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Commodore Fuel Pump Replacement

Today we are taking a look at what is involved in replacing the fuel pump on the VL (internal) to VS Commodores. Before we start I need to stress that safety comes first when doing this job, it might sound obvious but accidents do happen and it’s vital that you take precautions to avoid turning your car or even worse, yourself into toast. An open, well-ventilated area is a must and naturally no smoking or ignition sources within the area that you are working. You might not think it will happen to you but let me tell you a story from when I was an apprentice. I was replacing a mechanical fuel pump on a Mitsubishi L300 van, a job I had done plenty of times before, and nearly had it out when it slipped out of my hands (I was working from underneath the van) and as it fell it shorted on the starter motor positive terminal. I didn’t get my hand out quick enough and although my hand didn’t have all that much fuel on it, it was enough to catch alight from the resulting spark and by the time I got to some water I had suffered 3rd degree burns across the top of 4 fingers. I had weeks of bandaging and working with my hand in a glove but the worse part was when the doctor had to peel dead skin off to let the new skin grow over, not an experience I would like to repeat I can tell you! So TAKE CARE while doing this job.

**Just a little note here – if you suspect the fuel pump has died and you need to move the car grab an assistant and while they crank the engine stick you wing under the back of the car and bang on the underside of the fuel tank with the palm of your hand. You can do this as hard as you are game to and SOMETIMES it will be enough to shock the pump into life and you’ll be mobile again. You won’t find this method in any workshop manuals and the pump will still need to be replaced but in an emergency it’s worth a go!**

DIAGNOSTICS

On the Commodore a dud fuel pump is typically easy to diagnose, there is no ‘buzz’ heard from the rear of the car when the ignition is switched on or the engine cranked (if you can get an assistant to operate the ignition while you listen at the rear of the car, just behind the drivers side wheel) but before condemning the fuel pump to death we first need to do some checks to confirm our suspicions.

Checking for pressure at the fuel rail is as easy as (carefully!) removing the return line from where it connects to the regulator. If the pump is functioning there will be pressure in the line and fuel present when you remove the hose. If it’s not functioning there is likely to be little pressure and perhaps a dribble of fuel remaining in the rail and hose. If you have a spare length of hose and a suitable container you can connect this to the fuel rail outlet and crank the engine. If the pump is functioning there will be a good flow of fuel, if not there will be bugger all!

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Now it should be established that we have no fuel pressure so let’s rule out any switching or electrical issues, a blown fuse or dodgy relay is a lot easier and cheaper to replace than the pump so lets look at those first. The fuse and relay for the fuel pump is located in the fuse box in the engine bay. Check the fuse (info on doing that HERE – opens in a new window) and check the relay by feeling for a ‘click’ while an assistant turns the ignition on and off. The fuel pump is set to operate for a few seconds when the ignition is turned to the ON position to pressurise the system so you should be able to feel two distinct clicks from the relay as it first closes the circuit to the pump and then returns to the open position a few seconds later. If these check out ok we have one more check to do.

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For the final diagnostic check we need to check for power at the pump. Raise the rear of the car and support it on chassis stands. Let’s take a look at what we have at the front of the tank.

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  1. Fuel supply (pressure) line
  2. Fuel return line
  3. Fuel gauge connector
  4. Fuel pump power and earth.

To check for power we need to separate the pump power connector and with a test light or multimeter check for power at the terminal with the Purple wire. It’s a good idea to use the earth terminal in the connector as the earth for your test light or multimeter to rule out any wiring issues. Have an assistant turn the ignition on and off a few times and you should have power for a few seconds at a time at that terminal. If this all checks out ok it’s time for a new pump.

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PUMP REMOVAL

Murphy’s Law dictates that an in-tank pump will usually fail when the tank has plenty of fuel in it and if this is the case you will need to prepare some containers that will fit underneath the back of the car and are clean so that the fuel is not contaminated and preferably with lids or caps so they are not left open. A large funnel comes in handy also. Of course if you can move the vehicle or raise the front so that it is higher than the rear will help also. Before doing anything I like to clean as much dirt and crud away from the front of the tank and surrounding area so we don’t contaminate the fuel that is drained out.

In our case we have a VR that has Independent Rear Suspension but if you have a live axle Commodore you will find that removing the Panhard Rod makes life a lot easier when getting the pump out. It’s reasonable straight forward, after marking which end is which remove the bolt and nut from the bracket on the body and remove the nut and retainer from the diff end and move it out of the way (I’ll get some info up on doing this as soon as I can). Either that or raise just the body of the car (while the diff is supported) so the position of the panhard changes.

With a clean tank and the containers in place we can remove the bottom two 7mm bolts, just be careful not to get fuel all over yourself as they come out!

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With the tank drained to a level we can work with remove the gauge electrical connector and the two fuel lines. I find the best way to do this is to undo the clamp and then twist the hose around side to side until it loosens and then pull it back off the outlet. With these removed we can remove the remaining 5 bolts (7mm) and start the fun part of getting the assembly out of the tank. The fuel pump sits in what is known as a swirl pot, this is designed so that the pump won’t starve for fuel. Getting the assembly out of the swirl pot takes a bit of manoeuvring and on VR-onwards models there is a return hose that runs from the swirl pot to the return outlet that needs to be disconnected before the assembly can be removed from the tank. This return hose needs to be secured protruding from the tank opening so that it can be reconnected when the time comes, zip-ties are handy for this!

Below is a really good cut-away image showing the swirl pot, fuel pump location and the return line that needs to be disconnected. This will hopefully give you an understanding of why the assembly can be a pain to get out! The whole assembly needs to come up at the pump end and be rotated before it will come out, while being very careful not to bend the rod that the fuel gauge float is attached to or the gauge will read incorrectly. The float itself will take a little bit of persuasion to come through the opening also.

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Image sourced from JustCommodores forum.

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The arrow points to where the return line should be attached, ours had been torn off previously and was nowhere to be found in the tank. The downside to this is that returning fuel is not delivered straight to the swirl pot and when low on fuel the engine is likely to stall when going around corners as the pump starves. As it’s just a cheap run-around car we will live with this and just keep the tank more than 1/4 full at all times.

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Hopefully removing the assembly hasn’t been too painful and you can now get on with replacing the pump and associated bits and pieces. To remove the pump you need to unclip the electrical connection, prize off the filter screen on the bottom and push the outlet coupling up away from the pump body.

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In a typical fuel pump kit you will get a new filter screen, cork gasket and a rubber insulator for the bottom of the pump. The top insulator/rubber on the right in this pic is reused from the original setup. Replace the cork sealing gasket and mount the pump by fitting the bottom first (including the insulator) and then sliding the coupling over the pump outlet. Clip the electrical connector in place and then fit the filer screen by pushing evenly around the sleeve that fits over the end of the pump. It should only take finger pressure but should be nice and secure once it’s all the way on. Below is a pic of the completed assembly which shows how the screen should line up compared to the rest of the assembly.

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**A quick note on the electrical connection. If you buy a Bosch kit as we did you may need to use the electrical adapter that they supply, depending on the model you have. Be careful when pushing the connectors together as the wires aren’t all that secure in the terminal! I got all the way through this job only to have the pump not function and after pulling the pump assembly out again I found that the earth wire wasn’t all the way in the connector (see pic below). Wouldn’t have happened if I was more careful and my eyesight wasn’t as bad as it is but please don’t make the same mistake, very frustrating!**

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Now to fit the assembly back into the tank, you get maximum points if you can do it with less than a handful of swear words! I don’t know if there is a trick to it as such, but what works for me is to slide everything in until you have about an inch or two of the assembly showing, being careful not to bend the float rod or dislodge the filter screen as you go, and then rotate it until it is in approximately the right orientation (outlets and terminals facing the right way, see pic below) and then push it in. If you’ve managed to find the swirl pot it should go back easily and the assembly will only rotate a few degrees each way.

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Approx. correct position for pump assembly.

All going well you can now line the gasket up and fit the 7mm mounting bolts and attach the fuel lines, supply line (has the filter in it) to the top outlet and return to the bottom one, electrical connectors are self-explanatory. It’s a good idea to start all of the bolts before tightening any and tighten them evenly so the cork gasket is compressed evenly. Some people like to put Loctite or a sealant on the bolts, I’ve never had the need to but that is more personal preference than anything.

If everything is looking good it’s time to add some fuel and stand back and admire your now functional motor vehicle! I typically add just 5 or so litres and check for pump operation and leaks etc. You don’t want to go adding copious amounts of fuel only to have an issue and have to drain the tank again. As a final step I always like to go over the mounting bolts again just to make sure they are evenly tightened, don’t go overboard with tension though as they are only small bolts and cork easily compresses to a point where it’s useless as a gasket.

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