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Dead 2.5L???

M

Mcstiff

NAXJA Forum User
Location
Boulder, Co/ Lansdale, Pa
So I was driving down the road and it just died like it ran out of gas. I filled the tank but it will not fire up only crank forever. I figure it is eather a fuel pump or relay. One of the relays on the PS is making noise and the fuel pump was not whining at all previously.
So I figure it is the relay. The other possability is a short cookign the computer (the wireing is sub par as the p.o. blew some fuseable links and had to rewire them).
What do you guy's think, relay, pump, or comupter?
 
I would check to see weather or not the pressure is where it needs to be.
 
how did it die? stumbling or just shut down?
 
swap relays and see if it starts. If so, replace the fuel pump relay. You should hear the pump prime up for about 2 seconds when you switch the ignition, and then stop. If it doesn't whirr up when you key it, it's not getting any power.
HTH,
Jeff
 
I had a similiar problem on my 4.0 a while back. I was low on gas and it just wouldn't start. I tested the cps, tps and fuel pump and they were fine. I decided to change the fuel filter, and then the Jeep would start but only if I had the pedal at full throttle and kept it there. I was getting wierd codes that made no sense.

Finally I decided to disconnect the battery and reset the computer. Disconnected it and let it sit for about 15 minutes, reconnected it and it started up fine. I have not had a problem since. Try it out, it's worth a shot.
 
It just shut down. I'll try reseting it. Swapping the two relays which are next to each other did nothing but they both should need to work for the car to run right? The fuel pump is not priming.
 
Sounds like a dead pump, or one that's not getting power. If you have a meter, check for voltage at the pump with the key on. Follow the wires back from the pump to the connector, disco it and check for power. If none, I'd say replace the relay and/or check for a fusable link gone bad pre-pump somewhere. If yes to voltage at the connector, check continuity of the pump wiring with the meter. If it's open, check the ground wire where it attaches to the top of the pump assembly on the outside of the tank. It could be corroded, or it could have snapped off there. If volts and ground wire are o.k., I'd suspect the pump.
Also, not sure if you have a ballast resistor in the pump circuit..it's a white ceramic thingy mounted on the DS firewall with a wire at each end. If you do have one, and have no power to the pump, try jumping it to see if it's not the culprit.
Good luck!
Jeff
 
What year?

What year is the 2.5? TBI or mfi? Those little blue bosch relays are notorious for failing. I keep two extra with me at all times.
 
It is a '86 TBI. I replaced one relay but still didnt work. So I tested the V at the pump and it had a positive reading so the pump must be dead, right? The red wire spiked then dropped to 0 and the yellow (white) was steady. Does this sound right? Looks like I'll put a pump in tomarrow.
 
wiring

The red wire is your power for the pump. If it is spiking then I would still suspect a relay. The other wire is the tank level sending unit and should be tan colored. It should have a steady power reading but I believe the resistance fluctuates with tank level. Go to your diagnostic plug #1 and make sure you have power when the ignition is on (orange wire). If you are getting a constant voltage then next make sure you are getting constant voltage at the pump. If not, it's the wiring. If it is, change the pump or injector (you can check for voltage at the injector too). You can point your timing light down the throttle body while you crank to see if the injector is working. For further troubleshooting get a fuel pressure gauge. I don't have a source for the pump other than the dealer but you can get a reconditioned injector at:BBB automotive
Hope this helps:D
 
If it turns out you still need the pump, I have one that is only about 3 months old. I'll take $30. I'm installing a stroker and it takes a different pump.

Tom Houston
Loveland, Colorado
 
Where is diag. plug one? I took the readings from the plug near the pump (~12" away) since the pump itself does not have exposed wires.
Tom, is your pump from a TBI 2.5? I'll take it if it turns out to be the problem.
 
Yes, it is from a tbi 2.5L. Add and extra $15 and I'll throw in my spare backup pump as well. I always keep a backup unit. I can't tell you how many fuel pumps I have seen bite the dust on trails.

Tom Houston
Loveland, Colorado
1-970-667-2001 home/office
1-970-690-6270 cell
 
Diagnostic Plug

The diagnostic plugs are under the hood. There is a larger and a smaller one, both with yellow covers. The larger one is the one you want. Just find the orange wire and check it for voltage.
 
ARRG! Well, it would seem to be the wireing not the relay or the pump. Dose anyone have the normal readings for the relays and the diag. ports with the ignition switch on? Somthing is dead between the battery and the pump.
Is there a way to by pass all the BS so I can drive it home (30mi)? Direct connection with a inline fuse or somthing? Is is really a pita to have to drive to the park & ride in Morrison every time I need to test somthing. ;)
 
Last edited:
It looks like the problem is the O/B wire (position 30) from the ECU. I assume this means I can jump position 87 to position 85 (red to orange; positive to fuel pump) and make it work untill I get home. What is the safest way to do this?
 
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