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Leaking Control Unit-Excess Fuel Lever On


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Hi,

 

I've just noticed a slight leak from the side of the control unit when the engine is first started with the excess fuel lever fully on. There appears to be no leakage during normal running with the lever off.

 

I've recently replaced the diaphragm between the metering unit and the control unit and it appeared to be properly seated.

 

The PRV is set at 680 KPag (99 psi) and the engine operates normally when hot although it seems to miss on one injector sometimes when cold.

 

Before I remove the MU to check the diaphragm again , can anyone suggest anything else I should check beforehand.

 

Thank you.

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Reading the Lucas PI Red Book, a good place for me to start is checking the fuel distributer return line. From the Book this seems to bleed pressure from behind the diaphragm and mine reduces down to a 5mm OD copper pipe for a fair part of its length. Chances are it's blocked with dissolved rubber hose. I'll check it tomorrow.

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IIRC a blocked cavity drain will make the car run excessively rich. Still worth checking though especially the short piece of hose visible above the l/h half shaft with the wheel removed. Open the fuel filler and disconnect at the MU and blow through the line.

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Thanks macs6.

 

Did you replace the return line with another of the same diameter? My current line is about 1/8" diameter , it looks to be the same size as shown in the photos included in the Triumph 2000 manual I use as a guide ( wish the Brown Book also had photos).

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  • 2 weeks later...

I'm currently getting the metering distributor rebuilt and recalibrated. The technician confirmed that the UK sourced diaphragm I had fitted was made of nitrile rubber. It was expanding when exposed to Australian high octane fuel and

slipping/ leaking where it fitted against the follower piston. After a few days on the bench the diaphragm dried out and fitted tightly again.

 

I'm having it replaced with a viton diaphragm. I don't know enough about UK fuels to comment on the suitability of nitrile rubber PI components there, but this may be of interest to Australian/NZ owners.

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Mike

Only a few threads back we went all through this.

Best to fit viton B to every rubber part (quite a few on MU and pedestal) you have to work from tank right up to injectors.

That's quite a bit of rubber including pipes preferably with 30jR14 rubber pipework.

T

Just wish I'd confirmed the diaphragm material was viton before I bought the last one. I took it for granted that it was suitable for modern fuels- wasted a few hundred dollars and a few weeks getting the defective one delivered to Oz, installing it and generally trying to get it to work..

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Thanks Malcolm.

 

That's the same set up as I have. I've now replaced the rubber bits in mine and blown it clear.

 

I believe my leaking MU was caused initially by a perforated cam follower diaphragm , which was replaced by a nitrile diaphragm which quickly loosened on the follower shaft when exposed to unleaded high octane.

 

Hopefully the viton diaphragm now being fitted will cure the problem

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