ford explorer rough start up then runs fine.

[Fordtruckman01]

Ok First off I want to say I am pretty impressed on this forum I have learned alot. I am a big reader. But I am just pretty much puzzled at this point and before I spend more money I was wondering if anyone had any pointers for me.

I have a 2001 Ford Explorer 2 door sport 4X4

The Explorer only has a bad startup when its cold. so If i do not run it for 12 hours, when I get in and turn it on it will be a bit rough, I have to keep my foot on the pedal otherwise it will stall out, after about 5-10 minutes it runs absolutely fine. ( For some reason on damp days it seems to start up a little more rough vs dry days.) But after its warm it will run completely fine.

The spark plugs have been replaced along with new cords.
The MAF has been replaced
The EGR Valve has been replaced
The IAC sensor has been replaced

- What I am getting
P0171 & P0174 - fuel trim or air error - something like that.
Cylinder 4 is misfiring
Oxygen sensor is bad just one I know where it is.

I have seen on the internet that that a bad oxygen sensor will cause a cylinder misfire, but I am not sure if this is true or not.

Anyone with any suggestions I would love to hear from.

Thank you.

[my98nnj]

I suspect your intake manifold is leaking. It's a common problem.

[Fordtruckman01]

Originally Posted by my98nnj

I suspect your intake manifold is leaking. It's a common problem.

Sorry I didn't put this in before. I did read about that, and it would be antifreeze correct? I have kept my eye on the antifreeze and it hasn't moved at all in the 3 months.

[Fordtruckman01]

Originally Posted by my98nnj

I suspect your intake manifold is leaking. It's a common problem.

but thank you

[Fordtruckman01]

anyone else have the around the same problems?

[jremington59]

A bad O2 sensor can cause problems. Did you change it yet? The 171 code is a lean code in bank 1. What code did you get for the O2 sensor? I'm betting it's in bank 1. Bank 1 is the passenger side.

[Fordtruckman01]

Originally Posted by jremington59

A bad O2 sensor can cause problems. Did you change it yet? The 171 code is a lean code in bank 1. What code did you get for the O2 sensor? I'm betting it's in bank 1. Bank 1 is the passenger side.

Its bank 1 sensor 2

[jremington59]

The O2 sensors tell the computer what ratio of air and fuel to give the engine. Your problems could be that sensor.

That sensor will be the one after the cat. The one closest to the manifold is number 1. I just changed mine and mines a 97 and I had to go through the floor to get to the connection.

[Fordtruckman01]

I had the explorer for a while, and now that i think back it would always have a rough start even when the check engine wasn't on. I put about 30,000 miles on it myself. But the it just kept on getting longer and worse with the start and waiting time on starting up. I was putting a lot of used gas in it and even sometimes old gas, i remember one day i put some real bad gas in it, then the warm up time took even longer from there on. I am starting to think it might be the fuel filter itself. Maybe. I think I will buy a new one tonight and replace it. The only thing is I am not sure where it is.

[Fordtruckman01]

Originally Posted by jremington59

The O2 sensors tell the computer what ratio of air and fuel to give the engine. Your problems could be that sensor.

That sensor will be the one after the cat. The one closest to the manifold is number 1. I just changed mine and mines a 97 and I had to go through the floor to get to the connection.

I'm going to replace that too tonight.

[jremington59]

You can change the filter if you want, but I'd say the problem is the 0 2 sensor. It's not giving the computer the right info and it's running lean causing it to sputter.

If you're getting a code for the sensor then it's not working.

[Fordtruckman01]

[jremington59]

My apologies. You have 3 sensors on bank 1.

[Fordtruckman01]

Originally Posted by jremington59

You can change the filter if you want, but I'd say the problem is the 0 2 sensor. It's not giving the computer the right info and it's running lean causing it to sputter.

If you're getting a code for the sensor then it's not working.

Thank you for your help so far.

My one question is though.. Is for 2 months it was running like this and i probably drive 400 miles a week at least.. and the check engine light never came on about this and i still had the rough idle.

I have took this to a few mechanics and 4 different ones and more than once so i am just to the point i am trying to learn about it myself.

[Fordtruckman01]

Originally Posted by jremington59

My apologies. You have 3 sensors on bank 2.

what do you mean by 3 sensors? All 3 plugs would be bad?

[jremington59]

No, only the number 2 sensor is bad.

I'm confused by the photo. Look at the wiring diagram for the vehicle and see which side the number one cylinder is on. It will be the second sensor on the number one side.

[jlsparky7]

Could be a clogged injector. Try some injector cleaner.

[chapsdeva]

My money is on the intake gasket leaking.

[2000StreetRod]

I have a 2000 Sport and didn't realize the 2001 exhaust configuration was so different. Thanks for including the drawing which greatly clarifies the numbering scheme which I find quite confusing. If the diagram is accurate then Bank 1 Sensor 2 applies to both banks and correlates with DTCs P0171 and P0174 (both banks too lean).

If you have the SOHC V6 (drawing shows a V8) then there's a good possibility that your intake manifold gaskets are leaking (common with SOHC). Your Bank 1 Sensor 2 may be good and accurately reporting a too lean condition. The symptoms are rough idle with tendency to die on cold mornings. The gaskets shrink with cold and leak more. Air enters your intake that has not passed thru the MAF sensor and results in a lean condition. Antifreeze is not related to the problem.

The only thing that puzzles me is the cylinder #4 misfire. What was the specific DTC? That could be either ignition or fuel related. I agree with jlsparky7 that you should add some fuel injector cleaner (I use Techron) to your fuel tank. Also, if you haven't changed your fuel filter in the last 30,000 miles I suggest you do so before adding the cleaner. You may have a clogged injector(s) causing a lean condition. However, a clogged #4 injector should show up as a lean condition on Bank 2 only. You can verify if #4 is misfiring by warming up the engine and note the idle rpm, then disconnect the #4 wire at the plug or the coil and note the decreased rpm. Reconnect and do the same thing for another cylinder and compare the decreases. If #4 is truly misfiring then the decrease for it should be less than that for any other cylinder. I'm guessing that its ignition related instead of fuel injection related.

Once you isolate and fix the misfire then you can focus on the lean condition.

[2000StreetRod]

According to the Ford 2001 OBD-II operations summary:

"If a single cylinder is determined to be consistently misfiring in excess of the catalyst damage criteria, the fuel
injector to that cylinder may be shut off for 30 seconds to prevent catalyst damage. Up to two cylinders may be
disabled at the same time. This fuel shut-off feature is used on many 8-cylinder engine and some 6-cylinder
engines. It is never used on a 4-cylinder engine. After 30 seconds, the injector is re-enabled. If misfire on that
cylinder is again detected after 200 revs (about 5 to 10 seconds), the fuel injector will be shut off again and the
process will repeat until the misfire is no longer present. Note that ignition coil primary circuit failures (see CCM
section) will trigger the same type of fuel injector disablement."

According to the above, consistent misfiring could cause a lean condition from disabling the injector.