720 feedback carb ecu diagnostics

[jonnymcfly]

Hi all, I am new to the forum. I have a 1986 z24 720 longbed with a feedback carb. The ecu under the driver seat with 1 green light and one stray wire that looks like u might short it to get codes. I had problems with it idleing a few days ago and removed the idle cut solenoid and cleaned it and also checked it with a hot and ground jumper to verify it works. Seems to have helped some but it still stumbles at idle occasionally and gets bad gas mileage. I want to see if and how this ecu can give me codes? Thinking I might also change the o2 sensor and as seen in this forum cycle the igniton off and on and listen for a click on the idle cut to verify its getting current from the wires. Any help on getting codes ? 

[datzenmike]

Only the late 720 with the Z24i throttle body injection has code storing capability. The feedback carb might have a green light but maybe just to show it has power.

 

 

Do you have two wing nuts or one holding the air filter on???

[jonnymcfly]

1

[jonnymcfly]

1 wingnut

[datzenmike]

Just checking that you indeed do not have the EFI set up.

 

The loose wire may be a ground. Check that the two rectangular wire plugs are firmly seated. The O2 sensor is to be replaced every 60,000 miles.

[Telkwa]

Do you have any recommendations re: the O2 sensor?  Is there a way to check it?  Or would you recommend just replacing it and seeing if there's improvement?  Our truck has well over 100K on it.  I don't believe the O2 sensor's ever been changed.

 

I didn't know there was a computer of sorts under the seat monitoring the carb and ignition....

 

Whoever picked the spot for the oxygen sensor, I'd like to kick him or her in the shins.  If they'd moved it down a friggin' inch a guy could get to it.  I can't get a purchase on the little monster.  O2 sensors are so cheap, I'd just replace it and move on if I could.

[jonnymcfly]

I didn't find the o2 at all difficult to get to on my 720. Especially after I swung the cable bracket out of the way. What I did find difficult was seperating it from the adapter they put on it before in goes into the pipe. Those o2 sensor sockets help alot. I also found my feedback solenoid is buzzing upon turning key to on. I am wondering if its starting to fail.

[jonnymcfly]

I also did read a way to test them. Supposedly you hook a meter up to the wire on the o2 as hot and then other lead to common. Then it should read between .2 v and .5.when going through the rpms But you gotta have a decent meter to do it. I have never tried it though. 

[jonnymcfly]

I am still wondering about being able to pull codes. I read a post on a TBI Z24 that had 2 lights a red and a green. 1 color for each digit. You intiate with a sequence of pushing the clutch in and shifting into 4th or 5th gears. I found though mine has only a green light, it also has a clutch switch. Which leads me to believe its for something like diagnostics cuz I can't see what other purpose it would serve.

[Telkwa]

You can also test the sensor

.  It's not highly scientific but will at least tell you whether the sensor has totally failed or not.  I don't know how fancy the meter would have to be.

 

Does your ECU and wire loom look like mine?  Scroll down to Post #17.  Our ECU also has just the one green LED, plus that one side wire that I believe you were referring to.

[datzenmike]

I am still wondering about being able to pull codes. I read a post on a TBI Z24 that had 2 lights a red and a green. 1 color for each digit. You intiate with a sequence of pushing the clutch in and shifting into 4th or 5th gears. I found though mine has only a green light, it also has a clutch switch. Which leads me to believe its for something like diagnostics cuz I can't see what other purpose it would serve.

 

It would have to have the red and green LEDs to do this. To my knowledge only the later EFI Z24s had this. If the O2 is cheap, replace it. It only functions once the motor is warm.