What are the facts about 280z ECU compatibility and differences

[Zed Head]

Breaking the Pin 1 circuit might work but the standard method is to make and break the coil circuit.  Create a spark at the coil.  Pin 1 needs to be connected to the circuit, of course, like it would be on the engine.

Somewhere out there I think that there might be an actual Nissan write-up on it.  Can't remember.

[Dave WM]

ok so on my spare engine I will go with ign on, jumper the neg side of the coil to ground (tap tap tap go ground that is), that will simulate what the spark module does and create the pulse in the primary side of the coil (and generate a spark for that matter). I don't think I would need to disconnect the spark module for this. Heck I even have a spare dizzy that I just installed a new reluctor on, could just hook it up and spin it! check my spare dizzy and look for the injectors firing as well.

The spare dizzy is really nice, good working vacuum advance, zero play in the shaft, nice smooth feel to it. the old reluctor had some chips in it like it got too close to the coil.

Edited February 12, 2020 by Dave WM

[Zed Head]

Here's the FSM test procedure for 1978.  It still uses engine cranking, but distributor spinning gives the same effect.  I still think that there is another test procedure out there, maybe in the EFI Guide.

[Dave WM]

todays test:

small ge47 light in stalled in place of an injector (just unplugged the harness from the injector, then plugged in the light to the harness) started the spare engine, starts right up with obvious miss, but light is flashing so I know that works with the good ecu. turn off engine.

Next hook up spare dizzy in P with the existing one (I have the installed one hard wired to the  module so I left it in circuit. with ign in the run and the fuel purged via the fuel pressure gauge so as not to squirt gas into the engine from residual pressure, I manually spin the spare dizzy by hand, can hear the injectors fire and can see the light flash. That test the spare dizzy. ign off

install spare bad ecu, ign back on, spin dizzy light flashes. hard to say if it was noticeably not as bright a flash or a duration of flash, but it did and the injectors were clicking as well. So the bad ecu def is functional just seem way to lean. I test this by trying to start it again,m would run for a few seconds (fuel pressure good, light flashes, spark there) then stop. If I depress the AFM flap manually.it will idle, if I throttle up  while manually depressing it can transistion to running on its own but will forward fire (back fire thru the AFM) if I start to back off the throttle. It actually launched my poorly attached AFM, nearly hitting my parked Z.

Clearly it wants to run lean. I wonder if I need another sensor/s input for this one,. it appears to use all the pins (they are all there and soldered to pads with traces). Maybe an O2 and/or a altitude sensor? I wonder if its seeing a high altitude (I am at sea level) with NO sensor and leaning the mix out?

 

 

 

 

Edited February 15, 2020 by Dave WM

[Zed Head]

You might check the PCB circuits in the ECU that are connected to the sensors that control fuel enrichment.  Coolant and air temperature sensors, for example.  The AFM pins.  If I had it sitting in front of me I might just check continuity from the PCB trace to the pin at the connector, for starters.  Broken solder joints at the connector have been found and fixed, in past threads.  If those are solid, then the components at the ends of the traces.  Depends on how far you want to dig in to it.  Could be fun.  Finding that it starts lean. too lean to keep running, is a big clue.

Edited February 16, 2020 by Zed Head

[Dave WM]

will be digging in. for starters I am going to see if the 78 FSM has any mention of other sensors as well. I think that is the year that the ECU pins were all connected. I don't know for sure what year this ECU is from. I do know it has large alum guide ears on it if that is a clue.

[Zed Head]

Some of the ECU's have all of the pins but many are not connected to anything.  There's been a discussions about it.  Chalked up to manufacturing "efficiencies" or overstock or things along those lines.  

[Dave WM]

Yea I read that, but visual inspection IIRC had traces to all the pins, all soldered and going somewhere (not just pads). I will be confirming that.

I just read up on the alt comp, leans it 6%. Also if I read the 1978 FSM correct I should NOT have continuity between 12 and 9 for low alt (sea level). The wiring harness I have does not support a alt comp device so I presume "as is" there is no continuity, therefore should NOT be an issue. That and a 6% even if I am wrong does not seem to be enough to require such a large deflection of the AFM flap. I don't know how the signals are coupled to the circuit, I assume since the sensors are DC, then no capacitor issues, possible a resistor has gone out of spec, but without a schematic its like shooting in the dark. I don't want to go around probing with a multimeter set to resistance and end up frying a IC. Besides that the parts look to be high reliability so will have to stick with just a visual and look for an obvious defect. The fact that it works at all make me think its a base signal issue, the AFM flap effect it, the trigger is working. I suppose I should try it with the engine completely warmed up to see if the cold enrichments could be the problem (air/water/start). Still would not know how to effect a fix if one or more of those was the issue.

IF its a base signal, IC2 seems responsible for setting that up, Not sure how the freq is derived, been a while since I messed with IC wave generators, IIRC I made some up as a kid from 556 and resistor/cap values.. CO HELP!!!! I don't even know if the IC's have marks on them, they are the round can types not DIP.

If it had vacuum tubes I would be more comfortable....

Edited February 16, 2020 by Dave WM

[Dave WM]

oh and the 78 did NOT have an O2 sensor either. Guess that came on the later ZX. Again since all my pins "seem" to go somewhere I really don't know what I have in the way of an ECU.

[Dave WM]

I am going to try hooking up my AC analog simpson and see if I can get a voltage reading instead of just the lamp. will do with good and bad ECU. I recall disconnecting the temp sensor trying to get it to run, but I forgot to look a the light to see if was flashing brighter (FSM check for correct operation of ECU). If that is inconclusive (the simpson) I will get out the scope. That should give me some clarity on the signal for comparison. I will do this with the spare dizzy so I don't have to spin the engine over for testing.

[Captain Obvious]

9 hours ago, Dave WM said:

If it had vacuum tubes I would be more comfortable....

LOL!

The IC's have numbers on them, but there's no info (that I can find) anywhere about what's inside. My assumption is that they are parts made by Hitachi for use only inside Hitachi produced devices and they didn't publish datasheets for them outside their own business.

So you put a lamp in place of one injector and it blinked. That tests one output transistor. Can you move the lamp around to the other injectors and make sure the second output transistor is "working" too?  If the wiring harness hasn't been messed with, I believe the injectors are grouped 1-2-3 and 4-5-6. You can pull the ECU off the harness and Ohm out the wires to the main ECU connector if you have to.

As for the altitude compensations and stuff like that... The cars that did not need that stuff (non CA?) simply did not have them installed. My assumption is that the ECU defaults to "normal" non-altitude corrected if the other stuff is just left as no-connects. In other words, I strongly assume that you can just leave all the altitude compensation pins unconnected and it should work like a 49 state version.

 

[Zed Head]

The engine will run on three cylinders.  Somebody actually cut one in half and ran it that way, if you recall way back.

The Kent Moore Analyzer manual has more info that might help understanding.  There might be a pdf file on the site but in the meantime there's this web site, broken down by single pages.  - http://datsunforum.com/efi-troubleshooting-kent-moore-j25400-analyzer/