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1983 Bosch Fuel Pump

1983 Jaguar XJ-S

Bosch/Lucas Fuel Pump

Kirby Palm removed his original fuel pump and replaced it with a new one, and partially disassembled the old one.  First, a picture of the pump itself:

The edge of the aluminum can has been uncrimped for disassembly.  It's easy to uncrimp, almost as if it had been designed for ease of disassembly.

The larger fitting formed into the aluminum housing itself (right end in this picture) is the inlet, while the smaller fitting at the plastic end is the outlet.  EFI fuel systems have a check valve to maintain pressure when the engine is shut off; the check valve in systems using this pump is in the outlet of the pump itself, that wide spot between the spade terminals.  In general, this type pump doesn't seem to have check valve problems.

The two electrical spade connectors are two different sizes to prevent accidental reversed connections.  They are clearly labelled + and -.

The new pump in place:

No, Palm didn't bother to clean things up for the picture!

Note that the short length of hose connecting the outlet end to a metal tube is Palm's doing.  The car originally had a length of hose that went all the way from the pump outlet to the fuel filter inlet, but when Palm was trying to correct a fuel odor problem he replaced the hose with a carefully-bent section of metal tubing with short hoses at the ends.

The mounting reflects the fact that a pump is a source of noise.  Around the pump is a doughnut of soft foam, and the foam is clamped with the metal support bracket. This, the rubber hoses, and the two power wires are all that touch the pump; there is no metal-to-metal contact between the pump itself and the rest of the car.  When properly mounted, it should be possible to grab the pump and move it around on its mount.

The pump inlet is at the upper right, and the outlet is at the lower left in this picture.  The hose connected to the outlet fitting is jammed right against the floor of the trunk, and may be a source of noise; the pump is supposed to be free to vibrate, but if the outlet end is jammed too tight against the floor the hose may not be able to isolate the vibrations effectively and may transmit sound into the floor.  Unfortunately, there's nothing to hold the pump upward, so it may slide downward within the foam mount under the influence of gravity and its own vibrations, and jam against the floor and get noisy.  You might opt to pull the pump upward into its correct position and then wrap a few layers of tape around the outside of the pump to keep it from sliding downward through the foam doughnut again.

Here's another view, showing more of the plumbing:

Here you can see the two studs that actually hold the mounting collar.  You can also see the surge tank and the line from the surge tank to the pump.

To get the pump open, uncrimp the edges and insert a rod into the inlet end and push the guts out.  You'll be pushing against the end of the rotor shaft itself, which is plenty strong even if you find you need to tap on it with a hammer to get it apart.  It actually would be better to mount your rod in a vice pointing straight up, slide the pump down over it and tap on the can to get it off, since the can weighs far less than the guts.

As you can see, taking the aluminum can off doesn't reveal much!  One of the motor's brushes is evident, but the only reason is to ease reassembly after it's been taken farther apart than this; that opening provides a way to hold the brushes back while putting the motor together.

On the black plastic piece at the upper left in this picture is an O-ring groove.  This O-ring seals the plastic housing to the aluminum housing, rendering the entire pump liquid-tight.  There is a second O-ring that installs on the step on the pump stator at the bottom center of this picture.  This O-ring separates the high-pressure outlet from the inlet so the fuel can't just recirculate around inside the pump housing.   When disassembled, these O-rings were found to be as hard as ceee-mint and probably would not seal upon reassembly.  When reassembling a pump, new O-rings are a good idea.

Here's a pic of the inlet end:

The semicircular slot is the inlet into the pump itself.  There are stainless steel rollers evident within the slot that are the fuel impellers themselves.

The protrusion at the bottom is a pressure-relief valve; if outlet pressure gets too high, it relieves fuel right back to the inlet.  This might work OK briefly, but if this pump is deadheaded for long it'd probably get very hot inside indeed.

If you're in there, check the operation of the pressure relief valve.  The poppet of this valve has a small post that sticks up through the center of the spring, so the end of it is visible in the photo above.  It should be centered within the spring, and if you grab it with a pair of hemostats, you should be able to pull it off its seat.  If it is stuck, get it unstuck -- which might be easier to do if you take the pump apart as described below so you can push on it from the pressure side.  Unfortunately, other than getting this valve unstuck, there is little you can do to service it; it is permanently installed in this housing.

Within the pump, trapped within the chamber at the right side in this picture when the aluminum can is installed, is a small plastic capsule.

This capsule appears to be empty but totally sealed, and there isn't quite enough air in it to fill it so it's slightly collapsed.  It's Palm's theory that this capsule creates a permanent "bubble" inside the suction plenum, serving as a damper on the vacuum side of this pump and helping keep noise and cavitation to a minimum.  One thing's for sure: it's not there for nothing.  Make sure it's back in place when reassembling.  If it's lost or damaged, it may be possible to fashion a substitute by plugging both ends of a short piece of Tygon tubing; be sure to pinch part of the tubing while plugging it to create that slight vacuum inside that the capsule had.

You can see that brush again in this picture, as well as the upper O-ring groove.

To get the pump farther apart, you simply grab the two ends and pull.  It will separate easily into three sections: the brush housing with the outlet; the magnet case; and the pump itself, which will have the rotor of the motor attached to it.  Here's what the brush housing looks like:

Note that this one appears to be in excellent condition, with plenty of life left in those brushes.  The curled tab under the electrical connector post at the upper left in this picture contacts the inside surface of the magnet case when slid together, evidently ensuring the magnet case is securely grounded and avoiding possible arcs; it is not essential for powering the motor, since both the 12V power and the ground are via the spade connectors at the other ends of these posts.

Here's what the pump itself, with motor rotor attached,  looks like:

In case you haven't figured it out already, this pump operates full of fuel.  The motor is completely full of fuel, and is therefore fuel-cooled.  The commutator and brushes are full of fuel.  When running, the gasoline (at pump outlet pressure) comes out of the openings in the stator (that square box at the left), passes all around and through the motor itself, and eventually passes out of the pump outlet beyond the right end of the shaft.  It occurs to Palm that firing this pump up with air in the system might actually cause a small fire within the pump, but there are no known reports of problems.

If you have your pump this far apart, you might want to consider a minor modification to ensure the pump stator won't spin in the housing.

If you wish to disassemble further, note that the shaft itself does not rotate; it is securely fixed into the pump body at the left and slides into a snug recess in the plastic brush holder and the other end, and the rotor revolves around it.  At the right end in this picture is a C-clip that can be removed and the rotor slid off of the shaft.  Make sure to keep track of washers and the order they came off; there is typically a thick washer followed by a thin washer under that C-clip, then after the rotor is slid off there is one more thick washer at the other end.

After that there is another C-clip, a washer, and a plastic coupling -- but you might not want to fiddle with any of them.  You can get the pump itself apart leaving those items in place.  First, very carefully note or mark the positions of the two plates that make up the pump stator; each one goes on only one way, but there is no indication which way that is after you've taken them off!

Two screws take off the first plate, which will come off around the plastic coupling at the center.  At this point, the five rollers in the impeller will fall out if you turn the pump over.  Two more screws take off the second plate.

Pete Crosby says, "The Bosch pump you show appears to be identical to the one in my XJ40, with one exception (and yes, I have taken it apart).  The pump on the early XJ40's is also a Bosch pump but it has a threaded output to accept a non-return valve identical to that shown in the pictures of the early Bosch/Lucas pump.  As I recall, the outlet section of my pump is metal, not plastic or bakelite like the one in your picture."


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