I have my tow tune working pretty good. 5000k through the Rockies over 4 weeks and I only had one grade that I couldn't hold 60mph and keep the egts in check. Unfortunately I forgot my efi cable at home:( and am having trouble with the grade braking. When coming down a 6 to 7% grade, in 3rd gear at around 3500rpm, you come to the bottom and start to feed in some fuel. I get a terrible knock until the trans shifts up. I think its too much timing for the rpm and minimum fuel but am not sure. It didn't even cross my mind when I was playing with timing. When I am out of the mountains I will not use the grade brake again for a while so I can't map the condition but would still like to fix the problem when I get home. Any one else had the same problem?

knock? How so?

are you sure its not pilot injection shutting on and off?

When I begin to accelerate at the bottom of a grade I get a really bad rattle, like a fuel knock, until the trans shifts to 4th then 5th. I can't tell when the pilot inj shuts off or turns on. Before I had the injectors done I could hear the sound of the pilot turning off but not any more. With the efi, I did reduce the pilot pulse width a bit and reduced the pilot timing a little. I guess what I need to know is what part of the timing table does the ecm use when under a grade braking situation or when recovering from grade braking.

I guess what I need to know is what part of the timing table does the ecm use when under a grade braking situation or when recovering from grade braking.

If you get a log of that happening the cursor in the Tune tool will track from the data in the scantool so it should be easy enough to find.

Cheers,
Ross

if its around ~2500 rpm or 85mm3 fuel rate as shown with a scan tool, it is your pilot injection shutting off. I have my pilot injection set to never shut off. Keeps the motor quiet and I see no advantage to having it shut off. Factory has it shut off over 85mm3 for emmissions reasons IIRC.

fuel consumptions is one of the big reasons, and exhaust temps. Pilots heat up the cylinder a ton, and hurt your fuel injection.

fuel consumptions is one of the big reasons, and exhaust temps. Pilots heat up the cylinder a ton, and hurt your fuel injection.

is this true?

I was getting the knock under very little fuel but at over 3000rpm. (Bottom of a steep grade in third gear at about 55mph) Just as the grade begins to flatten out and I add throttle to shift the trans up, I get a wicked rapping. As soon as the trans shifts to 4th then 5th alls quiet. I am estimating the tps is 15 to 20% at most. When the engine is over 4000 the grade recovery is quieter. I would have loved to capture data under those conditions, it would help make a very good tow tune. I don't have anything close to those grades where I live so mapping now is impossible. On the positive side I won't be using the grade brake for a while. I've never used it stock so I don't know how it acts. I am not sure if the knock is from too much timing, too much or little fueling or a pilot inj. problem. If someone could send me a log of the above conditions it would be much appreciated.

turbo-Max it's true, I've got data to prove it. If you think about it, it's pretty simple really.

Think about when you shoot the fuel in. Normal timing is say 10-15 before, and continues well after TDC (stock injectors/timing maps). With a pilot you begin shooting say 30-40 before, but the piston is still traveling up a pretty good amount. You are not getting any work out of the pilot, merely noise, and emissions reduction. So you are wasting the fuel and since your main shot gets bumped out, your main shot is delayed, and your exhaust temps are higher.

but dangit,that's what keeps our trucks from sounding like a pile of crapola ferd. :(

that's the trade off unfortunately.

oh well,i just crank in abit more boost and temps stay way down compard to stock.