1987 Jeep Cherokee-4.0L I6 auto tranny 4WD. Fuel pump will engage if straight wired but not if plugged in, engine will crank but not turn over, checked all relays & relaced battery cables &...
If you turn on the key and you do not hear the pump in the tank running for two secounds ( the same time your warning lights on your dash light up and goes off) then 1 you need to replace the pump or 2 it has low voltage to the pump or 3 both. I just repaired a 1987 pioneer what you need to know is the pump requires 12v at the pump, however OEM has placed an inline ballast resistor located on the driver side front engine compartment near the hood latch that is made of white ceramic with two connection both wires are orange with a black stripe. A. Check the voltage on both sides of the resistor 12v in 12v out use a volt meater - to battery + to resister if no voltes check the relay the passenger side of the engine compartment ( there is 4 relays from front to back it is no. 2 from the battery) looks like a small blue box newer relays are black, if they do not click when the key is on then your CPU may be bad or fusible link is bad If you have voltage to the resister and you have 12v in and less than 12v out your next test will be at the rear connector to the pump, three wires close to the fuel filter using a volt meater check the black wire with the orange / black stripe if voltage is less than the voltage out of your resistor then there is a bad wire in the system and a new wire is required. confirm this by jumping the battery to the pump wire black to- and orange to + the pump should run. Note. running the pump with lower than 12v will damage the pump and cause it to fail! If the pump works you can check the fuel pressure on the fuel rail, remove the cap to epose the shearder valve (looks like the valve on your tires) depress the valve stem and fuel should come out, caution fuel is under pressure have a rag under the valve to catch the fuel, if low pressure the pump is bad and/or filter is plugged Replace filter first recheck this test then replace pump and recheck. Note!!! when the pump is out of the tank recheck the voltage at the pump this will show true voltage at the last connector it needs to be 12 volts! Reconnect the pump wire the stock wire and check, on the pioneer I worked on was 4 volts so I rewired it to a new battery source using the orange /black strip wire that had 12v in to resistor as a trip wire for a 65 amp power relay. The owner noted an increase in overal performance " it now has more power now" hope this helps
Feb 23, 2011 |
Jeep Cherokee Cars & Trucks