78 280Z - no injector pulse

[FastWoman]

Captain, my faith in automotive manufacturing has been restored. I suggested long ago that there's no way a manufacturer would waste 6 pull-up resistors in the design of a circuit. We had speculated that it might have been just one of those charming '70's things or that the hypothesized pull-up resistors might have been for diagnostic purposes (e.g. to be able to test both sides of an injector plug to confirm power to the ECU). However, a Deutschmark is a Deutschmark (Bosch), or a Yen is a Yen (Hitachi). Anyway, yes, the backfeed through a common transistor connection would explain the +12 on the ECU side of an injector connector without indicating anything about whether the ECU has power.

Kelly, if your fusible links are in typical condition, they're probably pretty awful. I, too, would begin my diagnostic efforts with regard to power to the ECU. However (and this is important), I would not start pulling apart the fusible links to do it. Start methodically at the ECU connector to see if you have power. If you don't, then move back to the EFI relay. If you don't have power there, move back to the fusible links. The reason is that if you have a marginal connection somewhere, you can make it good (for the moment), just by jiggling it around. However, sometime when you're out on the highway, it might decide to go bad again, leaving you stranded. Faulty connection gremlins are sometimes very skittish, so to catch them, it's better to diagnose from afar and to sneak in on them -- catching them by surprise before they can clean up their acts.

[voice of Elmer Fudd] Be veeeewy veeeewy quiet! I'm hunting gwemlins! Eheheheheheh!

Edited August 30, 2014 by FastWoman

[Captain Obvious]

These Z-Cars don't go off unless you hit them juuuuusst right.

Edited August 30, 2014 by Captain Obvious

[Zed Head]

Your diagram makes it all clear. Thanks. Should have spent some thought on it before. I've been lazy all these years. It seems so Obvious now.

Virto, if the key was On when you tested the injector plugs then you really want to go directly to the EFI fusible links, the two green ones, right off the battery positive. Look at the 1978 diagram I posted above. They feed the EFI relay and the power to the dropping resistors, which CO has shown supply both sides of the injector connectors. If you have enough juice for the buzzer, there should be enough to register on your meter at the injector connectors.

[Captain Obvious]

It seems so Obvious now.

Why yes... Yes it is. Haha!! Glad to help!

Of course, if you have an Ohmmeter that is capable of truly working down in the low ohm area, you should be able to tell what went where just by checking resistances. My meters aren't that good... I have one that might work for that, but it eats batteries and seems like every time I grab it, the battery is dead.

Honestly, I almost always find myself reaching for my cheap (disposable) HF meters. I've got one in every room of the house. Cheap and good for reality checks, but I wouldn't trust it to tell me the difference between a half an Ohm and one Ohm.

Edited August 31, 2014 by Captain Obvious

[Virto]

Update time.

Injectors have 12v

Tach bounces when cranking

ECU pin 1 has 12v, key on

ECU has power, pin 10, key on

ECU grounds, pins 5, 16, 17, 35 all have continuity

12V leaving the green fuse links

Relays click when key on

Fuel pump runs, there is pressure at the rail

We pulled the EFI main relay and tore it apart. Remarkably clean inside, seems to be doing its job.

When you first crank the car, it sputters and wants to fire, but there's no fuel. It very nearly catches, so it seems the cold start injector is working.

I'm going to print out and drop off copies of the EFI wiring diagram on my way to the office tomorrow. I'm hoping I can get her home soon - she looks like hell.

[FastWoman]

You're absolutely certain you have no pulse? Is your noid functioning correctly? It should be a VERY brief flicker once every rotation.

If you turn on the ignition with the ECU unplugged, can you ground the individual injectors at the ECU plug and hear them click?

[rossiz]

per sage direction from others on this site, i keep a set of christmas lights with the ends cut, stripped & twisted for easy insertion into the injector plugs - they work great as a little test light to check for pulses.

[Zed Head]

You're absolutely certain you have no pulse? Is your noid functioning correctly? It should be a VERY brief flicker once every rotation.

If you turn on the ignition with the ECU unplugged, can you ground the individual injectors at the ECU plug and hear them click?

These are two good ideas. You're about to the point where it might be the ECU. The FSM and maybe the Guide Book will show which pins are the grounding pins for the injectors. You can ground those directly since the injector solenoids have resistance. I have made little copper probes to insert in to the ECU connector to make it easy to attach alligator clips, by smashing a piece of solid copper wire flat. With the key on, and power verified at the injector pins of the ECU connector, a quick tap to ground should cause the injector to click. That will show you that things should work if the ECU transistor does its job. If you do that a few times for each one, the engine will probably start and run for a second or two.

A probe in pin 1 across your voltmeter leads - pin 1 to meter - other side to ground - should show a flicker when cranking the engine over. Or the christmas tree light should show it.

I have had an ECU go bad to where the engine would not start anymore. First it flooded the engine then it just quit doing anything. So they do go bad. If you can borrow an ECU it might be worth a shot to just go directly to that. Seems like you've done enough to justify it. If you were close by, I'd loan you one.

[Virto]

Honestly, no. I didn't run the noid myself, but I'm pretty confident that I can believe him when he says it wasn't lighting.

So, key on and then just a length of jumper wire from the ECU plug to ground? Is there any way to test the dropping resistors? That seems to be the only thing in the path I haven't looked at.

[FastWoman]

When you ground the injectors via the ECU plug, current has to flow through both the drop resistors and the injectors for you to hear clicking injectors. So if you can ground the ECU contacts and get clicks, you know that... (1) Your injectors have power, I believe through the ECU circuit, (2) Your drop resistors are good. (3) Your injectors are good, at least mechanically. That's not to say that they aren't clogged. (4) Your wiring is good. (5) If the ECU is also operational, then you should get an injector pulse.

[Virto]

If you can borrow an ECU it might be worth a shot to just go directly to that. Seems like you've done enough to justify it.

If only. Most of these cars have long since rusted away in Chicagoland. Windy City Z club is almost entirely new model Z cars, from what I've seen these days. I've run across plenty of people that say "hey, I remember these" or "I had one of these in the 80s" but they are an extreme rarity to actually see on the road. I guess I'll start keeping an eye on eBay - I don't really want to send MSA 350 bucks if it's not the issue. That having been said, is there a difference between the M/T and A/T computers, or was that only in the S130?

If anyone has a good one they want to loan out for a week, I'd be happy to pay the return shipping and then slip some cash into the box with it to cover your time and assistance.

I'm going to jot some notes down and deliver them tomorrow when I drop off the wiring diagram. If I can just get her to start, we can hang the rest of the exhaust, slap the fan back on and get it into the garage at home. I really do feel pretty sad when I look at it now, thinking of the time I wasted while the car was in better shape.

[Zed Head]

You know I kind of lost track of the problem and its symptoms since you switched threads. But, going back to Post 29, if you're getting some activity from the engine like it wants to start, I would pull a plug or two and see if they're wet or dry. Also, consider that the gas may have gone bad.

If you're getting signs of life from the engine try some starting fluid. Maybe you just need to purge the bad gas from the injectors and get things flowing and moving again. Actually, I would probably just try starting fluid right now.

Could also be water in the gas. Where has it been sitting?