NocturnalEmber

In regards to the fuel system (all of these were done when I got the car a few months ago): Pump is new, (aftermaket unit.) All soft fuel lines are new. New engine bay fuel filter New injectors and seals (x6) Fram clear filter coming off tank feed line (that is clean.)

I suppose I will test it shortly and report back. For such a simple test it could provide valuable data, or eliminate a variable as you say.

I was getting the correct PSI a few months ago when I was troubleshooting the hard start/no rev situation. Not that its related (just for a timeline point of view) but back in October ish when I had that fifteen page thread going, I swapped in a used distributor because mine had a chipped tooth on the reluctor wheel and that got the engine in a slightly better state. After I got the brakes and clutch done last week I finally pulled it into the garage instead of having it backed in, so I started running the engine again, did the test drives, and that is what made me I notice the low fuel pressure issue. The only time yesterday I got the PSI to go back to "normal" was after I put the gas in it and started it up. It held within normal FSM ranges for *maybe* a minute or so of it running. After that it just slowly began to fall and settled around the 12-14 PSI its been since this problem started. That was the only time the fuel pressure was correct when I was testing yesterday, after I had put the gas in. Right at startup and for *maybe* one minute while running. Pressure continuously fell after that period of time down to the 12-14 psi I mentioned. Should I still move on or check the fuel system further @Zed Head ? The fact that it held correct pressure for such a short period of time has me thinking that I should check the supply side of the fuel system, but that being said, I will default to the expert opinions here and move onto the resistance check of the water temp circuit if you believe that is the best course of action. (Actually I'm going to check it anyway, I just want to know if its safe to "rule out the fuel supply side of things (ex, tank & pump.) Edit Edit: Downloaded the 80 EFI bible. Are you referring to the water temp sensor checks on page 79 ?

I replaced the temp sensor with a new one, verified with the FSM that the connections were hooked up right, for 78 its Black to green on the main efi harness. I don't think the previous owner really..messed with anything. This car from what I can gather, sat inside a garage for probably decades. The clutch master cylinder fluid had turned to a fine powder. I've never seen brake fluid dry out. I had to replace the entire clutch hydraulic system minus the hardlines, and the same with the front brakes just so it would run and stop. Fuses were oxidized so bad current wasn't passing through because of the increased resistance. Not that any of that directly relates to why I'm getting fuel pressure issues all of a sudden, but the car sat for awhile. I could be wrong on this but I don't think it was really tampered with much. Both hoses I replaced (PCV and the one on the valve cover) were so brittle they had gaping holes from dry rot/heat. The brand new plugs I put on it when I got it were black with soot, so whatever it is is causing an extreme rich condition, but now I've got the fuel pressure issue to contend with. I'll try filling up the gas can again and removing the feed/return lines and using the gas can as a portable fuel source today and see if the fuel pressure changes. If not, then I'll move onto the pump. Even though its been replaced already, and I've had an inline fram filter on it since day one (that isn't dirty), Possibly the pump is bad, who knows. Ideally I'll have more results by the end of today. I think I might just adjust the valves while I'm at it, the FSM did have that listed in the troubleshooting steps, and I could stand to re seal the cam cover anyway, who knows if that gasket is suspect or not. Hose kit also came today, so all of the vacuum hoses are getting changed out. Maybe if I'm lucky I'll be able to accomplish all of this today. Will report back with results. As always, if anyone has anything to add, it is sincerely appreciated!

Late night update: So I started the car and put a vise grip on the return line coming off the fuel rail. - No change in fuel pressure. I didn't think the car was low on gas considering its only ran for maybe an hour or two combined since I've owned it, but I only put in two gallons to begin with. I decided to trust the fuel gauge that was pegged on empty, and put two gallons of gas in it. After I put the gas in, I started the car, and fuel pressure shot up to exactly where it should be (high 20's, low 30's.) I pulled the nipple off the FPR and I want to say it even read around 36 when I did that. Of course the problem during all of this is the engine was still running like in the video above, The fuel pressure also began to slowly fall, eventually settling on 14 or 12 (back where it was since this problem appeared) before the car eventually died on its own. I assume my next step in the process is to look at the tank and pump. Unless there's something in the tank I wouldn't see, the fram inline filter I have coming off the tank is clean. That doesn't preclude a blockage in the tank though I suppose. All of the soft lines, pump, and engine bay fuel filter were all installed new a few months ago. I feel it worth mentioning that for some reason, the car seemed to sound like it was running better when that PCV hose was sucking in vacuum from atmosphere. Even when I pulled the vacc line off the FPR (which had suction from the hose, not the FPR itself) the engine seemed to smooth out (though the fuel pressure was still low.) Just weird that vacuum leaks seem to make it want to idle better and not die, but still run rough, and closing up the leaks just makes it run rough and also want to die. Edit: Assuming I end up having to replace the tank if there's some sort of blockage - Do the s30world tanks for the 78Z fit the 2+2? I ask because, well, my car is a 2+2, build date of 12/77 I want to say. What are the rubber insulators they are talking about on the website? It says you can re-use the old ones, but I'm just wondering.

Will do, I'm about to head out to the garage and do the test. Luckily I have someone that can turn the key to start it while I observe the gauge in the engine bay and clamp down on the return line. Will report back. Pressure didn't drop immediately after the car had been off when I did the priming test last night, but I noticed it had leaked down a few PSI after about an hour or so. I guess I should probably clarify the pump noise level. In a dead quiet garage, you can hear it running when turned to start (without the starter engaging.) When the car is running or if there were ambient noise around, likely it would be hard to distinguish unless you knew specifically what to listen for. Yeah, it wouldn't get above 14 PSI running and after disconnecting the starter spade connector and holding the key to start four separate times at about 15 seconds each~ it barely reached 22. This wasn't an issue before, definitely looking into the tank as part of the tests. Ironically leaving that PCV hose vented made the engine run smoother, the exact opposite of what is supposed to happen. Once I ran the PCV line it now has more pronounced issues. I'll find the solution, just gotta keep digging.

I've looked at the tank and from what I can tell everything coming out of it is clean. I suppose it won't hurt for me to just take the feed line off and put it in a gas can, though. If the fpr isn't operative when the car is off, why does the manual say to test the fpr with the engine off? Genuinely curious, not trying to be sarcastic or anything.

I managed to find a hose that fit, luckily an auto parts store had one in stock from another car that involved some minor trimming to length. However, it is as I feared. With that hose connected (aka, the pcv valve not sucking in air from atmosphere) the car is back to wanting to die again after running. I had to back the idle screw out about 1 1/2 - 2 turns to keep it idling. Ive included a video of it below, but its doing the same thing it was doing, but worse; Idling rough, missing, etc. Eventually it died after about half an hour of continuous running (temp gauge got to the lowest point but not far past it, I just added half a gallon of coolant so I assume it was low. Yesterday it would get up to slightly less than or about halfway on the temp gauge.) Fuel pressure seems to be down now, too. the inline gauge was reading 12PSI when it was struggling to run, giving it gas didn't seem to increase or change it much. A few days ago it was getting around 28 PSI. I've got an inline fram filter coming off the tank and the gas doesn't look contaminated (though the filter only has fuel present in the bottom portion of it, but it was always like that since I installed it.) EDIT: I decided to try testing the fuel pressure with the engine off. I disconnected the spade connector at the starter, battery has a good 12 volts. I've done this before, and pressure was fine when I first redid the pump/lines/filters a few months back, but I figured that it was 12PSI just now, why not retest? Turning the key to start, it took a surprisingly long time to get the pressure to reach 28-29 PSI. I mean holding the key to the start position for 15 seconds about 3-4 times finally got it up there. Fuel pump is loud and clear (and new.) All the soft lines are new, fuel filter is new, gas looks clear. I did notice that the vacuum line on the FPR seems rather easy to take off, but nothing seems to be holding it on, either. Could this be an issue with the FPR itself? EDIT EDIT: Being that my car is a 78, it looks like FPR's are basically unobtanium. EF-37 mentions that if the fuel pressure isn't at 36.3 PSI to replace the regulator...and it took forever to just get it up to 29. So it would seem that connecting the PCV line has indeed made the running/idle problems worse. It was misfiring before, but now with that hose connected its worse and likes to die after it has been running for awhile. It will restart with some cranking, but I'm at a bit of a loss as to what my next steps should be. V_20240304_223924_ES0.mp4

Well, It appears I had a lapse in memory. The receiving end of that bung does indeed point out to the side and not down. The replacement hose looks to be out of stock. So I'm off to source a brass coupler and a 1" hose to join them together. Also, I included a picture of just what that hose looked like coming off the car.

Looking at EC-2 on the FSM makes the BCDD look like it has a bung on the bottom of it in the initial picture. That's on me for mistaking it as such. Leave it up to me to do something dumb like that in a community I'm new in. I did find a picture from ZcarDepot, but I swear the other bung that hose came off of (the larger one) was pointing straight at the ground which is likely why I confused it with the BCDD (because it looks like a bung in the fsm, or I suppose one could confuse the drawing as it having one.) Then again I could have just been entirely mistaken due to lack of sleep. I'll double check shortly. The post from Zcardepot: I could be wrong, and like I said I'll look shortly, but I swear that bung did not point out parallel with the car, instead perpendicular to the ground. Edit, now that I think about it, that pcv valve under the intake manifold did seem further back towards the engine bay, too. But again, this will be cleared up momentarily. Edit: appreciate the continued help @Zed Head (and anyone else giving their time to contribute.)

The plot thickens... Honestly the more I work on this car, the more confused I get. So, I replaced the hose in question that runs from the cam cover to the throttle body with a 5/8ths, making sure to transfer the flame arrestor as well. I wanted to replace the hose under the intake manifold, being as how it had an entire side missing, but unfortunately it seems like the side that originates off the bottom of the intake manifold is way smaller of a diameter than bung it connects to at what I think is the BCDD according to the FSM. I started the car to check if either one of those bungs draw vacuum by attempting to plug them with my hand while the car was on and the end on the bottom of the intake manifold seems to do so (which I believe is the PCV valve?), while the other connecting end on the BCDD valve does not. Here's an interesting discovery I made: The engine will idle and run on its own without dying (while continuing to feel like its misfiring) so long as that bung under the intake manifold (PCV valve?) remains open to just suck air in...weird isn't it? If I plug it, the car will go back to what it was doing, running more rough than it already does, and eventually dying if I don't tap the gas when the rpm's get low. The car still misses when you try to rev it WOT and breaks up the higher the rpms get. Part of me decided to look and see if adjusting the distributor timing might help/hurt; I was looking for some kind of change. However, with the car running, you can turn the distributor entirely to the left or entirely to the right and there's virtually no change in engine RPM whatsoever. I'm not sure how the L28's work, but on other cars I've had that had a distributor, making dramatic adjustments like that (full retarded or full advance on the distributor) while the engine was running would at least prompt a change in the idle. I didn't notice anything. So part of me wanted to check and make sure I have the distributor on right, even though I've checked it before. Can someone verify I have the plug wires connected right? I'd think adjusting the distributor timing should at least prompt an audible change, but it didn't, so I want to verify I have the plugs connected right. There isn't any line on the side of this distributor cap to aid in any markings of the cylinders. Also worth mentioning, The car had been running a brand new set of plugs for maybe an extreme total of an hour runtime over the combined past few months of troubleshooting. I checked them and they were black, soot/charcoal black. Absolutely covered. I replaced them with a fresh set today. Plug wires as they sit: If anyone has any ideas on what to do further, I'd greatly appreciate it.

Gotcha. If the kit doesn't have the means for me to cut to length and run that specific hose (or any others I suppose), I'll buy them separately if available or the proper size and cut to fit. The picture they have of the kit installed looks pretty comprehensive though, so hopefully I'll have everything I need hose wise. I went with black hoses personally, but it gives an idea of what it replaces I think. Uploading photos seems to not be working right now, so I attached the link to the kit below. https://hpsimotorsports.com/collections/datsun-280z-silicone-vacuum-hose-kits/products/hpsi-silicone-vacuum-hose-kit-datsun-280z-and-zx-1978-1983

I think it includes a certain amount of feet of each size hose on the car and I have to cut to length. I would assume they would include enough hose for the pcv hose, but as far as just a pcv hose itself, I don't believe so.

I've ordered that hose kid I've mentioned, eta is on a Monday. So ideally I'll be able to get all the hoses replaced with healthy, fresh material. Edit: Diagram on EC-2 was a bit interesting to read, but good enough to narrow down the location. I was at least in the right vicinity.

Car has been operated on private road twice, < 1/4 mile each time with lug nut torque checked before and after, will not see public roads until this issue is rectified. I'm not new to working on cars, but mounting this one rim seems to be the only problem child in the scenario. Rear wheels are secure, drivers wheel is secure, no clearance issues otherwise so I think this may be an isolated issue with the studs. I do appreciate your help and advice, and I will make sure/verify the studs are pulled in and look at the angle of the studs as well as cleaning up the hub surface.

Looking at the studs from behind the hub, they look like they are pressed in all the way; But I honestly have no way to know that they are aside from that simple visual, and if they're the same length, I'm thinking there's either a rim difference, which I don't see, or they aren't in all the way like you are saying (but they are all sticking out the same length on that wheel.) I did order a stud installer, would that work better or should I stick with the nut or lug to draw it in? Anything I need to watch out for in terms of deforming the metal around the hole? Here's the stud tool I bought: https://www.rockauto.com/en/moreinfo.php?pk=2784232&cc=0&pt=1001095&jsn=5

About that bottom hose, is it located on the accordion pipe coming off the afm as well? I was looking under the intake manifold and I couldn't see it easily, then again I could have just been looking in the wrong place? Ordering that hose kit tonight and going to get busy changing out al the rubber air hoses/vacc lines, I don't think it would be a bad idea to assume they are all suspect at this point.

I assume the hubs are the same thickness, but I didn't measure. Just by eyeballing it they look to be the same. I could very well be wrong but I'd guess if the difference was that significant it would be something I could spot right away? They both came off the car, but I noticed even before I had the old studs knocked out, the passenger side hub still only had 2/4 lugs on it.

Yeah, I fixed the clunking noise, that was coming from the drivers side, and was because the shank on the lugnuts were too long. These lugnuts on the passengers side are definitely not going on. I've tried for about two hours. The lug nuts will thread on fine by themselves, but they will not all go on if the wheel is on the hub. The most I can get is 3 and that was insanely difficult to manage. No matter how you try to move/hold/align the wheel, you can not get all four of them on there, the space around the studs aren't even. I've tried about four different types of lugnuts before on just the studs themselves and with the wheel on the hub, something isn't right, it just won't catch, the other side went on fine.

So, early morning (still night for me) update! I started the car, drove it around the block a few times, it definitely missed and sputtered on WoT, but would climb up there. At one point it did die while sitting in my driveway (fairly certain it was warm by this point because I had driven it around the block already a few times.) It initially didn't want to restart, but after 5-6 tries it did, and then proceeded to idle for half an hour almost before I turned it off. RPMs would fluctuate at idle at a random interval (1,000 - 1,500), but this time it didn't want to die like it did yesterday, so the problem is definitely sporadic I guess you could say? I did grab the linkage while the car was running and attempted to push the throttle closed, and it didn't seem to want to close any further, per Zed's suggestion. HOWEVER! As I was staring at the engine, pondering life, I thought to myself "look at the hose coming off the valve cover" So I did, and it was very loose. VERY loose. I felt the underside of it and there was a gigantic crack; I attempted to pull the already loose hose off, and it just fragmented into two pieces. I put my thumb over the end that led back to the AFM accordion pipe, and the idle audibly lowered, so maybe I've got vacuum leaks to chase down? Would that cause the missing/stuttering because its metered air that's lost? Also, as I turned the car off I could hear a definite air hissing noise that stopped after maybe 4-5 seconds as it waned. With that being said, does anyone have any recommendations on any complete kits for the vacuum/air hoses? I found this one, and it seems pretty complete, was hoping to get some opinions: https://hpsimotorsports.com/products/hpsi-silicone-vacuum-hose-kit-datsun-280z-and-zx-1978-1983

Okay, so! I changed out the lugnuts on the drivers side, sound is gone. Thanks for posting that drawing, that helped a lot actually in determining if the lugs were the right size or not. However, I still have an issue: I can not for the life of me get all four lugnuts on the passengers side front wheel on, it's not happening. I think the machinist bent the studs when he put them in. I did take pictures to the best of my ability, but I'm not an expert to tell if they are bent. Can someone with a better eye for these judge for me? I tried to get a picture from the front, left, and right. Something to note: The studs on the drivers side stick out past the holes in the rim, they do not stick out past the holes on the passengers side. This is very odd. I bought eight new studs of the same kind and had the machinist press out all of the old ones on the front hubs and press in the new ones. Unless he mixed up the studs (or rock auto send me exactly four of the wrong length) these should all be the same studs, so why would one side stick out past the stud holes on the driver's side, but not on the passengers side? I guess the length isn't super important so long as I can get the studs to go in right, but why would they stick out longer on one rim if they're the same length studs? (unless these rims are different on the back versus the front, I believe they are factory rims? The picture after the stud photos shows the passengers side front rim. The lugs will thread onto the studs no problem without the rim being on the hub, so I know the threads aren't damaged, but you absolutely cannot get all four on there, the studs aren't in the holes centered. From what I can tell, they are pressed in all the way on both hubs. If anyone could help me make sense of this..I'd really appreciate it.

Makes sense. I guess at the time I figured if it was sticking it would be sticking whether the engine was on or not. Lack of foresight on my part. I'll give it a try tonight, I appreciate the insight!

You're saying to grab the linkage and push it towards the closed position? I did try that the other night, and it seemed (to me anyway) that the linkage was opening and closing properly. With no pressure on the throttle, the linkage didn't seem to want to budge any when I tried to push it closed.

Indeed they are. It's simplistic in a way but challenging at the same time. I'll get a video tonight if possible, not that it will help much, but it will hold that idle pretty steadily before it starts to stutter and drop but a tap of the gas keeps it alive. It did die once (because I let it) and started back up fine, though. I'm moreso scratching my head because I could understand a vacuum leak keeping the idle high, but something is making the rpm's drop after an extended period of time. Maybe when I document it with the video it will show the timing of it better. I let the engine get fully warmed up as well just to see if it would change, this seems to be the case whether its cold or warm.

Would the AAR or BCDD be symptomatic like that though? I'll default to the experts here easily. But the behavior of it is just weird. While letting the car sit and idle, it will stay at 1,500~ RPM, slowly drop down and stumble/die when the idle gets low enough that it can't keep itself alive. Giving it a stab of the gas pedal will bring it back up to rest at 1,500 and then the process will repeat. What could cause it to hold idle at 1,500 that long and then drop slowly/moderately to the point the RPM's get low enough to start wanting to die? I'd think if it were a vacuum leak that the idle wouldn't drop like that, but again, I'm really new to this platform. Edit: Also checked throttle linkage, doesn't seem to be binding up or having any issues.