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-   -   Fuel Problems (https://www.rx7club.com/2nd-generation-specific-1986-1992-17/fuel-problems-995157/)

satch 04-20-12 01:08 PM

The negative terminal to the battery or the alternator housing are good ground candidates. And the Brown wire at the TPS should have 5 volts w/key to on as this will reflect that the ECU is powered up properly by the Black/White wire. So if the Brown wire has proper voltage then you know the B/W wire must have proper voltage as well.

NaD00D00 04-20-12 04:43 PM


Originally Posted by satch (Post 11062542)
The negative terminal to the battery or the alternator housing are good ground candidates. And the Brown wire at the TPS should have 5 volts w/key to on as this will reflect that the ECU is powered up properly by the Black/White wire. So if the Brown wire has proper voltage then you know the B/W wire must have proper voltage as well.

Ok, I checked the two wires referred to in the post before the one I quoted, the ones near the leading coils, and they are good, like 12.2V.

The brown wire on the TPS, though, was like, in the mV. 303.4 to be exact. So power is getting to the leading coils, but not to the TPS/ECU, correct?

satch 04-20-12 05:06 PM


Originally Posted by NaD00D00 (Post 11062744)
Ok, I checked the two wires referred to in the post before the one I quoted, the ones near the leading coils, and they are good, like 12.2V.

The brown wire on the TPS, though, was like, in the mV. 303.4 to be exact. So power is getting to the leading coils, but not to the TPS/ECU, correct?

And the Brown TPS wire was measured w/key to on? You can check the same color wire at the Boost Sensor as it should read 5 volts w/key to on.

NaD00D00 04-20-12 05:10 PM


Originally Posted by satch (Post 11062761)
And the Brown TPS wire was measured w/key to on? You can check the same color wire at the Boost Sensor as it should read 5 volts w/key to on.

Yes, only a few over 200mV at the Boost Sensor.

This could be a total shot in the dark, since I have no idea what I'm really doing while looking at the wiring diagrams, but could it be the fuel pump relay/resistor? I'm not sure which wire to check, though I'm guessing it's probably the black and white one...

satch 04-20-12 05:34 PM


Originally Posted by NaD00D00 (Post 11062768)
Yes, only a few over 200mV at the Boost Sensor.

Disconnect the AFM and check the Brown wire w/key to on at either the TPS or Boost Sensor. If the ECU is powered properly, but the Brown wire has practically no voltage, then chances are the AFM is shorting out the ECU. You can also check pin 3I (Black/White wire) of the ECU as this is where the B/W wire from the Main Relay ends up. Should have 12 volts w/key to on. If 3I has battery voltage then the AFM is the likely cause. If 3I does not have battery voltage w/key to on then this would be the problem you need to solve.

NaD00D00 04-20-12 05:42 PM


Originally Posted by satch (Post 11062786)
Disconnect the AFM and check the Brown wire w/key to on at either the TPS or Boost Sensor. If the ECU is powered properly, but the Brown wire has practically no voltage, then chances are the AFM is shorting out the ECU. You can also check pin 3I (Black/White wire) of the ECU as this is where the B/W wire from the Main Relay ends up. Should have 12 volts w/key to on. If 3I has battery voltage then the AFM is the likely cause. If 3I does not have battery voltage w/key to on then this would be the problem you need to solve.

I tried both the AFM and the fuel pump relay/resistor...I got no voltage when I unplugged the AFM, but 5V when I plugged it back in and unplugged the fuel pump relay/resistor.

Is there any way to bypass it and get the car to start? Or repair it? Or do I have to wait to get it swapped out?

Maybe I could jumper the fuel pump check connector like before, but I'm so paranoid about screwing things up further that I don't want to try it, lol.

satch 04-20-12 06:06 PM


Originally Posted by NaD00D00 (Post 11062791)
I tried both the AFM and the fuel pump relay/resistor...I got no voltage when I unplugged the AFM, but 5V when I plugged it back in and unplugged the fuel pump relay/resistor.

Is there any way to bypass it and get the car to start? Or repair it? Or do I have to wait to get it swapped out?

Maybe I could jumper the fuel pump check connector like before, but I'm so paranoid about screwing things up further that I don't want to try it, lol.

If the Fuel pump Relay and Resistor being unplugged causes the voltage to be restored to 5 volts on the Brown wire w/the AFM plugged in then unplug the fuel relay and jumper one of the Blue/Red wires in the plug to one of the Blue wires in the same plug. Doing this will bypass the relay. Just unplugging it would kill the fuel pump.

NaD00D00 04-20-12 07:00 PM


Originally Posted by satch (Post 11062813)
If the Fuel pump Relay and Resistor being unplugged causes the voltage to be restored to 5 volts on the Brown wire w/the AFM plugged in then unplug the fuel relay and jumper one of the Blue/Red wires in the plug to one of the Blue wires in the same plug. Doing this will bypass the relay. Just unplugging it would kill the fuel pump.

Satch, thank you so much for all of you help. I really couldn't have done it without you, and you got me out of a tough spot, I wish I could repay you somehow. I'm going to try to get a relay while I'm off at school and change it out when I get back from out of town.

Last question, does the relay that I bypassed have anything to do with the water temp sensor/gauge? If not, I guess I have another thing to replace, lol.

satch 04-20-12 07:11 PM


Originally Posted by NaD00D00 (Post 11062870)
Satch, thank you so much for all of you help. I really couldn't have done it without you, and you got me out of a tough spot, I wish I could repay you somehow. I'm going to try to get a relay while I'm off at school and change it out when I get back from out of town.

Last question, does the relay that I bypassed have anything to do with the water temp sensor/gauge? If not, I guess I have another thing to replace, lol.

You could probably go w/o the relay for a while as there are those that run w/o it all together. And this fuel relay is not directly related to the water temp sensor/gauge, although I'm not sure what you mean by that.

NaD00D00 04-20-12 07:26 PM


Originally Posted by satch (Post 11062883)
You could probably go w/o the relay for a while as there are those that run w/o it all together. And this fuel relay is not directly related to the water temp sensor/gauge, although I'm not sure what you mean by that.

Ahhh, I see. Cool, that's good news for now. Again, thanks so much for your help.


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