JTY Posted October 31, 2023 Report Share Posted October 31, 2023 Just wondering: has anyone ever permanently installed a fuel pressure gauge for the PI system? E.g. https://nl.merlinmotorsport.co.uk/p/mocal-52mm-oliedrukmeter-0-160psi-m-opg160 or https://www.merlinmotorsport.co.uk/p/racetech-oil-fuel-pressure-gauge-0-160psi-p16b If so, how should one go about it? Or just a bad idea to begin with? Quote Link to post Share on other sites
Waldi Posted October 31, 2023 Report Share Posted October 31, 2023 This has been discussed before, suggest to do a google search. I would never install a fuel line in my cabin. Waldi Quote Link to post Share on other sites
JTY Posted October 31, 2023 Author Report Share Posted October 31, 2023 Not saying cabin, could be engine bay maybe. Quote Link to post Share on other sites
trchris Posted October 31, 2023 Report Share Posted October 31, 2023 Why ??? chris Quote Link to post Share on other sites
Andy Moltu Posted October 31, 2023 Report Share Posted October 31, 2023 If you want to check the pressure in use/under load the gauge needs to be a remote wired one rather than having petrol in the cabin. Quote Link to post Share on other sites
PodOne Posted October 31, 2023 Report Share Posted October 31, 2023 3 minutes ago, Andy Moltu said: If you want to check the pressure in use/under load the gauge needs to be a remote wired one rather than having petrol in the cabin. +1 done it with FI projects with a sensor in the fuel rail but I can't see any need in a TR6 other than a take off port at the MU (which I've done) to plumb in a gauge to access pump pressure/setting and aid any future fault finding. Quote Link to post Share on other sites
JTY Posted October 31, 2023 Author Report Share Posted October 31, 2023 1 hour ago, trchris said: Why ??? chris Just a feeling of control :) Quote Link to post Share on other sites
John Bracher Posted October 31, 2023 Report Share Posted October 31, 2023 I have one. Mounted on a bracket in the glove box. I inserted a takeoff into the fitting under the metering unit, to an electronic pressure transducer gauge intended for oil. Seems to work fine, and is only visible if I want to see it. Checked against a calibrated rig, works to about +/- 1 or 2 psi. Quote Link to post Share on other sites
KiwiTR6 Posted November 1, 2023 Report Share Posted November 1, 2023 This is mine. Quote Link to post Share on other sites
stuart Posted November 2, 2023 Report Share Posted November 2, 2023 19 hours ago, KiwiTR6 said: This is mine. Hate to say this but that R6 hose may not like continued Ethanol usage Stuart. Quote Link to post Share on other sites
KiwiTR6 Posted November 2, 2023 Report Share Posted November 2, 2023 8 hours ago, stuart said: Hate to say this but that R6 hose may not like continued Ethanol usage Stuart. Hi Stuart. We don't have ethanol mix over here thankfully Gavin Quote Link to post Share on other sites
marting Posted November 2, 2023 Report Share Posted November 2, 2023 Electronic VDO gauge with Smiths petrol gauge cover Quote Link to post Share on other sites
marting Posted November 2, 2023 Report Share Posted November 2, 2023 Sender unit attaches to Malpassi type PRV in the boot. Apologies for upside down picture Quote Link to post Share on other sites
stuart Posted November 3, 2023 Report Share Posted November 3, 2023 Quote Link to post Share on other sites
mleadbeater Posted November 3, 2023 Report Share Posted November 3, 2023 From recent readings into the mystic workings of the PI system, I so far conclude that the two critical parameters of the system are a) engine vacuum. and b) fuel pressure, this seems most critical, as it seems the the regulator is effectively a variable-stroke pump, driven by fuel pressure. The oscillating shuttle ( or double ended piston) is driven by a pressure differential between the inlet fuel pressure , circa 110psi, and the opening pressure of each injector, circa 50? psi. Am I correct? Whilst we already have an oil pressure gauge, with the potential to leak oil into the cabin, the consequences are at worst a possible scald, as is the more likely hazard of a burst heater hose. A leaking fuel supply to a gauge has also a fire risk, either due to developing a leak , or, more likely , as a result of a harness fault and fire, which is the most common cause of an under-dash fire in my view. Therefore an electronic fuel gauge seems a good option. I believe both a vacuum and fuel pressure gauge, permanently plumbed-in, would be an enhancement, a helpful indicator of engine problems whilst driving just as are the oil pressure, water temperature and voltage. Inside the glove box?, On the dash pane?l, under the dash? in the engine bay? .....options of personal preference. There are certainly too many driving distractions due to over instrumentation with moderns, for example the heater controls on my Honda HRV are very distracting to adjust whilst driving, requiring looking downwards, precise finger positioning to adjust and concentration to read the digital settings. The latest model of the HRV has resorted to more traditional "feelable" heater controls, I wonder how many road accidents have been due to use of touch controls. Cheers, rant of the day over with, Mike Quote Link to post Share on other sites
astontr6 Posted November 3, 2023 Report Share Posted November 3, 2023 On 11/2/2023 at 1:14 PM, stuart said: Hate to say this but that R6 hose may not like continued Ethanol usage Stuart. You are right, its a bad choice. Bruce Quote Link to post Share on other sites
Spit_2.5PI Posted November 3, 2023 Report Share Posted November 3, 2023 2 hours ago, mleadbeater said: b) fuel pressure, this seems most critical, as it seems the the regulator is effectively a variable-stroke pump, driven by fuel pressure. The oscillating shuttle ( or double ended piston) is driven by a pressure differential between the inlet fuel pressure , circa 110psi, and the opening pressure of each injector, circa 50? psi. Am I correct? Not quite! It's the stroke of the shuttle (controlled by the vacuum) which determines the quantity of fuel delivered. It should be pretty independent of fuel pressure (excepting small variations due to elasticity of the tubing), provided the pressure is high enough to deliver the maximum quantity at the highest rpm. I think this is the reason the inlet fuel pressure is so high - to cope with 6000rpm at wide-open-throttle! The pressure regulator is just a spring loaded valve. When the fuel pressure exceeds that of the spring, the valve opens and bleeds the excess back to the tank in a linear fashion - a "shunt regulator" in fact. It shouldn't oscillate, but some people have observed oscillation with an unfortunate choice of after market pipe material/length/position/etc. Much like undesirable sounds from your central heating, it shouldn't due that, but can be the devil's own job to eliminate if it does. Cheers, Richard Quote Link to post Share on other sites
mleadbeater Posted November 3, 2023 Report Share Posted November 3, 2023 (edited) Sorry to disagree, to me, the piston or shuttle discharges from alternating ends;, fresh fuel at the high pressure inlet provides the thrust on the other end to drive the piston to the other stop, overcoming the lower discharge back pressure of both the non- return valve and injector. Then the cycle reverses, fresh fuel is admitted to the previously discharged end, and the remaining fuel in the other is discharged to another injector. Without this alternating pressure differential the piston would have no force to cause it oscillate and therefore pump, the remaining fuel in the discharge end would loose its pressure as soon as the non return and injector have cracked open unless its then pumped fully by the piston. As you state, there is an adjustable stop at one end, which is controlled by the vacuum diaphragm and linkage. This varies the volume of fuel discharged , relative to the engine vacuum. The main unknown to me is the purpose of the three adjustable positions of the coaxial thread screws on top of the vacuum diaphragm. Agreed on the principle of the regulator, which can sometimes vibrate at a resonant frequency. I’ve experienced this on an Aston’s power steering pump, which would make a groaning noise when on full lock. Both Workshop manual and Lucas service notes describe the PI system, its my interpretation of the fluid dynamics they haven’t mentioned, but the piston won’t oscillate and pump on its own. Maybe others have a different view on workings the PI system? Mike Edited November 3, 2023 by mleadbeater Quote Link to post Share on other sites
Spit_2.5PI Posted November 3, 2023 Report Share Posted November 3, 2023 (edited) Mike, I agree with everything you've just said. Previously you mentioned the "regulator" and I misinterpreted that as meaning the pressure regulator in the boot. I see now that you meant the regulating - or metering - action of the metering unit. I merely intended to point out that the fuel delivery is somewhat independent of fuel pressure - except for high rpm & WOT. Apologies for the crossed wires. Richard PS: Someone's going to come along now and point out that the correct pressure gives a good spray pattern - which of course it does! Edited November 3, 2023 by Spit_2.5PI Quote Link to post Share on other sites
KiwiTR6 Posted November 3, 2023 Report Share Posted November 3, 2023 5 hours ago, astontr6 said: You are right, its a bad choice. Bruce Hey guys, I live in NZ and we don't have ethanol in our everyday fuel unless I specifically use a Gulf E10 product, which I don't. So what's the problem really?? SAE 30R6 Tube: Chemigum® Cover: Chemivic™ for exceptional abrasion resistance. Reinforcement: Two-spiral polyester. Temperature range Up to 212 °F (100 °C) Specially designed for gas, oil, diesel and other fuels. Minimum Burst 175 psi (1.2MPa) Meets and exceeds SAE J30R6 specifications. Quote Link to post Share on other sites
Mike C Posted November 4, 2023 Report Share Posted November 4, 2023 I use Gates Barricade. I used to use SAE J30R6 and SAE J30R9 but I was getting 2-3 years out of a set before the Australian high octane unleaded blends destroyed them. I changed the hoses over to the high pressure version of Gates Barricade in the winter of 2017 and they've worked ever since. The hose life will depend on the composition of your NZ fuel blends. Quote Link to post Share on other sites
KiwiTR6 Posted November 4, 2023 Report Share Posted November 4, 2023 Thanks Mike. I've just checked back. This hose has been in place for over 5 years and still appears to be as good as new. Perhaps people shouldn't be so quick to jump to conclusions! Quote Link to post Share on other sites
Mike C Posted November 4, 2023 Report Share Posted November 4, 2023 No worries. Your lucky the NZ fuel suppliers haven't taken to adding strange chemicals to your petrol- as has happened in much of the rest of the world. Quote Link to post Share on other sites
Waldi Posted November 4, 2023 Report Share Posted November 4, 2023 (edited) Hi Gavin, you should be glad there is no ethanol in your fuel, unlike in Western EU. SAE J30 is a specification used for vehicle fuel and oil hoses, below are some extractions (this is from an old 2008 copy I found on the WWW,so it may not be correct anymore). The rated burst pressures in this specification are not the same as the maximum allowable working pressure! Additionally, the maximumm allowable working pressure (MAWP) will reduce with increased temperature and/or smaller bending radius. The specification lists a MAWP of 50 psi for the R6/7/8 hoses. A specific hose may exceed the (minimum required) properties in this specification, but in case of doubt I recommend to contact the supplier. Now for those interested in the properties of SAE J30 R14 hose (and Gates Barricade Fuel Injection Hose complies to this standard): This hose also has a MAWP of 50 PSI (!) rated at Conclusions: The rated burst pressure is not relevant when selecting a fuel hose; the maximum allowable working pressure (MAWP) in combination with the maximum working temperature is more relevant for selection. Sometimes these data are not available, or the supplier is not aware. SAE J30 R14 has the same rated burst pressure as R6 hose. When I selected my high pressure fuel hose a couple of years ago, pressure, temperature and permeability were important. Gates recommens their Barricade Fuel Injection Hose for this application, see properties of this hose below, it also has excellent low permeability. It should be mentioned that good quality PTFE lines hoses have a lower permeability. So this is why many people on here use this specific hose, although it is harder to get than the prettiest girl in high school, so to say, at least for me). Best regards, Waldi Sorry for the multiple posting of screen-copies, I could not remove them. Edited November 4, 2023 by Waldi I TRied to remove multiple screen-copies Quote Link to post Share on other sites
astontr6 Posted November 4, 2023 Report Share Posted November 4, 2023 9 hours ago, Mike C said: I use Gates Barricade. I used to use SAE J30R6 and SAE J30R9 but I was getting 2-3 years out of a set before the Australian high octane unleaded blends destroyed them. I changed the hoses over to the high pressure version of Gates Barricade in the winter of 2017 and they've worked ever since. The hose life will depend on the composition of your NZ fuel blends. +1 I use Gates Barricade SAE J30R14, mine are over 5 years old no smells. Quote Link to post Share on other sites
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