DanO55

Hello Guys, I have a 88 Comanche with a 4.0 , Auto Trans, 4x4

To Begin with, I know this is the Cherokee Tech Section but I got no response from the Comanche Tech section , so thought I'd try posting my problem here, PLEASE HELP...
Vehicle in question : 88 Jeep Comanche 4.0 Auto 4x4
Problem : The Truck Just Died on me with No Warning at all.
Truck Was Starting and Running PERFECT up until this happened.
I can get it to start very Briefly, pumping the hell out of it but it will only run for less than 15 seconds and sounds like it's running on fumes. I believe it;s the Fuel Pump but before I yank it out I want to be sure it's not electrical. I put the key ON and pulled the plug going to the Pump to test it. Lite Orange Wire HOT, Other 2, ORANGE & BLACK, NOTHING. I assume the Black is Ground?? I Pulled the Relay out and tested the socket, HOT on 2 ONLY. Is this NORMAL? Thought of Running a Hot wire to the connector but NOT sure which wire to use and don't want to FRY something.
Any ideas or advice would be greatly appreciated. I hate to change that Pump and find out it's NOT the problem.
Thanks for the help , DanO'

DFlintstone

Hey Dan, and welcome! you are in the right place. (right enough).

First off you want to do Cruisers 1 through 5 for starters. Yea, allot of work, but almost a sure bet you will be glad you did. Doing 27 really stabs things as well. >https://www.cherokeeforum.com/f51/cr...x-tips-153657/

All of your major stuff goes through that C-101 connector. It's so bad Jeep even sold a harness/Kit to run your CPS wires right through the firewall to the ECU to get around it! (so it would at least try to run)

>>>>>>>>On the left inner fender (near the airbox/orange wires), is a ceramic resistor. It was only added to quiet the pump a bit. You can bypass or eliminate it. System power comes in the front and a few volts less goes out the rear directly to the pump. If that rear terminal has 10-14 volts and fuel pressure isn't up....the problem isn't electrical unless it's the power wire or the ground to the pump.

!!!**!!!>>> I always have the ign on while jumping to this rear terminal, since it back-feeds to the system. (actually not doing that doesn't seem to fry anything, but hey, either unplug it or have the ign on.... You might not have one Btw....

*There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage and you won't be happy.

*Anyone with an 87 to 90 Renix Jeep has two or three minutes to see that their CPS is putting out at least .35 AC volts. I don't mean to come off rude, but if you can't connect a meter and turn the key, we may not be much help. Easy as one, two three!
AC voltage CPS test; Small clips on the meter leads really helps. You need contact with those little pins while it cranks, maybe get someone to help.
#1 Unplug the connector at the back of the manifold with wires going down to the bell-housing/cps. (it's a three wire plug, with only two wires)
#2 Probe the two wires to the cps with the digital meter set on AC volts, a 200 scale on mine. Yours meter may have a lower 2 Volt, or “auto range”.
#3 Crank the engine and note the voltage. (jump it if your battery is low). .35 ( is minimum. .4 to .8 is more like it.
So, there's a start!