Air Flow Meter Fails Some Resistance Checks - Repairable?

[Willoughby Z]

Regarding #3 (jumpy tach)- I vote ignition module.

Rock Auto SMP LX511 $108.00

[FastWoman]

Willoughby, are you saying the Nissan Sentra IM will work in the Z? (I imagine it would.) Do you have a pinout or wiring diagram? I prefer the look of the connector on the Sentra module to the unprotected pins of GM's HEI.

I looked up the 280Z specifically and didn't see an ignition module. I did see a service whereby for a mere $275 a company called Jet would reprogram the PROM (programmable read only memory) chips on our analog ECUs (which don't have PROM chips!).

[Willoughby Z]

Sarah,

I'm saying the Rock Auto website lists the ICM for the 260/280Z. No diagrams, pin-outs, sorry.

Poking around on the internet, it seems that module works for most of the mid/late 70s Nissans.

I've had the issues with the crazy tach and the stumbling, hard to start, etc. and solved it with the ICM.

-Kris

New Standard LX511 Ignition Control Module 1975 1977 Datsun 280z | eBay

Edited November 26, 2013 by Willoughby Z

[FastWoman]

Sorry, Kris, the advertising links had me confused! Grrrr....

[Zed Head]

Ithree concerns:

1. I had a sudden cut out for a split second somewhere along the line - I have a feeling this is associated with the fuel pump - a replacement installed by the previous owner with questionable looking wiring. Very occasionally when I turn on the ignition switch (without cranking), I don't hear the fuel pump. Off and on again and its good. I once had to smack it with the handle of a screw driver but I'm not sure that really is what fixed it. I think I will uninstall it, inspect it, then re-install properly (for some reason he ran the ground wire all the way from the battery).
   
2. When I went to adjust the idle (by ear), it consistently stalled. It sounds to me like its at something like 1200 RPM but running really well there. I need to put a tach on it (the dash tach has problems - see next point) - maybe its just my ear. It was also really cold out yesterday (25).
   
3. The tach is very jumpy, especially at low RPM. Sometimes it just reads 0. Could be the tach itself or the ignition module or something to do with the distributor upgrade done by the previous owner. I need to figure this out.
   

On #2, the stalling, I would say that your AFM fuel pump contact needs a little adjustment, or that you have a vacuum leak. If the contacts are off a little bit, a low idle will cut power to the fuel pump when air flow through the AFM lets the vane close too much. Bit in your case you say that you have power to the pump when the key is turned on, which is not the way the factory built them. If you have fuel, you should be able to drop your idle speed down below 1000 RPM easily.

The jumpy tach and the cut out could be tied to the ignition system. What is this "upgrade"? There are many varieties.

Edited November 26, 2013 by Zed Head

[sscanf]

On #2, the stalling, I would say that your AFM fuel pump contact needs a little adjustment, or that you have a vacuum leak. If the contacts are off a little bit, a low idle will cut power to the fuel pump when air flow through the AFM lets the vane close too much.

Planning a yoghurt cup test over thanksgiving. FastWoman is the gift that keeps on giving (thank you).

Bit in your case you say that you have power to the pump when the key is turned on, which is not the way the factory built them. If you have fuel, you should be able to drop your idle speed down below 1000 RPM easily.

A keen observation. That behavior was with the old AFM which had the pin bent such that the fuel pump was always on when the key was on. I did not listen for the fuel pump since the replacement. I'm sure now that I wouldn't hear it.

The jumpy tach and the cut out could be tied to the ignition system. What is this "upgrade"? There are many varieties.

It has a zx distributor in it. I'm quite sure the prior owner followed the Atlantic Z Club instructions. I need to check his work but I assume its an all or nothing proposition (either its hooked up correctly and we have ignition or its not and we don't). I do think, though, that it is possible that the tach might not work properly as a result of this upgrade. After that I'm going to pull the existing ignition module and see if I might have a replacement transistor for it on my bench (my other hobbies provide me with some bench stock of 70's/80's era transistors - does anyone know what that big TO3 transitor is on that board). I will also shotgun the board with anything else I might have on-hand. From the photos I have seen on the web it looks like an easy board to work on.

Previous owner also replaced the fusable links with fuses.

Finally, I just picked up a GM HEI module - one way or another I'll get this thing done over the long weekend.

Thanks for all the help.

[FastWoman]

FAIW, I mounted that HEI module to the backside of a single, square, TO3 heatsink (like this one: Invalid Request ), using two mounting screws on opposite corners. (I think I had to enlarge them slightly to get the right spacing.) And then I mounted the heatsink/HEI assembly to my driver-side fender using the same two screw holes as the distributor pickup junction block (which I removed). The spacing was perfect, and there was just enough clearance between the fins and the hood. Best of all, this is a relatively cool part of the engine compartment.

PS I can identify much too well with your 70's era parts collection.

Edited November 26, 2013 by FastWoman

[Willoughby Z]

Sorry, Kris, the advertising links had me confused! Grrrr....

I'm not happy about the confusion caused by the "Shopping by SkimWords" worm, either.

[sscanf]

I just did the yogurt cup test and I have a leak. I didn't need any smoke to find it, I could hear it and feel it and it was in an unexpected place: There is a little hole on the side of the BCDD and air is leaking out of that hole. If I cover that hole, the test seems to go as it should - very slow leak down.

For now I am hoping that a little duct tape over that hole will help but it seems that I need to do something about it. Either fix it or eliminate it? Suggestions.

Dan

[Captain Obvious]

Methinks you've got a hole in your BCDD diaphragm.

I don't think you can get just the diaphragm as a replacement though. If you turn up a source, please share?

[sscanf]

Yes I do...

The other one was fine. I'm going to try to make a replacement diaphragm. Stay tuned.

Edited December 2, 2013 by sscanf

[Captain Obvious]

Haha!! Well THERE'S your problem!

Good luck with the diaphragm. There are several members who have simply removed and blocked off the BCDD completely and don't feel they miss the functionality. I've not tried this as my BCDD still seems to be working as intended, but others have. YMMV.