shutting off injectors while in decel?

[juxsa]

so I was wondering when making a cal, whats the point of having the injectors spitting out fuel while the car is decelerating? Why not sure them off or have them shoot out minimum fuel? Other then keeping the cat hot I can't think of a single reason to have the injectors firing while in decel mode (in a manual anyway) the motor is still turning all the accessories so power wouldn't be an issue. Just push the gas pedal and the injectors start firing again... Would some thing like this work? I would think it would increase mpg a good amount also.

[xrattiracer]

I was actually rather surprised to find out that chryco engineers did not turn off the injectors, since most other manufacturers do.
I suppose it can help with nvh issues (80s ford engines kick a little when the fuel comes back on during decel), and it certainly has some performance advantages (fuel is ready and waiting when you lay into it). notice that performance setups dump in enough fuel on decel to cause open flames out the exhaust.

[tkelly27]

you could probably use d-cal to shut them off at a MAP value of x amount less than idle. I doubt the cat would cool down in the max 10 or 12 seconds most people spend decelerating during normal driving. Would definately boost fuel economy if you are using the engine as a brake down a long arse hill. Hehe, try it and let us know how it goes!

[turbovanman]

Are you sure there not turned off, nearly every manufacterter turns them off at decel to stop the engine getting flooded with fuel and to aid in engine life and fuel economy.

[LynX853]

i dont think it would get flooded, cause the valves are still opening and closing and spark is still happening. I know for most the cars at school when we dyno them at the inital let off of the gas (example srt-4 we have) sometimes it pops a tiny bit cause the injectors were just still on max and the air was cut causing miniscule backfires, then the air/fuel go to like 22:1

i definetly think they stay on but the pulsewidths are minimal durring decel, so incase you need to punch it there isnt lag.

i could be wrong, but thats how i percieve it

[xrattiracer]

yeah you can tell they are still on by the backfiring that chryco products do under decel (if you have an open enough exhaust system to hear it anyway). it takes fuel to make (back)fire

[william]

What happens when I stuff the clutch with the injectors off? Would it turn them back on at a minimum RPM?

[xrattiracer]

yes, thats how the ford ones work. if the throttle is closed AND engine rpm above 2750, it shuts off the fuel entirely. change either of those paramaters and it comes back on.

[GLHNSLHT2]

Tkelly has it right. shut them off over a certain amount of vacuum. In my case they off at 23" on a steep downward slope from 22". I idle at 21" of vac. It's awesome. I can go down the freeway, let off the gas and turn the key off Exhaust note doesn't change and you just turn the key on and give the car gas and away you go. Yes simon they're on a bit on decel. Hence why you get the popping that Xratti stated. The S60 cal has quite a bit of fuel on decel. The SRT4's do as well and they increase it on the Stage cals to get even more of that popping on decel. The car is definately quieter without the fuel though. I love it on mine.

[Una]

I've always assumed the computers leave the injectors firing just a little bit so that the catalytic converter can continue to do it's converting. If your just pumping alot of warm air through the cat, it'll cool below it's ideal operating temps real quick. Chrysler has always been a leader in emissions (lean-burn crap in the 70's..), they have some odd ideas that Furd and others don't.
It's easy enough to turn off the fuel in the cal with d-cal.. The baseline fuel curve, just set it to zero below like 20".. Gotta play with the cal several times to find the happy spot, too high and the car is a pain the cruise at a steady speed with. Too low and you may hardly ever reach the cutoff. You also want to slope it up gradually from the cutoff so you have less of a WALL there when you tip into the gas. An A/F gauge (not a Dawes device) is priceless when tuning this sort of thing.
When you get it right, it's awesome because the Navigator pegs at 99 Miles Per Gallon FAST when you get off the gas..

[LynX853]

Quote:

Originally Posted by GLHNSLHT2 Tkelly has it right. shut them off over a certain amount of vacuum. In my case they off at 23" on a steep downward slope from 22". I idle at 21" of vac. It's awesome. I can go down the freeway, let off the gas and turn the key off Exhaust note doesn't change and you just turn the key on and give the car gas and away you go. Yes simon they're on a bit on decel. Hence why you get the popping that Xratti stated. The S60 cal has quite a bit of fuel on decel. The SRT4's do as well and they increase it on the Stage cals to get even more of that popping on decel. The car is definately quieter without the fuel though. I love it on mine.

all i gotta say is make sure your steering lock dosnt happen on the freeway when you turn your key off, it can only mean trouble!

[GLHNSLHT2]

hehe steering lock has been gone for years in both my cars. Makes pushing them around the garage very easy.

[tkelly27]

the picture is for juxsa. My van idles at 26ish" hg when its not in drive so cutting the fuel off at 28 would probably be where I'd feel safe doing it. Having it die while coming to a stop and squirting a crapload of fuel that won't get burnt while it returns to life would be counter productive. I've definately seen it up in the high 28's rolling downhill though. Back to the point, yeah you probably can, I'll give it a shot when (read: if) my van returns to the road and let you know how it goes.

[Shel-Game]

Quote:

Originally Posted by tkelly27 the picture is for juxsa. My van idles at 26ish" hg when its not in drive so cutting the fuel off at 28 would probably be where I'd feel safe doing it. Having it die while coming to a stop and squirting a crapload of fuel that won't get burnt while it returns to life would be counter productive. I've definately seen it up in the high 28's rolling downhill though. Back to the point, yeah you probably can, I'll give it a shot when (read: if) my van returns to the road and let you know how it goes.

You're using one of my old table files. The table labelled "RetardFromRPM?" is actually a fuel table. I've updated the files on D-Cal - you should at least get the newer table files. I've made many updates over the past few months...

[Una]

Rob rulez, when I grow up, I want to be like Rob.