my working on the car outside. I did get a few minutes of dry with it, but the battery is flat. I turned it over one time om battery power and swear I saw the tach needle bounce, but now that the battery is completely drained it won't do anything beyond weakly ring the seat belt buzzer.

It's stuffed in too close to another car for me to get into the driver's side, so no continuity tests for the moment. I did pull a couple of the injector plugs but got no movement on my old multimeter. It might also have a shot battery, so I'll replace that before trying again. Granted I tested after I murdered the battery by turning the car over.