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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
Bare with me because I don't know much about electrical. When I turn the ignition on I can't hear the fuel pump priming. All I hear is a small click followed by a slight humming sound back towards the passenger side firewall.
I checked the relay by swapping it with a known good one and got the same result. I then used a jumper directly from the battery to the relay socket with the relay removed and was able to replicate the click and hum. Based on this I believe power is getting through the relay.
It's an '87. Mine usually primes the way yours does. Not now. That's why I don't think any power is getting to the pump.
The click followed by a light hummimg or buzzing sound near the rear of the engine bay leads me to think there's a problem between the relay and the pump. Is the circuit uninterrupted between the relay and the pump, or does it go through something else first?
I've downloaded the FSM but unfortunately I forgot my tablet at my other house yesterday. I don't have internet at my weekend place and am trying to do this with my phone.
The pump is new as of December and only has about 300 miles on it.
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Like the man said, probe for power back at the fuel tank, and check that ground. That's the only way to know if power is getting that far.
Don't assume a new pump can't be bad. It happens.
I found this in an 88 service manual:
Voltage to operate
pump is controlled by Electronic Control Unit (ECU). A ballast
resistor is used in the fuel pump control circuit.
Ballast resistor is by-passed during start mode. During
running mode, ballast resistor reduces speed of pump by lowering pump
voltage. This ensures normal speed in running mode. The 1-ohm ballast
resistor is mounted on right side of plenum chamber.
Fuel pump control relay is located on front of right strut
tower. Battery voltage is supplied to relay from ignition switch.
Relay is energized when ECU provides a circuit to ground.
A multi-cell, roller type pump is used on all 4.0L MPFI
models. Pump and fuel filter are located on a plate, forward of rear
axle. Fuel pump control relay location for 4.0L models is on right
inner front fenderwell. Battery voltage is supplied to relay from
ignition switch. Relay is energized when ECU provides a circuit to
ground.
I was also able to find a wiring diagram and verify that the fuel pump relay output goes directly to the "Fuel Tank Unit". I presume that means the pump. It also feeds a number of other circuits which are not related to the fuel system, like your heater relay!
Orange lines connect off the top edge of the screenshot.
With the relay in the socket, when I turn on the ignition, there is a series of 3 clicks with 2 different tones. When I pull the relay I get only 2 clicks.
Can a bad pump show symptoms at the relay?
By the way, I've cleaned the spades on the relay and the connections in the socket.
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Originally Posted by Don X
With the relay in the socket, when I turn on the ignition, there is a series of 3 clicks with 2 different tones. When I pull the relay I get only 2 clicks.
Can a bad pump show symptoms at the relay?
Possible.
Originally Posted by Don X
By the way, I've cleaned the spades on the relay and the connections in the socket.
Don't care. Get your mangy carcass under that car and test for voltage back at the pump! And clean the pump's ground back there! Git!
I haven't replaced my multimeter since the time I shorted it and magic smoke appeared. Quite honestly all of those settings and symbols are Greek to me.
I poked around the CPS. Could barely get a hand on it. Unplugged it several times. Then walked away for awhile.
Started working on a bound up power window. Turned the ignition on numerous time. Finally the pump primed when I switched to on. Got the engine started. Restarted about 5 times without issue. Took a test drive with a stop thrown in. Drove well and started right up the time I stopped.
Smart me knows I need to replace the CPS. Stupid me keeps telling myself how hard it will be.
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
'Snot hard. Get yo'sef down to Harbor Freight and get this and this. Wrap a bit of duct tape around the U-Joint so that it will hold position, but can still be moved. Get the XJ up on jackstands and attack the CPS from below and behind. Might need a flashlight. From next to the transmissoin, with TWO of those long extentions, and the u-joint on the end, you can reach right up there and undo those bolts. 11mm, IIRC. Same thing in reverse.
05-22-2020, 11:24 PM
No power to the fuel pump
