Question on MS2/extra and dual fuel maps.

[TheSilverBuick]

In any of the megasquirt 2/extra variants, can a dual fuel map set up be triggered by a switch AND conditions settings (like TPS or kPa)?

I'm looking at going to an MS2/extra firmware this weekend and was thinking about tinkering with shutting fuel off to four cylinders while cruising. Using a TPS or kPa threshold won't necessarily work for all driving conditions, but if I could toggle a switch when I'm out on the highway so that when less than say 30% throttle is applied, run off one injector bank and when over 30% throttle run off both banks (so I'm not toggling the switch just to pass a slower vehicle) I think it could work well. I'd have to leave the switch off while around town unless I want to idle and such on half the engine.

Yeah yeah, I know that with out actually shutting down the openning and closing of the valves I'm still getting pumping losses, but I want to see what it does or doesn't do.


**Anyone hear from Matt Cramer lately? Says is last log in date was April 14th.

[Stich496]

don't see how this would work with batch..
other than having 4cyl lean miss

[TheSilverBuick]

don't see how this would work with batch..
other than having 4cyl lean miss

I'm okay with you not seeing how it would work, I'm not afraid to try it. I've ran on 4-cylinders/injectors a couple times, when I had a ground wire come loose, and it's exactly that, an intentional 4-cylinder miss. It had a hard time idling (cause it was just missing half the fuel..) but drove decently enough. With long and deep runners I'm hoping for relatively low cross contamination at low rpm.

[Bob Holmes]

I would think that the best way to do this is shut off one of a set of paired cylinders, running on only one bank of a V would cause some imbalance issues. ?? Do a two batch system, pairing your power pulses. Then when you shut off one, you should still have comparatively smooth sailing.

I like the way you're thinking.

Bob

[Bob Holmes]

Some related info:

http://papers.sae.org/2001-01-3591/

http://autoelectronics.com/mag/dynamic_cylinder_deactivation_residual_heatrecovery-1229/index.html

Ecomodder has several threads on the topic.

[TheSilverBuick]

I would think that the best way to do this is shut off one of a set of paired cylinders, running on only one bank of a V would cause some imbalance issues. ?? Do a two batch system, pairing your power pulses. Then when you shut off one, you should still have comparatively smooth sailing.

I like the way you're thinking.

Bob

I wired the injectors to be paired in the same fashion as the Cadillac 4-6-8 engine, so shutting of injector bank 2 shuts off fuel to the same cylinders as the Cadillac did in 4-cylinder mode. The Cadillac has the same firing order so I figure I should be good (and the fact I have ran on 4 before for short distances). I wired it that way before I fully understood how the Cadillac system worked. I still want to get a set of Cadillac 4-6-8 heads to study. Consider this a precurser to if I ever build a 472/500 with the 4-(6)-8 system on it.

[TheSilverBuick]

http://autoelectronics.com/mag/dynamic_cylinder_deactivation_residual_heatrecovery-1229/index.html

I've heard of the thermal imbalancing and lubrication issues before. I read it somewhere years ago about GM's DOD, where as the LS will only run on 4 cylinders for a certain number of revolutions or time (never gave a specific number) before re-activating to ensure cylinder lubrication, etc.

Clearly I'm not worried about NOx emissions on the higher loading, and am not sure on actual thermal issues with a low load and sufficient cooling, but the oil part does concern me, but I don't know how much to be concerned about.

[dieselgeek]

I see no problem with the switch controlling the power to those specific injectors you want to shut down. If you want the manual control... or perhaps you could use a spare output of the MS to control a power relay for those injectors. That might be better.

I say go for it! You can easily run one VE table per INJ driver (you have two), you could even use the VE2 table to "shut off" the DOD injectors by simply setting "0" in the map areas that you don't want those cylidners running. I see no reason why that wouldn't work smoothly - others here have used second VE table/INJ2 to inject race gas, methanol, etc. as "displacement on demand" and that's how they do it - set the secondary map to all Zeroes where they don't want the second injectors to fire.

[TheSilverBuick]

I don't want a switch to cut the power to the injectors because I want the 4 to automatically come back on if I suddenly mash the gas pedal or want to pass a vehicle without having to manually toggle the switch. But I don't want cutting down to 4-cylinders to be completely automated either as there will probably be plenty of times I want to over-ride it (namely around town and I only want it to operate in 5th gear). The switch is to let the MSII know it's ok to shut down 4 when the conditions are right, because I don't want it cutting 4-cylinders out every time I run through the rpm/load range in each gear. (I hope I'm making sense...)

I figure I need two maps because I'll probably have to richen up the 4 running cylinders a bit to take up some of the extra load, but don't want them richened up (same injector driver) when all 8 are running. Basically if all 8 cylinders are running I can maintain ~15.5:1AFR, with out mis-firing, but if I have 4 cylinders lean missing intentionally (~50:1afr??) and 4 cylinders hitting solidly on a ~14.0-14:5 afr (also ?? since the O2 readings go out the window with the empty cylinders pumping air), I "think" I may be ahead on fuel consumption. After all, it's still a 3.8L 4-cylinder at that point

[TheSilverBuick]

I guess it might be better said, that only one Map is used at a time.

Fuel Map 1: Controls both injector banks, uses essentially the existing map I have made. Fuel Map 2 is ignored.

Fuel Map 2: Only controls injector bank 1, and the system shuts off bank 2 (unused hi-idle relay output cutting power?). Fuel Map 1 is ignored.

The system will only switch to Fuel Map 2 when the following conditions are met:
1) Toggle switch in position to "okay" the use of Fuel Map 2, not just automatically switch to Fuel Map 2.
2) When the right rpm and kpa ranges are met.


I can see using the high idle relay to kill power to injector bank 2 when the right conditions are met, but can I lock it out to keep it from doing that when reading Fuel Map 1? Because then I could just make Fuel Map 2 a slightly richer version of Fuel Map 1 and just let the relay kill power to Injector Bank 2 when the right rpm/kpa conditions are met.

[CTX-SLPR]

You need a comparitor cuircit for the MS trigger leg. Something like this is what I see:
Leg 1: Switch (going high or low for what the MS2 wants to see) for the disabled condition with a diode on the output
Leg 2: TPS breakout feeding into a comparitor with a pot on it so when the TPS voltage goes over the comparitor trigger point set by the pot, the circiut goes to the opposite of your switch and overrides the switches signal to turn the table back on. Also need a diode on the output of this one.
Splice both legs onto the MS2 trigger pin. I have a box from Caspers electronics that has a pair of TPS enabled outputs using a DIP switch to set what rough percentage of throttle it puts a logic level output that I use for my SP400 kickdown and switch pitch. I did have to have him custom make it at around $100 for a sealed unit that plugs into the TPS.