Need assistance from the Zed Collective Conscience!

[ZCurves]

Thanks everyone. I am still working on this one. I want to make sure to lick this one and post the solution for someone else in the future.

2fiddyZ: I have to admit that I have been looking to bring the Z into the 21st century and look for modern EFI management systems. Megasquirt, etc...

[siteunseen]

A member here had me run a fuel pressure gauge up to the windshield wiper and zip tie it to the wiper. I could watch it as I drove.

[2fiddyz]

I know you cant watch your tach 24/7, but if you happen to notice the tach exactly as it happens, and the tach hits zero RPM's hard and stays there, that is how mine responded with the corrosion issues I had, and would definitely indicate an ignition problem.

[ZCurves]

A member here had me run a fuel pressure gauge up to the windshield wiper and zip tie it to the wiper. I could watch it as I drove.

That's on the menu this weekend!

[TomoHawk]

Just in case, the oil pressure shutoff will have the same effect- a sudden shutoff- but you didn't mention how your oil pressure goes, so I'll assume it's always got enough oil pressure. Even a loose oil sensor plug would cause the engine to stop suddenly.

[ZCurves]

Just in case, the oil pressure shutoff will have the same effect- a sudden shutoff- but you didn't mention how your oil pressure goes, so I'll assume it's always got enough oil pressure. Even a loose oil sensor plug would cause the engine to stop suddenly.

I will take a look at this too. It seems that when I was experiencing the problem, that I could unplug the Oil Pressure sender and the fuel pump would run. I will definitely take a second look.

[Captain Obvious]

It seems that when I was experiencing the problem, that I could unplug the Oil Pressure sender and the fuel pump would run.

I used to think (up until a few days ago) that the fuel pump on the 78 would only run if there were both oil pressure AND a spinning alternator. However, I've now taken a closer look at the design and I no longer believe that to be the case.

I now believe that the fuel pump on the 78 will run if there is oil pressure OR a spinning alternator. So your experience above of unplugging the oil pressure sender connector and finding that the fuel pump continues to run makes sense to me.

All that said... I still think you should start small and try to figure out which camp you're in... Fuel or spark.

[FastWoman]

(Deja vu!) Yes, Captain is correct -- either alternator OR oil pressure, or else there would be situations where the engine wouldn't run when it should -- immediately after an oil change (no oil pressure for several seconds), when alternator dies.

I also agree with the "start small" suggestion.

[TomoHawk]

Maybe the fuel pump will run if you have no oil pressure, nut I do know that the last time I pulled of the connector from the oil pressure sensor, the engine immediately stopped.

[Captain Obvious]

I don't have a 78, so I can't test it, but if my understanding of the system is correct, the engine should not have shut off. Maybe there was a problem with your alternator, or maybe my understanding of the system is still flawed.

I can tell you that the documentation is confusing!

[rcb280z]

Its my understanding that the fuel cut off happens when there is no oil pressure in the 78, hence the 5 pins in the AFM. My 77 has 7 pins because the fuel cut off is in the AFM. That's why Tomo got the results he got with his 78. You could even listen for fuel pump run to see if you hear it stop just before engine stall. Lots of good suggestions for you to try. Keep us posted.

Edited November 14, 2013 by rcb280z

[Captain Obvious]

Right 78 is different than 75 through 77, but it's not as simple as just the oil pressure switch. The alternator is involved as well.