Injection problems

[ryan]

Rebuilt a 78 L28 and only have 3 cylinders working, 1, 2 and 3. 4 , 5 and 6 are firing but the plugs are dry. It runs suprisingly smooth at idle, I'm guessing it's cause 1,2 and 3 are every other one in the firing order.

I was looking thru the WD and it seems thers is some kind of connection in these sets of cylinders in the ECU, which would be my first guess as to the problem. But from the WD I can't tell whether the connection is actually in the ECU.

Any advise is welcome

Thanks

ECU.pdf

[sblake01]

Wires number 15, 33, 32, 14, 30, and 31 are from the ecu to injector 1-6 respectively. While wires 37, 38, 40, 41 are injectors 1-4 to dropping resistor 1, and 55, 56 are injector 5-6 to dropping resistor 2.

[sblake01]

Since I couldn't edit fast enough, but before I went into what I was saying in the last post, I should have asked what's not working, spark plugs or injectors?.

[ryan]

Plugs are firing. No fuel in cylinders

[sblake01]

If you know that you're getting a pulse to all 6 injectors, do you know for a fact that they're all good? For whatever reason the first four injectors are on the first dropping resistor and 5 and 6 are on the other so we can rule out where I was headed in post #2. It would seem odd that three injectors would be bad, I've never experienced that, but it's possible. Probe your injector connectors one a time with a voltmeter while the car is running. If you get a reading of about .6~.7 volts you have a proper signal and either the injector is bad or the connection is bad.

[ryan]

OK. here's all the info I have at this time. I can put 12 volts to the injector and it will operate, (clicks). With the key in the on position I get 12 volts on BOTH wires. I was told by a Nissan tech that the volts are constant and the ground pulses. I don't get a ground at any time on any injector. Reading the wiring diagram the ground has to come from the ECU. Pins 14, 30 and 31 have some kind of connection in the ECU. That is why I suspect the ECU. The resistors check good as I knew they would. If I have volts at the injector that means the relay and the resistor stack are good.

[sblake01]

14, 30, and 31 are the wires to the ECU side of injectors 4, 5, and 6. If you're getting 12 volts from those connetors with the key on (engine not running) that's correct. In that same situation you should also get 12 volts from wires 41, 55, 56 which are the other side of those three injector connectors and they come from the dropping resistors. The 'grounding' only takes place when engine is running and the dropping resistors are energized. If you check the voltage on any one injector connector by putting one probe in each side of the connector and starting the engine, you should see voltage, usually - or + .4 and up depending on rpm and depending on which probe is on which side. Leave the other 5 connected so that the engine will at least run. The signal oscillates so fast that it won't show the actual 12 volts but at that point all you really need to see is something other than 0. If you see those readings, you're getting a pulse. I hope that makes sense. It's easier for me to do it than it is to explain it.