Pi Bosch Fuel Pump Kit - TR5-6

Bosch Fuel Pump Conversions

During the late 1980’s, supplies of rebuildable Lucas Pi pumps were already showing signs of drying up. The specialists used their knowledge and experience of alternative options and universally settled on models from the Bosch range. Many conversions using this generation of pump were performed. The siting of these pumps varied according to both supplier and customer’s individual tastes: some went under the boot side floor, some went under the LH rear wheel arch, some went on the wheel arch in the position of the original pump, and some were fitted in the LH front corner of the boot, to take maximum advantage of gravity to supply fuel from the tank, One thing was and still is certain: healthy supply of clean fuel would ensure a long reliable life. Some TR’s found extra benefit from a Bosch-friendly fuel tank, part no GAC5110X, which features a larger bore outlet pipe. Some owners retained the original filter, with its bleed screw on top, enabling easy purging of gases. Others favoured the Bosch inline filter.Even a combination of both has been seen.
Bosch have moved on to the next generation of high pressure pumps and filters which are slightly smaller than the ‘old’ type, so advantage has been taken of this to use up the front LH corner of the spare wheel well with a plate-mounted set-up, with the added bonus of maximum gravity feeding from the nearby fuel tank outlet. This mounts to the redundant Lucas filter mounting holes and no cutting or drilling is required. With boot floor and lining boards in place, nothing non-original should be visible, which should appeal to original-appearance seekers.
To fit the conversion, the fuel tank needs to be drained, so this is obviously the time to flush out by disconnecting the out let hose at the filter, after first clamping the pipe to halt the fuel flow until you’re ready with a suitable catch tank. The fuel should gush out - if it doesn’t you’ve definitely got a major tank problem. Repeat this flushing several times and inspect the catch tank for undesirable material. If there is a lot of it, the tank may need professional cleaning or even replacement. It is now safe to proceed with the pump change, and this should connect up with all the original electrical and fuel connections without problems, unless, of course, something has been changed in the past. Before reconnecting the electrical supply replace the fuel and check for leaks. The system may need air-purging.
For those who still have an as-built TR5 or early TR6, the following recommendations are made: Remove the air purge pipe from the top of the Lucas filter housing and blank off the connection with the correct type of plug and sealing washer. The vertical pipe should be cut about 9” up from the housing. The PRV return pipe to the filter should also be removed and re-routed (the filter connection being blanked), to connect with the now open end of the air purge pipe, back to the tank. This will mean that the Bosch filter and mounting bracket will be of little use, but the conversion is really intended to eliminate all the undesirable features of the Lucas system, not merely replace the pump. Early TR5’s had the PRV on the chassis so to install this kit on such cars, it will be necessary to purchase an extra long hose to connect the pump to the PRV, part no TGK1255 Some of the early installations of Bosch pumps placed the pump out in open air. Ironically this might well have benefited the original Lucas pump, but it will make no difference to the Bosch pump.

Unlike the Lucas fuel pump, the Bosch pump is dedicated. Both pumps deliver fuel at adequate pressure but the Bosch pump is capable of supplying a larger volume, hence the possible need for the ‘Bosch’ fuel tank. The early TR Pi system circulated excess fuel back into the filter from both PRV and metering unit, which, especially on warm days would rapidly warm up sufficiently to form fuel vapour (i.e. gas) which of course does not pump, but merely compresses i.e. cavitates in the pump. The only solution is to cool the pump right down, make sure there is plenty of fuel in the tank and even then the gas might have to be purged before normal running resumes. The Bosch pump, being capable of shifting more fuel, does need a very adequate fuel supply. If the early Pi system were retained, fuel would still overheat and cavitation would occur, as with the Lucas pump. So the solution is to ensure it can’t happen by installing the correct fuel return system, which it is designed to run with. As with the Lucas system, low fuel reserve will also adversely affect a Bosch pump. Dirt can find its way in, in spite of the presence of a filter, which would indicate a failure in this region, so we’re back to the old chestnut of deterioration of the tank lining. Water in the system will cause misfiring but as long as it is immediately fully purged out, it shouldn’t cause harm, though its cause must be found and eradicated.
Another problem that affected TR5’s was fuel starvation on long left-hand corners. Under hard cornering the fuel can climb to an amazing height on one side of the tank. If the fuel level is below even one-third of a tank, the fuel can climb away from the fuel outlet. This causes the engine to cut and the fuel system has to bleed itself before normal performance resumes- sometimes taking several minutes. Triumph mostly cured this by fitting a tun dish or trough around the outlet to retain about a pint of fuel, wherever the bulk of it went. The problem was finally as good as eliminated by feeding the returned fuel (from PRV and the metering unit) via a long pipe into this tun dish, as long as there was at least a gallon sloshing around. The tun dish is fitted to Moss replacement tanks.