Still have a lean condition, and the long term fuel trim is at 18 to 20 while short term is at 0. Will be replacing the up front o2 sensor this week. But can somone help me understand what would cause such a big difference in the fuel trim? Is the o2 sensors used in this setting?

 

determine if you actually have a lean condition.. it may be an exhaust leak at the collector or unwind.. do you have headers

Next, check your fuel pressure.. pressure is crucial to delivering fuel..

Have you got a hard code for lean conditions?

 

Doing this from phone.. sorry for crazy word exchanges... Upwind, not unwind..

 

Yep. Long term is what the PCM has learned over time. Various factors influence it, fuel pressure being one. Also, the 'trim' is the difference between what the tables say, and what the O2 sensor tells the PCM is needed (plus or minus) to maintain ideal mixture. Short term comes into play if you are changing elevations, or radical temp differences. (like driving thru a mass of cooler air.) This is ALL the O2 sensors doing. When you replace the sensor, make sure you disconnect the battery while you are at it, so the PCM 'forgets' all the pre-learned data, and starts fresh.

 

The computer is not throwing up a lean condition, but you can see it on a snap on scanner. So if I understand correctly, if the upstream o2 sensor is sending the in- correct info to the computer and the computer thinks the truck is running lean, then it is dumping more fuel to compensate, which affects the long term fuel trim, causing it to be high? The fuel pump is putting out right at 49 psi. I stated 45 psi in another thread, which was wrong. I also did not replace the intake manifold bolts when I put the intake back on, which I guess I'll be pulling it back off and replacing gaskets and bolts. Why does dodge say you can re-use them? Frustrating. And thanks guys for your help.

 

There is a bit of debate on whether you can re-use them or not. Hughes says you can, everywhere else I read says TTY bolts are single use items...... I don't know which way to go on that, replacement is cheap, and good insurance.

If the scanner says its running lean, PCM will indeed richen the mixture. If the O2 STILL sees a lean condition, and the PCM can't compensate further, it will set a code. If the engine actually IS running lean, then you either have another failed sensor somewhere, or, a serious vacuum leak.