03 Mountaineer running rich only at idle, any throttle and it gets to almost 0

[edcantu9]

I am running at -13 to -15 LTFT only idle, when I hit the gas at all it evens out to nearly 0 on both LT and STFT.

I have diagnostic equipment. IAT, ECT sensor, throttle sensor, maf sensor all check out. No misfires occurring.

fuel pressure okay, the regulator checks out.

No leaks occurring.

o2 sensors oscillating appropriately.

fuel pressure holds steady at 60 psi, so no injector or pump problems.

throttle is clean.

Any tips? I don't like throwing parts at cars. I like to make a definite diagnosis before purchasing parts, but every part checks out that is always mentioned on this forum.

 

[Number4]

Not sure if the DPFE sensor for the EGR could be an issue.

I believe they can clog over time before being plugged completely or throwing a code. But can still effect fuel trims.

 

[edcantu9]

I

Not sure if the DPFE sensor for the EGR could be an issue.

I believe they can clog over time before being plugged completely or throwing a code. But can still effect fuel trims.

I will hook it up the scanner and checks if there is variance in the DPFE sensor voltages. Thank you for at least a path to follow.

 

[Number4]

Mine went bad on my ‘04, but it’s integrated to the EGR. No codes at all but horrible fuel trims for a year. Finally it threw a code, replaced it, fuel trims went to normal.

As parts go, it’s an easy and cheap part to throw.

 

[edcantu9]

Mine went bad on my ‘04, but it’s integrated to the EGR. No codes at all but horrible fuel trims for a year. Finally it threw a code, replaced it, fuel trims went to normal.

As parts go, it’s an easy and cheap part to throw.

what were your fuel trims like?

 

[Number4]

-10 to +10 at times


Edit: I wold add that the fuel trims on mine were ~normal while driving. Mainly bad at idle. Though they became constant over time.

 

[lincolnshibuya]

could be more gas/fuel and/or less air coming in..

so check for leaking injectors, thermostat (not sure about this since you say fuel trims go to normal when at throttle), clog in air intake (dirty MAF and/or air filter), clogged exhaust (will cause intake air to be clogged too)

what's your Long term fuel trim and Short term fuel trim when at idle and at 2.5-3k rpm ?

 

[edcantu9]

could be more gas/fuel and/or less air coming in..

so check for leaking injectors, thermostat (not sure about this since you say fuel trims go to normal when at throttle), clog in air intake (dirty MAF and/or air filter), clogged exhaust (will cause intake air to be clogged too)

what's your Long term fuel trim and Short term fuel trim when at idle and at 2.5-3k rpm ?

At idle it is close to 0 on both +-4.

 

[lincolnshibuya]

what's "I am running at -13 to -15 only idle" ?

so LTFT is 0 and STFT is +- 4? getting confused with the numbers.. if this is your current number then nothing to worry about, it's normal wear on the parts..

it if goes beyond the acceptable range it will trigger a code and possibly a misfire, that's the time you have to worry and replace parts but you could still improve your fuel trims by just replacing all the related parts (pre-cat O2 sensors, injectors and seals, ignition coils, spark plugs, air intake, MAF, throttle body..) some can be cleaned and some needs replaced ( sort of a tune-up)

 

[MrPulldown]

I had a similar problem on another car. Rich idle, but as soon as it was off idle it ran perfect. Failed smog cause of it.

Turns out my car had a bad coolant temp sensor. Not bad enough that it would fault, but back enough that it thought the car was cold. Thus it kept it in cold start enrichment cycle. I guess it only does this for idle RPMS. I swapped out the coolant temp sensor and everything was fixed. I did not test the sensor first. I could have removed the sensor, place it in boiling water and checked the resistance. Looked up the value of the resistance of a properly functioning sensor at boiling and compared. But I knew that these sensors were known to go bad and they were relatively cheap.

 

[edcantu9]

I had a similar problem on another car. Rich idle, but as soon as it was off idle it ran perfect. Failed smog cause of it.

Turns out my car had a bad coolant temp sensor. Not bad enough that it would fault, but back enough that it thought the car was cold. Thus it kept it in cold start enrichment cycle. I guess it only does this for idle RPMS. I swapped out the coolant temp sensor and everything was fixed. I did not test the sensor first. I could have removed the sensor, place it in boiling water and checked the resistance. Looked up the value of the resistance of a properly functioning sensor at boiling and compared. But I knew that these sensors were known to go bad and they were relatively cheap.

The ECT is the popular answer around here. I used a scanner to check the data presented by the ect. Unfortunately its shows when it is cold and when its gets up in temperature.