Captain Obvious

Good eyes Zed Head. I wasn't even looking for details yet, just big picture stuff. That atmospheric vent on the valve cover will certainly throw off the mixture some, especially at idle. Can't see it in the pic, but I assume the hole on the rubber duct between the AFM and throttle body is capped off. There will be a small amount of air pulled out of the block through the PCV which would be unaccounted for by the AFM.

Great story so far. Everything, with the exception of the potential compression issues, is completely typical. Valves are out of adjustment. Timing is out of adjustment. Wheel cylinders and calipers are frozen or leaking (or both). Power booster has sucked down brake fluid and is a rusty mess inside. Whole bunch of little vacuum leaks throughout the EFI system. Whole bunch of corroded connectors throughout the system and most importantly, the temp sensor in the thermostat housing is probably not making reliable connection to the ECU. Throttle body is worn and sticky. AAR probably doesn't work reliably. Junk in the fuel tank, and if someone bypassed the fuel filter, you've probably got clogged or partially clogged injectors. If the car had been in the hands of "experts" in the past, they may have incorrectly adjusted the AFM. Questionable fuel pressure. Leaky (or bypassed) heater core. Empty A/C system. All the tubes in the HVAC system have turned to dust (they may "look OK", but in reality they are dust still holding the shape of a tube). Shall I go on? The little ray of sunshine that I am? Not even mentioning electrical modifications from previous owners or mechanics in the past. It may sound daunting, but all that stuff is really pretty simple. You just have to know where to look. It appears everything is there, and you sound enthusiastic and knowledgeable enough to bring it back to the realm of reliable! The only thing that concerns me at this point is the compression... Did you remember to block the throttle wide open while performing the compression test? Looks like a great project to me!!

Kats, Here in the USA, each state governs it's own inspection process. And as you could imagine, the strenuousness of those inspections vary wildly from state to state. Some states have even decided they do not need any inspections at all. Here in Pennsylvania where I am, there is a once per year inspection that I consider very thorough. For example... Lights, glass, fuel system, body and frame integrity, tires, safety equipment are all inspected. Put the car up on a lift to check the suspension, steering, and exhaust systems. Remove wheels to check the brakes, etc. And we also have an emissions test as well depending on the age of the car and the mileage it has driven per year. But one thing they do NOT check is the alignment. If everything looks OK and the bearings and suspension are tight and there is enough depth to the tire tread you're good. So if nothing is loose or worn and the car feels fine during a short on-road test drive, then a suspension out of alignment will not be flagged as part of the inspection.

Welcome aboard. Looks like a nice car for a project. If I'm ever in the area, you can kick my butt at Cricket. Just make sure the Z is out of the way!

Hi Kats, Thank you for the information on the side slip test. It looks like a fast "drive over" alignment test to check the toe settings. I've never seen that before. Thanks!

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!