LTFT anxiety

[Merkava_4]

Originally Posted By: Colt45ws
I imagine it will richen the mixture so the PCM will pull fuel trim down.


Does that mean the numbers go negative when the propane gets in there ?

 

[Colt45ws]

If it was for example, +10, it will drop.
Lets say it drops -5. The new STFT will be +5 after. Or whatever.

 

[Merkava_4]

So the what you're seeing on the screen in terms of fuel trim numbers is the effects AFTER the computer has made its decision ? If STFT goes +19, does that mean the computer thinks the engine is experiencing a lean condition ?

 

[Colt45ws]

Yes. Its telling you its having to add +19% fuel over what the preprogrammed fuel table has in order to make the O2 sensors come out correct.

 

[Trav]

I use one of these if a smoke machine isn't handy (the correct tool for the job), the long hose allows you get the nozzle in tight spots and you can lock the trigger. I open the valve fully.
Its not the best way but it works, the auto ignition point of propane is 842f and it doesn't pool like carb cleaner so its relatively safe. The biggest drawback is it has to be a calm day without wind and cars with belt driven fans, both render it pretty much useless.
A smoke machine doesn't need the engine running but they are a bit pricey for a decent one.

http://www.zoro.com/bernzomatic-hose-tor...mp;gclsrc=aw.ds

 

[Scott_Tucker]

If there are no symptoms and no check engine light, what are you even trying to fix?

 

[circuitsmith]

Update:
I never found anything definitive; decided to let it go since there's no CEL.
I have a bi-yearly emissions test coming up so I took another look at the data to make sure nothing's marginal.
Now at idle LTFT settles at +4 and STFT at 0.
All's well, but I'm curious why the #'s improved.
Could it be gas with varying ethanol content?
I don't buy any particular brand.