ZCar Forum banner
Status
Not open for further replies.
1 - 5 of 5 Posts

·
Registered
Joined
·
107,695 Posts
Discussion Starter · #1 ·
Problem: On my '76 280Z, a wire from the negative side of the fuel injection relay to the negative side of the battery was accidentally put on the positive side of the battery (I didn't do it man). This caused the fuel pump to not run. After I put the wire back on the negative terminal, the relay began to work and so did the fuel pump, but the car only started for a second and stopped. The engine has spark and there is gas getting to the injectors. I checked the ECU at the #1 and #4 injectors and the test light did not flash. I replaced the ECU and still no impulses to the injectors. Any ideas or experience on the matter would be greatly appreciated. Also, I need to find a component chart for the car.

Thanks, Max

P.S. The Fuel Injection Relay's coils and switches are fine.
 

·
Registered
Joined
·
85 Posts
Did you check your fusible links????? And by the way which wire was it(the positive and the negative)?????? You will have to test a lot of things to see if you did not burn them up when that mishap occured. Just think of everything that causes the injectors to fire. ECU(I know you already replaced it but that it is one of the items), Throttle postition switch, and Air flow meter with all need to be Ohmed to see if they are still functioning properly. Other minor switches that regulate the amounts of flow with the ECU are water temp and thermotime switch. These two items will not cause the injectors not to fire, but since you will need to check things out it would be a good time. On a side not, you will need to check all your wires. I mean all of them since I have heard of the wiring system melting in certain areas when the ground and hot are switched.
Start with the fusible links then just start with the ohm meter on all the things I mentioned. The last thing would be checking the wiring harness for shorts. Good luck and let us know what happens.
 

·
Registered
Joined
·
107,695 Posts
Discussion Starter · #3 ·
> Did you check your fusible links????? And by
> the way which wire was it(the positive and
> the negative)?????? You will have to test a
> lot of things to see if you did not burn
> them up when that mishap occured. Just think
> of everything that causes the injectors to
> fire. ECU(I know you already replaced it but
> that it is one of the items), Throttle
> postition switch, and Air flow meter with
> all need to be Ohmed to see if they are
> still functioning properly. Other minor
> switches that regulate the amounts of flow
> with the ECU are water temp and thermotime
> switch. These two items will not cause the
> injectors not to fire, but since you will
> need to check things out it would be a good
> time. On a side not, you will need to check
> all your wires. I mean all of them since I
> have heard of the wiring system melting in
> certain areas when the ground and hot are
> switched.
> Start with the fusible links then just start
> with the ohm meter on all the things I
> mentioned. The last thing would be checking
> the wiring harness for shorts. Good luck and
> let us know what happens.
If you replaced the ECU, I would still suspect the fuel injection relay since it actuates the fuel pump and also the fuel injection. The other thing that could cause the injectors to not fire are the dropping resistors, mounted on the fire wall near the windshield wash. Hopefully you have a manual and can do a continuity check on those relays. If you need anymore help or a fuel injection relay for a 76 you can email me.

DDT
 

·
Registered
Joined
·
107,695 Posts
Discussion Starter · #4 ·
> If you replaced the ECU, I would still
> suspect the fuel injection relay since it
> actuates the fuel pump and also the fuel
> injection. The other thing that could cause
> the injectors to not fire are the dropping
> resistors, mounted on the fire wall near the
> windshield wash. Hopefully you have a manual
> and can do a continuity check on those
> relays. If you need anymore help or a fuel
> injection relay for a 76 you can email me.

> DDT

First let me say thank you to the people who posted in response to my original post. At present, your responses have led me to testing the droping resistor. Everything else checks out fine, but the droping resistor may be bad. I was told in a previous post that I should be getting 3 volts coming out of it. Well, when I checked the voltage at the injector, I found that I had 12 volts going to both sides of the injector harnesses for all the injectors. When I pulled the droping resistor, I put 12 volts to the input terminals (blue and yellow wires attach to them) at the input of the resistor, and found that instead of 3 volts coming out, I was getting the same 12 volts I read at the injector harnesses. I'm assuming that the potiential difference between the 12 volts coming in from the ECU and the 3 volts that are supposed to be coming in from the droping resistor are what energize the injector coil, instead of just a positive and negitive configuration. This would make sense to me because the ECU can monitor this kind of setup (at least I think so?). I also Ohm'd out the resistors from the blue and yellow terminals to their corresponding output terminals on both sides of the droping resistor and found aproximately 6.2 Ohms on all of them. Since I'm getting 12 volts with this resistence, I would think the resistance should be much more then this. I'm going to try and find one at the wrecking yard and Ohm it out, and if the resistance is much higher, I'm going to get it and try it out. I'll let you know what happens :eek:)

Thanks,
Max
 

·
Registered
Joined
·
107,695 Posts
Discussion Starter · #5 ·
> Did you check your fusible links????? And by
> the way which wire was it(the positive and
> the negative)?????? You will have to test a
> lot of things to see if you did not burn
> them up when that mishap occured. Just think
> of everything that causes the injectors to
> fire. ECU(I know you already replaced it but
> that it is one of the items), Throttle
> postition switch, and Air flow meter with
> all need to be Ohmed to see if they are
> still functioning properly. Other minor
> switches that regulate the amounts of flow
> with the ECU are water temp and thermotime
> switch. These two items will not cause the
> injectors not to fire, but since you will
> need to check things out it would be a good
> time. On a side not, you will need to check
> all your wires. I mean all of them since I
> have heard of the wiring system melting in
> certain areas when the ground and hot are
> switched.
> Start with the fusible links then just start
> with the ohm meter on all the things I
> mentioned. The last thing would be checking
> the wiring harness for shorts. Good luck and
> let us know what happens.
check your ignition control module under the dash on the passenger side. if that goes bad it can cause the problems yu described
 
1 - 5 of 5 Posts
Status
Not open for further replies.
Top