Fuel Pump Troubleshooting and Replacement

[Short Bus 80]

The 80 started acting up a couple weeks ago and I finally got time over the weekend to get her running right. Here is the step by step (Mostly) on troubleshooting and correcting the problem that turned out to be a bad fuel pump.

The Truck:
91 FJ80
3FE motor stock
235K miles

The Problem:
The truck has been hard to start for a couple of months (Takes 2-3 tries to start, fires then dies) but wasn't that big a deal. Driving home one night she was very low on power and would not accelerate. If I put her in neutral she would rev-out but then bog down when put back in gear. Starting now became very difficult, you had to feather the gas peddle like you were starting a carbureted car that had been sitting for years. The idle was also a little rough.

Troubleshooting:
I started by checking the Throttle Position Sensor. The FSM covers this well and there are a bunch of posts on the TPS so I'll skip the details. The TPS tested fine.

Next I check the Air Flow Meter. The FSM covers this well and there are a bunch of posts on the AFM so I'll skip the details.

I decided to check for fuel next. I removed the output line from the fuel filter (located on the frame rail under the passengers feet) and jumped FP to B+ on the test block on the passenger side of the fire wall. When the key was turned to the run position fuel flowed through the filter.

I had fuel flow but now need to see if I have enough pressure. I went to O'Reilly's and borrowed a fuel pressure test kit #67091 ($110 deposit). This kit had the correct fittings to interface to the Land Crusher.
Pictures coming up next.

 

[Short Bus 80]

I connected the fitting for the pressure tester to the fuel rail where the metal line for the cold start injector is connected. Just remove the banjo bolt and be careful not to drop the 2 crush washers. Install the test fitting with crush washers.

On a side note I had a lot of trouble with this test gauge. When you connected the hose to the fitting there is a rubber seal inside the hose fitting that mates to the shrader fitting, when I tightened them together the seal blocked the pressure port and the gauge read 0PSI. I messed with this for 2 hours and finally got it working by removing the rubber seal and installing 3 small o-ring.

When I started the truck she only had 18 PSI. Next was to check and see if the problem is the pump or the fuel pressure regulator. I took a long screwdriver and used it to listen to the regulator, it was knocking which is normal and means it is trying to maintain pressure. Next I pinched the vacuum hose to the regulator which should allow the regulator to pass full pressure, no change on the gauge. Looks like it's time for a fuel pump.

 

[Short Bus 80]

There is access to the pump under the middle seats. Tip the seats forward and remove the plastic cover on the rear bolts. Remove the rear bolts and the front bolts and take the seats out. You need to remove both. Next take out the little foot steps from both sides, and the door trim. Pull the carpet forward and you will see the access cover.

 

[Short Bus 80]

Remove the access cover and you will see the pump/sending unit assembly. Before removing the banjo bolt for the pump it will help to remove the pressure in the system. The test gauge has a release valve to help with this but you can also crack the fitting at the fuel filter. Remove the banjo bolt, connector, and bolts around the edge of the assembly. The banjo bolt will still lead fuel but it wont spray out.

Note: It looks like there is a thermal couple next to the float. I can't find any info on this. If anybody knows what this temp sending unit does I would be very interested.

 

[Short Bus 80]

Now that the pump is out we need to replace the big silver part and the filter on the end. As you can see in the pic the pump had been replaced before, this is a Carter pump. As I was removing the old pump the Negative lead broke. The wire is held to the bracket with a rivet so I drilled out the rivet and made a new wire. I attached the new wire to the bracket with a bolt and star washers.

Parts:
O'reilly's
Fuel Pump Bestest BE16024 $118.99
Auto Zone
Filter Screen Airtex FS139 $19.99 (O'reilly's did not have the filter in stock)

NOTE: There is also a pump called Import Direct and is $125. This pump is not a direct replacement and will take a bit of work to make it fit. It is a much smaller pump. The Bestest fit right in with not mods.

 

[Short Bus 80]

Now we need to put everything back. Use new crush washers on the banjo bolt for the pump and put a little oil on them to help them seat. She cranked over for 2 seconds and fired right up and came into a nice idle. Pressure is now 40 PSI. We are back on the road. The job took 5 hours but I also messed around the the pressure gauge, made three trips to the parts store (I got wrong pump the first time) and had to make a new wire. If I had to do it again total time including troubleshooting would be closer to 2 hours.

 

[ttubb]

Nice write-up. Thanks, T

 

[LongDuck]

Thanks for the directions, always nice to know how to get to important things that aren't immediately accessible from underside. Nice pictures to make it easy to follow, as well.