co-MAN-che

I have checked my fuel pressure. I have checked my pump and sending unit. I have checked the circuit to the pump and sending unit. I have replaced every relay and fuse associated with the fuel and ignition system. I have replaced every sensor and switch associated with the fuel and ignition system.Is there something I'm missing that could lead the truck to start, idle quite high for 3-4 seconds, then begin to slow down so much in idle speed that it starts shuddering until it utterly dies? I'm starting to think this truck cannot be fixed.

DFlintstone

You said you checked the fuel pressure. Still, after it dies, does it spurt a little fuel into the rag you are holding there if you depress the thingy on the tester valve? On the inner fender by the air cleaner is a ceramic ballast resistor for the fuel pump. It can be by-passed. Also , fyi, the rear terminal goes straight to the fuel pump. For testing that can be jumped straight to bat +. (Ign on).

Any magor hissing from a big Vacuum leak?

Also> 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 it will be pig-rich. (black smoke, fouled black plugs).

Also, the "Key trick">>>
OBD1 Models: 1991-1995
1) Start engine (if possible). Move transmission shift lever
through all positions, ending in Park. Turn A/C switch on and then off
(if equipped).
2) Turn engine off. Without starting engine again, turn
ignition on, off, on, off and on within 5 seconds. Record 2-digit
fault codes as displayed by flashing MIL.
3) For example, fault code 23 is displayed as flash, flash,
4-second pause, flash, flash, flash. After a slightly longer pause,
other codes stored are displayed in numerical order. When MIL begins
to flash fault codes, it cannot be stopped. Start over if count is
lost. Code 55 indicates end of fault code display.

co-MAN-che

still get some fuel squirting when I depress the shrader valve on the fuel rail while off.

----have no current going to the ballast resistor when key is "on", even after bypassing.----

Hooked fuel pump right up to battery with no improvement. Inspected hose leading to map sensor and it is intact. neither I nor the neighbors (multiple sets of ears are better than one) heard any vacuum hissing. No engine codes are being thrown except for 12 (battery unplugged in past 50 keystrokes) and 55 (end of codes)

DucMan

I know you probably checked this but....have you disconected the fuel filter and tried blowing through it?? The pump will push through a plugged filter and have a similar symptom!!?

DFlintstone

I haven't yet figured out everything for 87-90. Yours shares plenty there though.

You didn't mention how it runs. Is it just an idle issue? If so there are a couple if things...

You might do yourself a favor and go ahead on Cruisers Tips on top in my signature. Lots of posters report ether a specific, or general improvement after checking/cleaning the ground side, as well as other wiring connection issues. 1 through 5, unless you are post 88 with no C-101 connector.

And you know...the pump just runs a couple of seconds after key on, you can hear it. Then cranking it gets power right from the start relay, (87-90), then after starting the CPS tells the puter to keep fuel flowing.. (for you that would be the PCM telling a different relay to provide fuel)

That said, the IAC and it's plug/wires are very important for idle.

co-MAN-che

DucMan - I have a brand new fuel filter that i went ahead and verified was clear of obstructions

DFlintstone - I have followed Cruiser's tips in the past as far as I can, but not having a Renix jeep means not all of his tips work on my vehicle. As for the PCM deciding which relay operates fuel, I have replaced all my relays as a precaution when I first purchased the truck, and have tried 3 different PCMs in hopes that was the issue with no improvement. I'll head to the IAC and its corresponding wires and inspect it.

also, I have no current going to the ballast resistor when the key is in the "on" position

co-MAN-che

No trouble codes reported by computer either

revolver

clean the throttle body maybe?

co-MAN-che

I'll try anything at this point in time

co-MAN-che

Force fed power to the fuel pump, retested my fuel pressure and it measures at 40 psi. Now it starts but still immediately dies. I can't get my hand out of the drivers window and 2 feet to the throttle body in time to try to hit the IAC with throttle body cleaner to see if it helps any

corbinxj

I had the same issue jus yesterday after I took the throttle body apart and cleaned it along with the IAC. To make a long story short, in my cleaning of the IAC I unscrewed the top cone of it and it allowed the gap to widen(pushed by the spring) after about six attempts at tightening it down I finally got it to a spot where she purrs like a kitten.

I'd suggest pulling your IAC and clean it and the throttle body completely, should only take about an hour. And don't be like me and accidentally unscrew the spring!

Good luck!!

2heapjeeps

Comanche doesn't have a security system right?

co-MAN-che

Corbinxj - went ahead and got a brand new throttle body, IAC motor, valve, sensor, and hose so I didn't have to worry if I got it clean enough. No improvement in performance

2heapjeeps - no, my comanche doesn't have a security system

Crayfish03

May of mentioned this but have you checked to be sure the ground to your fuel pump isn't unplugged? This happened to me and my ground was unplugged.

co-MAN-che

when I force fed power to it I verified that everything leading to it was plugged in and intact.