Help with a random misfires problem P0300, P0303, P0304, P0316

[sevans17]

Smart ford owners, tinkers and mechanics;

Looking for assistance, help and advice! We have a 2004 Ford Explorer 4.0L SOHC v6 with about 71k miles on it and misfire problem that I haven't been able to get to the bottom of yet. I have a scanner with live data capabilities if there are other things I should check with that hopefully pinpoint the problem so I can fix it. Here's what I know and the things I've tried / changed so far.

Symptoms:

• Random misfires
  • often shortly after startup
  • regularly inducible between 43 - 48 MPH with RPMs in the 1200 - 2500 range.
  • other more random / inconsistent times
• Occasionally slow to respond to accelerator being pressed

The only diagnostic codes it gives are P0300, P0303, P0304, P0316

Parts replaced so far:

• Spark Plugs of cylinder 3 and cylinder 4
• Ignition Coil Pack

Diagnostic attempts:

• Check diagnostic codes and read about each
• Visual inspection of hoses, air box etc no signs of splits, cracks, holes etc
• Visual inspection of spark plug wires / boots
• Mist spark plug wires / boots with water looking for indicators of damage / short

 

[mostly_broncos]

If you have live data graph the short term fuel trims , try pulling a vacuum line off while watching the graph , if you can see fuel pressure on a 2004 graph that , look at the upstream O2 sensor graphs , look at values of stuff like IAT or ECT and do the numbers agree with your environment?

Like is air temp 150 degrees or 32 degrees when its 70 out ? Is the coolant temp starting low and going up to whatever thermostat temp you have installed.

Play around with the scanner and get a feel for it and you will get ideas

In other words you could have sensors that are not off enough to throw a code but aren't right either. If the PCM thinks hot air is coming in but it isn't it will make adjustments that go in the wrong direction .

If you have a vacuum pump you can test some sensors , use it to open your egr valve at idle and you can hear the motor react and see fuel trim numbers move , maybe its even stuck open?

Once you get scanning you will want to try out things to see how it reacts

 

[sevans17]

If you have live data graph the short term fuel trims , try pulling a vacuum line off while watching the graph , if you can see fuel pressure on a 2004 graph that , look at the upstream O2 sensor graphs , look at values of stuff like IAT or ECT and do the numbers agree with your environment?

Like is air temp 150 degrees or 32 degrees when its 70 out ? Is the coolant temp starting low and going up to whatever thermostat temp you have installed.

Play around with the scanner and get a feel for it and you will get ideas

In other words you could have sensors that are not off enough to throw a code but aren't right either. If the PCM thinks hot air is coming in but it isn't it will make adjustments that go in the wrong direction .

If you have a vacuum pump you can test some sensors , use it to open your egr valve at idle and you can hear the motor react and see fuel trim numbers move , maybe its even stuck open?

Once you get scanning you will want to try out things to see how it reacts

Thank you for the detailed ideas! Certainly got me thinking about more things I can look with the live data.

I'm wondering if the IAT could be on the fritz a bit. After running the car for about 10 minutes while scrolling through live data. The IAT was showing a temp of 42ºC while the ambient air temperature was showing 21ºC which was almost exactly accurate with the conditions today.

Short term fuel trims appear fairly normal both banks fluctuating basically in unison between -3.5 and +4 for that 10ish minute period I watched. Long term fuel trims have a little more variation with bank 1 reading 8.6 and bank 2 reading 10.2

Looked at the O2 sensor data too but have not evaluated that yet.

 

[mostly_broncos]

if you are more accustomed to imperial measurement see if you can change the units your scanner uses.

 

[sevans17]

if you are more accustomed to imperial measurement see if you can change the units your scanner uses.

Yes I'm more accustom with Imperial units, I'll try and make that change. But is my thought process correct that the IAT temp and the ambient air temp should be almost the same if the IAT sensor is working correctly?

 

[ptf18]

sevens17. What scanner system are you using?

 

[sevans17]

sevens17. What scanner system are you using?

A Foxwell NT301 like this:

https://www.amazon.com/dp/B00UJV3E12/ref=cm_sw_r_cp_api_i_BuOBDbSFE7QPN