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77 280z Starts (kinda), stops trying as soon as i let go of key

no start

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#1 Jp76z

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Posted 21 July 2016 - 04:04 PM

  Hello people,

  I have start  and run issues that I believe has to do with the ignition unit, or power going to it, or some open circuit relating to that.

So this was a running car untill....

  I installed a turbo head and the parts needed to turbo it, along with megasquirt 2. The ms is for fuel only right now and made my own harness adaptor to go from the ms2 to the stock harness using the connector from the stock ecm. I had it running off of ms before i took the engine apart using the stock ignition like im doing now. After putting the p90 head on it and stock manifold, I got rid of all emisions and everything else exept clt sensor.  I added a few, so the only sensers that i have are tps, clt, iat, o2. i cut the plug for all the other sensors off to clean the harness up untill i make a complete one. Also i have high ohm inj's so i eliminated the resistors as well. What is happening is the engine is trying to start while cranking and firing, untill i stop cranking. I dont know if i made an open circuit cutting the harness up, but I jump power to the main relay for the pump and all, have power to the injs and coil when key is on. the injs stop clicking when not cranking and I believe its because the coil stops sending the signal to the ms. BTW, the ms is triggered by the negative side of the coil as a tach signal, and fuel psi is good.. I have not yet checked all the powers to the ignition module yet. Does this ring any bells, or anyone have any ideas?? Any opinions or help is greatly app.



#2 NewZed

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Posted 21 July 2016 - 04:17 PM

There are two wires that power the coil - one for Start and one for Run.  Sounds like only your Start wire is connected.

 

Or you haven't addressed the fuel pump relay contact switch in the AFM.  Usually the engine will run for a few seconds before dying if it's the fuel pump contact.

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#3 Jp76z

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Posted 21 July 2016 - 04:46 PM

Thanks for the reply, Im leaning toward the run side of the coil. This wire is connected to the resister? which one is it. See I have constant power at the pos side of coil with ign on. I removed the afm and cut the harnes so i was jumping the fp relay.



#4 NewZed

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Posted 21 July 2016 - 05:05 PM

I would get in to the wiring diagram and see what has power at Start and what has power at On/Run.  The ignition module needs its own power supply as you noted but you may have disconnected it.

 

This diagram doesn't seem right since it doesn't show power to the module during Start (the short path (BL) is Start, the long one through the resistor (BW) is On) but it does show that W and BW at the module need power.  Check those with the key at On.  Maybe you have power there at Start but not On.

 

The diagram is simplified, the ignition relay might actually be in the circuit.  The full circuit with all components is in the link.

 

http://atlanticz.ca/.../electrical.htm

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#5 Jp76z

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Posted 21 July 2016 - 05:46 PM

I will check that out tomorrow. Thanks alot for your input!







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