Just cleaned fuel injectors, now no start - Page 3 - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #21 of 37 (permalink) Old 01-27-2019, 10:38 PM
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that link is excellent, pg 63 describes what I was trying to cover on testing for batter voltage, it just test it by checking at the 36 pin connector.


Note always turn off the ignition and disconnect the battery before removing or connecting the ECU. The test on pg 63 has you testing after the ECU connector is off, and then you can reconnect the battery. Just make sure before plugging in back in you disconnect the battery again. Bottom line don't connect or disconnect the ECU with the battery connected.
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post #22 of 37 (permalink) Old 01-28-2019, 12:22 AM
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I wanna say the 75 bosch injection system is a batch fire 3 and 3 injectors. Hopefully something simple to fix. These wiring harnesses are pretty old.

1975 280Z F54/N47 MSA 6-1 Header 2.5 Exhaust
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post #23 of 37 (permalink) Old 01-28-2019, 01:28 PM
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Nissan's FSM's for the 280Z EFI systems are like school books for understanding EFI. They fire all six injectors at one time, each time with half of the calculated fuel for a combustion cycle, on each crank shaft revolution. It's a good read, the Engine Fuel chapter.
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post #24 of 37 (permalink) Old 01-28-2019, 05:51 PM
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Nissan's FSM's for the 280Z EFI systems are like school books for understanding EFI. They fire all six injectors at one time, each time with half of the calculated fuel for a combustion cycle, on each crank shaft revolution. It's a good read, the Engine Fuel chapter.
EFI bible knows all! Now I know.

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post #25 of 37 (permalink) Old 02-02-2019, 01:51 PM Thread Starter
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All right, major revelation and I would think it is so simple. It seems, most/many circuits it does not matter if pos goes to pos and neg to neg (I may be wrong there). In testing the wiring harness I had 3 working and 3 not working. I was putting together a new LED test light and by testing it just on a battery, I realized + has to go + and vice versa. So this told me the same would apply on the connectors, and sure enough if I switch sides on those wires, all my connectors are working. So the question is probably obvious, does + have to go to + between the injector and the connector? I am thinking yes and that is where all my problems stem from. When I put the new connectors on to the wiring harness, the wires in the wiring harness are both white so there is no designation as to which is +. So simply, do I have to verify that + goes to +?


And one oddity, my car runs better without any of the injectors connected to the harness than it has since this started. Turning it over to check the voltage and the engine keeps starting.
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post #26 of 37 (permalink) Old 02-02-2019, 02:05 PM
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there is no designation as to which is +. So simply, do I have to verify that + goes to +?
And one oddity, my car runs better without any of the injectors connected to the harness than it has since this started. Turning it over to check the voltage and the engine keeps starting.

Polarity does indeed matter! Also, you are probably running off the cold start valve. You have to be getting fuel from somewhere for it to start.

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post #27 of 37 (permalink) Old 02-02-2019, 02:48 PM Thread Starter
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Thanks, yes I have determined that. And sitting thinking I figured it was the cold start injector feeding gas but due to my lack of knowing polarity matters, I thought it didn't work at all. At least now I know it does. Is there a way to know which side of the injector connection is positive?
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post #28 of 37 (permalink) Old 02-02-2019, 04:51 PM
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Polarity does not matter for the injectors. It's just a coil that creates a magnetic field. That's why both wires of the new connectors are the same color and there are no markings on the injector.
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post #29 of 37 (permalink) Old 02-02-2019, 05:13 PM Thread Starter
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Well that was my first rationale that polarity did not matter. Sure enough, I have all the wiring harness with the same polarity going to the injectors and nothing is different. It runs as if only one, maybe two cylinders are firing. As I said earlier the thing ran better with the injectors disconnected and just the cold start injector working. It actually ran smooth for a short period before I shut it off. My wife even came out and said, "you got it going" - it sounded that good. I guess I am going to have to look at air in the fuel lines as someone earlier suggested. This has now become very frustrating.
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post #30 of 37 (permalink) Old 02-02-2019, 05:26 PM
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The air would be in the same line that feeds the CSV. Are you sure it's not flooding? The CSV will stay open for th same amount of time whether the injectors are connected or not. If it runs better with no injectors that's a sign of too much fuel.

Check the coolant temperature sensor circuit. If that circuit is open the injectors will stay open much longer, adding too much fuel.
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