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MG MGB Technical - fuel pressure meter

Dear All, Much discussion has occured on the site re fuel pumps, pressures, ( of fuel), servicing, of points,( pump.) etc, I have now aquired an in-line fuel pressure guage,0-15 pound per square inch. at very reasonable cost from an industrial suppliers of hose fittings, unions, and the like. A robust large dial, more that the usual automotive 2" presentation, $27 Australian, bargain.( Hot tip here, buy from specialist engineering shops rather that the 'automotive' outlets.) I wish to fit it in the engine bay, close to the carbs. Any recommendations? I probably should avoid kinks in the line, obviously away from great heat? Mike
J.M. Doust

Use a brass fitting that allows you to connect 4 lines to it. One fitting, for each carb, one for the fuel inlet and one for the gauge. Mounting the gauge on the inner fender should keep it away from the usual heat sources as well as vibrations. RAY
rjm RAY

I connected a 15 psi guage to mine when I was troubleshooting the overflowing float bowls. It was an Australian made guage so I hoped it would be accurate. However when I eventually returned my pump to SU Midel their quoted output was a couple of psi different to the guage I was using. If you want to know your real fuel pressure on an SU system you need a guage that is very accurate at low pressures.
Ian Buckley

rjm Ray thanks. Interesting, why would I need a four lines union? Surely I just attach the meter to the fuel line before it enters the carbs?
In retrospect, I may have been able to specify a dial gauge with a 5 pounds per sq inch range, I don't know.
And Ian, I know I have no overfuelling problems at the moment so a measure even with this gauge will give me 'a' satisfactory pressure( according to this gauge.)It would then be interesting to see what it registers, compared to book pressure. I've just had another idea; I use at the surgery, quick-disconnect couplings. You can use them with air or water. What if I had one of these couplings on a 'T' piece, and connected the gauge only when I had to check? I suppose a disadvantage or risk might be as one connected/diconnected there would be a possible spill of fuel ( may be not if done while the system was off ( ie pump not running.)But the little vale in the quick-disconnect could in time deteriorate and leak? Mike
J.M. Doust

Surely a bit OTT? If you have no overflow and no running problems there is nothing to worry about. A Tee anywhere in the main line from the pump or a line feeding either carb will show the pressure, it will be the same no matter where you measure it, like voltage along a wire. Remember with the SU fuel pump you still have pressure in the line after the ignition is switched off, for several minutes, unless you happen to turn it off just as a solenoid operation was about to commence. Fuel is different to air or water so may affect the quick-disconnect couplings differently, and it would be inadvisable to return them to the surgery after trying them on your car :o)
PaulH Solihull

Hello
A lot of fuel injected cars, specially US marketed cars have or had a Schraeder valve in a click on fitting on the fuel rail, I think it was in the design rules there for a while but the US engined cars sold here now don't seem to have them anymore
It was an excellent idea, we had a gauge that just clipped onto the fitting and it opened the valve as it went on. Similar to AC fittings.The gauge also had a tap on it so that volume under pressure could be checked.
It's a shame all cars don't have them - it makes fuel pressure/volume checks very simple
IF you are going to make up a gauge, I would suggest you have the hose long enough to get the gauge out from under the bonnet to a place where you can see it while driving
Then you can check to make sure your pressure doesn't drop off under load/speed as that is when most fuel problems start
Cheers Willy
William Revit

My gauge (liquid-filled , 0-15psi), was mounted on the inner fender, "T'd" on the main fuel line...A single, and simple, "T" fitting...Never had a problem with it.
My main objective, was to know the fuel pressure from the pump....and that's what it did.( Mounted fuel filter in the same line).
Edward


E.B. Wesson

Thanks EB,William and Paul for you input. Really I just like the idea of having as much information as possible about everything on the MG! The Liquid filled gauge looks impressive the st up on the inner wing is probably ideal. William, that system you recount would be ideal. I shall get on with the job this week-end. Mike
J.M. Doust

This thread was discussed between 04/10/2011 and 06/10/2011

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