Explorer: Check Engine light - Lean on Bank 1 ?
 

115k miles on my '98 Explorer v6 sohc.

Check Engine light came on last week and it said it was had detected misfires on cylinders 4, 5, and 6.

I replaced the spark plugs and wires - if it weren't for the internet, I don't think I would have tried to get the plug up against the firewall on the passenger side. It wasn't bad after removing the front tire.

After driving it to work this morning the check engine light came back on and the code says it's running lean on bank 1.

I was told that the most likely suspect is a loose vacuum line? Visually I don't see anything. I was told that if I spray brake cleaner ( I think I'll opt for WD40 instead ) that when I spray near the leak the rpms will increase.

Is that the best method? Any other suggestions?

I'm quite the novice mechanic, but I did own a french car once, so I had to learn some. That car was a nightmare - Renault Fuego turbo.

What exact code numbers are you getting? The OBD-II has some many possibly codes, the interpretation of each one is a little different.

I assume you changed all plugs and wires since the passenger side is 1,2,3 not 4,5,6 where you said you had the codes.

My 93 had a left side lean but the plugs were actually black - rich. The O2 sensor was bad telling the PCm it was lean so the PCM richened it up and blackened the plugs.

Any other symptoms, drivability problems?

I don't suspect a vac leak at this point since any extra air getting into the intake will after all cylinders, not just one bank. The O2 sensors only see one bank at a time.

I disconnected the battery last night, so I'll have to wait for the codes to pop again.

I went to Autozone and had them reread the code and he said that it said it had 2 codes running lean on both banks.

When it starts, it runs really rough (idle up and down almost stalling) for a couple minutes, but then evens out - no misfires. No other drivability issues. It runs great.

Last week when I was driving home, the engine was missing badly and within a couple of minutes the check engine light started flashing. That code (misfire 4,5,6) prompted the plug/wire change.

Initially I couldn't get the plug out closest to the firewall on the passenger side and after changing the other 5, I took it for a short drive and it ran very rough (idle up and down) and the check engine light came on solid (not flashing).

After reading how to get that last plug, pulling the front tire and splash guard, I got it easily changed out and took it to my neighbor to read the code

He told me that I had definitely fixed the misfire problem in that it was running very well. He reset the code - lean on Bank 1

Drove it approximately 15 miles to work yesterday and the code came back on. On my way home I stopped at autozone and he said it was lean on both banks. On his suggestion, I disconnected the battery for 5 minutes last night - he seemed to think that the computer might be compensating for the old worn plugs and this would reset that? Seems like a stretch to me, but I'm quite the novice.

Haven't driven it today, so no code yet.

Thanks for the help and insight.

So if you gave me the exact code numbers I could feel more comfortable with a diagnosis. What you gave so far, I would change the O2 sensors - I think you have 3 total. If they have never been changed in 115K miles, count your blessings for getting this far. And changing them now is only prudent. You will get better performance even though you may not notice it.

Yes a vacuum leak will give you a lean condition on both sides. And your idle will be crap. I once lost a vaccum plug on the vacuum tree at the back of the manifold. On start up, the idle would go up and down and then settle in but would be rough still - just as you mention. Check out this tree as there are some prongs on the bottom that youcan't see and have to feel for a plug.

So the PCM (powertrain control module or the vehicle's computer) is a complicated little bugger. It starts by looking at fixed tables for Air/Fuel mixture and spark advance curves. Then as conditions change with time, such as an O2 sensor going bad, the PCM will begin plotting correction factors that are multiplied to the fixed table values. These multipliers can richen or lean a A/F mixture or advance/retard a spark. All of this is done to endear emissions and fuel economy. So when the Autozone guy said you might be running off the old plug data, this is what he meant. I'm actually impressed that an Autozone guy knew that.

So all these compensation factors and even the memory code numbers are stored in KAM - keep alive memory. KAM lives in the PCM. KAM is powered off the battery all the time, does not need the key on to receive power. This way, it keeps alive the correction factors and all conditions for controlling the engine remain current, up to date. So when you disconnect the battery, KAM dies and all correction factors go to 1 (1 X means no correction, 1x1=1, 1x2=2, get it?) and the codes are also dumped.

So everytime you make a significant change to a key engine component - be it plugs, wires or other maintenance (not oil canges), or change to any controls component (O2 sensor, coolant temp, intake air temp sensors...) you need to disconnect the battery so the PCM can start from scratch. So in other words, if you took every control component off and replaced with new, then the PCM would want to look at and control a new engine, in essence. Removing the correction factors let's it start all over. Check out this link http://www.fordfuelinjection.com/
It covers the basics. I've dowloaded a bunch of documents with more details. Send me a private message with your email and I'll forward what I've found, if you're interested. Preety cool stuff learning how your car works.

I just reread you first string. Forget about the WD40 trick for now. We're not at that stage yet. This would be to verify that an intake manifold is leaking at a mating surface like the block or head. Maybe even at an Injector connection. It's more of an old fashion technique used to find leaks under carburators and such.

More than likely, if you do now have a vacuum leak, you probably knock off a hose changing your plugs and wires. Need to be carefull because there a vacuum lines going all over the place. Check for the obviuos stuff first, then it gets more evasive such as loose lower intake manifold bolts, which do tend to loosen up -at least on the OHV motors.

may want to also clean your MAF sensor. Not sure the layout of yours, compared to an earlier one like my 93. This web page has instructions on the earllier models so it should help you understand what needs to be done. When a MAF gets dirty (2 little sensor wires in the airstream) it tends to not sense all the air going into the engine. thus the PCM doesn't give as much gas as it should and it runs a little rich. If this is only a little dirty, the O2 sensors can help make up the difference through the correction factors I mentioned on other reply. But when it gets to dirty, the truck gets a noticable loss of power and will likely start to ping, a lot. I don't think this is your problem - either a vac leak or bad O2 sensors is - but it is a prudent maintenace item.

http://draco.acs.uci.edu/explorer/

Thanks for the tips and the links....I'll check the vacuum tree and plan on swapping out the O2 sensors next.

Having success on the Explorer gave me the confidence to change the plugs and wires on my Expedition today. Fortunately, I don't have the coil on plugs ('97 Expy), so I'd say changing the plugs on the Explorer was actually the harder of the 2.

Thanks for being so helpful! I really like working on the cars, but often find it a little intimidating.

Yeah my dad was talking about that new coil on plug design - something like a $100 piece? I think I like the older technology better. Funny, I never had a problem with #3 cylinder plug. Just stuck the spark plug puller on a u-joint extension and right onto the ratchet. Yeah you have to get your arm way down in there but no big deal. One time I did it the way you mention but only because I had the wheel well splash gaurd already removed because I was pulling the exhaust manifolds and adding headers. Figured I might as well change the plugs while I was there.

I changed all 3 on the passenger side through the wheel well. Just looking at the one closest to the firewall from the top made me think it was not possible.

With the wheel off, it was actually the easiest on that side for me. I found the middle one on that side to be the most difficult. I couldn't get the plug in with any extension, and doing it blind on top of it made it difficult. Of course, afterwards I read about putting an piece of fuel line on top of the plug to use as a guide and impromptu handle to get it started nicely.

It was wire boot removal that made it so difficult. It's like they become one with the plug.

LOL - yeah getting the freaking boots off is usually half the battle!