Error codes, 3rd Gen
I have a '99 sr5 cali smog 4runner (5spd swapped!). I got a full tank of fuel the day before yesterday. Driving home it started idling very rough/surging at stop lights. After getting home, I did a walk-around and check over, and saw my tailpipe, which is normally bare metal, was completely covered in black soot. At first I thought it was burning oil, however, the soot and the exhaust odor do not smell of burning oil, and the smoke is dark black, no blue-ish hue to it. So it appears it is running Extremely rich.
I plugged in my code reader to check the CEL codes. In addition to the shift solenoid and trans.temp sensor codes, it was throwing a "P1133 air/fuel sensor circuit malfunction."
I am assuming I got a bad batch of fuel, but I was already a 1/3rd of a way through the tank at that point and I have no way to drain 10 more gallons of bad fuel and store it safely. So I drove to a gas station, topped off with ethanol free premium, then added a can of sea foam to the tank.
I cleared the codes before driving to work this morning. The P1133 did not come back until this evening on my way home. However, it also threw another code, "P0171system too lean bank 1."
Reading online it seems the two codes together indicate that the air/fuel sensor is malfunctioning or failed.
Has anyone else run into this issue? It's a 21 year old sensor at this point, so I would assume it could have just given up the ghost, but the timing with a full tank of fuel seems to point to it being thrown out of whack by poor fuel quality, leading the ecu to flood the engine with fuel resulting in soot buildup which further blocks the sensor from reading correctly. Is my train of thought logical?
Thanks for any help.
Posted Sep 18, 2020, 4:36 AM UTC
Not familiar with your particular engine and emissions setup, but I might offer a couple of places to from a generic perspective.
Gas cap or overfill? - Your fuel system is supposed to be closed. If the gas cap leaks, you can throw a few different codes. Did you force fill some gas after the pump shut off? If so, it can force gas into the carbon filter used to recirculate fumes. These usually cause a lean mix, but nothing surprises me anymore. Both of these checks are cheap to check.
MAF sensor - This device measures the amount of air that is available and fuel is matched to it. You can clean this, but only use MAF sensor cleaner. Then let it dry before you reinstall. Again....cheap. And oh yeah...check your air filter too.
NOX sensor - This measures emissions from the engine. If it throws nonsense to the ecm, it confuses the system. These aren't cheap, but you can see what it's doing with a good scanner. Only use OEM part if needed.
Injector - Again......scanner is best. You can check the plugs to see if you have a very dirty or a very clean one on a cylender. If so, change the plug, move the injector and see if the problem follows the movement of the injector.
These are shots in the dark. A scan tool is really needed to narrow your search. In any case, don't operate it too long running that rich or you can wave goodbye to your catalytic converter(s).
Edit: I saw that you had a scan tool. But do you have one that can read each particular sensor or control in real time?
I avoid "topping off" the filler neck for these reasons. The odd pump out there has overfilled my vehicle, but thats the exception, not the rule. The gas cap itself is tight. If I fill up with the engine running it hisses when the seal is cracked, so I dont believe the gas cap is contributing in this instance.
I'll give this another cleaning, and Im likely in need of an air filter as well. Same thing as with most of the other sensors, its OEM and pushing 21 years of operation. I'll have to see if there is a way to bench test it.
Not sure that theres a nox sensor. From my reading, '99 and earlier 4runners had an upstream Air/Fuel sensor and a downstream O2 sensor, with the '00 and later models using two O2 sensors. This code should be referring to the A/F sensor.
I replaced all 6 injectors about 2-1/2 years/35kish miles ago. I had two that tested way, way out of spec for the resistance reading the FSM listed. I kept the other 4 original injectors that were still in spec. I'll pull the injector harness plugs and test them all.
I'll check my plugs too.
I have a scan tool, but its more of a code reader. It can display some info in real time, I'll read over the manual and see if it can check individual sensors.
Thanks for your response.
I borrowed a better scan tool. It can show some sensors in real time. It cam show voltage in real time from the MAF and "both" O2 sensors (bank1 should be a air/fuel sensor).
I'm not sure where I could locate what voltage ranges I should be looking for to determine an issue.
Ok, so I've been driving around to log data with this other scanner. Its still limited, but it does show the real time voltage readings from the AF sensor and O2 sensor. At idle they both jump up and down all over the map. Now, to complicate things, it is not throwing either the P0171 or the P1133 code, nor does wither show up under pending codes, at least so far.
As I haven't worked on these particular engines and systems, I can't give you specific specs. There are online manuals/services like Alldata (and others) that are probably more detailed than your scanner can give you.
You seem to be covering the basics pretty well. But have you checked for vaccuum leaks? Replaced the PCV? Any weird found on a single spark plug? If all check out, I would start suspecting that it might be the MAF sensor. It could be the O2 sensor itself. There is likely a test for this by grounding one side (I forget which) of the connector and see what the voltage is on that sensor.
This is like trying to put together a puzzle over the phone. There might be things that you are or aren't observing that are important pieces. Just approach it systematically. You have or had a rich state. Was that due to a misfire to 1 cylender or the computer getting bad info and fucking all 6? They are 2 different branches of the same troubleshooting procedure. Since the ignition and observable side (loose bad wiring, vaccuum leaks, etc) are easiest and cheapest start there. What did you see on the plugs?
Edit: Unless there is something weird found on the plug of a single cylender, I wouldn't reinstall an old plug. They're just too cheap for that.
If you do find something weird on a single, then you start methodically swapping coil packs and injectors to see if the problem follows either.
Yes, did a smoke test yesterday, no signs of leaks. I pulled the intake runner apart and cleaned the joints and rubber boots and put it all back together.
I have not replaced the PCV valve, I went ahead and ordered one.
No, all are about even. Dirty (but not caked/carboned up), worn, my book says it about 68k since my last set of plugs, so I have a set and plug wires on order.
Cleaned it after the smoke test, and replaced my air filter.
I'll check Alldata and poke around T4R to see if there are voltage specs.
I drained the last few gallons of fuel from that tank I got into a can. Them filled up with ethanol free from a marina. I also cleaned the rim of my tailpipe to see if it was still smoking/running extremely rich. After clearing the codes and getting it up to temp I took it for a longish drive. The lean code and a/f sensor code have not been thrown again, nor are either code appearing in the pending code queue.
My conclusion is that I am in need of a tune up, and that, coupled with a batch of Very bad fuel, resulted in a condition of poor running, where the ecu was getting poor information from a fouling A/F sensor which resulted in it adjusting the fuel gates wide open, which exacerbated the issue.
I'm going to swing past the same gas station and ask if they have had complaints from other customers about poor fuel over the past week.
I appreciate your help and insight, I kept responding to you for two reasons, 1- so that you could follow up with me, and 2- because all too often there are threads out there where someone has had an issue, but fails to follow up with their own thread if they manage to resolve their issue or if they find a solution elsewhere, which can be frustrating to other people who cone across the thread at a later date.