Runs rich, idles high, code 41

[extreme_exploder]

I have a 91 Explorer that has baffled me. It idles high when warm, it stays steady around 1000 rpm after I adjusted down as low as I could go; before it was about 1200. Also it is getting pretty bad mileage. It use to get 15-16 around town. Now I'm getting 12. Also there is a pretty strong exhaust smell when its idling. It will occassionally throw a CEL for code 41. So the computer either thinks its lean or that the O2 sensor isn't working. I've replaced the O2 sensor already with no effect. I've tested the TPS, temperature, and the MAF sensor. I can't find any vaccum leaks, and the FPR and the fuel pressure is good. It all seems fine. This all happened around the time after I replaced the fuel injectors. I just don't see how the new injectors could cause a high idle, a code 41, and bad mileage. What do you think is up?

 

[FIND]

I have a 91 Explorer that has baffled me. It idles high when warm, it stays steady around 1000 rpm after I adjusted down as low as I could go; before it was about 1200. Also it is getting pretty bad mileage. It use to get 15-16 around town. Now I'm getting 12. Also there is a pretty strong exhaust smell when its idling. It will occassionally throw a CEL for code 41. So the computer either thinks its lean or that the O2 sensor isn't working. I've replaced the O2 sensor already with no effect. I've tested the TPS, temperature, and the MAF sensor. I can't find any vaccum leaks, and the FPR and the fuel pressure is good. It all seems fine. This all happened around the time after I replaced the fuel injectors. I just don't see how the new injectors could cause a high idle, a code 41, and bad mileage. What do you think is up?

If you replaced your injectors with the wrong size injectors, or if you have a bad/leaking injector. That would cause it.

 

[extreme_exploder]

The reason I replaced them in the first place was that they were leaking down pretty good, it would huff black smoke on startup, but it was running fine otherwise. These ones don't leak down at all, they hold preasure well. They're 19 pounders, thats what is supposed to be in there.

 

[moosejaw]

Idle fuel control is fed back from the O2 signal once warm and closed loop. Have you been able to read the O2 voltage while idling? It is probable there is an exhaust air leak fouling the O2 reading into a lean condition at idle. Under load this won't show up as a problem due the magnitude of exhaust flow vs the leak.

You said you replaced the O2 sensor so that part should be good. A rich voltage is 1.0vdc and a full lean is 0.1 - 0.0vdc. A proper idling engine should flip around ~ .7vdc back and forth.

Not knowing the exact arrangement of the exhaust flanges on these vehicles yet, I would bet on a leaking flange. This is very problematic on Mustangs with aftermarket exhausts or after any exhaust work. I have seen some mechanics use rtv red or black to ensure an air tight seal after maintenance.

Check the exhaust for damage or leaks if you can. Good luck.

 

[ExploringNC]

Could be your fuel pressure regulator going bad. Mine was going bad then went out all together and found vacuum line full of fuel. Had been dumbing fuel into vacuum line straight into upper intake.

 

[extreme_exploder]

I'll check the O2 sensor signal as soon as the blizzard stops outside. My fuel pressure regulator is good, I already checkked that because I know that its a very common problem with many Explorers.

 

[extreme_exploder]

Alright, I tested the O2 sensor to see what it was doing. I tested it right at the computer to make sure all the wiring was good. With the engine warm, I started it up, and the sensor was doing exactly what it was suppossed to do, bouncing between about .1 to .8 volts. But after about a minute or two, it went full rich. The reading stayed around .9 volts, and the idle went up a bit. And the exhaust started stinking, too. The only way to correct this was to pull a vacuum line, and the O2 readings would start varying as normal, and the exhaust would smell clean (of course the idle went high as well). I'm going to swap back in the old injectors to see what happens. Maybe there's something wrong with the new ones. FIND might be right about my injectors.

 

[moosejaw]

Hmmm. Try unplugging the MAF when it pigs up to force speed density maps. If it dies it should restart with out the maf plugged in. Alternately you can unplug the O2 sensor and force open loop to see if it still goes rich.

Need to find out if the overfuel is mechanical or electrical. It really sounds like big injectors or a faulty maf but your maf was fine before the switch. Some times the injector voltage offsets are not the same and when the system voltage drops it will richen too much or lean out depending on type of injector.

I have a lot of experience with eec iv on mustangs but it has been a while. This is the kind of thing you could use an adjustable fuel regulator to 'tune out' to make it drivable.

 

[Reejerey]

Honestly it sounds like a problem in the HO2S Circuit. The engine is seeing a lean condition being monitored by the HO2S, and is adding extra fuel. It's a common misconception that a rich or lean O2 code means that an O2 sensor is bad, when actually the O2 sensor is fine and there is either a wiring issue or a mechanical issue. With a lack of other codes I'm inclined to think its either a vacuum leak (if you say it started around the time you replaced injectors I'm really inclined to think this, get a can of starting fluid and spray round the base of the plenum, all the vacuum connections, ect, listen for rpm changes), unmetered air entering the system between the MAF and the throttle body (check your air tube) or a short/open in the HO2S wiring.

 

[94explorerEB]

Early 4.0 OHV's came with 14# injectors, but they switched to the 19# injectors in 92 I believe. I gotta try to double check that this afternoon.

91-2000 has the 19lbs so disregard my post.

 

[Reejerey]

The really odd part here is that you're throwing code 41, which is an O2 reading lean, while your O2 is actually reading rich. If you've tested that at the computer, I'm inclined to believe that your ecm is bad. I've seen similar failures (ecm internal problems) on other circuits and other vehicle models, so its safe to say that it could happen on an explorer also.

The big thing to remember here is that if everything was working properly and it was a mechanical/wrong injector issue the computer would be seeing a rich condition and throwing a code 42 for O2 sensor stuck rich. As you are getting a code for O2 sensor stuck lean as your only code present, my years of experience in the repair industry lead me to believe that you have a computer issue, or a connection issue at the ECM connector.

http://www.asashop.org/autoinc/june/Tech2tech.htm is a link to a thread with some very good tips for O2 and fuel trim diagnostics.

 

[extreme_exploder]

It was the injectors. I was driving the other day, and after I stopped at a store and came back out and restarted the Explorer, it was skipping pretty good. Then it started pouring white smoke out the exhaust, and it smelled like raw gasoline (lots of burning gas will be black smoke; pouring unburnt fuel through the exhaust will be white). The #5 injector was stuck wide open and pouring fuel through the cylinder. I cleaned the old injectors and put them back in, and all is well. My guess is that the injector was sticking a bit while it was running, making the exhaust mixture rich, and the other cylinders probably went lean to try to compensate, causing the problems I was having. I will drive it some more to make sure all is well.