Will a spedo cable cause problem???

[wranglercory]

My MJ won't run anything over idle after its warmed up to opperating temp. Could my spedo cable that is disconnected cause my problem. The truck is a 1987 MJ with a 2.5 liter AX5 trans and is 4X4. I just thought of this while going through the flow chart of troubleshooting.The chart called to check a speed sensor and I thought it could feed from the cluster to the ECU ???? Just a shot in the dark at this point.

[Geonovast]

Nope.

[wranglercory]

GRRRR This sucks I think Ill start swapping the sensors from my bad 87 to my good MJ one at a time to see if I can get it that way???

[Eagle]

Let's try a bit of Sherlock Holmes style deductive reasoning. The problems occur after it reaches operating temperature. During warmup, it runs in "open loop" mode, ignoring certain sensor inputs and using a programmed fuel map in the ECO to control the fuel delivery. Once it warms up and switches to "closed loop mode." it then responds to input from sensors.

 

Clearly, then, the basic systems are okay and the problem lies with one (hopefully not more than one) of the sensors that get bypassed in open loop mode. The oxygen sensor is one of those, so that's one to check. Not sure if the MAP sensor is skipped in open lop mode. What else is there?

[Geonovast]

Is your knock sensor plugged in? I've read that if it's unplugged, it can cause the ECU to make it run in some sort of "safe mode"