Fuel trims are not correct?

2004 FORD EXPLORER

225,000 MILES • 4.0L • V6 • 4WD • AUTOMATIC

RUNOXX

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So, my fuel trims are all messed up, I attached a picture showing what they are at idle, this is warmed up. They do go down to 8-14 while under load but the second the vehicle stops, they skyrocket to about 24 on both banks. The short-term trims are usually close to 0. The truck also constantly hard starts, will usually start up first try in the morning though.

I’ve cleaned the EGR valve, throttle body, and MAF sensor. I do have a P0405 code for EGR sensor circuit A low. MAF sensor reads normal so it’s not that. I installed new intake manifold gaskets not too long ago; I just replaced the fuel filter as well. I’ve also run plenty of injector cleaners over time as I’ve had this issue for like a year. My fuel rail pressure also sits at 39-4 PSI at idle. Any help is appreciated greatly!

Image (Click to enlarge)

Oct 20, 2023 at 6:55 PM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

Hi,

It appears to be adding fuel to compensate for a vacuum leak or there could even be an exhaust leak pre-cat. It could also be a non-functioning EGR system.

However, the EGR code has me interested. Have you done anything other than clean the EGR? Have you done any diagnostics related to the P0405? I ask because before I send diagnostics, I want to be sure. There are pages of them. LOL

Also, did you do anything with the EGR position sensor? I ask because the code is related to the EGR sensor A circuit (low voltage). This could be causing the issues because the PCM uses the EGR position sensor signals to control and adjust the operation of the EGR valve.

Let me know

Joe

See pic below.

Image (Click to enlarge)

Oct 20, 2023 at 10:38 PM

RUNOXX

MEMBER
12 POSTS

So, I do have a very small exhaust leak, not enough to cause the LTFT to be 24 on both banks though, I believe it’s a small leak on the driver's side manifold at the flange gasket. As for the P0405 the only thing I have done is cleaned the EGR, I was thinking about picking one up and trying to see if that will help any.

Oct 21, 2023 at 9:17 AM

JACOBANDNICKOLAS

CERTIFIED EXPERT
110,175 POSTS

Hi,

Anytime there is unmetered air entering the system pre-cat, it causes the oxygen sensor to think there is a lean mixture which results in the PCM adding fuel. I don't know how bad the exhaust leak is, but anything is possible.

As far as the code is concerned, I attached diagnostics below. Take a look through them and let me know if you are comfortable performing them.

Take care,

Joe

See pics below.

Images (Click to enlarge)

Oct 21, 2023 at 7:49 PM