Dave WM

last one

video

the single DPDT relay did the trick. wired up 240dkw described, works great. I deleted the old video to avoid anyone following in my foot steps. will post a revised later.

After going thru this same kind of thing, I ended up just fixing my old alt, in had a shorted diode pack, replaced it (3 wires maybe 30min total job) and been running it ever since.

roger that, I think my previous had an issue with the motor back feeding one of the coils anyway, making it a random event on which way it would go. Not sure but I like this setup better thanks for posting

Messed with it all morn, went so far as to remove the valve springs and see if I could feel any oddness in the feel of them as I spun then in the seats. No joy. So going to just drive it for a while, then will pull the head and see if I can figure out what is going on. It starts smooth in the morn but as soon as it warms up a little you can pick up on the miss at idle, and its from 3# (been saying #4 all along, duh was counting from the back). I put a new plug in to get a reading, its def firing just weak on compression. BTW the valves would hold themselves up under pressure without the springs, the intake seemed better at holding (took more pressure to break away) than the exhaust but not a lot. I seems like the valve seal should have been worse considering who down on compression it was. I still think the valve as the leak down points to that,

got up early to wring it out, still missing at idle, pull #4 plug wire, little to no effect on idle. Will be trying another compression check to see if still at 125psi. If so will use the leak down to confrim rings or valves. From there I am prob going to pull the manifolds and see what I can see from inside the open ports. From there will most likely pull the head and examine the valves and seats. Best case is some clean up and lapping. If I see anything big time wrong (like a burnt valve) I will prob just swap the head to the MN47 that seems fine on the test engine. Update on the relays, coming in today so I hope to get a video of the antenna working with the old OE up down switch. 2nd Update on antenna, going to try yet another mast from ebay, If I ever find one that works I will post up. I wonder if there are some refurbishers out there that know a subsitute mast out there and are just keep mum on it so they can sell refurbed units for $$$$

got the new starter in, warm engine, #6 was 165 psi, all the rest were about the same but now #4 is 125 argh!!! did a wet test, no change, getting late, will do another leak down on #4 pretty sure its not the bottom end since there was no change with oil added to cylinder. I did a quick valve lash check on #4 all good there, even made some minor tweeks (engine was not hot or cold but warm so I aimed for the inbetween setting of .009 in and .011 out). Still no change. leak down should id the offending valve. Guess another I Italian tune up is coming.

Trying to stay with the OE installed antenna switch (SPDT center off). The antenna came with a pre wired center off DPDT X configured switch.

too many episodes of battle star galactica for me to do that.

came up with this

I would not drive it until got a good alt JIC it gets worse. On mine it was way over volting based on the brightness of the head lights.

maybe a solid state fix

I messed up my OE power antenna (bent mast badly). Found a replacement on ebay. Looked perfect right number of sections, harada, same wire colors and bullet connectors to fit my 75. Works fine when powered up with outside source BUT does not use a center tap motor, so you have to reverse the polarity of the wires for up and down, there is NO center tap ground section. The stock radio up down is a SPDT sending B+ to one wire at a time, B- is thru the chassis ground. So it seems like the only solution is TWO SPDT (or more commonly avail DPDT) 12v relays. Each coil will get Ground and one of the existing wires from the harness so each relay will work independently of each other, depending on the up or down of the antenna switch. With that it should be simple run both a B+ and B- thru each of the switched sections of the relays, then connect up the antenna motor to both, one reversed from the other. Unless a relay gets stuck it seems this would work out fine. I dont know if there is such a thing as a dual coil relay that I could configure like a DPDT switch with a center off, like an old DPDT knife switch I used to mess with doing this reversal thing (in that case the antenna motor goes to the center off, then reverses power is provided to the two poles, pulling the center to one side or the other reverses the center polarity).

Yes but it did it on mine regardless of engine speed. Also when it went to the charge side my headights got much brighter. It always started with a few seconds of high discharge, like 30-40 amps out of no where for a second or two then would jump back to 30-50 amps charge and much higher than normal voltage (again head lights) I was concerned that if not for the load of the battery, the voltage would have skyrocketed even more. At 1st I assumed it was a VR issue (i had the external VR) however a swap to a known good did not correct the issue. I replaced the alternator and have not had an issue since. Now the swings I mentioned were for full seconds not fractions, enough to make you think someething bad was about to happen. I have always gotten momentary spikes bot those were indeed momentary. Not sure what is causing them, but does not seem to hurt as I have put a lot of miles on the car with no electrical issues since the fix.

The Mast got bent fully extended right at the bottom, so the bottom most shaft will not retract. it bent and torn. I have it back up and working but for that one part. Also, the acorn nut got damaged, the plastic top part. I wrapped it with electrical tape as a temp fix to keep water out. I was able to find a donor power antenna on Ebay that may work, hoping the bottom rung of the mast is the correct fit. As a backup I scored an OE era correct Harada that may be a direct fitment. That is on the way as well. Somehow, I will get it back on-line for full retract. Good news the misfire is gone, seems like the Italian tune up is holding. I will try for another compression test as soon as my new starter gets here. My old one had a smoked armature (wires brunt, string wrapping toasted clean off. I got a rebuilt Hitachi from a Nissan dealer, my Autozone replacement that I am currently using has an iffy Bendix, it engages but does not pass power consistently, I presume the contacts are getting pitted (it was the one I had on my engine test stand) I have a spare Bendix that i pulled from the smoked starter, filed the contacts clean so may try that on the autozone starter, reinstall to new turbo test stand. Lots of musical chair's games on starters lately.

good point. decided to only respond to regulars here. I have a couple things coming that may help with the antenna issue. ebay stuff.

on to other stuff, Starter replaced, but my replacement is intermittent so will prob have to get a new one or rebuild my old if I can find a local rebuilder. Had a very hard time starting. finally after getting started (long crank times) i was messing with it and decided to check wiggle the temp sensor, bingo instant off by just touching the sensor. I had a spare sub harness plugged that in seems to have fixed it. I will make sure I have a spare temp sensor just in case its a problem. I did deoxit all. can wiggle the connector but one time I did hear a hiccup so not sure if its fixed. I may just make up my own with some better injector terminals. Idle is smooth now, power balance shows all holes are about the same. Back to the temp sensor, the plugs looked to be a bit rich to me so I may just go ahead and replace the sensor (hope I can find a nissan ) as well as the harness and then treat dat boi to some new plugs. Overly rich mix and grandma like driving may have combined to add the problem of excessive carbon build up.

I called (he supplied gave me a cell phone number, I used a cell phone), response was "google cell phone person not available", left a message. my message was I suggested he list on ebay, as I would not want to take advantage of him. Explained his low post count as my reason for not wanting to deal directly. I like to give people the benefit of the doubt. But I also know you cannot con an honest man so ebay is my way of being honest. he was getting back to me pretty quick, not so fast after I recommeded ebay.

almost back in business. replaced smoked starter (guess to much compression testing and oil flow checking out of the spray bar), re test #3 and #6. All good now. Before the started smoked I used some brake clean, aimed thru the spark hole at #3 exhaust valve, good shots, then added some engine oil to account for the brake clean washing the cyl walls clean of any oil. Just about a cap full of oil added back thru the spark hole. Turned over engine all plugs out to clear #3 of residual oil, then retest, about 175 (normal for a wet test). Pretty sure I have all holes working up to snuff now. Only thing left is to fix the antenna, have a lead from the classifieds, but not sure if legit, a poster with only a very few posting. Any way trying to follow up on that. I went ahead and got a NOS looking semi auto antenna off the bay, just is case I can't salvage my existing unit. anyone here know a "frankly100" member?

View Advert antenna mast for power antenna 280z looking for a donor power antenna or just the lower mast section (broke bottom mast when fully extended. let me know what you want for it. thanks Dave Advertiser Dave WM Date 10/13/2022 Price $50 Category Parts Wanted Year 1975 Model 280z

that is my plan, will post up results videos later.

well will have to see if #3 comes back, seems odd to go from 160 to 125 just like that, my guess is a bunch of carbon from the redline FI cleaner is flaking off the tops of the pistons. I did borescope #6 it was dry black carbon on top with lots of large clean areas as well. Not just around the perimeter like an oil leak coming up but more like large flake patterns. IF it persist i was considering pulling the manifolds back to expose the ports, then pull the valve springs and shoot in some cleaner to the tops of the valves. I am mainly thinking the exhaust valve. tops since that is where the trouble is. then manually putz with the valve stem to break up any deposits that may be sitting right at the valve seat. But for now will just do some more fast driving to see if I can clear up #3

Italian tune up did the trick! #6 at 155, but now #3 is at 125, hmmm seem odd as it was fine. I suspect I just need to do some more hard driving. Got video of the results (otherwise it did not happen). Same deal on #3 Exhaust valve (wet test no change, blowing smoke from smoldering rag out tail pipe at 90psi from leak down test). I am a beliver in the Italian tune up now. I would take it up to 5500-6000 and some hard pulls thru the gears maybe 15 miles out on the Tpike. So the head will stay on for a while. also managed to break my antenna mast coming into the garage, not sure how. will be posting in the classified for a donor...