Error codes P0171, 0174, 0302. | Ford Explorer Forums

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Error codes P0171, 0174, 0302.

danfritz

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Joined
May 7, 2009
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City, State
Warsaw, IN
Year, Model & Trim Level
'98 XLT Sport 4WD 4.0L
New member, first post. I have a '98 Explorer Sport, 2 door, 4.0 liter engine, 4WD, manual transmission, 192,000 miles.

Nice chat group- very helpful with some error codes that I recently had. I can fill everyone in on what I learned w/ the error codes listed above.

P0171/P0174- left and right banks too lean:
1. Found that the hoses for my MAF were split. In the course of changing them I found that the backside and bottom of the MAF plastic body were melted. You couldn't see it when the MAF was mounted to the engine, but it was very obvious once you removed it.
2. Checked fuel pressure- $54 gage from Advance Auto. Spec is 30-45 psi; my pressure was 30 psi.
3. Changed the fuel filter and the pressure went to 32 psi. That helped a little but still got the error codes.
4. Changed the upstread O2 sensors. It's worth the time to up the car on ramps or jackstands so that you have room to work. Don't try to take the sensors off cold; you'll probably ruin the threads in the exhaust pipe. Use a torch to heat the exhaust pipe (have a bucket of water nearby). I still chewed the threads up, but was able to chase them with an M18 x 1.5 metric tap.

P0302-Misfire on cylinder #2
1. Someone on the chat group recommended swapping the #2 spark plug with the plug from a different cylinder. If the problem stays in cylinder #2, then it's probably fuel. If it moves w/ the spark plug, then it's probably the plug. I swapped #1 and #2 with the engine hot (right after I drove home from work). I found that the #2 plug was fairly cool to the touch, but that I could only hold the #1 for a couple of seconds as it was hot. Figured that meant I had a bad plug. Replaced it with a new plug and everything is fine.

Decided to change the ignition coil and plugs wires as they were 11 years old. I learned a few things, but don't want to write a book here. If anyone is interested, let me know.
 












Please post what you found...I am curious to see what you found

I have worked with a 99 Explorer Sport with a 4.0 liter OHV engine and recemtly got pending codes of bank 1 too lean and the 2 downstream o2 sensors not switching... I knew I had a fuel delivery problem but didn't know how bad until I cleaned out the gas tank...The buildup of crap inside was unbelieveable....

When I corrected that issue, the 2 pending codes have not returned in the past 3 days...I bought new o2 sensors when I bought this truck but I have pulled live data to watch them cycle as they should with the engine running so as long as they perform as designed I will hold onto the new ones...

Which engine are you working with? I did not know that Ford mounted the MAS on the engine...Mine is on the passenger side of the engine bay kinda on top of the radiator...

Since your engine has a fpr on top of the engine, what is the fuel pressure when the vacuum line is pulled from it? Was your fuel filter plugged up or restricted to flow when you removed it? You probably got the misfire fixed with the plug replacement but I would look at the entire fuel system health at this point..

One step I have been doing when I replace a fuel filter is to open the supply side to the filter and use a plaqstic bottle to catch a sample of fuel...I cycle the key 3-4 times to get about half a pint of fuel and look at it to see if there are any debris in it coming out of the pump and before hitting the filter...
 






98 Explorer w/ P0171/0174 and P0302 Errors

Thanks for the tips about checking the health of the fuel system. At 11 years and 192k miles, I'm sure it's not the best. I've had a sneaking suspicion for a while that I should replace the fuel pump, possibly the tank as well, sometime soon as I plan to drive the car as long as possible. Just been putting it off because it doesn't look like much fun. I have a '79 F-150; had to replace the fuel tank after about 12 years as it was starting to rust thru. That was back in the day when things were easier...

I have an "X" in the VIN, which means that the engine is 4.0L, EFI, OHV. The MAF is bolted to the engine on the driver's side 4-5" above the EGR valve and 2-3" in front of the top of the dipstick.

I didn't check fuel pressure w/ vacuum line removed after I changed the filter. No reason other than I didn't think about it. Forgot to mention in my first post that I changed the FPR at the same time I changed the filter.

Regarding the ignition coil/plug wire change- The biggest things I learned are: a) on the coil, terminals for cylinders 5 and 6 are flip-flopped- 6 is the center terminal, 5 is closest to the front of the car (I thought that this was a misprint in my Haynes service manual until I tried to start the car...), b) plug wire for cylinder #4 (driver side, near front of car) is longest, #6 cylinder (driver side, near firewall) is next longest, then #5 (driver side, center), all three wires on the passenger side are basically the same length.
 






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