8.1 cyl volume

[Road]

I bought a tuned ecm off the internet and the cylinder volume is reduce .0250 is there any reason why the tuner would have lowered the cylinder volume?

[C5 2000]

Will run rich that's way he did it.

[Road]

Thanks for input this tune its in 26000# motorhome I have been fighting + 10 to 15 fuel trims melted 3 sets of donut gaskets in 5000 miles after no help from the supplier of my tune I bought hp tuner and I adjusted maf 10% now running - 1 to 4 fuel trims. I adjusted cyl volume up and down did seem to make much difference I figured got to be a reason he lowered the cyl volume? Seems like a lazy way to adjust fuel mixture? May be a trick of the trade for a canned tune? Thanks for the input I just trying to understand why a experience tuner would change cylinder volume. Should I set the cylinder volume to the correct setting?

[MikeOD]

The cylinder volume constant won't change MAF fueling...it will only change speed density fueling. If he's still got speed density blending with the MAF then it may have a minor effect once in a while depending on transient conditions, but for the most part it probably won't matter.

Post up the tune file. We may have some advice for you

[Road]

Ultrapower stock tune.hptultrapower 5% torque 1.09% maf increase best tune.hptThanks the first tune is the one from the tuner the second is my revised one

[MikeOD]

There's a stock 2004 8.1 liter truck tune in the repository, that runs less spark advance...not a LOT less in the high load area, but less is less, and more is hotter exhaust. The AFR spark correction plus the main advance table is commanding 5-6 degrees higher than stock...not ideal in my opinion. It's also very hard for that engine to ever get into power enrichment (which when setup properly will cool things down)...probably because it's moving so much weight, the mileage would suffer fast. Cat Overtemp is also slowed down a lot...giving the PCM no time to save the exhaust when it starts heating up.

Go here https://www.hptuners.com/customers/tune.php? and search for 2004 and 8.1...leave all the other fields blank. Open your file as the main file, open the file I pointed you to as a comparison file. Most of what I see different in the engine portion of the tune points me to things that would make the exhaust too hot, especially when pushing 26,000 lbs of vehicle.

[Road]

Thanks should I change power enrichment back to stock too?

[mowton]

I normally use the MAP (load) to tell me when PE is needed. Lower the TPS enable to like 8-10 and MAP enable to like 80/85. Log and verify or modify TPS/MAP as required. Like Mike says, the extra fueling will help heat issues and provide much needed torque.....fuel is cheaper than a fried motor :-)

Ed M

[Road]

Thanks for the help ya'll was right you could have climbed Pikes Peak and never got it in pe mode that explains why it ran so flat. I set it to come on at 80% tps 2 sec delay and back timing down some too. Still haven't figured out why he changed the cyl volume? Thanks

[MikeOD]

Still haven't figured out why he changed the cyl volume?

Because he doesn't know what he's doing.

Did you fix cat over temp protection?

[Road]

yes and timing too thanks again