mike barrett Posted August 25, 2014 Report Share Posted August 25, 2014 Hi just back from a wonderful time driving around Europe with 7 other triumphs, including visiting the roof of the Lingotto factory and the Montiverdi museum in Basel and of course Stelvio. All the PI cars (TR6, TR5 and PI 2.5 Gitfire) suffered going up the passes (I got thru 3 sets of plugs) with the PI going very rich, plugs getting wet and then bad misfiring. Is there any short time solution to this problem for touring around the alps or is the only solution carbs or EFI? Apart from the problem on the passes the car was fabulous. I have only had the car since last December but wish I had brought one years ago! cheers mike Quote Link to post Share on other sites
Denis Posted August 25, 2014 Report Share Posted August 25, 2014 (edited) Altitude sickness...give it the kiss of life, remove the intake trunking? Edited August 25, 2014 by Denis Quote Link to post Share on other sites
peejay4A Posted August 25, 2014 Report Share Posted August 25, 2014 There have been some interesting theories on here about how the metering unit could be modified to cope with altitude. Quote Link to post Share on other sites
mike barrett Posted August 25, 2014 Author Report Share Posted August 25, 2014 So what did Triumph do when they sold the cars new or did they avoid high altitudes? cheers mike Quote Link to post Share on other sites
Nick Jones Posted August 25, 2014 Report Share Posted August 25, 2014 Mike, Some PI equipped cars seem to cope ok up to at least 2500m. I think it has alot to do with how rich they run normally at lower altitudes. A car which is bang on or slightly lean at sea level will cope better than one that is a bit rich. EFI with barometric correction works...... but not a small project. Nick Quote Link to post Share on other sites
RogerH Posted August 25, 2014 Report Share Posted August 25, 2014 Hi Nick, having TRavelled behind many many TR6's and 5's I thought they were all way too rich - orrible things. Roger PS - Where is Prof. PeteC when you need him. Quote Link to post Share on other sites
Peter Cobbold Posted August 25, 2014 Report Share Posted August 25, 2014 http://www.tr-register.co.uk/forums/index.php?/topic/31042-pi-versus-altitude/ and several others on here. Quote Link to post Share on other sites
peejay4A Posted August 25, 2014 Report Share Posted August 25, 2014 IIRC Triumph could supply a metering unit which was calibrated for high altitudes but of course that would then run weak at sea level. It's a quirk feature of Lucas PI. Quote Link to post Share on other sites
North London Mike Posted August 25, 2014 Report Share Posted August 25, 2014 Age old problem, on our trip last year the PI 5s carried spare plugs, which were wire brushed clean ready for the next pass Convert to carbs? Moby runs twin SUs on a TR6 engine taken out to 2.7, romps up the Alps, no problem........ Works 2.5Pi saloons for the World Cup Rally had a switchable altitude settings so it was a know problem way back then. They never really solved it and the last 2500 saloon rally cars had triple weber Quote Link to post Share on other sites
john.r.davies Posted August 25, 2014 Report Share Posted August 25, 2014 "Metering needle"? What metering needle? This is Pi! Problem is that Pi relies solely on the intake manifold pressure to determine fuelling. When it is low, it assumes that the throttles are wide open and so increases the amount metered. Low atmospheric presure automatically richens the mixture, even with a closed throttle. It's a built in fault, that doesn't become apparent until you exceed about 2000 metres, and at approaching 3000 causes real problems of over choking. In a Pi Spitfire we only JUST got over the Col d'Iseran, the highest pass at 2770m. It is possible in theory to adjust the M/u - see the manual at http://www.lucasinjection.com/Lucas%20Mk2%20manual%20page%203%20CONTENTS.htm - but at the risk that it will go very weak as you go down again, causing detonation, which is a reason for Pi being rich normally, even as sea level, as it tends to be weak at full throttle. Lucas did make some high altitude M/u's. Here's pic of one showing the extra casing at the base, that muct contain some pressure compensiating mechanism, but I have never seen one for real or found an explanation of how it works. JOhn Quote Link to post Share on other sites
peejay4A Posted August 25, 2014 Report Share Posted August 25, 2014 Who referred to a metering needle? Quote Link to post Share on other sites
stuart Posted August 25, 2014 Report Share Posted August 25, 2014 There is also this type of unit. Stuart. Quote Link to post Share on other sites
mike barrett Posted August 25, 2014 Author Report Share Posted August 25, 2014 Thanks guys all very interesting! If the mixture is so dependent on the atmospheric pressure do you notice a change in performance when the weather changes from high to low pressure? I don't think I have used the car enough to notice yet.... BTW The lowest atmospheric pressure seen in the UK was 926 millibars (in 1884) which I think is about equivalent to going up to 3000m. Good thing the Lucas PI had not been invented then... Stuart: what the device you have a picture off, is that a motor driven mixture control? Peter: will read the links you posted to understand how the Lucas PI works. regards mike Quote Link to post Share on other sites
Peter Cobbold Posted August 25, 2014 Report Share Posted August 25, 2014 (edited) Hi Nick, having TRavelled behind many many TR6's and 5's I thought they were all way too rich - orrible things. Roger PS - Where is Prof. PeteC when you need him. He's volcano watching! http://volcanocafe.wordpress.com/2014/08/24/bardarbunga-nature-of-the-beast/ And yes, PI is sadly deficient in acceleration-enrichment, hence the lean spike. Meaning it has to be run rich at cruise to kill acceleration pinking. Its not 'right'. Peter Edited August 25, 2014 by Peter Cobbold Quote Link to post Share on other sites
stuart Posted August 25, 2014 Report Share Posted August 25, 2014 Thanks guys all very interesting! If the mixture is so dependent on the atmospheric pressure do you notice a change in performance when the weather changes from high to low pressure? I don't think I have used the car enough to notice yet.... BTW The lowest atmospheric pressure seen in the UK was 926 millibars (in 1884) which I think is about equivalent to going up to 3000m. Good thing the Lucas PI had not been invented then... Stuart: what the device you have a picture off, is that a motor driven mixture control? Peter: will read the links you posted to understand how the Lucas PI works. regards mike Its a stepper motor control. Stuart. Quote Link to post Share on other sites
john.r.davies Posted August 25, 2014 Report Share Posted August 25, 2014 My bad reading, Peejay, apologies! You wrote "metering unit". John Quote Link to post Share on other sites
Nick Jones Posted August 25, 2014 Report Share Posted August 25, 2014 Hi Nick, having TRavelled behind many many TR6's and 5's I thought they were all way too rich - orrible things. Roger PS - Where is Prof. PeteC when you need him. Yes Roger, Having chased various PI equipped TRs and 2.5 saloons around the Alps in my lowly 2.0 Vitesse, we can always tell when the altitude is getting to them as we can not only keep up with them, but get past them. And getting past them is necessary to avoid choking on the evil fumes coming out of the back. Some are definitely less afflicted than others though and it's all down to the base settings. Nick Quote Link to post Share on other sites
mike barrett Posted August 25, 2014 Author Report Share Posted August 25, 2014 Who made it? It looks like a DC servo motor (not stepper motor only 2 motor connections) with no direct feedback from the motor spindle. Maybe they are monitoring the mixture and using that as the feedback element of the control loop? cheers mike Quote Link to post Share on other sites
Peter Cobbold Posted August 25, 2014 Report Share Posted August 25, 2014 Who made it? It looks like a DC servo motor (not stepper motor only 2 motor connections) with no direct feedback from the motor spindle. Maybe they are monitoring the mixture and using that as the feedback element of the control loop? cheers mike Neat! Quote Link to post Share on other sites
stuart Posted August 26, 2014 Report Share Posted August 26, 2014 Who made it? It looks like a DC servo motor (not stepper motor only 2 motor connections) with no direct feedback from the motor spindle. Maybe they are monitoring the mixture and using that as the feedback element of the control loop? cheers mike Cant remember, someone on here years ago was investigating altering the mixtures for altitude use and I think it was one of his ideas. Factory rally PI saloons used a manual control similar to a choke cable I believe. Stuart. Quote Link to post Share on other sites
Willem Posted August 29, 2014 Report Share Posted August 29, 2014 I would welcome a manual mixture control with some kind of readout to check its correct setting Quote Link to post Share on other sites
Peter Cobbold Posted August 29, 2014 Report Share Posted August 29, 2014 I would welcome a manual mixture control with some kind of readout to check its correct setting A wideband oxygen sensor in the exhaust - a UEGO - will tell you the mixture. The link I posted earlier shows a cable-operated adjuster for the passeneger. It alters the end-stop for the fuelcam. Peter Quote Link to post Share on other sites
jean Posted August 29, 2014 Report Share Posted August 29, 2014 Wonder if there are still any metering units available that were fitted on TR6's dispatched to Switzerland,they were fitted with the barometric devise but must be very rare these days. Quote Link to post Share on other sites
saffrontr Posted August 29, 2014 Report Share Posted August 29, 2014 TR Bitz had one recently, I'm sure they would be open to offers if they still have it. As far as I am aware they were only offered by Triumph on the late CR series TR6 and not for the CP series. cheers Derek Quote Link to post Share on other sites
Willem Posted August 29, 2014 Report Share Posted August 29, 2014 A wideband oxygen sensor in the exhaust - a UEGO - will tell you the mixture. The link I posted earlier shows a cable-operated adjuster for the passeneger. It alters the end-stop for the fuelcam. Peter Thank you Peter, seems a nice winter project in any winter to come ;-) Drove the Stelvio and several other high alpine passes, the car was not very happy there. No stalling or plug cleaning but the smoking and severe loss of power I remember. Can't be good for the engine. Regards, Willem Quote Link to post Share on other sites
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