mike barrett Posted October 23, 2014 Author Report Share Posted October 23, 2014 Peter yes you are correct, it was a wideband AFR sensor and readout! regards mike Quote Link to post Share on other sites
JohnC Posted October 23, 2014 Report Share Posted October 23, 2014 Hi Mike, Out of idle curiosity, do you know which adjustment he used on the CU? I'm guessing it was the large (A1) screw, but I wonder if he moved the datum track itself - I think the mixture enrichment lever has exactly the same effect as this adjustment, so could be used to perfectly reverse the adjustment when at low altitude. Drawback is it has to be done off the car; it's fiddly; it's hard to replicate... Cheers, John Quote Link to post Share on other sites
Peter Cobbold Posted October 24, 2014 Report Share Posted October 24, 2014 'Vitessesteve' lives at 5000feet and adjusts the full throttle stop screw. http://www.vitessesteve.co.uk/LucasStuff/TR6PINOTES.htm It's very difficult to adjust as it's on the block side of the MU. Should be possible to fit an extended adjuster forwards past the disy pedestal. Peter Quote Link to post Share on other sites
Spit_2.5PI Posted October 24, 2014 Report Share Posted October 24, 2014 (edited) So ... if you were to lower the pressure regulator somewhat - yes, I know our systems *must* run at 105psi but hear me out - if you *did* lower the pressure, I wonder how much less fuelling that would give before it seriously effected the spray patterns and uniformity of the injectors??? I'm guessing the minimum pressure would be quite a bit more than the 50psi of the injector poppet valves. Cuz if it were enough to run at altitude, simply put two pressure regulators in series with a valve or tap on the return to disable the low-pressure one. Run as normal at high fuel pressure until engine misbehaves, then run around to the boot and set to low pressure mode and continue up the pass. Has anyone experimented with lowering the fuel pressure? Richard Edited October 24, 2014 by Spit_2.5PI Quote Link to post Share on other sites
Peter Cobbold Posted October 24, 2014 Report Share Posted October 24, 2014 (edited) Richard, I had wondered about that, but I doubt it will work. The metering is done by shuttle which needs 105 psi to push the moving stop against the counterspring and firmly onto the fuel cam. If the pressure is lowered to restrict shuttle motion it would have to be such that the moving stop wont contact the cam- by a precise gap, but one which is no longer controlled. So I'm doubtful that would work. On the other hand, lets assume the fuel cam remains in in contact at the new lowered pressure, and the shuttle motion necessarily remains the same. The consequences will, I imagine be thus: We want the pressure set so low that the full 'shuttle-full' does not eject from the injector. But the ejection rate will depend upon the time available, so I doubt that metering would be maintained at all rpm. Thus, at low rpm wth lots of time the full shuttle-full will be squirted, especially at low loads. But at high rpm and fuller throttle the bigger shuttle-fulls wont get completely ejected. So it would lean the top end but leave the bottom end unchanged. The chosen 105psi and 50 psi cracking pressure is presumably enough to ensure that at highest rpm and biggest shuttle motion ( ie biggest load ) all the 'shuttle-full' of fuel gets ejected. So at low rpm and cruise the 105 fuel pressure is super-adequate to eject the smaller boluses. Also, if the 105 were lowered, differences in injector pipe length and cracking pressures would leave some cylinders taking more of their bolus than others: not good. 105 is I guess set to ensure it will squirt the complete shuttle-full at high rpm, full load and through the most resistant injector-line. As the psi is lowered those three parameters start to influence fuelling, but not really in the way we would hope. Peter Edited October 24, 2014 by Peter Cobbold Quote Link to post Share on other sites
Spit_2.5PI Posted October 25, 2014 Report Share Posted October 25, 2014 Peter, thanks for that - I hadn't considered the possibility of the metering unit going non-linear (failing to follow cam &/or shuttle not completing travel) at lower pressures, or an rpm dependant effect such as incomplete injection. Back to the drawing board! Richard Quote Link to post Share on other sites
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