94 jeep 4.0l will not start

Scott86MJ

Well-Known Member
Joined
May 3, 2006
Location
Dallas
I have a jeep Comanche with a 94 XJ engine. It's been sitting for a year. I tried to crank it a couple of months ago and fuel seeped from the rubber line at the fuel tank. So I replaced the line but it wasn't cracked maybe needed tightening. I was thinking maybe clogged line caused the fuel to seep. I bypassed to fuel filter on the frame rail with rubber hose. It will crank if you spray starting fluid but dies as soon as it is gone. Has fresh fuel. IOD fuse was blown but replaced it. I can't hear the fuel pump come on but I can't remember if I could hear it before. Doesn't seem to have power at the fuel pump when in run. I ran a 12vdc wire directly to the pump and I could hear anything. Tried 2 different sending units. Any ideas? Thanks
 
Got fuel pressure at the rail? A gauge would be best, but you could just tap the schrader valve with a screwdriver, see if fuel squirts out.
 
If the pump doesn't run when putting 12V directly to it then it is bad, if it does but won't prime when you turn the key then you need to trace it back... could be a grounding issue, loose wire, or even the ECU but fuel pump relay is the most likely culprit. Do some voltage checks at the relay with the key on to see what you find.
 
The ethanol in the fuel usually rots the hose that connects the pump to the sending unit. Check that when you pull the sending unit to change the pump if necessary.

First is to check psi at the rail
 
Got fuel pressure at the rail? A gauge would be best, but you could just tap the schrader valve with a screwdriver, see if fuel squirts out.
I will get a fuel pressure tester. If you hit the valve at the rail fuel comes out but I wouldn't say squirts. What should the pressure be? Thanks
 
If the pump doesn't run when putting 12V directly to it then it is bad, if it does but won't prime when you turn the key then you need to trace it back... could be a grounding issue, loose wire, or even the ECU but fuel pump relay is the most likely culprit. Do some voltage checks at the relay with the key on to see what you find.
I'll check the ground. Would the jeep crank with starting fluid with a bad ECU? Thanks for the help!
 
hey even though u have 94 motor, the jeep is MJ so my first question is what year...that will say a lot...
 
if it's a renix mj, you have fuel pump ballast resistor by the air box...bypass it by touching wires to see if you get power at pump...then on renix you have the starter relay by the batt/relay center and one wire on it at the bottom, i think, goes to the fuel pump ballast resistor so check 12v on that wire with key on and cranking...swap around relays real quick making sure ASD relay and Fuel pump one is good (2most left relays towards firewall) then check the wire at the pump under rear seat where the fuel pump wire goes through floor...seen many get frayed right there. just some stuff to check for you. good luck
 
I'll check the ground. Would the jeep crank with starting fluid with a bad ECU? Thanks for the help!
I'll check the ground. Would the jeep crank with starting fluid with a bad ECU? Thanks for the help!
Not 100% sure since I don't know if your ignition relies on the ECU, but as long as its getting spark it will fire on starting fluid but cut off as soon as it burns off.
 
hey even though u have 94 motor, the jeep is MJ so my first question is what year...that will say a lot...
It's an 86 that came with a 2.5 but I put the complete engine and wiring harness ,ECU ,trans and transfercase from the 94 xj. So the body and fuel tank is the only thing MJ.
 
It's an 86 that came with a 2.5 but I put the complete engine and wiring harness ,ECU ,trans and transfercase from the 94 xj. So the body and fuel tank is the only thing MJ.
oh ok well that changes most of what i said earlier.
I didn't understand before..you swapped different fuel pumps and still nothing?
You also put direct power to the pump and still nothing?
 
I will get a fuel pressure tester. If you hit the valve at the rail fuel comes out but I wouldn't say squirts. What should the pressure be? Thanks
32-42 psi if I remember right. Your fuel line could have a hole in the tank, rubber line between pump & sender or the sender could be rusted out. You can also do a volume and dead head pressure test to check the check valve and fuel delivery.
 
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