OBD1– Code 41- Lean Condition- Passenger Side O2

[Julian]

So I was driving last Friday thinking how well the mustang was running. About 3 miles from home, the car lost power. When I stumbled home, I pulled the codes and got code 41 KOER. Lean Condition- Passenger Side O2.

My question is, aside from possibly the O2 going bad and a vacuum leak or bad ground on the O2 I wonder if there’s any significance to only one O2 reading lean. Any thoughts? Why not get both 41 AND code 91?

Also, from researching online, people suggest checking the ground. Is there one ground for both O2s? If so, if the ground is bad– again, why only throwing a code for one side and not the other?

This is an 89 mustang gt v8 manual.

Thanks!
Julian

Topic

[Joe]

Probably the best thing to do off the bat is to get an analog voltmeter and check the sensor. Backprobe it and check to see if the needle is bouncing up and down pretty steadily. If it just sticks in one spot then the sensor is bad.

Otherwise you’re probably running lean on your passenger side head. The EFI system you have doesn’t inject fuel into each individual intake port like on newer vehicles, so something as simple as built up dirt in the intake or a leaky intake gasket could cause the entire head not to get enough fuel.

[college man]

see if this helps. check for vacuum leaks, clean the maf, do a power
balance test.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Julian]

makes sense to me. I ran a bottle of fuel cleaner about a month ago too– wonder if it dislodged something somewhere as well 🙂

[Julian]

One more question. While the car sat idling and I was checking different things, I noticed that the driver side exhaust had a water puddle behind it, where the passenger side exhaust– the side throwing the lean code, didn’t. Is a sign of anything? Has to do with the head being lean? Or, just a coincidence? 🙂

Thanks again!

[college man]

[quote=”juels98″ post=102228]One more question. While the car sat idling and I was checking different things, I noticed that the driver side exhaust had a water puddle behind it, where the passenger side exhaust– the side throwing the lean code, didn’t. Is a sign of anything? Has to do with the head being lean? Or, just a coincidence? 🙂

Thanks again![/quote]

If your lean your not producing heat/combustion gas or very little
so no water.

[Bill]

Those engines are bad for sucking in the upper intake plenum gasket in the center but the resulting lean condition usually causes a higher than normal idle speed also.

It’s probable that the o2 sensor has failed as it is a common problem on older Fords but you should be sure before you throw one at it. They usually set a slow response code.

[Julian]

Thanks collegeman and thanks wysetech! Funny you mentioned the higher then normal idle. I think I did get code 12- Idle speed control out of specified range. My code book I think specified that it was high. However, I ignored it for what I thought was the more important issue of Code 41 and the fact that I’m running under-drive pulleys 🙂

I’m still waiting for free time to work on the car, but gathering info for now 🙂 Besides looking at the O2 sensor, knowing that this is only happening on the passenger head– should I be focusing on something more particular– or things like the MAF and O2 ground, fuel pressure… could still be a problem? Wouldn’t those affect both heads?

Also, if I unplug that O2 sensor, would the computer switch to closed loop for that sensor? Same with the MAF? And if things improve at that point– would it make sense to pursue those further with testing?

Finally, one more question. The code puller that is used on the 89 mustang says to hold the clutch pushed in for I believe the KOEO tests. I know if I don’t do it– it complains of the neutral switch problems 🙂 However– does not holding in the clutch prevent/trigger other findings? I looked online for the extension code for the tester– it’s more expensive then the tester itself :):):) :woohoo: Would rather not buy it. Please advise!

[Joe]

It really depends on how your exhaust is built but I wouldn’t worry about the water puddles that much. If you have an X or H pipe (the mustang came from the factory with H pipe) exhaust chances are there’s just a point on your driver’s side exhaust that sits lower than your passenger side so all the water goes to the one side.

Stuff like a dirty/bad MAF or bad fuel pressure would affect both heads. Still there’s no harm in checking your fuel pressure if you just want to check and see if it’s in the correct range.

I would actually check the O2 sensor with an analog voltmeter first. Then if it’s flat-lined pull the connector and actually check for ground and such. There’s pretty much a guarantee that you won’t see any improvement in performance by unplugging either your O2 or your MAF.

I have no idea about your code reader problems. I would assume that there’s nothing holding in the clutch would interfere with during code reading.

[Bill]

You should be able to find a vacuum leak by spraying WD-40 around the intake manifold. You will hear the engine sound change or slow down. The gasket splits about center beside the runners for 2 & 3 cylinders.

It’s common for ford diagnostics to have you depress the clutch and sometimes cycle the A/C. On automatic trans cars they want you to cycle the overdrive switch also.

Bless the old EEC-4 systems. 😛

[Julian]

Just wanted to give a quick follow up. I had a couple of hours to play with the car. Here’s what I did:

1. I unplugged the battery for about an hour to clear all the codes.
2. I replaced the metal filter and grommet of where the PCV plugs in to the passenger side bank (it would come out too easily). The valve itself is new. (This didn’t fix the rough idle)
3. I hooked up a vacuum gage to the unused port on the vacuum tree which is on the firewall. It gave a reading of 20-18. Only when the idle would drop and be rough, the vacuum would then drop to about 15. When I revved the engine—the reading would drop to 0, come up to about 25 and within about 2 seconds steady itself at 20-18.
4. I hooked up the fuel gage as well. At idle, it showed about 33-34. With vacuum removed from the regulator—it’d go up to about 45 if I remember correctly.
5. I kinds heard a hiss by the upper intake manifold. I played with the vacuum hose going from the Upper Intage Manifold (UIM) to the Charcoal Canister and it seemed the hissing would change. I pulled off the hose and it didn’t look like it was tight on the air inlet on the UIM. Plus, it was old and cracked. It seems like the hose is the same size diameter as what I had in the garage, but the difference is is that the tip is wider than the rest of the line. Since I don’t have an expender, I couldn’t make my new hose work. However, I did just cut off the outer most piece of the original hose and pushed it back on to the manifold and clamped it better than it was before.

The car seemed to idle better. The vacuum no longer dipped to 15 but stayed at 20-18 for a while. Also, it sounded good enough to take for a ride around the block—and it seemed the hesitation was gone. Fingers crossed that’s the end of that issue. When I have some more time—I’ll run the computer diagnostics again to see if the codes cleared too.

Just curious—I noticed that one of the caps on my Charcoal Canister is missing. Can that cause any issues as far as vacuum? I looked online and it’s a 1.50$ part with $10 shipping 

Thank you for all your help!

[EricTheCarGuy]

Sounds like you might have found the problem, or at least part of it. Vacuum leaks can cause the O2’s to read lean. As for the port on the canister I honestly don’t know. It could be normal. Keep us posted on what happens after you replace that line if you haven’t already.

[Author]

Replies