nose vs computer
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Most common on the 5.4's is the PCV elbow at the back of the throttle body, but it could be anywhere.
The problem with hunting with propane is the computer adjusts the mixture so fast it may be hard to pick up on the rpm change. You should probably be watching live data on a scanner while spraying the propane.
It could be losing vac to the heater system. With the heat blowing to the floor does it switch to the defroster when you accelerate? Just a thought.
Also take a good look at the hard vac lines that run behind the battery. Then check the vac reservoir, the black ball looking thing by the battery.
Plus you didn't say if you have an exhaust leak.
If you type 171/174 for the keyword in the search box you will get a ton of hits, and your solution will probably be there.
Good luck and don't forget to post what the fix is once you nail it down.
The problem with hunting with propane is the computer adjusts the mixture so fast it may be hard to pick up on the rpm change. You should probably be watching live data on a scanner while spraying the propane.
It could be losing vac to the heater system. With the heat blowing to the floor does it switch to the defroster when you accelerate? Just a thought.
Also take a good look at the hard vac lines that run behind the battery. Then check the vac reservoir, the black ball looking thing by the battery.
Plus you didn't say if you have an exhaust leak.
If you type 171/174 for the keyword in the search box you will get a ton of hits, and your solution will probably be there.
Good luck and don't forget to post what the fix is once you nail it down.
#7
Join Date: Oct 2002
Location: St. Louis (Out in the woods)
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You should probably be watching live data on a scanner while spraying the propane.
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#11
My thoughts also
I agree it sure looks like it (if it looks like a duck). However all soft hoses have been replaced and hard hoses (and vac tank) checked with a vac pump.
What kind of vacuum leak only shows itself in cold weather?
What kind of vacuum leak only shows itself in cold weather?
Vacuum leak.
The computer, when it tried to enter closed loop operation, was adjusting the fuel trim to try to get the sensors to start switching. When they reach the limit of enrichment without positive result, the computer essentially gives up trying and declares a fault.
The computer, when it tried to enter closed loop operation, was adjusting the fuel trim to try to get the sensors to start switching. When they reach the limit of enrichment without positive result, the computer essentially gives up trying and declares a fault.
#13
I'm not sure a scanner would help me track changes that well, when it does it the idle cycles from 1200 to nearly stalling every 1 to 2 seconds
#15
When you don't find something on Google, you don't assume it's not there, you rephrase your search. This post was my attempt to understand the subsystems of fuel control to aid me in the larger quest of why the truck idles rough.
You also suggested paying someone to work on it. The top three local shops and the only dealer that is not a 4 hour drive away tried and failed. I have been chasing this cold weather only issue for 5 years now.
So to all of you responding to my post, I am sorry if you feel your time wasted. This far into the project I am trying to be creative in research and diagnostic. My thought is that if I can not see directly what it is, the only course is elimination of what it is not. Thank you all for the posts, every bit does help.