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Engine Braking


apoc
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Hi,

Looking to increase engine braking as much as possible (or reasonable) on my BF engine in my Patrol.

From a look at the tune and a datalog, it seems to be commanding around 18-25* of timing while in decel fuel cut. From some reading, more advance seems to generally help with engine braking performance while in dfco.

auF16630 (MBT timing) is around the 40* range, auF16593 (Bldn Timing) is 50, and auF0228 (Decel spark angle) is set to 63.

Is the ignition retard coming from the CFC torque on rate (auF0149) and Torque spark retard (auF0263)? So if I increase the former to around 0.8 to test, it should pull less timing?

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In DFCO you have complete injector shutdown, as the injectors are shutdown the spark timing makes absolutely no difference to engine braking. The only way to further increase the engine braking would be to change the cam timing on decel. Eg change the commanded cam angles in the various low load (0.1 etc) cells.

On decel the spark value is 100% determined via auF0228 "Spark angle to use under deceleration conditions". This will increase engine braking before DFCO kicks in.

The other item that would assist is the dashpot airflow, you want this as low as possible to ensure the ETC is held closed for maximum vacuum,.

What is the ultimate goal you are trying to achieve with extra decel braking?

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That's what I would have thought too, but there seems to be a 'internet opinion' that the injectors still are pulsed a tiny amount. I'll have a play with the cam timing, to see what helps it a bit! Still working on the dashpot adjustment, which table should I be adjusting for it? Increase the maximum on auF0034 and auF16506 at >2000rpm?

My end goal is to maximize engine braking in low gear, as I drive it in 4wd high country vic. It runs on a bit more than I would have expected, I assume because of the lighter rotating assembly than the old motor, but also the tuned-in manners for a lighter street car. It would save my brakes a fair amount when going down kilometers of steep hills!

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The injectors are only pulsed if the deadtime is wrong. What is your AFR on decel? it should be maxed out lean. Regarding the dashpot, try setting really absurd values in there and experiment with the affect. You will probably find that gives you the most affect.

How low is the rpm you are talking? if its 1200rpm etc then DFCO won't be kicking in, in that case drop the decel timing all the way down to 0 degrees and see how it goes.

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Hmm, just checked the deadtimes, I have an FG manifold on a BA lpg motor, with BF cams and BF pcm. Looks like the BF deadtimes are still in there, am using the FG injectors. Will swap to the FG ones.

I didn't make this tune, it was done by a shop via SCT and I'm trying to make it more consistent, and run better. Only had the fuelling and idle cleaned up, and 2* of timing across the board from 0.5 load upwards (in the borderline knock table).

The dash still reads 4-5L/100km when in full decel mode, will see if the deadtimes change anything. Haven't got my wideband on at the moment as fuel trims were good to begin with, may have to add it in though. How long until your logging / scanning functions are available?

Regarding the RPM, it doesn't have to be low, can be >2000rpm if need be. What I meant is it would be in low range gear, going down a steep hill.

I appreciate the fast responses too. Cheers!

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