Captain Obvious

Diaphragm pumps like that require two check valves. One on the input, and one on the output. If either of those check valves aren't working properly, the pump won't. I gotta believe the answer would be in this thread somewhere: https://www.classiczcars.com/forums/topic/50679-rebuilding-the-nikki-fuel-pump/

Kats, Great inspection results. I've always believed that if an engine is tuned and running properly, the emissions numbers should look pretty good even without todays emissions controls. Of course, it won't be as good as running through a modern catalytic convertor, but you should be able to do OK like you did. I have a question... What's the "side slip test"?

@Zed Head cut an FPR open some time ago and took a pic. Surprised he hasn't mentioned it by now, but it looks like this inside: Some other details in this thread: https://www.classiczcars.com/forums/topic/47764-inside-an-fpr-the-valve/

Yeah, I was wondering about mechanical deformation as well. If you would crush in the end where the spring seats, you would increase the spring force, and hence, increase the operating pressure. But I think it would be an obvious significant deformation. How about just plugged up with crud? I'd be hard pressed to be convinced that it would provide a constant offset, but crud could certainly raise the equilibrium pressure. How about a 40 year old diaphragm that is stiff and doesn't flex as easily as it did when it was first produced? Now it takes more vacuum to pull the seat off the outlet orifice? In any event, a six psi offset is something that should be taken care of.

Gauge looks like it works great. Isn't it nice to see pretty much rock solid numbers there even when you goose the throttle? So, as for the numbers... It's definitely looking like a faulty FPR. Running the return line into a bucket is a good idea, but I'd be surprised if a partial blockage there would result in such a constant deltaP on the gauge. Easy to check though. However, like you, I'm having a hard time coming up with a way the FPR would run high though. Anyone got theories on that?

Flat tops ftw.

I would replace the brass tube with a piece of steel tube and tack weld it in place. Would look like this:

Nice score. It's a good thing that I'm at the other end of the continent from Jim!

Wow, he looks so sad. Do you look exceptionally happy to compensate?

Well I've kinda lost the pea on where the vacuum measurements are being taken at this point, but I've easily seen 20inHG when measuring on the port vacuum source at the throttle body. You get the throttle plate in the right position and that vacuum really spikes. Depending on how it's running and if you need the throttle open far enough just to keep it running... Interestingly enough, I don't remember if I ever measured a non-ported source on the main intake manifold log on my car. Not sure I ever needed to.

I know I would. I know beauty is in the eye of the beholder, but if I had one of those in my stable, you'd have to pull me out of the garage every night.

The manual says it exists to prevent hysteresis in the advance mechanisms. No idea... Makes me think they were having some small issue in the field and management went to the engineering department and said "Don't care how, but fix it". No idea if there really was a problem, but that's what it smells like to me.

Wait!! I knew you looked familiar!! You're D-Day, right? You almost ran over me one night while I was playing guitar on the stairs!

I believe that is the "contactor". We discussed it some in this thread a number of years ago: https://www.classiczcars.com/forums/topic/42650-distributor-question-the-contactor/?tab=comments#comment-384319 Unfortunately the pics are gone, but I can reload them if it would help. I don't know if the page numbers are the same in everyone's FSM, but in mine, the contactor get's mentioned on pages EE-25 and EE-26.

kinser, Thanks for the gauge details. I had found the datasheet, but didn't see that gauge mechanics document. It looks identical in theory of operation to the one I have. If it works as well as mine, you're gonna love it. So it sounds like the car is running well enough to drive it now? That's a great improvement from when you started! Your next task... Clean some electrical connections and double/triple check for vacuum leaks. It's likely you have several small leaks throughout the system.

Oh. I was going from the text above when the OP said "At this point I felt the fuel pump was too much for the car and we pulled it and replaced it with a Delphi stock replacement." and "With the stock pump replacement, the fuel pressure still seems a little high but not as high as with the previous pump." I didn't have time to sit and wait for all the videos to load and run calculations on multiple gauges and stuff. I was just going off the text and assumed there was a reduction in fuel pressure with the stock style pump.

I take the tank off my motorcycle every year for winter storage. Drain it completely and then (on a nice sunny dry fall day), let it outside in the sun to dry for the day. Once it's completely dry inside, I put it in the basement where there is a dehumidifier. Doesn't rust if you keep the humidity low with the dehumidifier.

Well for twenty-five bucks, it's certainly worth a shot. If it works as well as mine, it'll answer any questions about the real pressure that the injectors actually see. I took a quick look at Ashcroft's website and I couldn't find a diagram that explained the basic theory of operation for the internals. I did see some mention of magnet(s), so I assume it's the same magnetically coupled meter movement concept as the one I have, but I couldn't 100% determine. This whole thing sounds like a typical 280Z story to me. Most of us have been through it. So far, you made a simple mistake and screwed up your ignition timing and vacuum hose routing, Your PO put in a fuel pump that was incompatible with the stock pressure regulator. And you paid for an injector cleaning that had to be done twice because the first time didn't work out as intended. Nothing unusual so far. Admiral goal to keep that sort of stuff from happening to anyone else, but I wonder if you're trying to prevent the un-preventable.

I didn't dig into the specs of that Ashcroft differential gauge, but the biggest thing you would have to watch for is something compatible with gasoline. The Orange Research gauge I have is all metal body and piston and has Teflon seals. It also magnetically couples the internal piston to the meter movement so the gas never gets to the needle. It's completely segregated. I don't know anything about the Ashcroft, but if it can handle the gasoline, then it should work fine. I don't remember what I spent on mine, but its very convenient having it at my disposal. No math. No units conversions. Direct reading.

Haha!!! "Never do this." I understand completely!

Haha!! Looks like something out of Tron. He better be careful going out like that or he might get uhhh... shot - key? I'll be here all night, folks. Seriously. Where else am I gonna go?

Thanks for the info guys. Maybe next engine I overhaul will get a similar treatment.

Here's the theory for the differential pressure gauge I have. It's essentially just a piston (which also happens to be a magnet) sliding back and forth in a tube. That magnetic piston is coupled to the gauge needle so there is no process fluids (whatever you are measuring) in the meter movement area. Operates like this: And this is hooked up to the car. Too big to leave in there all the time, but it's fantastic for diagnostic purposes. One side pushes while the other side pulls. The pressure reading would go down if you disconnect the vacuum side because that side isn't pulling:

They didn't bond the neutral. The full alternator output is Line to Line in a 3-phase "Y" configuration and for normal stuff, you don't need it at all. Just run full wave rectification between all the L-L and the neutral is unnecessary for the 12V alternator output. One side of the six diodes becomes ground and the other becomes alternator output. No neutral needed. However, they brought the neutral out to supply a couple things like the brake check relay and the voltage regulator. Not sure why they did that instead of just using the full output, but that's what they did. For some reason, they thought using Line to Neutral was a more reliable indication that the engine was running and the alternator was turning and working. Maybe it has to do with losing one phase or something? Someone here with more 3-phase experience could maybe provide input? How's that for a thread diversion?

All that said, I'm intrigued by the reduction in valve mass. I don't know what a typical valve weighs, but you mentioned that you took off 2g of material. What is that in percentage of total? Anything significant? And if so, are there any performance gains possible from such a change? (Thinking less valve float at high RPM for example due to the reduced momentum?) I'm beyond my pay grade with evaluations like that, but it seems possible. Have you experience that deep with engine details?