Engine rough running - at wits end

[the_tool_man]

20 minutes ago, SteveJ said:

Just keep in mind, @the_tool_man, if you go with the Frontier alternator, choose from the offerings under New.

Thanks @SteveJ. I've already got one in my cart, with the connector on my Amazon list. Reading all I can find on the wiring changes needed for my 77.

[Patcon]

@Zed Head

Thanks for the chart. It does appear we were just inside spec when I took that pic but it had been over 15.8V for 20 minutes or so before that. We were probably in the low 70s or high 60s F. Maybe some of that is just lack of use.

Is the 280z regulator serviceable or adjustable?

[SteveJ]

8 hours ago, Patcon said:

@Zed Head

Thanks for the chart. It does appear we were just inside spec when I took that pic but it had been over 15.8V for 20 minutes or so before that. We were probably in the low 70s or high 60s F. Maybe some of that is just lack of use.

Is the 280z regulator serviceable or adjustable?

If it's a Nissan regulator it is adjustable. If it's aftermarket, who knows?

[SteveJ]

[Patcon]

@the_tool_man

Did you see that^^^

[Yarb]

Did you order a new Frontier alternator from RO?

[the_tool_man]

22 hours ago, Patcon said:

@the_tool_man

Did you see that^^^

Yes. I'll investigate adjusting te VR. I didn't have time today because I WAS TOO BUSY DRIVING THE CAR!!! It runs strong and pulls to 5k. The hesitation and backfiring from before is completely gone. Of course I've got a new list of issues now; restoring the fuel tank, adjusting the voltage regulator, the brake booster inoperative, and after driving for a while the tachometer has developed a mind of its own. For now I'm extatic.

[the_tool_man]

21 hours ago, Yarb said:

Did you order a new Frontier alternator from RO?

Not yet. Gonna mess with the VR first.

[Patcon]

I love what you engineered for a fuel tank!!

I think I would switch back to the main tank and verify the problems return. It's possible your other repairs solved the previous problem.

 

[the_tool_man]

6 minutes ago, Patcon said:

I love what you engineered for a fuel tank!!

I think I would switch back to the main tank and verify the problems return. It's possible your other repairs solved the previous problem.

 

I can't take credit for the tank, and you know it. That was all you, my friend.

[Captain Obvious]

4 hours ago, the_tool_man said:

I didn't have time today because I WAS TOO BUSY DRIVING THE CAR!!!

Wooo Hooo!!!   

[the_tool_man]

Tonight @Patcon and I switched the car back to the fuel tank to test it, or tried to. I think we had issues getting the fuel pump to prime. More on that in a minute. Skipping ahead, I had already made up my mind to drop the tank and inspect it. When we did, we found rust, and lots of it.

 

 

I guess my cleaning and rust prevention work didn't do the job. I'm glad I followed my instinct and looked. Even if the car had run, it would have eventually clogged the filter or failed in some other way.

At this point I'm going to enlist help from a friend who can help me cut the tank open and get it properly cleaned out and welded back together. We'll get a close look at the pickup tube and baffles, repairing what needs it. What's the best coating to use afterwards? I plan to run ethanol-free gas, but can't necessarily guarantee it.

Back to the testing: I had the tank hooked up when Charles arrived. When the pump ran, it wouldn't build pressure. We tried just running the pump and it got to 11psi. We started the engine and it sputtered and shut off. Our assumption was that the pickup in the tank was perforated or clogged (we put only 2-3 gallons in it).

We switched back to the jug, just to confirm it would run again...BUT IT DIDN'T. It behaved exactly the same. After some head scratching we unhooked the pump discharge and dumped it into a bucket to test the pump. It flowed strong. We hooked it back to the car and it built proper fuel pressure. The car started right up.

Clearly the pump needed help priming. But why? We were sucking out of tanks that were higher than the pump. In the case of the jug, it was lifting a foot or so to the neck of the jug, and then downhill to the pump. If the pump builds 35psi it should push air or fuel past the FPR. I can only speculate that the pump has too much clearance allowing air to backflow (at around 11psi). Does that mean the pump is bad? FWIW it is almost new, with maybe an hour on it. I'm curious to hear what you think.