Fuel Delivery Troubleshooting – How to Change 2.0L Protege Fuel Pump

As some of you know, I stored my protege over the winter but I made the mistake of not filling up the tank till December 2014. In Dec I topped it off with winter gas and added fuel stabilizer to the tank. I’m trying to start the car now and it cranks but no start condition is present.

I’ve redone my haltech wiring, checked for spark(its there), and listened to the fuel pump with a stethoscope (I can hear the motor or w.e starting in the fuel sending unit while cranking), checked voltage on all inj wires (11.6v -11.8v on all 4 while cranking for 3 seconds), checked voltage on fuel pump harness and it gets 11v to the gas light wire and 11.6v on the main thick red wire.

Yesterday I swapped out my factor fuel pump unit for the Walbro GSS342 upgraded pump. For anyone that’s attempting to change out your fuel pump please spray PB blaster on the rusted screws for atleast 6 hours before attempting the job. Get yourself a hand impact tool and a set of screw extractors to be on the safe side.

Follow these instructions at your own risk! This is only a personal log. I am not responsible for anything you might break while attempting this. Before proceeding disconnect both battery terminals!

Step 1) Remove rear seat/fuel sending unit top plate cover and spray PB plaster/ Liquid wrench or some strong penetrating fluid on all 8 screws.

Protege rear sending unit

Protege rear sending unit

Step 2) If you’re able to start the car, start it and remove the fuel pump relay from the engine bay fuse box. This will cause the fuel lines to depressurize and ultimately kill the engine. Once the engine stops running you know for a fact that the fuel lines are fully depressurized.

Step 3) Use the hand impact and start removing all 8 of the screws by hammering on the impact end while turning the screw driver. The impacting along with the turning motion should release the rusted screws. There is a very high chance that these will strip hence why I mentioned to keep a screw extractor handy.

This is some new information I came across while struggling with this job. The screws used by mazda are NOT Philips screws as you might think. They are actually JIS screws used as a Japanese standard.


Sending unit screws

Sending unit screws

I was able to get all 8 out with the help of the screw extractor.

Step 4) Remove both electrical connections from the sending unit assembly, remove both the return and feed lines by pushing on the green tabs on each side and sliding off the black cover. Be patient with these as they gave me a bit of trouble.

Keep a cloth near you to catch any fuel spills.

Fuel spill prevention

Fuel spill prevention

Step 5) Remove the whole sending unit out but be sure to drain all the fuel before pulling the unit across your interior. I transferred the unit into a plastic bag to avoid any spillage and screwed on the top plate cover to limit the smell of gas in my garage.

Fuel sending unit

Fuel sending unit out

Step 6) Now the fun part of disassembling the fuel sending unit. Remove both white plastic retaining holders that keeps the pump in place, disconnect electrical connections, and gently pull the pump from the unit. once the pump is half way out you will notice another black electrical connection going directly to the pump itself. unplug it and completely pull the pump out of the unit.

Its a good rule of thumb to compare the new part to old and make sure they’re both the same.



rebuild comparison


Step 7) plug the black electrical connector to the pump, remove any rubber plugs, and reinstall the new pump to the unit. Then plug in both white connectors to the unit. Transfer the fuel filter and locking washer from the old pump. You always have the option of getting a new filter.

You will notice that the Walbro pump is slightly longer than the OEM unit.

This is where slight modification was required to make sure the pump did not move when the car is moving. The white plastic retaining holder you removed earlier will have to be cut to accommodate the longer length of the new pump.


Pump holding tabs

Above picture shows the cuts I made to the piece. You will not be using the top round section of the retaining holder. Hold the tabs in place and weaver a zip tie through the openings creating a locking mechanism when tightened.

Pump held together by zip ties

Pump held together by zip ties

Step 8) The OEM brass screw are 4Mx7 however, I got stainless steel 4Mx10 screws with 3 1mm washers to equal OEM 4Mx7 size after installing.

M4x7 screws

M4x7 screws

Step 9) Reinstall the sending unit to the fuel tank, reconnect both fuel lines and electrical connectors. Plug in the fuel pump relay to the fuse box. and reconnect the battery terminals.

New pump installed

New pump installed

Step 10) Turn they key to ACC and let the pump prime for a minute and TURN KEY

This did resolve one of my issues of fuel not getting delivered to the fuel rail. I removed the feed line from the rail, put it in a bottle and cranked. It was a success and the pump was working perfectly. Doing this I was able to figure out that my pump, fuel hard lines and rubber feed line is functioning properly.

I re-installed the feed to the rail and cranked while the rail/injectors were removed. No fuel squirted out the injectors. Now I know for sure its a clogged rail, injectors or FPR. This is bad news but mainly good since I have a new external FPR, Hydra fuel rail waiting to be installed.

Stay tuned!

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