Hi everyone, this forum has been a big help over the years... this is the first time i've had to start a thread

96 explorer 4.0 sohc, 4x4, 200k+ miles

Trying to pass inspection, had code p0125 Insufficient Coolant Temperature For Closed Loop Fuel Control, and the temp gauge wasnt going past cold very much. So I replaced the thermostat and temp sender. Temp is now normal and no more cooling related codes BUT..

The very next start of the engine it's been running very rough, nearly stalls at idle and got the p0301 misfire cylinder 1 code I don't believe in coincidences when it comes to auto work and I have to think it's something I did in that repair.. I didn't shove a towel in the intake and I did a ton of scraping/blowing calcium off the thermostat housing... any chance I got debris in the intake???

More misc info: I've been plagued by p0171 and 174 for years, (lean mixture bank 1 and 2) is it even possible for the car to run so lean to cause misfiring?

thanks for past help, and thanks for any help this time!
randy

 

Your lean codes can be initiated by several circumstances,

• Leaky intake gaskets,
• Dirty MAF,
• Leaking intake tubing from filter to T/B,
• Leaking EGR
• Leaking vacuum hoses,
• low fuel pressure
• Leaky/bad PCV

A lean miss fire can be attributed to any of the above....... Philip

 

While it is possible for the lean codes to be related to the misfire, many of the common issues that cause a P0171 AND P0174 code would not lead to or be the result of a misfire code for an individual cylinder. If the P0301 were related to the lean codes, I'd expect it to only be the P0171 for Bank 1.

To start with, I'd suggest removing the spark plug from cylinder 1 and inspecting it. If it looks fine, swap it with another cylinder. If the misfire code remains on cylinder 1, then swap the plug wire with another one of similar length. And if the misfire code still remains P0301, then you may need to perform a cylinder leak down test or swap fuel injectors with another cylinder. Generally I'd expect an issue with the plug or wire to cause a rich condition, but swapping plugs and wires is quick (assuming you don't have a leak down tester) and there's still a good chance that the misfire code is NOT related to the lean codes.

-Rod

 

actually lean codes and misfires can be related. Lean operation causes heat build up and uneven heating. If the lean condition is caused by an intake runner leaking (common on this motor) then one cylinder can be much leaner than the others, possibly to the point of a lean misfire. But more commonly, the high heat from the lean condition can damage valves, crack spark plug insulators, etc.

But lets not assume the worst. You need to determine what is causing the misfire. The easiest tests do involve swapping plugs to see if the problem follows a cylinder or a plug. If the problem moves to a new cylinder then either the wires or the plug is causing the issue.

It is false to assume that an issue with a plug of misfire would cause a rich condition and here is why. The computer doesn't measure fuel. It only measures oxygen (thats why O2 sensors are called O2 sensors). Anything that causes fuel to not be burned properly will cause excessive oxygen too. Since a misfire is an incomplete burn, you get large amounts of unused oxygen entering the exhaust. The O2 sensors detect the excessive oxygen as a lean condition. I have seen a lot of lean codes caused by or exaggerated by misfires or partial misfires.

On my '97 4.0L Aerostar engine damage was actually caused by a lean condition. Lean burning warped the valves and caused multiple engine misfires, in my case on #1, #4, #5, and #6, with #4 and #6 being the worst. The #4 plug actually cracked from overheating. So lean codes should not be ignored.

 

Was the engine swapped ? This year has an OHV ONLY! I have this truck. There are two main issues on this engine.
If you are planning on keeping it I would swap both LOWER AND UPPER intake manifold gaskets. The lowers will eventually leak coolant. That will solve any air leaks too.

The second is carbon buildup, that you will see when you take off the intake.

Third issue could simply be a dirty maf. Clean it and see if the codes go away. Do that first.

LIke others suggested there could be ignition issues like coils, plugs, wires etc on that cyl.