Need some help 72 to 78 EFI swap

[MikeyZee]

Mike,

 

I'm pretty much out of ammo, but let me tell you what I think I know.

 

First, your car should eventually start regardless of whether the cold start injector is firing or not. During cold start operations the cold start injector only adds extra fuel until the themotime switch opens the circuit. I can't imagine it's that cold in Colorado in August. It was 70degF in Anchorage today.

 

I downloaded the '78 FSM from xenons30.com because there are differences between the '75-'77 and '78 years. I own a '75. The '78 FSM shows Pin 21 on the EFI box being used for the cold start injector circuit. Pins 19, 20, and 22 are not used. Are you sure you have a '78 EFI box? Because Pin 21 is used according to the FSM. ???

 

Second, the cold start injector should have 12VDC with the key on the "start" position. After the engine starts, the cold start injector should continue to have 12VDC from Fuel Pump Control Relay and will continue to have 12VDC so long as the engine runs. Only when the thermotime switch heats up will the cold start injector cease to fire. At least that is the way I read the '78 FSM.

 

Final thought is that your fuel pump should not be running while the key is in the "on" position and the car is not running. I don't know how, or if, this might be related to your no start condition, but it is a nontypical condition.

 

Actually, one more question and a thought - Are you running MSD6 yet or the still the Jacobs ignition? And don't worry about your tach operation until the car starts reliably. The tach does not affect operation of the ignition or fuel injection circuits in any way. Worry about getting the tach to work correctly later.

 

I have checked the voltage and operation of the cold start and seems the thermo time switch may be bad. There is no continuity on the switch when cold, nothing changes at all on the switch from being in the fridge to being in boiling water. Bad thermo time switch. In Colorado mornings have been down in the 60s, soon to dip down into the 40-50 range within 2 months. I want to make sure it's pretty easy to hop in and just start. I have done some research and the thermo time switch actually completes the ground of the circuit and introduces a ground to the cold start injector to allow it to fire. If I ground the cold start injector while starting it fires right up. The #21 is filled in the harness but since the ground is handled bu the thermo time switch the wiring for that going back to the #21 in the harness is not needed, thus no connection to the ECU and no pin in #21 on the ECU. I have researched and it's the same ECU for 76, 77, and 78. Both of my ECUs are this way (A11-600-000).

 

I have the 78 manual and looking at the other ones would just confuse matters since it's a different animal then the other years I have found.

 

I know the fuel pump should not run when the car is in the on position when the car is not running and my problem with that seems to be a bad fuel pump control relay. The relay is a dual relay, saying that both must be switched on to get power to the fuel pump. My relay as tested will allow the fuel pump to run regardless of if oil pressure is present or not. Bench testing shows that is I power either side of the relay the circuit will be energized, either....not both. As an in car test I had the car running and unplugged the connection to the oil pressure sender and the engine continues to rum, thus a bad fuel pump control relay. These are not easy to find it seems and may have to make my own to make it work properly. I have heard that some EFI Zs will run the fuel pump for a few seconds when you turn the key to the "on" position to allow a "prime" but have not been able to confirm that for sure. I may have missed something from the EFI bible but that was written based on a 76 so some things are different.

 

I am still using the Jacobs ignition and it is working flawlessly. It looks like I'll put the MSD in my Dakota if I'm not using it in the Z....bonus!!! The tach is still off but not real worried about that until we get the starting glitch, the fuel pump control relay, and a few other issues worked out. Although timing it accurately without knowing the actual RPM is well....impossible. We may go ahead and put a 280z tach in it to eliminate extra "stuff" under the hood but who knows at this point.

 

All in all I think things are coming together nicely. Starts (with the jumper), runs, and drives this point, down to fine tuning at this point. I really appreciate all the help with these issues and could not have done it without all the help from the board members. The good thing about this board is that you get many different opinions on what may be wrong and sometimes helps you think outside of your box. Oh and thanks again for the tach adapter, that will help immensely! I guess at this point we can call this solved! Thanks so much again!

 

I know my son is just so excited to get his Z with the new guts back on the road.