NewZed

Need more detail.

That is right. So, basically, your wiring is not as the factory intended it. Get the factory wiring diagram and make it like it was. Try the Electrical chapter - http://www.nicoclub.com/FSM/280z/1981/

Just a refocusing type comment, but driveline balance and runout problems would be more tied to drivehsaft RPM, not load. The original comments about angle changing due to diff nose lifting seem most likely. Based on the stated facts. Something that changes when load is applied. Seems like this latest effort might be helpful but off target.

Don't forget that if the air in the engine bay is just recirculating through the radiator it won't do much cooling. A lowered car with a front air dam might not allow the hot air to leave. Your observation about what happens with the hood open is a clue. Maybe focus on getting the air out from under the car, or through the hood, or access panels. You might be just spinning your fan blades otherwise.

You need a diode on one of the wires from the T plug. You didn't say what year car you're working with. But it's a common problem, after people rewire their 240Z's to use an internally regulated alternator. Pretty sure that the L wire is the one that needs a diode. Position the diode so that current only flows to the alternator but not back. Found a good description. I think that all you need to do is add the diode. Post #4. Assuming that somebody else already rewired everything else for an internally regulated alternator. http://www.zcar.com/forum/10-70-83-tech-discussion-forum/110443-more-73-240z-voltage-regulator-swap.html

Where's the Google link? It is odd-looking, that's for sure. What kind of Z are you working on?

Don't mean to be a downer but if you still have a rubber diff mount in the back, after the PO installed 500 horses, there might be a lot more lacking back there. Kind of sounding like it might be a build budget depletion sale from the PO. Good luck and read some of the SUNNY Z and RebekahsZ threads, among many others, on breaking things and how they fixed them. You might still have the original open diff.

We used to call that dog-tracking. It's caused by the rear wheels being on an axis that is not parallel with the front wheels' axis, when all wheels are parallel to the car body. If you can see something odd about a rear wheel that's a good place to start, Could be worn bushings. How is the wear pattern on the rear wheels? Is this a right hand steering wheel car? Passenger side and right side are the same for US models. I found a few links on the old interweb. These cars don't have a lot of adjustment so you probably have a bent part or worn bushings. https://www.theglobeandmail.com/globe-drive/culture/commuting/dog-tracking-should-give-a-driver-pause/article1367167/

You have a thicker radiator, an AC condenser, and a shroud of some kind, with electric fans. Anything else up there? Cold air intakes, intercoolers (not clear what engine you're running), horns, alarm systems, spoilers..etc? Maybe you just have too much area blocked and a too long path for the air to flow. A simple test of coolant flow versus air flow might be to increase your idle speed and see if it overheats faster or slower. Since you don't have a mechanical fan all you'll be changing is coolant flow rate.

It might just be a different style of shaft, instead of a length of machined rod. Could be that the center piece locates and retains the shaft ends in the center of the diff. The sides of the piece also support the spider gear, and act as another bearing surface, probably reducing wear. It looks like just a more robust two pinion diff. Probably little benefit to swapping, unless the other diff is worn. Spend some time measuring wear on the other diff.

Nissan addressed a similar problem in 1974. They defined another phenomenon that they called percolation. Basically it's hot float bowls causing the fuel to evaporate, making the fuel-air mixture over-rich. They wrote a thing about it. http://www.classiczcars.com/files/file/60-fuel-system-modification-plus-73-74/

The RTz design can be modified if your angles are off. Holes can be slotted, the GM mount can be ground. You're right though, if it's good at cruise and decel now and you change the angle, you might create a new problem. The best way to go is to measure and make it right. Hoke probably considered angles when he designed his mount. You might send him a message and ask what diff angle he designed for. Apparently he monitors his Facebook page most closely so that's probably the quickest route.

Dang. I was just about to post a suggestion. It was a good one too, 5 years of thought behind it.

Just puzzle-working, but if it ran well when you shut it off in the evening then ran rough when you started it in the morning, doesn't that imply that the seat fell out over night, or just after you shut it down? The valve was open, the seat dropped, the valve started beating on it as soon as you restarted. And, just for consideration, it seems possible that the valve seat area cracked and let the seat loosen. I think I see the coolant to chamber crack in your picture, but have you checked the seat area for cracks. Just trying to get the story filled out.

Here's a good start - http://forums.hybridz.org/topic/58895-what-is-the-deal-with-solid-diff-mounts/ There are other descriptive threads out there, including one by Ron Tyler, explaining why he made the modified diff mount. His moniker here is RTz. Use Google and "site:hybridz.org" in the search box along with your search words to search the forum, the site's search function is very poor. It won't even use the three letters RTz so you can't search for Ron's post. And he's a moderator.

That would still be a two then. Don't know what that thing is. Spin the wheels and see what it does. Interesting puzzle. I've seen similar parts in images but haven't dug in to the various varieties out there.

Not positive but I think that the piece is part of a a four pinion diff. Your 3.9 is a two pinion. They're both open diffs, but the 4 pinion is stronger, I believe, or at least, more durable. Edit - #7 here shows a good comparison picture. http://www.gmh-torana.com.au/forums/topic/66959-mystery-diff-conversion/

Edited. A moderator must have deleted my other post, with its good information, in the other duplicate thread. So the comment that was here just looked like random rambling. Context, moderators, context. Consider all...

The diagram on page EFEC-70 of the 1982 FSM implies that only the AAC and VCM and a few other valves, like EGR system parts, are controlled by the ECU based on the TVS position. Not fuel. If you don't have those other devices it looks like nothing will happen.

Here's a list of other cars that used it, if you have to go junkyard. Watch out for 1975. 38210-N3100 http://www.carpartsmanual.com/datsun/Z-1969-1978/power-train/differential-gear/r200/37 http://www.courtesyparts.com/oe-nissan/38210n3103

That's a logical point. Misalignment only during acceleration. Not a lot else to go on. Assuming an LS3 due to forum name choice. And " Brand new driveshaft shop driveshaft and Hoke engine/trans mounts". Not even really clear what the Hoke parts are. http://hokeperformance.squarespace.com/store/ http://hokeperformance.squarespace.com/ls2-engine-mounts/

No offense intended to anybody in this thread. I think that we're all nostalgic for the more sophisticated conversations of the past. But this is just a tank, a pump, and carburetor on an engine that's been transplanted so many times that somebody wrote a book about it. The solution might even be covered in the JTR book. I don't have a copy myself, but even if it's not in there, for the Z's, there are thousands of simple electric pump to carb systems out there. That's why each pump has a full set of installation instructions and recommendations. Slow times on the old Hybridz site...

Still, all you need to do is measure. The pumps seem to be generally set at 7 psi. Should provide desired pressure at the carb after the pressure drop, easy to confirm with a gauge. These types of things should always be confirmed by measuring, no matter how expert the opinions are. Just like there's no best on Hybridz, there's no wrong. If it works as intended. There might be better, but saying it's wrong is wrong. Why spend a bunch of money and time if basic knowledge of pressure drops and proper installation, confirmed by measurement, get you where you need to be. Keep it simple. He's not building a top-fuel dragster, it's a simple 330 HP V8. There are hundreds out there.

Don't use the word modification if you're not modifying and don't want to say the same shit twice. Grammar matters.

Did you replace a BIP373 or did you switch from the old transistor? Kind of reads like you changed a few things along the way to the BIP373. Could be that you just never had the BIP373 installed correctly in the first place. https://www.diyautotune.com/support/tech/other/bosch-bip373-ignition/