obd2 code help

[90xjDave]

My 99 Expedition 5.4L has popped up with this code: P0174. The only info I can come up with is that the system is running too lean. I've changed the O2 sensors but that didn't fix it. Any idea on how to narrow down the code to find out exactly what's causing it to run lean??

thanks
Dave

 

[Matt S.]

I am pretty sure that is refering to fuel trim settings being lean. If a vehicle is lean you have to think about what CAUSES it to be lean. A/F ratio should be around 14.7:1 . Your leading cause of running lean on a EFI system is when you create a situation where you are allowing UNREGULATED air into the engine. Check all your vacuum lines first. Then check your Idle Air Control soleniod. IT controls how much air is allowed during idle and creates a cushion for when you are driving. After that, best bet is to try to get a scan tool on it and get us some numbers from your engine data! That is the best way to help find a problem.

If you cant get a scan tool, check all the Air system sensors, then move to your fuel system. I would start with checking injectors. They could be carbonized, or worn. But it is hard to just TELL you what it is without knowing what all is happening.

Matt

 

[Matt S.]

hey i was thinking about this more today, and I want to remove my previous statement!

When your fuel trim is LEAN, that is saying the computer is seeing a lean condition and trying to correct it by richening the motor. So... look for rich conditions. Sorry for the wrong info! still try to get a scanner on it though.

matt

 

[90xjDave]

the only scanner i have is the obd2 reader. I don't know if it will give me any other data than what the obd computer puts out???

If i understand you correctly though, your saying that the computer has detected a "lean" and so it's trying to enrich, or the other way around??

 

[Matt S.]

Ok... lol no wthis is confusing me.. lets see if i can get this clear now! I dont think i couldnt decide earlier.


Your engine IS running rich. So the computer says to start to run a little leaner. If it doesnt change from rich to normal conditions, then it throws a code. Which is what you have.

How many O2S you have?

Your reader... does it only give codes? or can it watch the engine data?

 

[90xjDave]

I think my reader only gives me codes, I don't think it will give me engine data.
I'm wondering if the K&N filter I put on is what's causing the problem. Although, it has been about 3 or 4 months since I put it on and the Check engine light only came up last week.

 

[90xjDave]

fixed

cracked vacuum hose at pcv valve - Go figure!!!!