I am having trouble with the wife's 03'Expedition with the 5.4. It is idling rough, and has thrown the P0172 code. The LTFT on B1:-25.7 and the LTFT on B2:18.7.
To the backyard mechanic (me) , that kind of tells me there is an issue affecting one bank causing the code that could possible affecting the other, but I don't know for sure.
It drives fine, gas usage is normal (for the 5.4L LOTS is normal!), and there are no other codes/issues.
It now has new plugs, coil packs, plug boots, injectors, and no apparent vacuum leak.

I have an identical spare parts truck that runs great, so throwing parts on it from that one if required isn't an issue, I just don't know where to start.
O2 sensors maybe?

Any ideas on this would greatly appreciated.

 

Those fuel trim reading are way out of whack. It sounds like one of the injectors on bank one might be leaking and causing a rich mixture. The ECM is compensating by leaning out the mixture, hence the -25.7 reading. You could try disconnecting the fuel injectors one at a time to see if one of them does not affect the engine.

 

Thanks alloro. The fuel trim numbers are pretty much the exact same before and after the new injectors were installed. Could it be a faulty signal to the injectors?
I will try what you proposed though, it will eliminate another possible issue.

 

Follow the hoses coming off of your PCV valve and make sure there are no leaks and look for vacuum leaks

 

I had the same problem before, pcv elbow had a hole, then I followed that hose all the way back to the throttle body and found another elbow in bad condition, secured the two hoses coming form the back of the throttle body (passenger side) to the the intake hose, replace the two little hoses (passenger side) connected to a box next to the EGR valve, replaced, plugs, boots and problem fixed.

 

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I have checked all the vacuum lines, plastic hoses, and elbows, and all is well with them. I have removed the injectors, coils, and boots from bank 1, and switched them all out with bank 2, and the fuel trim numbers stayed the same. I finally disconnected each coil and injector one at a time while the engine was running, and noticed a change in the idle "roughness" with each disconnect/reconnect.
I am really at a loss with this one. Any other ideas would be appreciated.

 

Based on what you've already eliminated, it looks like you could be down to a leaking intake manifold gasket.

 

Thanks Alloro, I appreciate the input. I think I am going to shoot some propane gas around the manifold, and see if it picks up a leak. I am pretty sure I will be pulling the intake.

 

I'm assuming that both of those fuel trims are negative, right?

I'm gonna guess it is something that is affecting both banks.

I'm don't think it is a vacuum leak, as the negative fuel trims are indicating that the fuel trim has been driven full lean, trying to compensate for a rich condiction.

I don't think it is an O2 sensor issue as the PCM frequently runs tests on the fuel control O2 sensors, checking them for switching time and cross count activity. If it finds a lazy O2 sensor it will set an O2 code.

I'd pull the MAF and check it to see if its dirty. Maybe clean it any ways.
You didn't indicate how many miles are on this rig, but I'd also check the air filter to be sure it isn't full of dirt or letting any 'stuff' get to the MAF.

If all is good with the MAF, I'd check the fuel pressure regulator to be sure the vacuum line isn't off it, which will bump up the fuel pressure. If the vacuum line is attached to the regulator, check that it isn't full of fuel from a leaking regulator diaphram.

Those are my ideas....for what they are worth.

 

Actually Jim, the LTFT on bank 2 was positive 18.7, which has me thinking it is somethng not affecting both banks the same, as bank 1 was negative.
I believe that may eliminate the MAF and fuel pressure issues. Just the same, I had cleaned the MAF earlier, and will check on the fuel regultor to be sure.
Still leaning towards intake issue as Allero mentioned.The truck has 140,000km, and is otherwise in perfect condition, which is why I really want to get this figured out. Again, I appreciate any input.

 

Okay, then I agree with alloro, also - those trims are "way out of whack".
Disregard my previous post. I think you are chasing two different issues.

Do you have an exhaust leak on the bank 2 side upstream of its O2 sensor? Or maybe a vacuum leak at one of the bank 2 injector o-rings?

Can you hear or feel if all the injectors on Bank 1 side are clicking uniformly? Or if someone has an oscilloscope where you could graph the current draw on those injectors. Since you swapped the injectors from side to side with no effect, I'm wondering if maybe you have an injector control wire that is begining to short to ground - that would hang an injector, making it slow to close ?

I'm out of ideas............................

 

No exhaust leaks. As I mentioned, I will be trying to shoot some propane gas around the manifold (and injectors) and see if it picks up a leak. Would an injector short to ground not give you a code?
Here is another thing to ponder. When at highway speeds, the fuel trims appear normal, the issue just rears its head at low speed or idle.

 

I claim bragging rights for starting that technical term.

 

At least for the lean bank, that's a sign that you have a small vacuum leak. (Think of a small pin hole - at idle, say the intake flows 10 CFM and the leak flows 1 CFM, or ~10%. At highway speeds, say the intake flows 200 CFM and that same vacuum leak will flow .5 CFM (because the vacuum in the intake is lower under load that at idle), so the leak will flow ~0.25% of the total flow. Hardly noticeable in the fuel trim.

(If the fuel trim was higher at highway speeds (i.e, the engine became more lean), that's an indication of a fuel supply problem, not necessarily a vacuum leak.)

The other thing to be aware of when you are using LTFTs, is the PCM keeps 9 fuel trim cells. Think of a 3X3 grid - the horozontal axis is the engine speed, idle, cruise, and high rpm. Along the verticle axis is the engine load, light, moderate, and heavy.

When your scan tool asks the PCM for fuel trim data, the PCM ships the trims from the cell the engine is currently operating in.

(That's why when you swapped the injectors from side to side, it would have been a good idea to clear the KAM (Keep Alive Memory) in the PCM so fuel trims would all start over from scratch. Other wise it would look like the swapped injectors didn't effect fuel trims.)

When your shooting the propane, keep an eye on the short term fuel trims as they will react much more quickly to the propane than the LTFTs.