Altitude tuning - Diesel Truck Forum -
Thread Details Posted by killerbee, this thread has received 0 replies and been viewed 2042 times.

LinkBack Thread Tools Display Modes
post #1 of 1 (permalink) Old 04-16-2007, 06:30 PM Thread Starter
Join Date: Jul 2006
Posts: 1,239
Points: 25,155
Thanks: 0
Thanked 1 Time in 1 Post
Altitude tuning

I was doing some datalogging up at Flagstaff this weekend and I specifically wanted to track down a possible source of why some folks report bad MPG where they live up high. And I think i found something.

It is very pronounced. I will look more closely at the logs later but for now,

The rail pressure drops significantly at cruise settings. Why, from what I can tell, the PCM is commanding it per a barometric schedule. What does this mean? When rail pressure is commanded lower, this act increases pulse width, or the time duration that the injector remains open. This is very important because injection timing (which does NOT change) is suppose to align with pulse width. So if timing was optimum, and then a change occurs to increase pulse width with lower pressure, then timing is now non-optimum, in fact too retarded.

With EFI, you can eliminate the baro effect on rail pressure, but unfortunately I did not have the time, my days were full with retreat activities. But if you have EFI and would like to eliminate this, it is easy to do, and maybe you can report back the results on economy.

Timing is important, and there is a lot of room to advance it at cruise, particularly at altitude. So hopefully this nute is at least partially cracked.

Vehicle Systems Engineer/Professional Tuner
04.5 GMC 2500HD SRW LLY


killerbee is offline  
Closed Thread

Quick Reply

Register Now

In order to be able to post messages on the Diesel Truck Forum - forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome