Specific DFCO for rock crawler

I am running a SBC 305 with a 4l60 which is manually controlled for now because the wiring was converted for carb use. I am in the process of getting the 7747 programmed with the help of Dave W (bin is set as manual trans). The engine/trans are in a Toyota FJ40 which is mainly used as a wheeler. I only drive on the street to get to and from off-road parks.

One of the things that many auto's lack is decent engine braking. With my previous Q-jet and the low first gear in the 4l60 I actually had decent engine braking. Not great, but not terrible. At least until I moved up to 36" tires. Not so good now. My axle gears are kind of tall (4.10's running 36" tires) which hurts in this department. I will be performing a gear swap (4.88's) in a couple years when I can afford it and that will help a bit.

Anyway, the purpose of this post is to learn more about getting better engine braking in first and second gear for those long downhill trails. I want to get my head around the needed changes to improve this when the time comes to mod the bin for it and not to make the vehicle undriveable on the street.

I am thinking that I need to change the following 3 tables.
DFCO - Enter ~ Exit RPM
DFCO - Enter ~ Exit MPH
DFCO - Enter ~ Exit MAP

I run about 45 KPa at idle in gear not moving. In 4-low and second gear I think 3,000 RPM might get me to 20MPH if that, but i haven't driven off-road in months so I don't recall exactly. When I enter a steep decline I am usually moving at a crawl with no throttle rather than slowing down from high speed.

What might be good settings for DFCO using the above info?

DFCO - Enter ~ Exit RPM
current enter: 1450, exit: 1200
proposed enter: 2000, exit: 950 (I'm not so sure of these values. I don't want to drop out if the RPM climbs over 2k on a steep hill)

DFCO - Enter ~ Exit MPH
current enter: 25, exit: 20
proposed enter: 20, exit: 1

DFCO - Enter ~ Exit MAP
current enter: 20.63, exit: 31.88
proposed enter: 30, exit: 40

I don't know if the above values make sense for DFCO or not so please post away :)


Thanks,

Steve

man, i wouldn't exit that low in rpm, totally unnecessary and pushes you into stall and rough running territory. that's a very dramatic change.

dont worry about it dropping out of engine braking as rpm climbs, it should keep in DFCO damn near until redline as long as it keeps pulling a bunch of vacuum.

the best thing to do would be to run a detailed datalog in the situations you feel engine braking should be active, pinpoint those areas in the log, and adjust accordingly, while at the same time making sure ordinary driving doesnt cross those thresholds...

my first guess, though, is to let it enter above 2mph and exit at 1mph, something like that, and just use map/rpm to keep it out of stumbly range. that way you can do really slow engine braking.

Agree with the too low rpm exit. During DFCO all fuel in the manifold is removed. The ECM should begin applying fuel before you need it in order to allow the cylinders to start firing again. Also look for timer value that counts down to DFCO after other conditions are met. They are generally set fairly high.

As a general note, 4L60's don't have decent engine braking in D because the trans is designed to coast when the throttle is released. You need (and are most likely using) a manual range lower than D for braking. Years ago I installed calibrations into 7747 / 4L60E vehicles that would cut fuel over a certain speed as a governor. The engines were stalling if the vehicle coasted down a long hill in D because the TCC the trans overrun clutches disconnect the wheels from the engine. The calibrations needed to be altered so they would pulse some fuel during a long period in fuel cut.

Quote:

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Originally Posted by srgould41

DFCO - Enter ~ Exit MAP
current enter: 20.63, exit: 31.88
proposed enter: 30, exit: 40
...

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This alone would never exit? Unless your engine idles above 40 kpa? The way these Enter and Exits work (on all that I have worked with...) are qualifiers. So all three (or more if there's a timer and probably is) is all of them have to meet Enter qualifications, then in this instance the engine has met all three and entered now you decelerate and it is decelerating and any one of the Exits are met to disable DFCO. It's kind of backwards as DFCO does not work in-between the Enter and Exit. It passes the Enter to meet qualifier and then passes it again until it meets the Exit dis-qualifier...

I am not concerned with engine braking in D, only 1st and 2nd at very low speeds.

Quote:

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Originally Posted by 1project2many

Agree with the too low rpm exit. During DFCO all fuel in the manifold is removed. The ECM should begin applying fuel before you need it in order to allow the cylinders to start firing again. Also look for timer value that counts down to DFCO after other conditions are met. They are generally set fairly high.

As a general note, 4L60's don't have decent engine braking in D because the trans is designed to coast when the throttle is released. You need (and are most likely using) a manual range lower than D for braking. Years ago I installed calibrations into 7747 / 4L60E vehicles that would cut fuel over a certain speed as a governor. The engines were stalling if the vehicle coasted down a long hill in D because the TCC the trans overrun clutches disconnect the wheels from the engine. The calibrations needed to be altered so they would pulse some fuel during a long period in fuel cut.

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Hmm, I am going to have to ponder what this means.

My idle is normally 45 to 50 KPa (has a mild cam).

This information is the whole point of this post. I am trying to describe what I want to accomplish and get advice on making it work as well as understand HOW it works :)

Keep the suggestions coming.

Thanks,

Steve

Quote:

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Originally Posted by EagleMark

This alone would never exit? Unless your engine idles above 40 kpa? The way these Enter and Exits work (on all that I have worked with...) are qualifiers. So all three (or more if there's a timer and probably is) is all of them have to meet Enter qualifications, then in this instance the engine has met all three and entered now you decelerate and it is decelerating and any one of the Exits are met to disable DFCO. It's kind of backwards as DFCO does not work in-between the Enter and Exit. It passes the Enter to meet qualifier and then passes it again until it meets the Exit dis-qualifier...

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you will gain a lot of engine braking just via lowering the ve table in low vacuam areas. DFCO is like the last resort engine braking scheme of the ecu.

Now that my tune is in the final stages I want to come back to engine braking.

Delcowizzid, you are recommending leaning out the 20 and 30 map columns in the VE table?

Reading different posts and descriptions of DFCO indicates that it completely cuts off fuel. The ultimate lean condition. However, with no fuel means no burned pistons. I like that idea rather than going truly lean.

Logging the area where I want engine braking is a bit tough because I would be off road in the mud and dirt. My laptop would not survive it.

I have plenty of logs of downhill coasting in 2nd gear. The area I like to drive for testing has a good 25mph hill to descend. This doesn't match my off-road needs though. Off-road I would be starting from 0mph at the top of a hill then the speed and rpm's would climb as I am heading down the trail.

It would look something like this

Idle MAP 45 ---> dropping to mid 30's
0MPH ---> rising up
700RPM ---> rising up
TPS 0%

I'm not sure DFCO can help with any of this. What would be really cool was a hack that would enable DFCO while a momentary switch was held down supplying 12 volts to a computer input. Or maybe interrupt power to the fuel injectors. That would mimic DFCO, yes? Not sure how much trouble to the engine that would cause.

Quote:

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Originally Posted by delcowizzid

you will gain a lot of engine braking just via lowering the ve table in low vacuum areas. DFCO is like the last resort engine braking scheme of the ecu.

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