Petrol Injection rebuild

[Ian3781]

Hello

We're rebuilding the petrol injection system, and have replaced the old Lucas pump with a "Bosch" unit + PRv procured from a Dutch supplier www.powerprops.com

According to my mechanic he measures 7 bar when the ignition is turned on, but the presure drops to 5.5 when turning the engine over and there's no fuel at the injectors.

He''s disamnatled and cleaned the metering unit, but it seems that's where the issue lies?

[Ian3781]

... and here's the PRV we were provided.

We don't seem to have any fuel at the metering unit exits, nor return pipe to the reservoir.

Next we'll check to ensure the red coupler isn't broken,

if so then I think the metering unit won't distribute anything,

If its fine and the shaft is turning, then could the metering unit be uncalibrated so badly that no fuel is delivered?

Thanks
Ian.

[iani]

7 bar is already slightly low, 5.5 is too low, do you have an adequate power supply to the pump, ie, not the original wiring? have you bled the injectors? Has the MU been fitted correctly? If your mechanic is unfamiliar with PI it’s easy to get it wrong. There is plenty of troubleshooting info online.

[iani]

I would recommend changing to a modern diaphragm PRV, this allows you to alter the pressure without dismantling the pipework. Pressure should also be taken under load, I have a permanently wired in fuel pressure gauge with a sender fitted to the MU, that way I see the pressure where it really matters.

[Ian3781]

Thanks for your repleis

Teh injectors are brand new as are the pipes to them, never been used.

Is 7 bar really too low?

I read this online " fuel at pressure 100-110 lbf/in2 (689.50-758.50 kN/m2" .

So thats 6.8 to 7.58 bar, sure 5.5 is probably too low but surely we should see SOME pressurised petrol at the outlets.

C Witor has suggested the sghuttle may be stuck and/or petrol passage gummed up.

Sounds like we'll need to replace it

Ian

[Alec]

Hello Ian 3781,

it does takle a lot of cranking to get fuel to the injectors and remove all the air.
The workshop manual states that when reconnecting an empty system that a fully charged battery is required.
While 80 psi is low it should be sufficient to get fuel into the cylinders, when it fires the pressure will increase. By the way don't bleed them as conventional diesel systems, connect the lines to the injectors and crank for what seems to be ever. The Lucas manual says the miniumum required is 50 psi for the injectors to function.

I would imaginge the Powerprops equipment is suitable as he is well known in the Lucas Injection field and works on such as the Maserati and racing Lucas systems.

Alec

[Ian3781]

Thanks Alec

yes we did anticipate that the wiring might cause voltage loss so we ran a seperate new line to be sure and the voltage doesnt drop at the pump.

Whilst the metering unti itself is a complex piece of kit from what I read, the rest of the system is relatively simple to understand and test

Our mechancic has worked on TR5/6 before and not had such issues, so I trust his diagnosis and that he has eliminated most of the usual steps in the system,

Te metering unit is old new stock "never used" we were told and shelved for years, so it may well need to be overhauled especially given its sensitivity.

Ian

[Alec]

Hello Ian,

OK, I didn't know if the mechanic was familiar with Lucas injection, as it mentioned 'bleeding' which is not normally done, except possibly to check for fuel.
The metering unit itself is quite a simple device, just a sliding shuttle in a rotating barrel. Possibly the shuttle is stuck? It would be a simple job to remove and check for that, as it doesn't entail any disturbance of the control mechanism (Apart from removing it, of course, from the metering body).

Alec

[Richard B]

I would suspect either the shuttle is stuck (gummed up) inside the metering unit or the red plastic key that rotates the metering unit internals has broken. The key takes the drive from the distributor and keeps the MU synched to the ignition.

I had the shuttle jam once when the car had been left standing, the clearances are measured in 'mircons.