Posts Tagged ‘repair’

Jeep Cherokee Fuel Pump Replacement

Tuesday, June 23rd, 2009

Jeep Cherokee Fuel Pump Replacement

This weekend while on an off road trip, Jenny’s Jeep began to experience the symptoms of a bad fuel pump. Her jeep would stumble and die at idle. It would only run if the rpms were kept over 1500 and it was low on power. It was also surging as the fuel pump lost pressure. It was making only 20 psi or so and that was simply not enough to keep the fuel from boiling in the hot fuel rail. It was a struggle, but we got her Jeep out of the woods under its own power and got it back to my shop.

Fist, we used the failing fuel pump to pump the remainder of the fuel from the tank. I used my fuel pressure tester attached to the fuel rail test port to pump the fuel into a can. I made a jumper wire and attached it to the fuel pump relay socket to force the pump to run.

Once the tank was empty, I disconnected the lines from the fuel pump assembly and disconnected the wires. I also disconnected the tank vent lines.

Next, I rigged up a lift to support the tank as I lowered it from the Jeep. I then loosened the tank support straps. After lowering the tank a couple of inches I was able to reach above the tank and loosen the filler and vent lines from the tank. I then removed the tank support straps and lowered the tank out of the Jeep.

With the tank out, I stood it up and cleaned the mounting flange for the pump assembly with a wire brush. I used a hammer and screwdriver to move the clamp ring off the pump. Then I carefully removed the pump from the tank taking care not to get dirt in the tank. The filter sock fell off and had to be retrieved with a gripper tool. Often the tapered grommet for the pump assembly will stay in the tank as well. If so, this has to be fished out. This one came out with the pump this time however.

To test the pump, Jenny made up a container for fuel and reconnected the pump to the lines and wires. The last time I worked on this Jeep there was a leak in the line between the pump and the tank outlet. This time however, there was no leak; the pump simply was not making pressure. Cold it would make only 30 psi not the required 48 psi. When the pump got hot it made less pressure. We measured 20 psi when the Jeep was trying to get home the day before.

We then tested the used replacement we had available. It easily made more than enough pressure. And still no leaks. The mounting bracket in this tank has been modified slightly in an off roading mishap so I had to adapt the new pump to fit. After some mixing and matching of parts and some creative routing of the expensive high pressure hose, I got it to fit. Jenny also had to put a wrap or two of Teflon tape on the pump inlet to get the filter sock to stay in place.

I carefully cleaned the pump mounting surface and the O ring. I then set the pump in place and tapped the retaining ring back into position.

We then lifted the tank up into the Jeep. With the tank almost in place I reattached the filler and vent lines. This was the most difficult part of the job by far. Once the lines were reattached, I lifted the tank the rest of the way back up and reinstalled the straps. I actually forgot to tighten the fuel line clamps before driving it. I should have tightened them right after I reinstalled the lines and attached the wires.

We put the fuel back in and ran the pump on the jumper a moment to prime the system and get air out of the lines. When I heard the regulator squeal, I knew the air was being purged. Jenny’s Jeep started right up. It stumbled a moment while the computer adapted to having the right pressure at the injectors again but it settled down quickly.

A quick test drive showed it all worked fine. With the exception of the loose clamps on the fuel lines I mentioned earlier. I had to tighten them in the street because I was afraid they might pop off if we drove it back to the shop.

Her fuel pressure is back in spec again. Hopefully this pump will last a while. The whole job took about four hours start to finish.

Trouble Shooting Will’s Jeep Cherokee

Wednesday, March 4th, 2009

Jeep Engine Repair

Will’s 1991 Jeep Cherokee 4.0 has been running poorly lately. It started dieing at traffic lights. We cleaned the idle air control valve several times. Each time we cleaned it, his Jeep would run fine for a while and them stall again. Naturally it would stall at an inopportune time.
Eventually his Jeep got to where it would run rough all the time. I began pulling plug wires to isolate the bad cylinder. The number one cylinder was dead. It seemed that the injector simply was not firing.

There was good spark, just not firing in the cylinder. Removing the plug wire did not change the engine speed at all.

The plugs were nice and tan but very worn. We replaced them along with the wires to see if it would help. The engine ran smoother but there was still the dead cylinder.

We posted the questions about the Code 27 that the engine computer was showing on a couple of bulletin boards. Both the XJ list and Hesco forums suggested that we test the injector before looking at the ECU.

Code 27 indicates trouble with the injector firing circuit.

The injector tested fine at bout 14 ohms.

As I was showing Will what was involved in swapping out the ECU, we noticed the connector looked strange so I wiggled it around a bit. When Will restarted the Jeep it ran fine.

Later we pulled the connector and sprayed some cleaner on the contacts. So far his Jeep continues to run great with no more stumble.

Hopefully all his troubles were related to this simple bad connection at the ECU.