PO175 Need some direction
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Senior Member
Joined: Dec 2010
Posts: 150
Likes: 0
From: Chandler, Tx
PO175 Need some direction
Hey guys.
It's been awhile since I've posted, trucks been doing really well. A little background. Truck is a 2002 FX4 Screw 4.6l with 265,000 miles, Gotts Mod and a K&N air filter still gets 15.5mpg on the highway and starts everyday. Got a flashing CEL a few weeks ago and replaced the COP on that cylinder, but PO175 also popped up cleared the codes and truck drove fine about 100 miles later the CEL lights back up. Go to Autozone and they tell me PO175, repair fix is to replace the air filter. Get home clean the filter and reoil it, clean the MAF and IAT at the same time, clear the codes again. 100 miles and lights up PO175. Go to the local dealer and they hook it up to their machine and do a real time scan. long term fuel trim is -20% on bank 2 and normal on bank 1. Tech clears the ECM's history and offers a few suggestions as to a fix ( run some injector cleaner for a couple tanks, check for vacuum leaks, check fuel pressure ) Did all that and still getting the code. Truck idles, drives and runs fine. Not getting any other codes.
Any suggestions
TIA
It's been awhile since I've posted, trucks been doing really well. A little background. Truck is a 2002 FX4 Screw 4.6l with 265,000 miles, Gotts Mod and a K&N air filter still gets 15.5mpg on the highway and starts everyday. Got a flashing CEL a few weeks ago and replaced the COP on that cylinder, but PO175 also popped up cleared the codes and truck drove fine about 100 miles later the CEL lights back up. Go to Autozone and they tell me PO175, repair fix is to replace the air filter. Get home clean the filter and reoil it, clean the MAF and IAT at the same time, clear the codes again. 100 miles and lights up PO175. Go to the local dealer and they hook it up to their machine and do a real time scan. long term fuel trim is -20% on bank 2 and normal on bank 1. Tech clears the ECM's history and offers a few suggestions as to a fix ( run some injector cleaner for a couple tanks, check for vacuum leaks, check fuel pressure ) Did all that and still getting the code. Truck idles, drives and runs fine. Not getting any other codes.
Any suggestions
TIA
Senior Member
Joined: May 2015
Posts: 362
Likes: 11
From: San Antonio, Tx
I concur with @glc - leaky injector.
They are kinda a pain to test or reliably check. You might be able to get an idea which one by looking for one black / sooty spark plug tip while the others appear white / chalky from running lean.
You didn't mention miles on Plugs. But it could also be intermittent misfires (NOT ENOUGH TO SET A 300 Series DTC), but enough for the ECU to attempt to compensate by decreasing fuel trim on that bank. Since injectors are hard to test, try getting an OBDII Mode $6 test done - which gives pre DTC misfire counts for each cylinder during the current drive cycle and the last ten drive cycles. That might help eliminate the second possibility and determine which direction to proceed.
If its misfires, a 'flakey' electrical connection on a COP plug, or at the ECU is a possibility. This age vehicle frequently experiences broken plastic electrical connectors and/or corroded connections. You might clean them with a good spray electrical cleaner and apply electrical dielectric grease to the rubber seals.
But I disagree about a "vacuum leak". That will drive Fuel Trims the opposite direction.
For some reason excess fuel is getting into the combustion process on Bank2 that isn't all getting burned up.
Hope this helps. Good Luck
They are kinda a pain to test or reliably check. You might be able to get an idea which one by looking for one black / sooty spark plug tip while the others appear white / chalky from running lean.
You didn't mention miles on Plugs. But it could also be intermittent misfires (NOT ENOUGH TO SET A 300 Series DTC), but enough for the ECU to attempt to compensate by decreasing fuel trim on that bank. Since injectors are hard to test, try getting an OBDII Mode $6 test done - which gives pre DTC misfire counts for each cylinder during the current drive cycle and the last ten drive cycles. That might help eliminate the second possibility and determine which direction to proceed.
If its misfires, a 'flakey' electrical connection on a COP plug, or at the ECU is a possibility. This age vehicle frequently experiences broken plastic electrical connectors and/or corroded connections. You might clean them with a good spray electrical cleaner and apply electrical dielectric grease to the rubber seals.
But I disagree about a "vacuum leak". That will drive Fuel Trims the opposite direction.
For some reason excess fuel is getting into the combustion process on Bank2 that isn't all getting burned up.
Hope this helps. Good Luck
Technical Article Contributor
Joined: Oct 2006
Posts: 1,770
Likes: 6
From: Michigan
Some very good information above. Just another idea that you may want to consider if the above actions don't work. I would remove the K&N air filter, reclean the MAF and install the factory air cleaner back on the truck...just to possibly prove something out.. I read that you cleaned the MAF and then reoiled the K&N filter... sometimes people tend to reoil using to much oil on these filters. The excess oil can migrate via the intake air stream past the MAF and contaminate the MAF which can generate false readings and give you issues. The symptoms generated by a MAF can be many and can be frustrating. Sometimes giving a code and many times not. Just a little food for thought for you.. Good luck.