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TR6 Metering unit fuel leak


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Hi everyone

 

Tr has been running really well until sunday when i could smell petrol in the car. I looked for a leak and can see a drip from the metering unit near the two bottom screws that secures the black plastic Lucas cover. Can anyone tell me if this is a common thing being new to all this. Is there a Gasket here that may have failed ? any advice would be a real help.

 

Thanks

Shaun

 

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Shaun,

Is this the recatangular plastic cover?

There should be no fuel behind that. There is a diaphragm between the airfilled cam chamber that it covers, and the barrel shaped part to the left. The diaphragm can rupture. It is supposed to confine the vacuum that controls the MU, as well as keeping fuel out, so I fear your MU is probably not working very well anyway.

 

If you have recently aquired the car, and do not know for sure that the MU has been renovated, it probably has the OE seals which are vulnerable to modern lead-free petrol. Consider a reconditioned unit.

The usual suppliers are Malcolm at Prestige (http://www.prestigeinjection.net/) or K.Raven Smith, who happens to have one on eBay right now: http://www.ebay.co.uk/itm/TR5-6-LUCAS-TRIUMPH-METERING-UNIT-AND-2-5-PI-/141009483837#ht_131wt_1170

 

John

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  • 8 years later...

Evening All, was there an answer to this as I too have got petrol leaking from behind the Lucas cover. I had not used the car for a while due to work commitments, too it out and filled it up and now have the leak. I have clamped the fuel intake and capped off the return pipe to stop the tank emptying onto the garage floor but now need to work out the next step.

Thanks in advance

Bob

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+ 1, likewise.

I also had the same problem last month, big leak from RHS below the LUCAS black plastic cover plate, had to be transported home by AA.

I removed the MU and had it refurbished by Neil Ferguson (K.R.S), brilliant service at a very reasonable cost. Refitted with no problems, but then found inlet main hose was also faulty and leaked fuel. This was replaced with new from TR Trader and now all seem good. 

I would say however, that these two components have lasted for 20 years without issues, so cant really complain :) !!

Colin. 

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I'd suggest that the elastomers in your fuelling diaphragm and hoses are being attacked by the fuel. Have your local fuel suppliers changed the composition of the petrol lately?

I had similar problems about 5 years ago and had to switch to Viton elastomers/Gates Barricade hoses

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11 hours ago, Bob59 said:

Evening All, was there an answer to this as I too have got petrol leaking from behind the Lucas cover. I had not used the car for a while due to work commitments, too it out and filled it up and now have the leak. I have clamped the fuel intake and capped off the return pipe to stop the tank emptying onto the garage floor but now need to work out the next step.

Thanks in advance

Bob

The diaphragm between the metering unit (the rounded part with the injector pipes and the control unit (the square part with the black lucas cover) is allowing fuel to leak past it. Needs changing, can be done DIY but if unsure send the unit off for refurbishment. It can also happen if the return line is blocked and displaces the same diaphragm, use an air line to blow through to check.

Gareth

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  • 1 year later...
On 9/5/2021 at 5:59 AM, Mk2 Chopper said:

The diaphragm between the metering unit (the rounded part with the injector pipes and the control unit (the square part with the black lucas cover) is allowing fuel to leak past it. Needs changing, can be done DIY but if unsure send the unit off for refurbishment. It can also happen if the return line is blocked and displaces the same diaphragm, use an air line to blow through to check.

Gareth

I assume you mean line from the PRV to the top of the tank? Mine has a cooling  coil in it.

My diaphragm was changed a few years back, before ethanol certainly, I'll fit a a new one to be sure if the return line is the cause of the same problem the OP's had.

Ken

 

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During long periods of standing the fuel trapped in the MU oxidises to make aldehydes that cross-link polymers in the diaphragm, which splits . Good idea to replace original rubber with ethanol-resistant nitrile.

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41 minutes ago, Peter Cobbold said:

During long periods of standing the fuel trapped in the MU oxidises to make aldehydes that cross-link polymers in the diaphragm, which splits . Good idea to replace original rubber with ethanol-resistant nitrile.

Thank you Peter, I will replace it. My pump is also being effected by oxidised modern fuel.

I was hoping somebody would confirm the referenced return line is the one from PRV to the tank.

It's 33 years since I rebuilt my fuel system/metering unit, getting it calibrated by Ken Mills. I became an expert then but, since all that knowledge has been moved to make room in my brain (which is slowly decreasing in capacity) for other knowledge.

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2 hours ago, ken foster said:

Thank you Peter, I will replace it. My pump is also being effected by oxidised modern fuel.

I was hoping somebody would confirm the referenced return line is the one from PRV to the tank.

It's 33 years since I rebuilt my fuel system/metering unit, getting it calibrated by Ken Mills. I became an expert then but, since all that knowledge has been moved to make room in my brain (which is slowly decreasing in capacity) for other knowledge.

Hi Ken,  if the return from the MU is impaired then the pressure build up behind the diaphrgam would indeed hasten its failure. But splitting of the diaphram horizontally is I gathered at an IWE talk rather common. Brain fade is a pet topic of mine............see the D3 thread from a few years back!

Peter

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3 hours ago, ken foster said:

I assume you mean line from the PRV to the top of the tank? Mine has a cooling  coil in it.

My diaphragm was changed a few years back, before ethanol certainly, I'll fit a a new one to be sure if the return line is the cause of the same problem the OP's had.

Ken

 

I'm embarrassed to say having looked twice at the metering unit.... I couldn't see the return line, hence my question about the return line in the boot.Oh I am such a Billy Sarsted (no relation to Peter Sarsted) It's staring me in the face, well it is with my glasses on. "ad a brain "ol man as my Cornish wife would say.

I will give it a blow through before I fit a new diaphragm, maybe I can calibrate the choke so it works a bit better same time.

ken.

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4 hours ago, ken foster said:

I assume you mean line from the PRV to the top of the tank? Mine has a cooling  coil in it.

My diaphragm was changed a few years back, before ethanol certainly, I'll fit a a new one to be sure if the return line is the cause of the same problem the OP's had.

Ken

 

Hi Ken, 

Not sure if you've found the information on the return line, but it's the small diameter pipe from the MU, either a push fit or screwed in (later MU) and it's in the area where the MU mounts to the distributor pedestal.

Gareth

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2 hours ago, Mk2 Chopper said:

Hi Ken, 

Not sure if you've found the information on the return line, but it's the small diameter pipe from the MU, either a push fit or screwed in (later MU) and it's in the area where the MU mounts to the distributor pedestal.

Gareth

I did once I'd got my head straight thanks.

Thanks Peter for your input too.

Ken.

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23 hours ago, Peter Cobbold said:

During long periods of standing the fuel trapped in the MU oxidises to make aldehydes that cross-link polymers in the diaphragm, which splits . Good idea to replace original rubber with ethanol-resistant nitrile.

Just looking online for a diaphragm, big difference on prices between suppliers. 
Trenterprises sell for 20 squid inc vat. 
any thoughts on them? I’m a bit out of touch with suppliers. 
Are there any other seals/gaskets needed for the job?
cheers ken

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11 minutes ago, ken foster said:

Just looking online for a diaphragm, big difference on prices between suppliers. 
Trenterprises sell for 20 squid inc vat. 
any thoughts on them? I’m a bit out of touch with suppliers. 
Are there any other seals/gaskets needed for the job?
cheers ken

Dunno Ken, I replaced PI with an SU 30 years ago. After 250k miles on the PI with no MU failures ( but daily driver and no ethanol likely hleped). Only fialure was the steel pipe over the drive shaft that pinholed from rust.

Peter

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23 minutes ago, Peter Cobbold said:

Dunno Ken, I replaced PI with an SU 30 years ago. After 250k miles on the PI with no MU failures ( but daily driver and no ethanol likely hleped). Only fialure was the steel pipe over the drive shaft that pinholed from rust.

Peter

It looks brand new. Put it back together and will try now I’ve blown through the return line. 
if it still leaks it might be the drive shaft  seal. 
ken

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34 minutes ago, ken foster said:

It looks brand new. Put it back together and will try now I’ve blown through the return line. 
if it still leaks it might be the drive shaft  seal. 
ken

There’s a fuel diaphragm and a vacuum diaphragm. It’s the fuel one that must be at fault. 
I only looked at the vacuum one. 
it’s slowly coming back to me now. 
 

ken. 

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19 minutes ago, ken foster said:

There’s a fuel diaphragm and a vacuum diaphragm. It’s the fuel one that must be at fault. 
I only looked at the vacuum one. 
it’s slowly coming back to me now. 
 

ken. 

VitesseSteve's site has archived PI manuals: http://vitessesteve.co.uk/LucasStuff/Lucas_Petrol_Injection_Manuals

and this is the diaphragm that leaks fuel: https://prnt.sc/HsUpY5oFdS0Z

 

 

Edited by Peter Cobbold
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39 minutes ago, John L said:

Im sure this will be a good part but worth checking with Chris, it is E10 compatible. https://www.chriswitor.com/proddetail.php?prod=519870V

John

Thank you, look good at £36 inc vat. just looked at tr trader which I believe is prestige and Neil Revingtons about £47 and £61ish dunno about postage for any. How do they compare on quality I wonder. 
ken

Edited by ken foster
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