My 98 only has two O2 sensors..... both pre-cat.

 

Sorry for the late update, have been super busy with work, school and life, just haven't had the time to work on the truck or even think about it. Hopefully some of you are still around cause things just got interesting but to start, a quick update and hopefully I can clear the air on the o2 sensor and exhaust set up.

If we start from the motor we have the exhaust manifold for each bank, which go into an exhaust pipe and on each side is an upstream o2 sensor responsible for that air fuel ratio of course (which shows up as bank 1 sensor 1 and bank 2 sensor 1). From there bank 1 comes all the way over and meets bank 2 into the cat and on the front of the cat is another o2 sensor, this one is showing up as bank 2 sensor 2. Then from the cat there is a single exhaust pipe that runs to the muffler and before the muffler we have the last o2 sensor I could find that shows up as bank 1 sensor 2. Weird since we are on one single exhaust pipe on bank 2 but whatever. I cannot for the life of me find the bank 1 sensor 3. It's a ghost sensor or it's somewhere where I can't see it. The readings come out like its a post cat sensor but can't find it for the life in me.

To answer some questions on the truck, it is a 99 2500 v10 Sport, out of California, auto, 4wd with a 4.10 rear end. 180,000 miles on it as well.

Now on to the new issue, drove the truck for the past week with no issues, doesn't rly have the power I would hope it would but it moves so that was good enough for me at this time until I went to start it up one night (after just driving it for a couple hours for work) and it immediately ran rough. Not to the point where it wouldn't run but it is shaking more than normal and up pops a code, P0302, Cylinder 2 misfire. Immediately I pull up the scanner live data and the STFT (short term fuel trim) is at -30%. So I pulled the spark plug wire while it was running and seemingly no difference in the shaking or how it was running but when I put the spark plug wire to the exhaust manifold I could see the spark arcing. So theoretically I have spark. I pull the plug and it seems to be pretty soaked in fuel. Go get a spark plug and while I'm at it grab a denso 02 sensor to throw on bank 2 to see if maybe the other one was acting up. Put it all in and nothing, same thing. Drove it for a few minutes and its definitely pissed. Thinking the worse, put a compression tester on it and it read 120, seems low to me but apparently is pretty normal for these trucks since they run low compression from what I've read. The new spark plug seemed to get soaked in fuel again. Now we are caught up to now. Cylinder is still misfiring but I look at the STFT and it's reading +30%, wtf!!! My thought is a cracked fuel injector but why would the computer want to dump extra fuel in if that is a problem??? Ran a fuel pressure test and it's at 50 psi, is that low for these trucks? Now this is all at idle, of course when I run the truck with some throttle the STFT seems to get closer to 0 leading me to think fuel injector even more.

As a wrap up of this word vomit, the problem of the LTFT saying +30% for bank 1 is still there but bank 1 STFT has never gone +-3% at idle. Of course now the 2nd bank LTFT is all out of wack because the computer is confused. Hopefully some of you are still around to help me figure this out. Other than these random issues and the truck being seemingly low on power I like it a lot and want to make it better since I know these motors are beasts and will last me quite some time.

Thank you for any help!

 

California emissions kinda complicate things.... I am use to sensor 2 being AFTER the cat.... You have three before, and one after. Do the three before seem to more or less agree on what's going on?? Are they all switching at the same rate/range? (which may be dependent more on the scanner, and the speed of the data bus, than anything else....)

Is the exhaust stock??? I thought the cali guys had dual cats??? If the PCM though sensor 2 bank 2 was after the cat on that side, sure would explain some of the weird behavior. But, if that's stock......

Maybe try swapping the injector on 2, with an odd side injector??

 

Ya it seems like a weird set up, honestly now that you say that it could potentially be custom but it seems weird for someone to do a custom set up for this truck cause its not any louder than a stock truck and of course that cat isn't deleted. I am not sure what's going on with it but yes the o2 sensors seem to be working together, except of course the bank 2 sensor 1 or the upstream air to fuel ratio on bank 2 since cylinder 2 is pissed right now.

That's a good idea I'll see if I can swap injectors and see how that plays out.

Am I wrong in thinking that it can't necessarily be a valve train problem since it has good compression and fuel is making it into the cylinder? i.e a valve can't be stuck open or closed since the cylinder has compression and fuel is making it in?

 

Since your compression is decent, I am more inclined to believe this is an electronics issue, not mechanical. Compression ain't the best, but, it is north of that 100PSI benchmark.... If all cylinders are fairly consistent, and you don't get huge jumps with a wet test, mechanicals are likely just fine.

 

Right that's what I'm thinking, thank you for all the help! I did do a wet compression test just now and there was no change, still at 120 so I'm gonna look into getting fuel injectors sorted.

 

On the CA V10s the two upstream sensors in the downpipes control the air/fuel ratios, the one after the cat supposedly helps fine tuning but also in conjunction with the sensor in front of the cat determines catalytic converter efficiency. I've never seen a "sensor 3" in any diag tool so I'd venture bank 1 sensor 2 and bank 2 sensor 2 are the sensors in front and behind the catalytic converter, just labeled confusingly.

Fuel trims are a reaction to whatever the O2 sensors read so try to make sense out of the readings. If bank 2 sensor 1 reads rich and the fuel trim goes way negative it might be a stuck/leaking injector on cylinder 2.

 

Well I finally got some injectors in and while I was at it put in some new plugs, plug wires and ignition coils. No more misfire, fuel trims are in check and it feels a lot more snappy. At some point I値l pull my camper and see how it performs with a load on it but so far I知 a lot happier with it and I知 sure the gas mileage is going to be much better.
Now to tackle the minor jobs that need touching up, thank you guys for helping me figure this out and it probably won稚 be the last you hear of me!