Zed Head

Here's the other one. If the ECU sees "full throttle" it will add 27% extra fuel over the base pulse. So, if 3 is shorted to 18, either in the ECU or at the TVS, you'll get a lot of extra fuel. Just realized that this might be the root cause of "bad" ECUs'. Might be worth tracing that circuit in the ECU, or the ECU plug and it's interface, if the TVS is not shorted.

Whichever you get take it apart and clean the bores out before using. Sometimes they leave honing grit inside that will kill the seals pretty fast. Reman quality.

TVS is the correct name for the "TPS". Throttle valve switch. No offense, but people often say that they tested something and it's correct, then we find out later that they didn't really know what "correct" was, or they only tested half of the system. The TVS has idle, full enrichment, and neither of those. Always best to give more details, way more if you can, than you think are necessary. If what you say is correct matches what we think is correct then everyone can move on. Otherwise, who knows, it's just an indirect argument about what correct means. If everything was correct there would be no problem. "Full enrichment" is 27% more fuel.

I had a similar problem with my car right after I bought it. It was the FPR, it seemed to stop regulating when it got hot. It was a hard problem to diagnose, I only measured pressure when the engine was cool. I replaced it with an adjustable FPR, set pressure to spec., and it ran fine. Just a possibility. Another one, that happens but is uncommon, is the ECU. They tend to run rich as they go bad. If you have spare parts, swapping and checking is an option.

What is mpg, in numbers? Yes. There should be a green label on it with numbers and letters, like A31-..... They're all very similar though. https://www.thezstore.com/page/TZS/PROD/11-3040

Is it a Nissan factory original AFM or Fuel Injection Corporation reman?

Did you actually compare the resistance readings to the chart? The G. or N.G. tests don't show much. The other fuel source is the CSV. The idle air bypass screw under the rubber plug on the AFM is only good for very fine adjustments, and only at idle. It won't affect much above that. I just went through a similar situation, trying to pass emissions. My engine ran fine and I could take the oil filler cap off at idle. It turned out that my AFM was "tuned" rich. I had to put an old stock Nissan AFM back on. You really should reset your AFM to the original settings. Adjusting the spring never works right, from what I've seen. It just makes a messy problem messier.

Did you check the FPR vacuum line for fuel? It's the hidden cause for rich running. A small leak can add a lot of extra fuel but still control pressure correctly.

Nissan's drawings and explanations really aren't very good at explaining the purpose of the various parts.

The testing seems to show that the problem is in the back. If z89 keeps "doing things" he'll probably find the problem. Use the same logic that was used to isolate it to the back end. There are similar tricks that he could do if he thinks about the pistons in the wheel cylinders.

You can remove the screw/bolt from the junction blocks of the hydraulic lines down on the fender well and frame rail. That will give you a lot more flex in the lines to the MC and let you leave everything connected. You might find fluid leaking from the back of the MC though once you get it apart. That's the common reason the booster fails. Don't let any fluid leak from the booster on to your paint. It will stain it, or worse.

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Do you have the stock drums on the back? Sounds like you need to adjust them. The shoes are too far from the drums. Take the drums off and turn the adjusting wheel that moves the shoes apart until you can barely get each drum back on. Then pull the parking brake handle up and down a few times to get the final automatic adjustment.

It's been show to cause overheating. It bypasses the radiator and the front half of the head.

Actually, just remembered...if the heater core lines are looped, aka bypass mode, the coolant can make a loop through that path without entering the radiator. At low RPM there might be enough flow through at path so that the thermostat sees very little. Is your coolant port blocked or looped?

You removed it with the engine hot? Should have had some overflow. Anyway, carry on. Just seems like being focused on seeing what the coolant is doing instead of what can't be seen. The water pump is certainly full of fluid and will push it through the engine. The only way out is the thermostat. Air will easily make it through the tiny hole in the thermostat. Have to say though that the FSM is way behind in 1976. My coolant level sits at the top of the filler neck after some heat cycles, with the reservoir working right.

Is the engine "nose up" or nose down on your engine stand. The pump will fill the engine with coolant up to the thermostat if it's nose up. If it's nose down there could be an air pocket at the back of the cylinder head. With a heater core installed that air pocket would end up there, instead of in the head. Maybe you can "burp" it from the heater core supply port. And, just curious, but is "air in the system" really a problem? It's just heat transfer fluid, if it contacts the hot surfaces and absorbs the heat, then moves out to the radiator, all is good. I've seen quite a bit of discussion out on the internets about what happens in the system, but , really, there's not much to them.

There's a whole carb tuning section in the FSM's, plus ZTherapy has a CD that they sell, and I think that there is some stuff in the Downloads section of this site. I think that there's more to it than lifting the piston and seeing what happens. I could be wrong, I'm not a carb guy. Good luck.

Have you given the engine a thorough tuneup? Adjusted valve lash, new spark plugs, set ignition timing? How many minutes of running are on the engine since you got it restarted after sitting for 15 years? Might still be some rusted and gummed up parts in the engine.

They pelled it wrong on porpoise.

Not clear what you're bummed about. Old parts in the oil pan are pretty common. People find all kinds of things in there.

That looks/sounds about right. I knew that I had seen something similar in the past. Too bad I took my box of old u-joints to the recycle yard, I'd replicate the picture, to see.

Not really clear where you're at on the project. Could be that somebody already rebuilt the head and those parts are from the past. How does the head and valve train look? I haven't looked back through the 7 pages.

https://www.thezstore.com/page/TZS/PROD/10-2041

It looks like ground up aluminum. I bought an old mystery transmission, filled it up with some old fluid and spun it on the back of my garage engine. The fluid looked like that when it came out. Ground up shift fork. With the lash pad, the seal material, and the silver, kind of looks like a camshaft might have damaged itself in the past. The camshaft tower bushing journals are aluminum. The cam rides right on the tower material. Lots of aluminum in other places too that could get rubbed on.