How to LPG installers map cars?

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richy_boy · #1 Post by **richy_boy** » Mon Sep 18, 2006 9:24 am

Hi all; I'm interested how you LPG installers go abouts mapping the car so it fuels correctly. For example, you install a system and then use the automated mapping tool provided by the software. This runs like a dog initially, so you adjust the 'mixture' of the 'driving' LPG map. - How do you know when the mixture is correct? Do you rely on the cars lambda signal, or do you use an exhaust gas analyser or a wide-band lambda at all? - With a high performance car installation, how do you ensure it doesn't run lean at high revs which could promote det? Do you 'tune rich' to be on the safe side generally? Rich

badger · #2 Post by **badger** » Mon Sep 18, 2006 9:58 am

Basically, the automated process is carried out first to get some sort of base mapping into the lpg ecu. Software or a monitor of some kind is then used to monitor the petrol injection times when running on petrol, then the LPG mapping is adjusted as required to ensure that the petrol ecu injection times are still the same when running on petrol. If it was set up using lambda signals alone, the petrol ecu will always adjust the injector pulsewidth until it sees the lambda reading it is programmed to control at, regardless of whether it is running on petrol or gas. The danger here is that the petrol injection timings could be way different on petrol to gas, causing changeover issues amongst others. Land-rover v8 engines with the Motronic management, for example, will "lock up" if the lambda trim goes beyond a certain value for a certain time. On cars that run open-loop at, say, full throttle - the gas would be mapped as above then tweaked slightly in the open-loop range if necessary to ensure it wasn't tending towards lean. In practice, if the gas ecu is mapped correctly at 7/8ths throttle (closed-loop) and the injection pulsewidths are correct, then as the petrol ecu goes open-loop it will enrichen slightly, the gas ecu following to suit with little or no further adjustment being required. Badger.

richy_boy · #3 Post by **richy_boy** » Mon Sep 18, 2006 10:31 am

Ahh interesting, thanks Brian. I forgot to mention my cars ECU goes open-loop when over 4k RPM (I think) so the lambda is only really used when cruising or driving 'normally'. You mention about ensuring it doesn't go lean in open-loop state, but how would 'Mr LPG' go abouts this? From my understanding the cars std. lambda is too slow reacting to be of any use. Rich

richy_boy · #4 Post by **richy_boy** » Mon Sep 18, 2006 10:34 am

Ahh interesting, thanks Brian. I forgot to mention my cars ECU goes open-loop when over 4k RPM (I think) so the lambda is only really used when cruising or driving 'normally'. You mention about ensuring it doesn't go lean in open-loop state, but how would 'Mr LPG' go abouts this? From my understanding the cars std. lambda is too slow reacting to be of any use. Something else which is puzzling is my car has a MAP sensor connected as it's a turbo'd motor. Does this simply calculate the intake pressure and increase the LPG pressure ot suit? So, for example, the higher the boost, the higher the LPG pressure and thus 'x' milliseconds of LPG injection delivers more fuel? If so, is this ratio normally adjustable? Rich

quantum · #5 Post by **quantum** » Mon Sep 18, 2006 3:59 pm

Any engine adjustment, whether gasoline or LPG, has to be a compromise. With the newer slaved systems like Prins VSI, you essentially set the LPG injectors to be open ~115% of the time that gasoline would be on. You just set this multiplication factor directly in the software. The Pris ECU monitors OEM injector signals, and adds some time for LPG. (It also tricks the OEM ECU into advancing timing by ~20 degrees) Then you put the vehicle under partial load, causing the injectors to stay open ~10mS running propane. (... watching this in the Prins software) Can't do this by just raising RPMs, the engine must be under load. Then you use a separate scan tool to monitor short-term and long-term trim (I use TekMate) while you calibrate injector settings in the Prins software, which modifies the LPG ECU. Once that's done, adjust the regulator output pressure. Very precise. By putting the engine under partial load, you are compromising in about the middle of its most common running range.

richy_boy · #6 Post by **richy_boy** » Mon Sep 18, 2006 5:13 pm

Ohh that Prins system sounds cool. My BRC Sequent FAST is capable of ignition advance, but you can vary it throughout the rev range. However, that said you need the RPM and CAS signal cables connected up, which they weren't then mine was installed <IMG SRC="http://www.my90.co.uk/lpgforum/clipart/sad.gif" ALT=":-(" BORDER=0> Bit of a none starter until I find someone capable and/or thinks it's worthwhile to set it up. Thanks again Bill, it's a shame there isn't extensive resources online to read about such technology! (Boy, I've tried!) Rich

quantum · #7 Post by **quantum** » Mon Sep 18, 2006 5:41 pm

I'm concerned about the declining quality of Prins VSI lately. Probably not worth the premium they ask. I've detailed it in other threads here.

classicswede · #8 Post by **classicswede** » Mon Sep 18, 2006 9:10 pm

Bill no offense to you or the prins system here just a couple of points about the prins system. I can say I only normaly hear good things about the prins system but I have a few conserns about how it works. As I understand it the Prins system does not read gas pressure(I could be totaly wrong here) If that is the case how does the system correct for any variation in vapour pressure? Surly NO reducer is good enough that the pressure does not vary at all! I know the omvl reducer will vary a little and the system has compensation curves to compensate for pressure devation. I am also correct in thinking that the prins sytem does not have a full map? Is it a case the you can only adjust idle and out of idle fueling? Is some of what I am saying correct or am I totaly wrong? If that is tru how does it work so well??? Mike

richy_boy · #9 Post by **richy_boy** » Mon Sep 18, 2006 9:21 pm

Would the variation between the fuels be a constant, so a full map wouldn't be required? I seem to recall my BRC only has a slider for idle and for off-idle, but maybe it has a full map capability elsewhere. Would be interested to hear a more informative explaination though <IMG SRC="http://www.my90.co.uk/lpgforum/clipart/happy.gif" ALT=":-)" BORDER=0> Rich

woody · #10 Post by **woody** » Mon Sep 18, 2006 9:25 pm

Hi all, Bill iam concerned about your concerns.The quality of Prins has not gone down, they have however had a few issues with the reliabilty of the regs,other wise they still use the same equipment as always.No system is fool proof hi Richy , nice to see you back again. The Prins system differs from all others in that, it does not use a dedicated map sensor or the signal from the cars own sensor.It pretty much relies on the speed of the software to interperet the petrol injector duty cycle.The differece between receiving a signal and delivering the new one is 0.03 ms BRC however use a map sensor, and i do think the overall result is better. All vehicles fitted with a lambda will run open loop over a given rpm,remember it is only for emissions results .Some vehicles will go open loop at a very early stage. The map sensor on your turbo Nissan reads pressure,the same as the OE one, other wise it would not know how fuel to squirt in .The vaporiser also receives a dose of turo pressure, this opens the diaphragm to increase delivery pressure. I have not yet tried the ignition advance [not convinced it will make any real difference with out upping the compression ratio]. But i am experimenting with opening up the whole map, there is a lot to play with and again it is only needed on certain vehicles. I am certainly capable of connecting you rpm and tps wires, but you will need a rolling road to see any difference, you decide if its worth it. On full load , open loop, the lambda still reads,so all you look for under max load at high rpm is a .7 - .8 v reading on the lambda, any lower than .6 and its starting to run out of steam. Cheers Keith

woody · #11 Post by **woody** » Mon Sep 18, 2006 9:35 pm

Mike , the Prins pressure sensor is in the lid of the dry gas filter. They use the original petrol map, via fuel trim and duty cycle.It also has an lpg corrction factor to adjust the lpg fueling,this is worked out from the lpg injector duty cycle against petrol DC and gas pressure Like i said its secret is down to the reaction time , and i know we have discusssed this before. Cheers Keith

quantum · #12 Post by **quantum** » Mon Sep 18, 2006 10:11 pm

Quote by CS_Autogas: As I understand it the Prins system does not read gas pressure(I could be totaly wrong here) ... I am also correct in thinking that the prins sytem does not have a full map? The Prins converter does have a pressure transducer. How else would it know you are out of gas? You are correct though, that it does not have a map. Richy is correct, that the difference between LPG and gasoline is constant. Prins does not pretend that they have the best idea for running on the thousands of different engines out there. So they leverage off the OEM's fuel trims. This automatically lets the factory ECU compensate for altitude, temperature, demand, etc, etc. It is a "slaved system", which eliminates many problems.

quantum · #13 Post by **quantum** » Mon Sep 18, 2006 10:13 pm

Woody, my concerns are: - The failing regulators. They put in a washer and didn't bond it, in a critical piece of the regulator. Although they have fixed this now. -When my reg seal blew, it blew out the filter's vapor inlet O-ring. Well, I didn't have the brass ring cinched right against the case, but it was tight and should have held better. This interface was poorly designed in the first place, as inherently it allows gas out the threads between the nut and elbow. - I bought Prins because it has the best rep in the forums. When my reg seal blew, I asked my dealer what the hey? That I know of Impco reducers that have lasted 20 years without a rebuild. His words were ominous: "Prins is not Impco. Expect to rebuild the reducer about every two years." - The converter liquid-in interface. This is about 1/4" pipe-thread, into which a brass fitting is supposed to screw and support the weight of the lockoff and liquid hose. I had to be damned careful in assembly,to avoid snapping it off, or stripping something. Too small and weak. - The ever-smaller wires. Every new kit revision comes out with smaller gauge wires. The Prins injector wires on my kit are half the diameter of the OEM wires,and I can not imagine that Jeep overspeced them. When I first converted I didn't have tanks, so ran on gasoline for a while. Suddenly one of my injector FETs burned out. The local dealer had never sold a powertrain ECU in 6 years, so they are reliable. So I found an ECU at the junkyard and transplanted the blown FET. I attribute this failure to the small-gauge Prins wires. And I notice the newer kits have wires even smaller. What's up with that? (continued...)

quantum · #14 Post by **quantum** » Mon Sep 18, 2006 10:13 pm

-The calibration. I used to know WTF the trim instructions meant, after my dealer went to much effort in explaining them, but I have forgotten again and can't figure it out. First they say: "When adjusting RC_inj, aim at a value for 'RC_inj + gas_cor' which corresponds with a petrol injection time extension of 115%." Unfortunately, my Prins software does not feature a "gas_cor". Then they say: "Set RC_inj so the so-called short-and long-term fuel trim values are between -3% and +3% ,as when using petrol." Well, when I use TekMate to look at short-term trim, for the most part it graphs between -.73 and -3.12,and long-term is rock-solid at -4.7. Fine, but this is not in relation to gasoline. The scanner doesn't know I'm running propane, so what are they talking about? It is just not clear. We must be doing New Science. Otherwise, the Prins gear is top-flight. Milled out of solid aluminum billets.

richy_boy · #15 Post by **richy_boy** » Tue Sep 19, 2006 9:34 am

Hi Keith. As you're probably aware, my car is a modified Nissan 200sx, which runs a modified fuel and ignition curve for better performance on fuel. Part of these changes incorporates igntion retard at the top end to reduce the risk of det. My concern when running on LPG is that this is the opposite to what I would like to happen. Due to the higher octane I should be able to run MORE advance and release a little more power, taking the calerific value into account, much the same as on super unleaded. A further concern are EGTs (exhaust gas temps) which, when running the timing less than optimal could cause exhaust valve problems, especially at 6500rpm at 15psi for potentially sustained periods! The trouble with me is, although it's not necessary I'm interested in getting the most out of anything I have - I guess that why I'm classed as an enthusiast! where abouts where you again Keith? On other comments, could the smaller cables not be due to better quality strands or less insulation? Rich

quantum · #16 Post by **quantum** » Tue Sep 19, 2006 3:32 pm

Not considering insulation, only the conductor. It is possible the Jeep wires are tinned steel, but I doubt it as I can solder to them. And Prins wires now seem to be 25% or less than their diameter. And why did my injector driver blow? I think the wires are too small, and that it's a false economy.

quantum · #17 Post by **quantum** » Tue Sep 19, 2006 3:33 pm

... meant to say that Prins wires are 75% less diameter than OEM.

woody · #18 Post by **woody** » Tue Sep 19, 2006 9:52 pm

Hi Richy , i am in sunny essex near southend on sea. Hi Bill , the sealing seat is supposed to be glued in, if it fell out , the glue has been eaten by the gas.{Prins are not the only make to suffer with this]. I have heard through the LPG grapevine that a new reducer is on the way,watch this space. With regard to the wiring size, or lack of it, i have never had any problems and i have probably converted about 50 or so with prins , both 4.0 and 4.7 variants. If you work out how much load the wires need to handle to fire the injectors , i think they are probably overspeced. Cheeers Keith