NocturnalEmber

A positive update (so far at least), I was able to get that stud out via welding a nut onto it. Took about four tries because the weld kept breaking, but the stud came out and it *looks* clean thread wise. I want to run a thread chaser inside that hole though before I go trying to thread the replacement oil sensor in fully. I did attempt to thread it in, and past a few turns I started meeting resistance so I immediately stopped, all threads look good though. I've read somewhere that its 1/8" BSPT, but I wasn't sure.

So an interim update, my ignition switch and my oil pressure sensor have arrived, and Thursday I'm going to attempt the extraction of that stud; I've had it sitting (and treated regularly) with Kroil, hopefully that will give it enough time. On a side note - Can someone recommend an oil filter sandwich plate that will fit the L28? I've searched google and surprisingly there isn't one that seems to be car specific or one that isn't part of a large kit. All I need is the sandwich plate that has two ports on it. Ignition switch will be ideally put in tomorrow @SteveJ. Will be following your guide and most definitely labeling the connectors as I replace them. Will report back when it is done!

I treated it with Kroil today, going to do that every day until probably Friday, then I'll start my attempts at extraction, which hopefully is met with success; Assuming I'm successful at getting it out, the next thing on the list is installing the replacement sensor; Ideally the threads won't have been damaged, and I can get back to the electrical troubleshooting.

So assuming I were to not go the welding route initially, would it be best to use the socket extractor that Zed mentioned above? or the one I have to hammer in? There's also the one I mentioned from advance auto parts above, I'll include a picture of it for ease of reference (but honestly I'm not sure there's enough stud protruding out of the block for it to really grab.) There isn't much room if any to hammer anything in there, that's my main concern with using something I would have to tap in with a hammer, I don't have the room to swing to build up enough momentum, and I have no way of knowing that I'm driving it in straight. Concerns about welding are definitely noted, and honestly if I went that route I'd have to clean and prep the area beforehand. The oil is a concern, but if I weld far enough back, I don't think there would be any weld getting into the tiny hole in the stud. If I felt more comfortable about being able to get a stud extractor in there straight that would be an easier method.

I forgot mention in my initial post about this that I first tried using the wrench to get it off normally, it moved a hair, but then started rounding off the heads (and if I had to guess I think it might have been rounded off already for it to get to that point.) The head was almost completely rounded off, and I was sure I had the wrench head on there properly, and the proper size. I attempted to cut off the body of the sensor to leave me with more room to get at the head, which didn't work, saw clearance wasn't possible and the blade I had didn't get very far. From that point I moved onto the vise grips, which sheared it off, leaving what is left now.

I honestly don't think I can get an extractor in there with enough accuracy to go at it straight on because of the clearance between the engine and the body. I'm not opposed to trying it if I felt like I could get it in there properly, but if I tap it in crooked I think I might mess it up even more. I started with B, then moved to A. Two forms of A in fact, the ones pictured, then ones with probably a foot and a half handle I found in Harbor Freight, I just didn't have the strength to get it to clamp tight enough; When i could get them to lock, the vise grips would just turn on the stud. I was originally planning on cleaning the area really good with brake parts cleaner, then washing it off really well by hand with soap and water to ensure there wasn't anything flammable nearby, and cover the engine bay in lightly damp towels to prevent any risk of fire.

I already tried the vise grip attempt, but I honestly can't really apply enough force to crimp it down tight enough (the tightest I could get the vise grips to clamp, I struggled, and I mean I *really* struggled to get them to clamp, and they just turned on the stud.) At this point I could always enlist the help of some much larger muscle and see if they can manage to get it clamped tighter.

The space for me to get it in there with any sort of accuracy is a big concern since I can't look at it head on, so I guess you could say I'm worried about making it worse, I couldn't get a hammer in there and have enough room to even swing it moderately with enough force to drive the tap in. I'm really hoping I don't have to pull the engine (wouldn't be the first time I've removed an engine by a long shot.) Just because of clearance issues I'm wondering if it might be better to rent a welder and weld a nut to that stud. Or I could try that socket stud extractor first, but I honestly don't think there's enough stud left that it could really grab onto to turn.

So based on that chart the fuel pump would still work even if the oil pressure switch was bad assuming the alternator was working? I figured if the oil pressure sensor was bad that would cause an issue with running when key was on. Also - I pulled the plugs to try and remove that oil pressure sensor when it was still whole. The plugs (that have maybe fifteen minutes of runtime) are black, so somethings making it run rich. Also @SteveJ Pictures as promised...It's not pretty. I'm not sure if I can get the drill bits or tap wrenches in there with any kind of accuracy. I did see a stud extractor socket that Performance Tool has (available at advance auto parts, depending on your location) that I was going to consider, but I honestly don't know if there is enough stud left sticking out of the block for that to work. Here's what I was considering - https://shop.advanceautoparts.com/p/performance-tool-stud-extractor-w83203/11931907-P?searchTerm=stud+extractor It's a bit hard to see in the first picture, so I held a light up to the block, you can see the silhouette of what is left remaining of the stud.

Just an interim update: Ignition switch and oil pressure sensor did arrive. However, the oil pressure switch was rounded off, and trying to use vise grips made it shear off, leaving me with a partially exposed stud ouside of the block and whatever threads are inside the block. As a result I am currently trying to tackle that issue, as I need a working oil pressure sensor for the engine to run being that it's a 78. I did notice there was a small amount of oil on the wire connection when I unplugged it, and it spun almost freely, so the sensor was likely bad.

Awesome, sounds like I have my tests planned out. For step 3 with testing the sensor itself, grounding the pin on the connector that connects to the fuel pump, is this the vertical connector?

I can't say I've seen the words "useless" in the FSM before, but that gave me a good laugh. So assuming I text the sensor as well as the harness side of things: You mention the vertical pin on the T is grounded by the oil pressure sender when the engine is running, Would I just set my multimeter to ohms and test between that terminal and the negative on the battery? Again, much appreciate help so far Steve!

Will do. I did have one question. Based on your explanation, this test is performed by probing into the harness on that wire with the positive lead and a good ground, can I use the battery for the negative/ground? Also, in terms of checking the actual sensor itself for functionality, is there a process for that? The FSM just essentially says "does the gauge work? If not replace it."

I've scoured the 78 FSM, and I can't seem to find anything related to how to test the oil pressure sender, am I going down the wrong rabbit hole while waiting for a replacement ignition switch, or is this something to look into? The best I can dig up on the FSM is "Clean contacts or replace" (paraphrasing a bit.)

@SteveJ, While I'm awaiting an ignition switch, I just go out and attempt to repeat the condition again with the car to try and establish it as consistent rather than erratic or coincidental. Car was cold, it started with a flick of the key (maybe 1/2 a second of total crank time.) The car ran rough, but ran, and I let it sit to see how long it would maintain that, and after about five or so minutes, I went to give it gas, and it immediately died when I tried to give it throttle, and would not restart. Gauges were working, brake light was on and bright, seat belt warning was on when key was switched to on when I tried to restart it, but the car would crank and sound like it was half firing (very fine lumpy noises if you get what I'm describing, as in it was trying to start but just wasn't managing.) I did notice the oil pressure gauge was non functional, and the car does have oil in it, I took the connector off and cleaned it and put it back on, but it still wasn't working. Doesn't the oil pressure switch have something to do with the fuel delivery? To summarize: I. Will start when cold II. Will run rough when cold and seems to keep running (and running just as rough) if left alone as it attempts to come up to temperature. III. Will die when throttle is applied (most times, I did have a few times where I tried to apply throttle, I believe when it was cold, and it would only rev a tiny amount, regardless of how much throttle was applied.) IV. Will not restart when warm.

@SteveJ, I spent some time with the car this morning and I have something interesting to report. I installed the four fusible links on the passengers side strut tower (mine were corroded at the wire connections, so I figured this would just be good maintenance at this point), and put the relay in. Upon turning the key to on, there didn't seem to be any difference whatsoever. I tried actuating the turn signals, and that just seemed like it put more load on the system and made the seatbelt light go off. I thought about what you had said regarding the fuses, and even though they had tested fine with the fuse tester, I pulled them all out and had a look. Turns out, the inside link of the fuses themselves had what looked like to me, oxidation and/or corrosion. I replaced the fuel pump level fuse, the turn signal fuse (basically what fuses you mentioned are in that fuse box that could be related to my issue). I turn the key to on, and the car came to life. Brake light was bright and shiny, fuel gauge went up to E (i only have four gallons in the tank assuming it was dry, so the sender might be off), the charge light illuminated on the volt meter, it seemed like the fuses themselves, while they tested good, were causing the issue. I tried activating the turn signals via the stalk. Left turn signal just illuminates and stays on, the right one will work inside and outside the car. I do not have reverse lights, and the AC blower motor doesn't work. At this point I started the engine, and the tach was reading about 500~ RPMs. The engine was behaving exactly how it did before though, running rough and dying when I would attempt to give it throttle. It did however restart when I tried, but I have no idea if it restarting a few times was just coincidental luck. One thing I did notice though, My thoughts are beginning to shift to the ignition switch as a possible culprit? I switched the key to ON and pushed/wiggled the key (it stayed in the ON position during this, I didn't change positions of the key physically), and the seatbelt light lost power. I pushed and jiggled it again and the seatbelt light came back on. I'm glad the fuses turned out to be the cause as to why a lot of things weren't working, but with those seemingly fixed, is it possible the ignition switch is malfunctioning with how it is behaving? I'm still stumped about the way the engine is running; It starts, but it doesn't run well and will die on throttle like I mentioned.

@SteveJ This actually just occurred to me, and I didn't think to mention it. When I turn the key to on, the "BRAKE" light on the instrument cluster is somewhat dim, it definitely does not look like it is illuminating fully...could this somehow tie in with corrosion on the relay building internal resistance ?

That's one concern I had, was that there had been some kind of previous band-aid fixes, etc that I would have no prior knowledge of knowing. Based on what I've seen in/around the car, the wiring looks untouched, but that is by no means a conclusive statement about the health of the harnesses. I'll break out the multi meter again and test the W/B at the connector and at the fuel gauge fuse to see if the wire is intact'

I appreciate the fine forensic analysis thus far @SteveJ ; it has been absolutely critical to assisting me with tracking this problem down. I'm going to go crawl up under the dash and look/feel the relay again, It was indeed bolted to its home, and it went in and out of the plug with what minor strength I could muster with one hand curved like it was, there wasn't any forced contortion of the harness, etc to get it to plug in, it went in rather easy. So its entirely possible I was just over thinking things on the "did I plug it in one column of pins over" part. What you are saying about it losing power, that makes sense because the car would start when cold and the issue would creep up seemingly after it had idled for a short amount of time. What confuses me though, is why would the fuel gauge fuse have such low voltage? Just seems awkward for it to be so low. On a side note - I have an ignition relay I can use as a test that I should be getting tomorrow, I believe it is known good working,so maybe that will shed some light on things.

@SteveJI only checked the radio and fuel gauge fuses, and on those I only checked the left side (closest to engine bay/front of car/firewall), I didn't check the right side for voltage for the radio or the fuel gauge fuse. I did however use one of those fuse testers a few days ago that came with a pack of the same type of replacement fuses the car has (the factory ones) that I bought from Home Depot, and all of the fuses tested okay. I didn't get a chance to look under the dash for the turn signal/hazard yet, but I will say the hazard switch and the hazards do work fine, turn signals do not. The car is an AC car. In terms of testing the relay, Being that the voltage readings were all what you expected them to be, does that point to the ignition relay being bad?

Whew, sorry for the delay @SteveJ, but I managed to crawl under the dash and get that testing done. All of your tests were showing the correct voltage when I probed the respective wires into the harness with the key in the position you instructed. (I had the negative lead attached to the battery ground and probed with the positive.) The radio fuse did give battery voltage, however the fuel gauge did not, it was 2.xx volts I want to say. That was the only anomaly I want to say out of the testing. Worth mentioning also before I began the tests I did put the key to ON to check and make sure the seatbelt warning and the brake light lit up on the dash, as I discovered and mentioned in one of my last posts that an apparent loose fusible link in the engine bay caused that to not happen. I confirmed the seatbelt warning and brake light were illuminated on the dash, and then I turned the key off and began to test exactly as you instructed. When I got to the point to turn the key to off and plug in the relay, I noticed when I plugged it in it made a connecting noise, but when I turned the key to on to measure the radio and fuel gauge fuses, the brake and seat belt light no longer illuminated. I unplugged and plugged the relay in a few times and they have since came back to life (is it possible to plug that relay in wrong? Like two pins over so only four are plugged in? I couldn't see when I was plugging it in as I did it by feel and not so much by sight so I wasn't sure if that was what was maybe what caused the brake and seatbelt light to not illuminate when I turned the key back on, and maybe I finally plugged it in right when those two lights started working again? But if it's impossible to plug that relay in wrong, maybe I'm just thinking too much into that) At any rate, that aside, all tests were what you specified they should be, with the exception of voltage at the fuel gauge fuse, which was 1.935x

I hadn't had an opportunity to test the relay yet, work pulled me away more often than I would have liked and I was just dead tired afterwards, but I will definitely do them today and report back! I have indeed, it's been a pretty great resource so far!

@SteveJ, I did pull the green fusible links out and tested for ohms/continuity. I think once the multimeter settled it was .3 ohms maybe at the maximum on each fusible link? So I would think that would mean they are good. I don't know how one would replace them if they were bad, though, I don't see any way to de pin those from the connectors. But at any rate, I will test the relay tomorrow when I am not dead to the known world and report back, I appreciate the help thus far from everyone as always!

I'm decently used to working on cars as a hobby, but this is my first Z. Diagnosing everything is definitely a long process but its worth it, and I'm learning a lot from the car I didn't know about to begin with. I'll hopefully have some answers to report back tonight once I manage to make it out to the garage.

I haven't been out to the car yet to check, but I'm going to get to it at some point tonight, work got in the way today more than I'd have liked.