Hi, I’m looking for some help diagnosing a fuel trim issue on my ’06 Charger R/T with a 5.7L Hemi… apologies for all the words.

I have only had the car for 3 weeks; bought it from a friend. It’s been off the road for 8 years and I just finished getting it back together. I’ve since put about 3000 miles on it.

First thing I noticed was my fuel economy being very crap, no matter how gently I drove it.

Then one day while pulling out of gas pumps, the CEL came on for both left and right bank being lean. (P0171 / P0174 if memory is correct). Clearing the code, I could drive for 2 hours to a day without it coming on, but it would only come on at idle or near idle conditions. I was on a road trip, so I was on the road 8 hours a day, and reset the codes whenever it lit up. It always came on with the engine warmed up, and just barely rolling, or idling at a light.

First thing I tried when I got home was cutting out the stock muffler, in case it was full of critters from sitting off the car for 10 years. It was clean. Oh no… now I have to install a mid muffler delete kit! 😃

Sitting on the lift running with straight pipes, at idle my STFT ranges from -7 to 3%, which seems to be okay, but my LTFT is at 33% on each side.

Next I held the engine at 2500 rpm, and now the STFT is up to 33%, and the LTFT drops to 0%. To be honest, I don’t really understand what this means, or why that would happen.

Now that I can hear the engine better, I noticed if I hold the gas pedal down every so slightly, the car almost stalls, and then catches itself, the throttle response seems a bit sluggish with no load. I did some WOT pulls and found it seems to hit a wall around 5k rpm, and then holds it for a second, and then hits the next gear. This typically only happens when it drops to second gear, but then it’s a rough shift to 3rd. This doesn’t happen in auto-stick.

My plan of attic is to first swap the MAP and air charge sensor, going to the scrap yard today to pull some sensors, just for testing purposes. I understand the MAP sensor is used to control shifts, so it’s a good place to start.

I am also going to rent a tool to test the fuel pressure (just installed new pump and sending unit on both sides), and maybe test exhaust pressure. Though I figured if it was fuel pressure related it would impact me more at higher loads. I’ll hopefully be able to measure backpressure, but that cats have been on the car, so it’s very unlikely any critters got in there, and no physical damage.

Overall, the car runs, drives and starts just fine. If it wasn’t for the fuel mileage being so bad, and the CEL coming on, I would not have checked the fuel trim or suspected anything wrong. I also never drove the car prior to getting it, so I don’t know what the power/shifts, etc should feel like. Driving around in granny mode, there is nothing suspect.

I’d appreciate any help with this. I am in into older cars, so diagnosing these OBDII systems is not my area of expertise.

Thanks, and will keep y'all posted with any successes... or otherwise

 

If that is plus 33% on the long term fuel trim, that's bad. Does the engine smell rich? (it should) I would be tempted to just replace the front O2 sensors... (ntk or denso please, skip bosch, Dodge doesn't like 'em.)

 

Thanks for the reply. It does not smell rich at all, in fact based on my testing last night I'd day it's definitely still lean!​
Last night I went to the scrap yard and pulled a MAP sensor; the results were the same.Next I disconnected the fuel line at the tank, and did a pressure test, which revealed that I’m only getting 28psi at the pump, half of spec. The pump (left side) and the fuel pressure regulator (on the right side of tank) was replaced with new.

I also noticed when I pulled the relay to depressurize the lines that the relay was very warm. Likely a ton of amps going through the pump.

My question now is: is the pump defective, or is the fuel pressure regulator unable to allow sufficient pressure? I wasn’t sure if the pump could be working overtime to push fuel through a faulty regulator. Just trying to rule things out before purchasing another new pump.

Lastly, I read one comments somewhere online that says you need to have a matched pump and regulator. This doesn’t make sense to me, as lots of people will replace just the pump. But it did raise a flag for me, as I know the brands are not the same between the two. Would be nice to validate if this is true.

Thanks for any advice.

 

Doesn't the regulator come as part of the pump module?? If pressure is low, time for a new one.

 

​​​​​​​My understanding is that the fuel pressure regulator is in the right side tank module, and the pump is on the left side. I did replace both previously. I ordered a new pump, so I should know by the end of the weekend if I am on track.

​​​​​​​Given that hot relay I have a feeling the pump itself is defective.