Long Term Fuel Trim - Rich

[2003XLTSpencer]

2003 XLT 4.6. Hello all, I just analyzed my LTFT's with a OBD II scanner and Bank 2 at idle is reading 6% and increases to 12% at approx 3000 RPM, while Bank 1 reads 3% at idle and increases to 7% at approx. 3000 RPM. The car is running rich. There are no DTC codes. My gas mileage is poor. Its my understanding that these percentages should rage from -3% to 3%. In addition, I've got some spark knock on acceleration. I just replaced 2 bad coils that were identified by DTC codes. Any suggestions as to why this is occurring?

 

[Skauber]

According to Ford specs, anything within +20 and -20 is "normal" and will not set a DTC. I myself like to see these within +10 and -10, so I think yours aren't that out of wack.. You might want to clean the MAF and check air filter, just to see if you can help it along a little..

 

[2003XLTSpencer]

thanks for your prompt reply. I cleaned the MAF 2 weeks ago. I understand that the LTFT's are within spec., however, shouldn't there be fluctuation between negative and positive values to average the fuel compensation as close to zero?

 

[Spades]

Actually a + value is trying to "add" fuel, meaning it is lean.... probably due to a vacuum leak

 

[Skauber]

The short term trims should fluctuate positive/negative, but the long terms should adapt to the current conditions, which includes engine condition, atmospheric conditions and so on, and they will be more steady.

 

[jacks3am]

Ide start with some maintenance items like plugs and an air filter and a fuel filter. Check the vacuum hoses around rear of the intake. They commonly break and are easily replaceable with common rubber fuel hose. Also a suggestion on coils, you can get a new set of 8 for 80 off of amazon, a lot cheaper than 100 for two!

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