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Wayne Woodward
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Trying this out.

Hello Scotty,

First, thank you for this wonderful service you provide the world.  It is a blessing to have someone to ask complicated car questions.  My wife and I love your videos!

My problem vehicle is a 2007 Jeep Commander 4.7 SFI (Non Flex Fuel) w/120k mi.  I was getting some codes (P0300,P0204) that led me to replace the TPS, IAC, and EGR.  The TPS is a problem on this model engine.  I had an intake backfire occurring, so I replaced the aftermarket spark plugs with the manufacturer recommended plug (Alldata says manufacturer requires factory plugs due to the chance of pre-ignition).  I checked pressure at the fuel rail which was right at 60PSI.  I checked cylinder pressures, the highest at 185PSI, the lowest at 160PSI.  Alldata says these are in spec (<25%).  I drove it and it drove smooth.  I checked fuel trims.  At 1500 & 2500, LTFT is close to 0.  At idle, LTFT was showing 9.6 for bank 1, which seemed high.  A little less for bank 2.  I probably need to get some more warmups before those are more accurate?

At idle, I noticed 2 intake backfires in about 2 minutes of idling.  I did not test the injectors (I don't have a noid set), so I don't know if I have a lean condition causing an intake backfire.  No codes set yet.  I probably need to get that nifty probe you show on your test injector video.  Another mechanic stated that the heads were shot and a valve was intermittently sticking due to carbon, causing the backfire.  His recommendation was to do a head job for $4,500 or a new long block for $7,900.  I thought it would throw a more cylinder specific code if that was the case.  I was thinking I have some sort of pre-ignition/lean situation.  I have filled the tank and added a bottle of Techron cleaner, hoping that will clean the injectors.  I figured if the  '#4 injector was bad, it would rethrow the code. 

Just thinking while I am typing, I run straight 87 and the trouble typically happens when it is hot, like now.  I wonder if I have an octane problem and need to move up the grade during the summer, with the summer gasoline formula and all...

Would you have any troubleshooting recommendations?

As an aside, I am borrowing my friends Innova 3160b ODB II scanner.  Would you have a recommendation for a scanner for domestic vehicles, that can also command the PCM for testing, like raising idle rpm, etc, and has the ABS & SRS modules like the 3160b, but without spending a whole lot of money?

Thank you!

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