Captain Obvious

I experienced the exact same failure of a pressure gauge. I could have sworn I posted about it a while ago, but (even with the advanced search**) I honestly I can't find it. So if I didn't talk about that, I'm sorry because I could have saved you the trouble. My experience went like this... I was hunting for hot restart issues and I installed a cheap pressure gauge just like you did between the filter and the fuel rail. I tracked the cause of my hot restart to a bad check valve at the pump, but after fixing that I figured I would just leave the gauge installed as a diagnostic tool just to keep an eye on things. Over the next few weeks my fuel pressure seemed to be gradually dropping. But the interesting thing is there seemed to be no change in the way the engine was performing. Tracked the issue to a failed gauge with eaten up brass gears inside just like you had. The pressure shocks of the constant hammering from the injectors opening and closing ate up the brass and started skipping teeth. I put a new gauge in the system and verified that it was a measurement problem only and my fuel pressure was fine, and then I took the gauge off the system so I didn't ruin another gauge. **Mike, if you see this, I'm not sure the advanced search works as intended... What I was thinking would be an "AND" search on keywords seems to be an "OR" search instead? Send me a PM if you want to discuss? Maybe it's just me, but I couldn't get it to do what I wanted.

Glad to help. Of course, I can condense all of my above ramblings above into the following... "My 77 behaves the exact same way yours does, and after reviewing the system and the documentation, I believe that's the way it's designed to perform. If you find that the tank has a VACUUM, you have an issue, but a little pressure is normal." The difficult part for me is that my non-Z daily driver never develops any tank pressure. Whenever I get gas, there's no "woosh". No nothing ever. I dug into it a little and it seems that it's about 50/50 with that car. Half the drivers get a woosh and half (like me) don't. I've not been able to figure out who's is normal. My 50 or their 50. It's OBD2 and I'm not throwing any EVAP codes, and that car isn't intended to be the project, so I just drive it.

I pulled my pump out a while ago for refurb and I didn't have any trouble getting it to prime when I was done. I know there's a statement in some of the manuals that warns against running the car completely out of fuel because it may be hard to get pumping again, but I didn't have any issue. I pulled the starter solenoid wire and the pump primed itself and got fuel up to the rail in a few seconds. Gravity did all the work. So you did make sure your fuel filter isn't plugged completely with crud, didn't you? Sorry, I have to ask... If the one in the engine compartment checks out OK, there's also a small screen filter on the inlet to the pump itself. Pain to check, but that could be an issue as well.

The good news is that I think that's exactly the way it's supposed to work for pressure. My read on the way it works like this... The fuel filler cap is supposed to be a positive check valve in that it allows air to flow into the tank, but won't let anything out. So why doesn't it build up pressure uncontrolled when you park the car in the hot sun and heat up the fuel and vapor in the tank? Because there is also a device that is part of the EVAP carbon canister system that they call the "check valve", and it's in line with the vapor line that runs from the liquid/vapor separator overflow tank in the rear wheel well up to the carbon canister in the engine compartment. Note that this "check valve" is not to be confused with the check valve on the output of the fuel pump. This one does vapor while the one on the pump does liquid. Here's a layout of the items involved in the EVAP system. The check valve is #8: It's not a simple normal "check valve" that allows flow in one direction, but blocks it in the reverse. Instead it allows unrestricted flow in one direction and restricted flow in the other. Here's the test procedure. Note that I had to go to the 78 manual to find this. Earlier manuals showed the check valve in the system, but didn't include test procedures: It's unrestricted flow if the tank runs a vacuum, but it's restricted flow if the tank pressure is positive. So I wasn't there when they design the system, but what I believe happens is that the pressure inside the tank will build up some until you reach the cracking pressure of the check valve and then the valve will "burp" into the carbon canister. Then the pressure will build up again until there is another "burp". This will continue as long as necessary until the pressure stabilizes right below the cracking pressure, and that's the residual pressure that's in your tank when you take the cap off to put gas in.

I'm with ya! I've lost count of the number of times now that I've studied the heck out of something and taken lots of pics... Only to find out later that I just reinvented the wheel and Blue already has the same analysis on his site from years ago!

Mike beat me to it... I wanted to ask if you're sure it's vacuum and not pressure. It would make perfect sense for there to be some pressure in the tank. As a matter of fact, it's all related to the vapor recovery system that includes the carbon canister in the engine compartment and it's designed to operate such that there could be some pressure in the tank. Either neutral, or positive pressure in the tank. But there shouldn't be a vacuum.

There shouldn't be any significant vacuum in the tank. There's a check valve built into the gas cap that's supposed to prevent that. (Funny that there's another thread running at this exact same time talking about the same thing. ) Here's some pics of the check valve. If you're truly getting a vacuum in the tank, maybe your check valve is plugged up? Here's the cap where you can see the air intake passage bulges: Here's the air intake passage from the side: Here's the check valve. I pried it up with a screwdriver: And here's the air intake hole on the under side of the cap where the air intakes get to the edge:

Page EF-22 of the 73 manual page has a decent cutaway dwg of the cap. It also describes how to test the check valve: 1. Wipe clean valve housing and have it in your mouth. 2. Inhale air. A slight resistance accompanied by valve indicates that valve is in good mechanical condition. Note also that, by further inhaling air, the resistance should be disappeared by valve clicks.* 3. When valve is clogged, or when there is nor resistance, replace cap as an assembled unit. Nice, huh? * I used #2 from the 74 manual because it's funnier. The other two are from 73.

I don't have documentation back to 71, but I've messed with later year fuel caps and if the OEM cap is functioning properly, I don't think it should be leaking like that. Back to at least 72 there was a check valve in the cap that was supposed to let air in (to replace gasoline taken out to run the engine), but not let air back OUT. Are you sure your check valve is working properly? If you've not ever messed around with one of the caps, it's the spring loaded metal disk on the inside center of the cap. If you pry that disk away from the cap, it opens an air passageway to the little radial bumps bent into the outside of the cap. The ridges that run perpendicular-ish to the grab handle? On edit - Found some pics. here's the cap where you can see the air intake passage bulges: Here's the air intake passage from the side: Here's the check valve. I pried it up with a screwdriver: And here's the air intake hole on the under side of the cap where the air intakes get to the edge:

The gaskets "packing" #20 on that diagram seal the lids to the distribution blocks, not the blocks to the cam towers. I don't know if they originally came with a gasket between the towers and the blocks, but I'd put one in. I'd use gasket material though instead of RTV because I think it would be more forgiving to the vibration? All of the blocks I've messed with had been chewed up a little on the back side from vibration against the towers.

If they wrapped a non-hardened shell around a hardened cylinder, then drilling it would be a breeze. But if these new ones pan out, of course that would be even easier. With the new ones, while they're off the car before you install, you might test the hardness with a file. If you're going to drill for a zerk, you could pull the caps off to clean out any chips. Of course, there's no guarantee that there's the same passageways in the bodies of new ones, right? You'll have to pull a cap or two to check. Either way, this could be a great find! New non-greaseable ones are still better than old dry non-greaseable ones. Keep us posted!

Don't want to pre-emptively bust your bubble, but seeing as how the cap is actually the outer race for the rollers, I'm sure it's hardened You got any carbide drill bits? Haha!

Yes, I believe the #5 inhibitor is for automatics only, so 1, 2, and 3 only makes sense for manual trans without A/C. Thanks for the help with the 78 point of view.

Thanks for the thoughts. Here's something that you might be able to do remote... This is a snippet from the 78 manual with a sketch of the late style relay bracket: Is that what yours looked like, because if so, it's completely different than the 77 version.

Seeing as how the yoke is actually the inner race for the rollers, I'm sure it's hardened. You got any carbide drill bits?

Of course that counts!!

Haha! No secrets! I got nothing but the ocean.

No worries! Bob, Thanks for the confirmation on the trans in your car and Chas, thanks for the pics. Those are great shots. I appreciate the help from both of you! PS - Bob, yeah Chas' car is a lot cleaner than mine too, but I don't let it get to me. Mine's much faster, and if he doesn't believe that, he's welcome to bring his around for a good ol' fashioned drag race. :laugh:

Great! I'd appreciate any pics. The issue for me is that I'm planning some electrical changes and I'm wanting to repurpose some of those mounting locations for other things and I don't want to put something new in a location that I'll regret using at some future time. I have a manual trans car so the seat belt interlock location is up for grabs, but can't figure out that other set of mounting holes on that front side. Anyone got pics of a 78 bracket configuration? Rossiz, if you're reading this, can you maybe stick a camera down in there and take a couple pics of the 78 design? Maybe they had holes laid out in 77 but didn't use them until 78?

Thanks for the help. I'm assuming your car is a manual trans? That would make sense that you don't have the seatbelt starter interlock relay.

Eastern Beaver (and no, it's not what you think). They are the only small onesie/twosie order friendly source I've found for the original Yazaki connectors used on the Zs. They don't have them all, but they do seem to have some of them. Here's their main connector page: Connectors And they've got one for sheaths: Sheaths If you're going to place an order with them, send me a PM because I might want to piggyback with you. Help you make minimum and split the shipping from overseas?

Thanks, but I don't think so. That stuff is mostly on the interior above the fusebox and I'm out in the engine compartment. Here's some sketches from the 77 FSM that seem to corroborate that the solo relay attached to the bracket in my pics above is for the air conditioning compressor. And it also appears that one of the relays to be mounted on the front side is for a seat belt interlock on the auto trans cars (#4 in the diagram). But what's got me is that I've got room and mounting holes for TWO relays on that front side, and I have absolutely no idea what the other one would be for: Here's another sketch from the FSM that shows a little more detail about the seat belt interlock relay.

This is a pic of the relay bracket from a 77 Z. There are mounting holes for relays that my car does not have. Does anyone know what the relays are that screw to this side? What are the functions of the two relays that screw to those four mounting holes on the side that faces forward toward the headlights: And for posterity, here are the other three sides. This is the side that faces the engine. The four screws attach the two fusible link blocks: Here's the side that faces the battery. The relay in the pic (I believe) is for the air conditioning compressor: And here's the side where the voltage regulator would mount:

[joke]Maybe he means you plug it in and then play with it for months trying to get the tuning right.[/joke] :paranoid:

I'm assuming they were licensed to be an authorized rebuilder of such things and were given enough info from Hitachi or Bosch to be able to test the module as a black box. Attach this cable and hit the "test" button. Probably runs through different simulated temperature, RPM, and air flow rates and then measures the pulse width output accordingly. As for the solder touch up, it doesn't seem to me that it would be that difficult to re-wave an already done board. Pretty much all you need to know is the outside dimensions of the board so you have locations to attach it to the fixture, right? Of course, I've got no idea if they are actually doing such a thing, but it doesn't sound that unfathomable. And, yes, I have verified (in my very limited experience of maybe three ECU's) that there are no electrolytics. Wait a minute... Are you talking about the module, or their owners?