77 280z Restoration

[280Zrewind]

Thank you!  I do wonder though why maintaining vacuum with injection is more critical than carbs.  Maybe the difference is with injection the intake manifold is pretty much wide open except for the throttle plate and carburetors have venturi and such that provide a little restriction and help maintain vacuum?

[Zed Head]

I think it has something to do with the way the fuel is metered from the carburetors.  With EFI the air flow is fairly precisely measured and the appropriate amount of fuel is added to balance the air.  With carbs the fuel is pulled up from the float bowls and basically spilled in to the air stream. There are emulsion tubes and other things but still the fuel gets pulled up in to the air stream, more air = more fuel.  If you have pulses of air from a lumpy cam (inconsistent air flow/vacuum) the fuel gets bounced up and down and accuracy/consistency is lost, plus the fuel does not stay well-atomized.  Carbs work best with smooth air flow through them.  EFI averages out the pulses back at the AFM or MAFS so is not as affected by a lumpy cam.

That's my basic understanding.

[dutchzcarguy]

19 hours ago, Av8ferg said:

I’m running the stock EFI.

Ofcourse.. STUPID me...  I didn't read it all but have you used some injectorcleaner? Old injectors deliver total different amounts of fuel, i would do some in half a tank of fuel, normally one bottle is for a full tank. put a bottle of injectorcleaner in your fuel. (Unless you have new injectors or already did this ofcourse.)

[Av8ferg]

Well, these injectors were sent off and refurbished so they should be good.  The guy sent me a report on each on with flow rates.  I sent him 10 and he picked the 6 that were the best.

Now I didn’t have the cold start injector sent off and like mentioned some posts back I need to make sure this one isn’t a bad actor and possibly operating when it shouldn’t.  It’s warm here so I don’t really need it.   

 

Edited September 16, 2022 by Av8ferg

[dutchzcarguy]

1 hour ago, Av8ferg said:

need to make sure this one isn’t a bad actor and possibly operating when it shouldn’t.

It's 2 screws, easy to take it out the inlet manifold, put it in a glas and see what it does.  Close the hole with tape and start the engine. it's in the serv. man. what it should do exactly but i believe it stops after 10-15 seconds.. i don't know.

[280Zrewind]

Here’s what seems strange to me - three in a row that are showing the symptom. Could be random chance, but how likely.  So looking at my rust bucket donor car it appears that the fuel rail is a little lower in the back than in the front.  Is it possible some contamination made its way into the back three injectors?  Pretty far out, but I can’t think of anything else that matches the three and three plug situation  

I like the suggestion of pulling the cold start valve and checking operation. I think it’s more likely a continuous dribble than a faulty signal.   Not sure how that would match the three and three situation though. 

[Av8ferg]

I’ll just pull the electrical connection on the cold start injector and start there. The car seems to idle a little rich by the smell of the exhaust.

News update: Ran the car off the E12-92 module today and wow is the difference remarkable. The car accelerates so much better on the HEI. With the Nissan module it is much slower through the RPMs. That Nissan module might not be good. I’m going to retest with one of my backups.
Right now the engine is singing using the Flame Thrower HEI. Never ran better and after the Valve lash adjustment and new plugs man is the motor sweet!

[Zed Head]

The E12-92 has an extra pin that adjusts timing through a temperature switch.  Might be that when you switched to it you inadvertently changed your timing.  I thought that you had an E12-80.  There's not really a good reason for a performance change unless the E12-92 is failing, or something else changed.

p.s. some people say that you have to short the extra pin to ground or run power through to stabilize the timing.  The 280ZX FSM probably shows how it works so it could be figured out.

Really though, you're about ready to just move on from the old Nissan parts.  

I'll just pile a couple more things in here for anyone with an E12-92 in the future.  Notice the idle switch and the thermo switch connected at the "IC".  Somebody with electronical experience might have fun figuring out what Nissan was doing here.

Last, maybe, edit - here's a zcar.com post from way back, with a reference to 240260280's friend Wayne Monteath.  Apparently, it doesn't matter if the extra pins are connected or not but the question would be where your initial timing is when you switched.  https://www.zcar.com/threads/e12-92-or-e12-80.116513/

 

 

Edited September 16, 2022 by Zed Head

[Av8ferg]

Okay so here are my test runs today.   I swapped out the Nissan E12-92 for a different one.   Second one ran worse it was also as 92 not 80, third one is an aftermarket one (92) and ran well so the tests were done with that module against the HEI.   Both ran well, but the HEI idles smoother and I feel the acceleration is cleaner or smoother.   See for yourself below.  

 

[Zed Head]

It would be useful to know if the initial timing changes.  Apparently the E12-92 retards timing by 8 degrees, but it's not clear exactly when.  Probably when the engine is hot and the throttle at idle.  For emissions.  Retarded is cleaner.  That's how the 280Z systems work, but with two pickups in the distributor.  When the engine is cold the timing is kept advanced at idle to help with idle RPM.  Not super clear how the ECU is involved unless it completes the ground based on engine RPM or some other condition.

Anyway, in your video you can see that idle PRM are lower for the E12 module.  That is what retarded timing will do, cause idle PRM to drop.  So, it might be that for your tests timing is retarded by 8 degrees for the E12-92.  A quick check with a timing light would answer that question.  Then you'd have to decide if you want to figure out how to make the two modules match.

But, the fact that it runs means that it is serving the fail-safe function, to get home if the HEI fails.

p.s. here is the 280Z description for the two pickup distributors.  When the circuit is open timing is retarded.  Which would fit with having the E12-92 pins disconnected.  I think that you'd have to run 12 volts through those extra pins to get the timing advanced to match the HEI module.

Thanks for letting me fill your thread with extra stuff.  An interesting puzzle.

Edited September 17, 2022 by Zed Head

[w3wilkes]

5 hours ago, Zed Head said:

Apparently the E12-92 retards timing by 8 degrees, but it's not clear exactly when.

The E12-92 will work identically to the E12-80 if you only connect up the "C" and "B" connection on the top of the module. The other connector is what controls the retard, without that connection it functions the same as the E12-80. I've been running a E12-92 for about 20 years now on my 240Z and it runs great.

[Av8ferg]

That’s exactly what my research led me to believe.   Without other connector attached it operates as an E12-80.   I think Zed Head had a good point and I will still place a timing light on the engine today and see where it’s at.   Before I did all the ignition changes it’s was spot on at 10 deg at 800 rpm and the mechanical and vacuum advance was perfect.  Off the top of my 17 deg of mechanical advance with a total around 35 at 3000 rpm.  Don’t quote that.   I’d like to find an adjustable vacuum advance Part number 22301-7901 and replace mine.  Would be fun to mess around with the advance curve and see how it effects performance.