Replacing The Mechanical Fuel Pump


Background:

This is probably one of the most neglected parts of the car in my opinion. This component works of sprung loaded arm which sits under a cam inside the engine block. The diaphragm inside works on a vacuum principle to draw the fuel from the tank to the carb. One side is in, the other goes up to the carb. 

On the way out for a little drive The car just died at the end of the drive on the way out. Thinking it was just a glitch as you get with old classic cars, I managed to restart the car after a few seconds of cranking over. I then carried on with my little trip. Restarting the journey back the same thing happened again but only worse while driving along. The car didn’t want fire up at all. I checked the fuel filter and it was dry, empty. I gave it a few minutes and limped home once it fired up again, luckily I managed to get home and parked her up, but it was running a bit uneven. 

I spoke to Adam at Mustang Maniac who gave me a few ideas to try, making sure the fuel was even getting to the front of the car, which it was. Topping the carb up with a little fuel poured down the carb then the car started fine. Definitely a fuel starvation problem. I needed a new part.  

The replacement fuel pump part from Mustang Maniac can be found here.

Process:

You are working with fuel, no smoking and protect your eyes skin, use common sense!

You will need a replacement fuel pump, fuel filter (optional – but recommended), gasket sealer, sharp scraper degreaser, sockets, fuel cut of clamp, fuel line, clips, rags and a drip tray. 

The bare basics are that you will need to clamp the fuel off, replace the pump and then reconnect the fuel lines. 

The fuel pump has an input which sucks the fuel into it, and the output which pushes the fuel up to the carb.

Removal Of The Pump:

On my setup I had fuel pipe from the inner fender, to a rubber pipe, to a fuel filter, to another rubber pipe then finally to the fuel pump itself.

First job is to stop the flow of fuel from the fuel tank, on these type of pumps they work of a cam from the engine, thus the pump will only move the fuel when the engine is running. As a precaution I just clamp the fuel pipe to stop drips or residual fuel leaks. The clamp is a simple screw up type to squash the rubber pipe as the picture on the right.

Tip: Place a dip tray or receptacle to stop fuel going everywhere.

Depending on your setup you just need to remove the connection to the fuel pump. There may be crushed (lemon) style clips or a simple jubilee clip. In my case the rubber was connected to the fuel pump by clips so I needed to cut the rubber pipe in order to start the removal. The rubber was aging fine but a little hard so I decided to cut the pipe and replace it anyway. I could of undone the jubilee clip, but I didn’t want to drip fuel from the filter onto the driveway. Once the pipe has been disconnected from the fuel pump there will be remnants of fuel that will probably run out.

The other side of the fuel filter if you have one, (recommended) either cut or disconnect which ever you prefer.

The output side of the fuel pump should have a metal pipe which goes up to the carburettor. The flared ended fuel pipe is held in place by a nut and needs to be unscrewed. Be prepared for any of remaining fuel running out. The pic below shows the flanged end pipe fixing has been unscrewed next to the oil filter.

Next remove the pipe from the output of the fuel pump. Note the fuel running out.

The fuel pump body is simply held in by two bolts. It’s up to you which you undo first depending on the setup of the steering pump if you have one, or even any air conditioning brackets that could block access to the pump bolts.

There are a couple of ways to remove this pump. One could take a little longer but much easier to refit the new one. Or just unbolt the pump and refit the new one and hope you can align the pump with one hand while inserting the bolt to the block.

Option 1:

The Recommended Option: Break both the bolts free and undo about half way so you can move the pump about. This is so that you can determine the location of the fuel pump cam. If the fuel pump is under a quite a strong sprung load then the cam is probably activating the pump. Crank the engine over by hand until the pressure on the fuel pump arm is at its lowest tension. This will hugely help when repositioning the fuel pump back onto the block later on when refitting.

Then fully remove both bolts for the pump and remove from the engine block. The fuel pump may have part of the gasket still stuck to it.

Option 2:

Undo the bolts and remove the pump. The fuel pump may have part of the gasket still stuck to it.

Important:

Don’t let anything fall into the engine block and take care with broken gasket and debris.

The picture below shows the fuel pump being removed with some of the gasket still stuck to the engine block and pump. You may be lucky and it comes away cleanly.

The arrow shows the remaining bits of the gasket stuck to the pump face.

Next we need to clean the engine block surface to make sure the gasket will make a good seal. I used a razor blade scraper.

Important: When cleaning or scraping the engine block, always work away from the opening working from the centre outwards.

With the gasket now removed clean the engine block to make it grease free. I used a degreaser on a lint free cloth to wipe the surface down.

You don’t have to apply any gasket sealer to the card gasket itself, but a it will help to hold it in place. Apply a thin bead to one side. Don’t over apply as you don’t want the gasket seal to go into the engine block. You could if you prefer put the gasket onto the pump first if you prefer, but you would need to have the both bolts in place to hold the gasket. the choice is yours.

The picture below of the old pump on the left and the new pump on the right are compared. Also marked the remains of the gasket left on the floor. The new pump has a slightly smaller diameter.

Fitting The Pump:

Optional step here is to apply another thin film of gasket sealer to the pump face. First clean the face with degreaser with a lint free cloth.

There is a specific technique to refitting this pump. The top arm of the pump has to be fitted under the cam in the engine block.

Tip: Whilst removing the old pump you could do a couple of test fits to make sure that you can feel the arm under the cam and how to mount back onto the block.

Get the first bolt in the pump ready to hold the pump in place, it doesn’t matter which side, which ever is the easiest for you.

When inserting the pump arm into the engine block opening, tip the arm downwards at a slight angle. When the pump is almost at the engine block tilt the pump face back towards the parallel of the engine block pump face. This will ensure that the arm is under the cam before bolting into place.

Depending on which of the options you performed from above, the spring loading to the pump could be hard work to align up to the block when trying to start the bolt. Especially if the cam is not in the ideal spot.

Offer the pump to its final mounting position while making sure not to dislodge the gasket. Start the bolt into the block to hold the pump in place. Then add the other bolt to mount the pump in the correct vertical position.

Tighten the bolts evenly each side to form the tight seal with the gasket and the engine block.

Plumbing:

With the pump in place next reattach the metal carb pipe to the output (female side) of the pump. Tighten the pipe into the mounting. See the picture above.

Tip: Depending on the design of your pump, you may need to hold the mounting point nut with another spanner in order to not break the spot weld on the pump. If you have a concourse pump replacement then you wont need that step as the casting is all in one.

You will now need to attach the input line of the fuel pipe onto the male part of the fuel filter. Below is the first part of the fuel line to the filter. Using a ‘lemon’ clip or an single ear clip with the correct tool makes it look neater. There will be a flow arrow for the direction of the fuel on the filter, make sure you get the flow direction correct pointing to the fuel pump. You can of course use a jubilee clip to attach the pipework if you prefer, or don’t have the correct tool to pinch the clip tight. The blue handled tool below on the right is needed for the correct application of the clips. Don’t be tempted to use pliers in place of the correct tool.

Make sure that the rubber fuel pipe is not kinked and forms a straight a route as possible to the fuel pump. Place the tubing to the fuel pump (male fitting) and secure in place, either with a clip or a jubilee clip as I have used. Note the fuel flow direction arrow on the plastic filter.

You could fill the filter with some fuel so it’s ready and primed. Or start with the filter empty, as then any fuel you see in the filter has been pulled into the filter by the pump itself when being cranked over without actually starting the engine.

When connecting back up to the fuel line coming from the inner fender, undo the clamp previously put in place to stop fuel seeping, and slip the new rubber pipe back over the fuel line.

Re-check the two bolts to the block and the clips are all secure. You don’t want a fuel leak or oil leaking from the back of the pump.

Crank the engine to make sure all is correct be fore trying to start the car fully.

Results:

Apart from the cosmetics of the swap, you can expect a much more consistent delivery of fuel up to the carb. Better starting, smoother running and a steadier idle.

Conclusion:

This is a fairly simple part to replace. The complexity comes from the cam on the arm of the pump. This can make it difficult to align back to the engine block.

The gasket is another important part to consider, do you put it on the block or put it on the pump, the choice is yours. I prefer to put it on the block as then I can see if it has been moved or damaged while fitting the pump to the block.

In theory it should only take half hour or so to remove and refit the pump. Making everything look neat and tidy can add time to the overall process.

when changing the fuel pump i strongly recommend a new fuel filter and new rubber pipe, this will eliminate debris and and the pipes won’t perish and crack causing leaks.

Hopefully you shouldn’t have to replace the fuel pump of course, but if you do I hope this helps.

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