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Poor running as fuel tank level drops


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The snagging on my newly acquired TR6 continues.

 

Having replaced a couple of sticky injectors, she now runs on all 6. An intermittent ignition fault traced to an almost broken wire inside the distributor and a duff condenser.

 

A Prestige modified PRV has dropped the fuel pressure from 120psi back to around 105psi which has stopped my hair sticking of neat fuel after every drive!

 

Some dodgy non standard wiring found bypassing a seized fuel cut off knock switch and another from the fusebox to the coil returned to standard. New fusebox will be required though as original corroded and shows signs of previous overheating.

 

The next issue, which is puzzling me somewhat, is that the car runs fine and revs hard and cleanly on a full tank of fuel. As the level goes down, I start experiencing a misfire at the upper end of the rev range. As the tank level drops further, I encounter misfiring driving around bends. All this points to not enough fuel getting to the engine. As the tank level gets lower, I "run out of fuel" when you can still see a couple of gallons sloshing around in the tank. Unfortunately my fuel pressure gauge sits under the bonnet and cannot be viewed when driving.

 

The car has a Bosch conversion, supplied by the TR Shop 5-6 years ago.

 

Any ideas?

 

Thanks

 

Mikey

Edited by mikeyb
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Cutting out on bends on a low tank is common and due to lack of baffling/no swirl pot. There are some solutions in the TR6 forum if you can bear to use the cruddy search facility. Or use Google and point it at the forum.

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Mike, yep does sound fuel related. Apart from checking as described , check the fuel filter the Bosch pump isn't as good as sucking as the Lucas so maybe as the pressure from a full tank drops with less petrol some **** may be restricting flow at the filter. Its got to be worth checking the whole circuit from tank to pump. Good luck.

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I have often read this compliant on here...but in 42 years of TR6ing I've never experienced this! Why would some cars do this, and not others then? (I've always had Lucas pumps)

Edited by Denis
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Fuel filter makes sense to me - I'd be willing to bet it's the same one supplied with the Bosch pump conversion! Can anyone tell me the part number/vehicle origination for these filters. I'm sure I can get and expensive one from a TR Parts Supplier, but would prefer to support my local motor factor!

 

Is the larger outlet conversion a rubber hose or a screw in adaptor for the tank?

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Mike, the 6 I have just bought suffers exactly the same problem and has done for years - faulty baffle / swirl pot in the tank? Or no baffle? It did it with both with the lucas pump/cav filter and the Bosch conversion it now has. I'm sure an external swirl pot will fix it together with a larger tank outlet - I have never had a good look in the tank but iPhones take great tank interior pictures through the sender unit hole to check for design issues and rust

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Fuel filter makes sense to me - I'd be willing to bet it's the same one supplied with the Bosch pump conversion! Can anyone tell me the part number/vehicle origination for these filters. I'm sure I can get and expensive one from a TR Parts Supplier, but would prefer to support my local motor factor!

 

Is the larger outlet conversion a rubber hose or a screw in adaptor for the tank?

It's a larger Screw in Adaptor to the Tank that allows you to use a larger diameter Hose to Feed Fuel to the Pump.
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  • 2 weeks later...

No hiss, so I don't think it's the breather.

 

My Bosch conversion is located in the boot, I have been told in conversation that this is not the optimal position for them and they need to be fitted as low as possible - ie. underneath the car.

 

as my tank sender unit is faulty, it needs to come out so will look into bigger outlets/blockages then.

 

thanks

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On a mate's 6 a similar problem was caused by the pump overheating (despite the coil of fuel line round it to provide cooling??). (this was Oz and summer.)

Next time it cuts out can you see if the pump feels overly hot?

 

I came across an interesting version of the "coil of pipe round the pump" solution. There was a really nice tightly wound coil of 5mm ID pipe round the pump body, not a problem there, except the pipe was in the inlet to the pump, rather than the overspill from the PRV.

 

Everytime you put your foot it would mis-fire and splutter. I reckon it was like trying to suck a thick shake up a straw.Poor old pump!

 

REmoved the pipe, pulls like a train now.

 

Cheers

 

Colin

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I have often read this compliant on here...but in 42 years of TR6ing I've never experienced this! Why would some cars do this, and not others then? (I've always had Lucas pumps)

Thats my experience too. Maybe the standard filter is big enough to act a swirl pot in bends? I never had any problems with Lucas until the bottom seal started to weep at well over 150k miles.

Peter

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I'm keen on a swirl pott, and have one on the Vitesse, but I don't think that a problem starting at half tank in a TR6 is likely to be fuel slosh in the tank.

But a filter may not deal with 'floaters' in the tank, too big to go down the tube, but quite big enough to block it temporarily.

 

Have a look inside, with a small torch, so you can see past it through the filler opening.

John

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Hi

I have design a small alloy fuel tank that fits in the spare wheel well about 4lts.the tank doesn't into fear with the spare wheel .

I have sold a few of these now and they will cure this problem of cutting out on low fuel and misfiring on cornering

Give me a ring 07788437528 kev

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Not much time to play cars this week, but did get around to poking a small torch down the filler hole. I had a good view of the bottom of the tank - looks nice and clean,couldn't see the outlet but I did spot something else that I could not identify. A bit of fishing and out came this... (spray can nozzle next to it for scaling!)

 

post-9197-0-48273100-1413662887_thumb.jpg

 

 

A proverbial pot of snake oil methinks! Not driven the car so don't know if there is any improvement, but fingers crossed.

 

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Well done!

Fat lot of good a filter would be for that!

 

I've never seen one of those "Broquets" before, that has sat in a tank for a long time. They are supposed to contain Tin, or Zinc, or Unobtanium - it varies from time to time - and you would expect them to suffer just a little change in apperance if the metal was to dissolve in the fuel, as advertised. More evidence of how much serpentine unguent they contain.

 

John

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I have noting in the paperwork for the car to suggest how long they had been in there - I suspect a long time! However they still look clean and shiny.

 

Sadly I have to report that the problem has not been cured.

 

On a trip to work this week, annoyingly about 3 miles past the last fuel, the car coughed and "ran out of fuel". No warning misfire at high revs or on bends this time, so maybe the beads did have a part effect? Luckily I had planned for contingency and had 5L in the boot. So with can emptied into the tank, I sped back to the petrol station with poor running and a noisy fuel pump. The tank when brimmed took 30L so I estimate that there was around 15L of fuel in the tank when it showed the symptom of actually being empty.

 

With a full tank this time though, the pump remained noisy for the trip to work and back, a quick glance under the bonnet at one point showed the fuel pressure to be low (90psi) and the needle oscillating wildly.

 

So next job will be to change take tank out I think!

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