0171 and 0174 Help

[Berky]

I have these codes. So far I've replaced the Fuel filter, plugs and wires. Cleaned the MAF. I've been reading different threads looking for tips. Some say these 2 codes are more than likely MAF. I have 134,000 miles so maybe just cleaning the MAF is not enough.
What should I do next,( BTW, the Explorer runs great!)

Buy a new MAF?
Replace EGR?
Replace intake Gaskets?
??

Thanks!

 

[2000StreetRod]

MAF testing

Thanks for starting your own thread. You haven't identified which engine - 4.0L or 4.6L. If the 4.0L here's a link to my thread about testing the MAF sensor: MAF Sensor Test Procedure . However, I don't know if your 2004 sensor is the same as my stock 2000 sensor. According to the 2004 V6 wiring diagram the MAF sensor out is the Lt Blue/Red wire and the signal return is the Gray/Red wire.

Edit: I just checked Rock Auto and the MAF sensor for your 2004 V6 is significantly different from my 2000 V6 so the voltages you read will be different than those I posted. However, the voltage should increase as the engine speed increases.

 

[Berky]

Sorry!

2004 4.0

 

[Berky]

Do you think if its running and idles good, the MAF should be ok?

Seem's I read a lot about EGR valves being the culprit.

BTW, thanks for clarifying the wiring and RPM's.

 

[2000StreetRod]

common to both banks

If both lean codes were generated at the same time then the source must be something that is common to both banks: fuel pressure, vacuum leak, MAF sensor, engine coolant temperature sensor, etc. Do you have an inexpensive code reader that can clear the codes? Clearing codes by disconnecting the battery also clears the fuel trims. If you have a code reader then I suggest trying to determine when the codes are generated - warm start, cold start, idle or cruise.

From the posts I've read on the forum for the 2004 model the fuel pressure sensor seems to be less reliable than the MAF sensor or engine coolant temperature sensor. However, many times an associated diagnostic trouble code is generated by the PCM when the fuel pressure sensor output is unrealistic. Unfortunately, when Ford installed the fuel pressure sensor the Schrader valve was deleted from the fuel rail so there is no easy way to independently measure the fuel pressure.

 

[Berky]

Clearing codes by disconnecting the battery also clears the fuel trims. If you have a code reader then I suggest trying to determine when the codes are generated - warm start, cold start, idle or cruise.

Is there a negative side to disconnecting the battery? and clearing the fuel trims? (Not that I know what fuel trims even are. )

So, the code reader, are you saying it also will determine "when" it is generated?

Which code reader is the best bang for the buck without buying junk?

 

[2000StreetRod]

clearing the fuel trims

The PCM uses the output of the O2 sensors to determine if the air/fuel ratio (AFR) is rich or lean. The PCM corrects the AFR by adjusting the long and short term fuel trims allowing an aging engine to meet emission requirements. When the trims exceed predetermined limits the PCM sets a diagnostic trouble code (DTC). When the DTCs are cleared by disconnecting/reconnecting the battery all of the "learned" adjustments are lost and the vehicle engine and transmission may perform differently until the adjustments are relearned. However, it may be possible to determine if the lean codes are being generated at cold start or warm start by disconnecting/reconnecting the battery. You could try clearing the codes after the engine has set overnight and then start the engine and just let it idle to see if the code is generated. If so, then let the engine warm up, clear the code and try again. Years ago I experimented with long term fuel trims at idle and I think I found that the PCM will not adjust them when the engine is idling. So you may have to alter the process. The PCM determines idle by the output voltage of the TPS when the ignition is switched from Off to Run. It "remembers" the value and periodically checks for a lower value. You may have to hold the accelerator down slightly after turning on the ignition key and then starting the engine to allow the PCM to adjust the fuel trims. When the Check Engine light illuminates you can assume the lean code is being set and confirm that with a code reader. Obviously, you can't disconnect/reconnect the battery while cruising on the highway so having a code reader allows you to clear the fault and see if it returns while cruising.

I purchased my inexpensive code reader about 5 years ago from a discount auto parts store to keep in my Sport. It only reads and clears codes - nothing more. I use an SCT X3 PowerFlash for diagnosing engine/transmission problems. Harbor Freight sells an OBDII and CAN code reader for about $50: OBD II & CAN Code Reader with Multilingual Menu I paid about $60 for my reader and it doesn't read CAN codes. AutoZone sells the same one I bought for $60 but now it reads CAN codes: Actron/PocketScan code reader

 

[Berky]

Thanks!! BTW, the Actron Pocket scanner is now on sale at Advanced Auto for $39