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Fuel pressure TR6


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Hi Donald/Mr Duck !

 

Youll find a lot of posts about fuel pressure if you try a search.

 

Common causes of low pressure are :

 

Tired pump

Inadequate wiring/poor earth

Prv in need of service /adjustment

 

Whereabouts are you and what pump setup do you have ?

 

Steve

Edited by SDerbyshire
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What symptoms make you think your fuel pressure is low ? To measure you need a take off adapter, a microphone hose and a oil filled pressure gauge, cost about £75 in total. You need to plumb in at the metering unit inlet where the thick rubber hose from the tank joins the MmU. Best describe your problem here and your location in order to get more informed help. Btw welcome.

 

Robin

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Hi Robin, if I remember rightly, we both went through this same problem, about 3 years ago....and both got through it !

 

But what's a Microphone hose ?

All the best,

Conrad of the Hood !

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  • 2 months later...

Hi Gents.

I'm new to the Forum and TR6, I believe I may have the same problem as Donald i.e. low fuel pressure but I need to test this to confirm why it won't start.

 

I've trawled the forum and can not find the detail I need to measure the pressure. Can you please put a bit more meat on the bone and define what is needed to connect a pressure gauge to the MU e.g connection, pipe, what union size and from where?

Many thanks Phil

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Hi Gents.

I'm new to the Forum and TR6, I believe I may have the same problem as Donald i.e. low fuel pressure but I need to test this to confirm why it won't start.

 

I've trawled the forum and can not find the detail I need to measure the pressure. Can you please put a bit more meat on the bone and define what is needed to connect a pressure gauge to the MU e.g connection, pipe, what union size and from where?

Many thanks Phil

Hi Phil

Welcome to the forum, you should find this post useful which details the parts you require. http://www.tr-register.co.uk/forums/index.php?/topic/46444-pressure-gauge-for-testing-the-pump-prv/?hl=%2Bfuel+%2Bpressure+%2Bgauge

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Ive said it befoer, an i,ll say it agen

testing fuel press at ign on, or at idle, just tells ye that yer pump is delivering x amount of fuel

 

Butt, try the same test at full fevs, foot to floor, and for a sustained time

IF, yer PSI reading is still 100, ish, then fine

but most likely it,ll be well doon, esp wid a OE pump

 

yer injectors crak open at 55-60 ish, say yer PSIs doon t,say 75-90.

then yer engine aint gonna get much fuel init, as it would if it were still 100+ PSI

 

so get a Lonnnng lead t,yer gauge, and set off an try a full load test at high revs an WOT

its the only way t,see if yer pumps upto it.

Ohh, need t,be sure yer filters aint clogged, or that will reduce top end readings alott.

 

M

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My Pi-powered Vitesse has a dashboard fuel pressure gauge.

This cannot be a directly connected device - no one wants a spray of 100psi fuel into the cockpit - so it's an electronic one, with a sensor in the engine bay.

 

Problem is that few moderns run at such high pressure, and most guages go up to 100psi, but electronic OIL pressure gages are available that go up to 120 or 150psi:

And they're very cheap!

https://www.ebay.com/itm/2-52mm-120-PSI-Digital-Blue-LED-Oil-Pressure-Gauge-With-Sensor-Auto-Car-Motor-/302045963101

 

Prestige sell a modern replacement for the OE PRV, that is easily asdjusted by a covered lock-screw, without dismantling the valve.

Not cheap, but makes adjusment very easy:

http://www.prestigeinjection.net/pumps.htm

 

John

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Ive said it befoer, an i,ll say it agen

testing fuel press at ign on, or at idle, just tells ye that yer pump is delivering x amount of fuel

 

Butt, try the same test at full fevs, foot to floor, and for a sustained time

IF, yer PSI reading is still 100, ish, then fine

but most likely it,ll be well doon, esp wid a OE pump

 

yer injectors crak open at 55-60 ish, say yer PSIs doon t,say 75-90.

then yer engine aint gonna get much fuel init, as it would if it were still 100+ PSI

 

so get a Lonnnng lead t,yer gauge, and set off an try a full load test at high revs an WOT

its the only way t,see if yer pumps upto it.

Ohh, need t,be sure yer filters aint clogged, or that will reduce top end readings alott.

 

M

Is the 105-107psi figure for idle or higher revs then?

If it is an idle figure ,then wouldn't adjusting at higher revs INCREASE the pressure at idle and put seals and the like at risk? I am basing this on what you say about the pressure dropping at high revs if set at idle and that the converse would apply.

Please don't think I am disagreeing with you ,I really don't know either way, but I am just interested.

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The term "PRV" is often but wrongly interpreted as "Pressure Reducing Valve", when in fact it is a Pressure Regulating Valve.

This is often needed in engineering, to ensure that a supply of gas or liquid for a process arrives at the pre-set pressure, despite variations upstream, due to emptying gas cylinders or a pump running on a varying voltage.

 

But it requires that the upstream pressure is always higher than that required. If it falls below that, the pressure for the process is the low pressure that the pump supplies - the valve can do nothing.

But high speed running with no load may not simulate hard acceleration up a hill, which is why an on-board pressure gauge has its uses.

 

John

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It is important and I follow the key point mentioned by few fox's, to consider and test the capability of the pump to maintain the defined pressure (~106 psi)at full throttle & under full load.

To do so, it is necessary to read the pressure gauge when driving (Extended pipes + pressure gauge inside the cockpit arear....)!

 

Nevertheless under standard circumstances(or w/o very specific and dedicated & careful design and installation), do not keep this test setting full time in the cockpit... For safety reasons, keep the high pressure pipes system as simple as possible (as close as possible vs the original set up... mainly pipes under the floor between the front and the rear) between the various injection elements and avoid high pressurized pipes full of petrol inside the car (Cockpit/Passenger compartment)

I let you imagine the incidence of a high pressure pipe failure inside the cockpit ....

 

Regards

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Is the 105-107psi figure for idle or higher revs then?

If it is an idle figure ,then wouldn't adjusting at higher revs INCREASE the pressure at idle and put seals and the like at risk? I am basing this on what you say about the pressure dropping at high revs if set at idle and that the converse would apply.

 

Asks Clive,

It really should be fora competition motoer, as thats where they will spend most of the time

as for being too dangerous t,the MU, the F1 cars, wid the engine driven pump, ran at 160+ PSI

this so that they could get moer fuel in at higher revs, in a short time

 

{note, they ran idle and int pits of an electric,n , but they electric,n, Same as oe Triumph just could nae provide the fuel needs at speed /power }

 

Marc, if yer gonna try this, then its gotta be a decent time span,

IE, not just a ..zoom rev up t,6K revs in 1 or 2 nd gears, but sustained in top, at high engine speeds and a WOT throttle

this gives the residual pressure int lines t,stabilize

 

A good B262 pump will hold it nee bother at all, { 100-105 } at idle and top end .

so too should the 044, IF, the pipes and tank outlet been med bigger 12-13 mm min ideally, as inlet t,pump is 12 mm as OE

 

but its got t,be an exceptionally good Lucas t,hold this pressure, moer likely it,ll be alott less.

so engine runs weak at top end, if it can actually have the poke t,get t,top end.

 

electric, an belt driven pump , the belt driven pump has got bigger gears init too

as the middle brass bit is deeper t,cater for em

 

http://www.lucasinjection.com/pump%20back%20sides.JPG

 

M

Edited by GT6M
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so it's an electronic one, with a sensor in the engine bay.

 

Problem is that few moderns run at such high pressure, and most guages go up to 100psi, but electronic OIL pressure gages are available that go up to 120 or 150psi:

And they're very cheap!

https://www.ebay.com/itm/2-52mm-120-PSI-Digital-Blue-LED-Oil-Pressure-Gauge-With-Sensor-Auto-Car-Motor-/302045963101

 

John, this is a great idea. I was looking to buy a test kit or make on up with the metre hose as suggested (to cure my returned starting troubles which I suspect are fuel related) but surely using an oil pressure gauge as such is much simpler? Put the sender unit in the fuel line before the MU, then run the electric wires to the pressure gauge mounted discretely in the cockpit - maybe in the glovebox or under the pax footwell where it could be pulled out to check and put away again out of sight.

 

Has anyone been down that path in a TR6?

 

https://www.autobox.com.au/saas-oil-pressure-52mm-gauge-black-face-sender

Edited by stallie
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The electronic route sounds a good idea as long as the sender is rated for pressurised unleaded fuel.

 

Otherwise a 100+ psi fuel leak in the engine bay beckons when the unleaded eats the seals

 

Steve

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I use one of these

http://www.spa-uk.co.uk/Product/Fuel%20Level%20Volts%20Gauge%205%20Position%20programmable%20(DG218)

Expensive but accurate. And you can measure the voltage at the pump if you want.

I found the seal on the cheaper oil pressure transducers leaks after a while and the sender fails. Doesn't leak fuel but stops reading the pressure properly.

David

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John, this is a great idea. I was looking to buy a test kit or make on up with the metre hose as suggested (to cure my returned starting troubles which I suspect are fuel related) but surely using an oil pressure gauge as such is much simpler? Put the sender unit in the fuel line before the MU, then run the electric wires to the pressure gauge mounted discretely in the cockpit - maybe in the glovebox or under the pax footwell where it could be pulled out to check and put away again out of sight.

 

Has anyone been down that path in a TR6?

 

https://www.autobox.com.au/saas-oil-pressure-52mm-gauge-black-face-sender

 

This is my setup installed around 6 months ago and I'm very happy with it. The sender and and display are a kit from the US whic is also used on Kenworth trucks. I can supply specific details if required.

 

post-14246-0-11036500-1513901032_thumb.jpgpost-14246-0-29804700-1513901046_thumb.jpgpost-14246-0-54167200-1513901060_thumb.jpg

 

Regards

Gavin

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Not wishing to widen this topic too much but I’m a back to basics man…

 

…if the car is having cold starting problems and you suspect fuel starvation then I would start with the electrics. A car battery on charge will deliver 14’ish volts but on a morning will be down to 11.5’ish. Once you start cranking the engine there will perhaps be 8 to 9 volts available at the fuel pump. So any pump will not be working in its comfort zone and may indeed struggle to deliver full pressure – albeit at a lower flow rate.

 

Once the engine fires and the key is released the voltage at the pump will rise back to 11’ish and then as the engine revs and the alternator kicks in the voltage will start to rise back towards 14’ish.

 

This is why the best policy is always to fit a fuel pump relay, heavier cable from relay to pump and pump to a bl**dy good earth – not just an earth!! Then fit a modern style PRV which is so easy to adjust compared with the original; 106 psi works for me.

 

Because the PI is a heavy old engine with inefficient starter motor and the need to have a good voltage at the fuel pump the CCA of a battery is really, really important for good starting. Size really does matter.

 

Yes I too used a cheap electronic oil gauge (£15 –ebay) to test my pump but once a PRV is set it does not alter so does not need permanent installation.

 

Turn the ignition on and listen. The pump will start and pressurise the fuel lines along the car to the metering unit. After perhaps 2-3 seconds the fuel delivery pipework will be at pressure and you will hear the PRV open to spill fuel back to the tank. I always wait before cranking the engine perhaps 30 seconds from turning the ignition on.

 

If you suspect a low voltage /current is part of your problem try connecting a battery charger to the car and fully charge the battery leave the charger connected (to keep the voltage high).

 

Alan

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This is my setup installed around 6 months ago and I'm very happy with it. The sender and and display are a kit from the US whic is also used on Kenworth trucks. I can supply specific details if required.

 

attachicon.gif20170217_185432_1513900726964_4.JPGattachicon.gif20170219_122736_1513900726081_2.JPGattachicon.gif20170226_164948_1513900726508_3.JPG

 

Regards

Gavin

Looks good Gavin

 

Was there a reason you put the sensor at the pumo end not the mu end?

 

Could you send a link to the supplier of the kit please?

 

Steve

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Looks good Gavin

 

Was there a reason you put the sensor at the pumo end not the mu end?

 

Could you send a link to the supplier of the kit please?

 

Steve

 

Hi Steve.

 

I purchased the kit off eBay in the US, the 150psi unit with blue display. Note, the gauge bracket wasn't included, I purchased it locally. 2" from memory. Link below, but there may be other suppliers as well, possibly with better pricing.

 

https://www.ebay.com/itm/Teltek-Fuel-Pressure-Gauge-for-any-semi-pick-up-Truck-or-Car-with-0-150-PSI-/322406126414

 

It wasn't cheap, but I figured that because fuel pressure is so important for these cars it made sense to be able to keep an eye on it whilst driving. I installed the sensor (a german made item) at the back as I was moving the pump etc out of the boot so it was a lot easier to accomodate it there than trying to connect into pipework at the MU. Luckily, the signal cable was just long enough to reach the display in the position I wanted to site it.

 

As I said earlier, I'm very happy with the result.

 

Gavin

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Hi Gavin,

Interesting to learn:

What does your fuel pressure read:

During starting (cranking)?

Idle?

Normal cruising?

Full throttle?

What pump and PRV do you have?

Thanks,

Waldi

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Hi Waldi.

 

I've not done a lot of mileage since installation, but it consistantly reads 107psi +or- 2 psi under all conditions, although the refresh rate is every 2 seconds from memory so there may be slight variations outside of these figures This applies to starting also as the pump (Bosch) now has a heavier feed wire (2.9 sq mm?) to the relay direct from the battery and holds a constant 12.0V. The original feed wire that came with the relay was only 2.0 sq mm and the voltage at the relay was dropping to 11.0V.

 

The PRV is the factory part but is inscribed as having been overhauled in recent years.

 

Regards

Gavin

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