Running rough then stalls

[garretthes]

You can swap the EFI connectors from injector 2 with injector 1 to see if the problem is actually the injector or back in the harness/ecu.

If it is the injector: You can tap on the #1 injector to try and loosen it with percussion energy. You can also connect a 9V battery to a spare injector connector then push it on and remove from the injector to hit it with a high current. Just hold on for ~ 1 sec then remove as the high current will heat the windings if left on too long.

Good call. I have tried tapping on it but no luck. I put a test light on the connector and it lit up nicely from both terminals.

I will try the battery trick tomorrow.

[garretthes]

btw I can't remember when Nissan moved the temp sensor to the back of the cylinder head next to plug #6. I think it was in 80 or 81 after the P79 came into existence.

If you can't find it in the thermostat housing then check the head.

It is on the thermo housing

[240260280z]

...... also replaced the coolant temp sensor with the same part from the parts car because the wire was suspect. It was frayed were it touches the sensor and corroded.

This is probably the problem. The temp sensor wires. The can be removes about 1' back in the harness are two bullet connectors.

Remove this "pig tail" and check it with your multimeter.

[garretthes]

This is probably the problem. The temp sensor wires. The can be removes about 1' back in the harness are two bullet connectors.

Remove this "pig tail" and check it with your multimeter.

Do you know what it should read cold? The book says 500 ohm at 150 degrees.

[240260280z]

If you take the sensor indoors it should read ~2,500 ohms.

The problem is that if any of the contacts or the wires to the ECU are corroded or loose, the resistance goes up and the ECU thinks you are at the north pole and dumps fuel in.

To ensure the ECU sees the correct resistance, check the resistance with the car cold at the sensor, then check 1' back into the harness at the bullet connectors, then check way back near the drivers left side kick panel at the ECU connector (pins 49and 13) on a 280z harness. All three readings should be very close.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html:

°C °F Resistance

-30 -22 20,300 Ω to 33, 000 Ω

-10 -14 7,600 Ω to 10,800 Ω

+10 50 3,250 Ω to 4,150 Ω

+20 68 2,250 Ω to 2,750 Ω

+50 122 740 Ω to 940 Ω

+80 176 290 Ω to 360Ω

[garretthes]

I believe it's pin 14 for a 79

I checked this yesterday and I think it was in speck. I will check again. My concern is whether or not I'm setting the voltmeter right

[Zed Head]

Here is a thread from the recent past, with a similar problem to yours - too much fuel.

http://www.classiczcars.com/forums/showthread.php?42574-MPG-timing-fuel-and&highlight=mileage

[black gold man]

Maybe afm flap sticks open sometimes flooding

the car. Take cover off of afm see if the weight

returns after high rpms.

[240260280z]

I believe it's pin 14 for a 79[ATTACH=CONFIG]47188[/ATTACH]

I checked this yesterday and I think it was in speck. I will check again. My concern is whether or not I'm setting the voltmeter right

Oops! I even looked at that too. Duh I am sorry :stupid:

[garretthes]

OK, replaced the coolant temp sensor. It was reading 1.75 at the sensor AND pin 14 on the ECU connector as well so the wiring is good. With the new sensor it's down to 1.5. I don't know if that will make much of a difference. It certainly didn't make a difference in the way it runs now. Same pattern. Starts right up and runs pretty good for about 30 seconds then goes to h*ll.

I'm going to purchase a vacuum and fuel pressure gauge tomorrow and see what I have. My next guess would be the FPR. What bugs me there though is I already swapped the one from the parts car and there was no change. Maybe it's not getting enough vacuum? Would that cause it to let the pressure run too high?

[240260280z]

OK so it is not temp sensor or wiring. 1.5 and 1.75 kohm are fine.

There are other items in the efi system but only two typically cause so much excess fuel.

If return line to tank is blocked or your FPR is blocked/malfunctioning then fuel pressure could be too high.

Another possibility is that your ECU is malfunctioning and holding the injectors open too long or your injectors are oversized.

Here is a graph showing sensors and ECU logic that contribute to the amount of fuel used:

[5thhorsemann]

Cleaned the plugs with wire brush and replaced them.

That is a major no no. The ceramic insulator is abrasive, it will pick up metal from the bristles and become conductive to an extent weakening or killing the spark. Replace them before going any farther, sorry I can't add any other input to help with the fule issue, I don't know a hole lot about these EFI systems, but the plugs aren't helping matters.