78 280Z - no injector pulse

[Zed Head]

Another bummer. A weak battery can cause many problems, some not so obvious. I've seen it said that the Z's EFI system gets flaky if voltage gets under 10 volts. Plus the weak spark from the ignition module. It can only pass the current it's given. And, the load on the alternator if it does start, charging a dead battery, can cause regulator failure (the solid state internal ones like your 78 has), as I understand things. The system is not designed for long-term high current. You really need a fully charged, good battery to make progress. I wouldn't even try to jump it, I'd swap the dead one for a known charged, good one. One less unknown to worry about.

[Virto]

Hoping to get it buttoned up and home this weekend, regardless of running state. If it's in the garage at home, I can at least run out and mess with it when there's a suggestion versus waiting for a chance to get over to the shop.

Just a random question, though - does the oil pressure sender kill the engine somehow if it has no reading? I only ask because I knocked the plug off while poking around and it seems to fit not all that snugly, and the plug is a bit corroded inside.

[rcb280z]

I would clean up that connector and re-install it and see what you get. I think the 78 will not run if there is no oil pressure, just not sure if it affects "starting". Hopefully someone will correct me if Im wrong. My 77 has the fuel cut off built into the AFM. IIRC the 78 fuel cut off is in the oil pressure circuit. Again I'm not 100% certain of this.

[EuroDat]

I think they changed over to the Oil pressure sender around August 77. Mine is May 77 and has it in the AFM. If the treminals on the sender are damaged, they could be causing problems with fuel delivery or lack of it.

It must be frustrating not being able to dash out and try things. Good luck getting her back home.

Chas

[rcb280z]

Thats right Chas, you and I have the same manufacture date. Yes things did change as of August 77. Hope that is the issue, would be an easy fix.

[FastWoman]

If I recall correctly, you get about 5 sec of fuel pump operation when you turn the key to "start." Thereafter, you don't get more fuel until the engine actually runs. For the '78, a running state is detected when you have EITHER alternator output OR oil pressure (or both). Your oil sender being unplugged would eliminate the oil pressure detection. That leaves the alternator, which wouldn't be putting out much while you're cranking. So I bet you have no fuel.

[Zed Head]

FastWoman described the pressure switch and alternator pump control. Those are both bypassed during starting though, powering the pump directly. On my 76 when the AFM contact stopped working, the engine would start, run for about three seconds, then die. It would do that over and over.

With a low battery the alternator powered relay may not be getting enough juice to keep the fuel pump operating. And a dry engine may not be generating pressure right away even with the switch intact.

Collecting all of the facts, if it were mine, I would get a good, charged battery in there, pull the small vacuum line that feeds the AC control bottle (the tiny nipple on top of the intake manifold), and squirt some starting fluid in to the manifold. Ideally, you would have a friend either running the can of fluid or the key, and just keep the engine running long enough to get things moving.

If that didn't work, I would probably short the fuel pump relay to keep the fuel pump on. Actually I would probably do that first, just to take the fuel pump control out of the picture. That's a little more involved though.

This leaving and coming back to the problem really kills the flow, just on the internet. Must be way worse trying to do it on the car.

[rossiz]

i'm no electrical savant, but i'm pretty sure the oil pressure sensor works opposite to the previous posts... unless mine is somehow wonky. unplugged would be infinite resistance, right?

on my 78 pulling the oil pressure sender plug when the key is on and the engine is NOT running is a quick way to run the fuel pump. it's how i used to prime my fuel rail when dealing with hot start issues. just turn the key to "on", pull the plug on the oil pressure sender and the pump would run until it was plugged back in. at one point i was going to put a momentary disconnect push-button inside so i could run the pump without getting out of the car.

quite handy, actually...

[Zed Head]

That's a good catch. So take the plug off, clean it up so it's an open circuit, then leave the plug off and try to start the engine. Much easier than shorting the relay. You've uncomplicated things.

I've actually cut the FSM section out on that before but forgot about it.

[kelley0352@att.net]

well I am still not understanding this problem with the failure of my injectors that have 12v juice & no pulsating Noid light. Everyone is talking about the #1 pin in the ecu. Well what & where is that & what is it suppose to do? Test it while it is hooked up to the plug is impossible! Makes no sense to me.

[kelley0352@att.net]

Please inform me @ Kelley0352@att.net

[Zed Head]