[Chris Altizer]

This has the 4.3l V6 in it. Great truck.. but I drove it for a while with backed up Cat's.. The code had been running for a while and then it blew an exhaust gasket. Now she's loud as can be, and stalling ALL the time. I'll be driving her and all of a sudden it sounds like it shuts off. SOMETIMES it will just kick back on, other times I'll have to put it in neutral and restart it.

The codes that come up are in regards to the Catalytic Converters Bank 1 & 2, the O2 sensors and an Evap sensor.

I'm guessing I may need to replace the fuel pump as well since the Pump & Filter are one unit.

So I know for a fact that the Cat Y pipe has to be replaced and the O2 sensors. I have a few questions

1 - How many sensors does my truck have? 3? or 4? I've heard both answers.
1a - When buying sensors online, do I need Upstream or Downstream? Never replaced these, so not sure what parts to buy.

2 - If its stalling like this and suddenly shutting off and coming back on.. I'm guessing its the fuel filter getting clogged. Does that sound like a valid diagnosis?

Thanks in advance for any and all assistance.

 

[Scott_Anderson]

Open the hood, and crawl under the truck to count the sensors.
You say there is a Y pipe, that suggests 1 cat converter, and most likely (3) O2 sensors(2 upstream before the cat, 1 downstream after the cat)

 

[Chris Altizer]

There are two cats. One on each side of the Y pipe. I've been under the truck, but recently hurt my back and hadn't counted them prior to this. I'm about to buy some parts online so I can do the job myself, but I want to get the right parts first.

 

[Chris Altizer]

Would there still only be 3? or would there be 4 now? and do they need to be Upstream or Downstream? IDK anything about O2 sensors unfortunately lol

 

[xPosTech]

If you have two cats you have 4 O2 sensors. The two sensors upstream from the cats sample the oxygen content to sense if that bank had enough fuel to completely burn all the oxygen getting into the cylinders. This sets the air/fuel ratio for that bank. The two sensors downstream from the cats monitor the efficiency of the cats for emissions compliance. That's all they do. The downstream O2 sensors are not used in controlling the engine.

Post the actual codes here. Dependant upon the codes you may not have bad O2 sensors. It sounds like you have a problem with both banks which means a possible vacuum leak or fuel delivery problem.

Ted

 

[j cat]

so what you have to provide is the codes .......the cat converters maybe be plugged up/ melted and the exhaust gaskets blew.. now since you operate the vehicle with all this and the codes my guess is the engine is with other damage.

the issues you have to repair requires the specific codes to be checked for why they have been thrown. O2 sensors are saying IMO the engine is not running properly due to ???? depends on code !

so many newbies do just throw parts at the vehicle with not troubleshooting why the codes throw.
being a V6 the distributor must be checked/ plug wires as this engine is with old technology more wear and maintenance..

example a poorly operating fuel pump [low pressure] can cause certain O2 codes to be thrown.

since the converters are damaged then the O2 sensors did their job...probably still good.

 

[Chris Altizer]

Hi everyone, sorry for the delayed response. I just found the page from AutoZone.

Error Codes Read
- P0420 - Catalyst System Low Efficiency (Bank 1)
- P0157 02 Circuit Low Voltage (Bank 2, Sensor 2)
- P0430 Catalyst System Efficiency Below Threshold (Bank 2)
- P0455 Evaporative Emission System Leak Detected (gross leak/no flow)
- P0506 Idle Air Control System RPM Lower Than Expected
- P0420 Catalyst System Low Efficiency (Bank 1)

 

[Chris Altizer]

so many newbies do just throw parts at the vehicle with not troubleshooting why the codes throw.
being a V6 the distributor must be checked/ plug wires as this engine is with old technology more wear and maintenance..

example a poorly operating fuel pump [low pressure] can cause certain O2 codes to be thrown.

since the converters are damaged then the O2 sensors did their job...probably still good.

That's why I came here before ordering all of the parts. Since I'm a newbie at this, I don't have the wisdom and experience to properly diagnose all of the possible issues. I'm glad you guys are here with some other experience to help. Thank you all so much!

 

[j cat]

the evap code is NOT an issue with the engine operation . this can be a broken canister next to the fuel tank or the venting line tank to canister etc.. hole in the fuel fill pipe etc...

the codes appear to be bad converters this will cause the engine to stall as the engine is a pump .. the engine sucks air/fuel then pumps out the exhaust ..if the converters are plugged up then the IAC low rpm will occur do to the exhaust issue restrictions..

now what can be done is remove the upstream O2 sensors both leave the o2 exhaust holes open .. this will allow exhaust to by pass the converters see if the engine runs better MORE power .. if so then the converters some how got damaged , due to a improper fuel management .. many things can cause this but the codes you posted is not revealing any of these issues ..

with the O2 sensors removed other codes will be thrown this is just a test..post back ..

 

[Differently]

Yes replace the cats and hopefully you'll be good to go. The o2 sensors are throwing codes because there doing there job...hopefully. after replacing the cats i would pull spark plugs and inspect for signs that it may have been running rich. Too much fuel will kill cats very quickly.

 

[Zach Smith]

the evap code is NOT an issue with the engine operation . this can be a broken canister next to the fuel tank or the venting line tank to canister etc.. hole in the fuel fill pipe etc...

the codes appear to be bad converters this will cause the engine to stall as the engine is a pump .. the engine sucks air/fuel then pumps out the exhaust ..if the converters are plugged up then the IAC low rpm will occur do to the exhaust issue restrictions..

now what can be done is remove the upstream O2 sensors both leave the o2 exhaust holes open .. this will allow exhaust to by pass the converters see if the engine runs better MORE power .. if so then the converters some how got damaged , due to a improper fuel management .. many things can cause this but the codes you posted is not revealing any of these issues ..

with the O2 sensors removed other codes will be thrown this is just a test..post back ..

No flow could be from, no flow also. I.E. engine isn't breathing because exhaust is restricted. Therefore low vacuum. Either way, the evap doesn't matter for the time, or relatively at all. Easy test, pull upstream o2 sensors...see that it doesn't die while reproducing same conditions that made it die in the first place. Just for your own edification... If you felt like it.

 

[Chris Altizer]

So, before the exhaust leak occurred, the truck was having massive issues going up any hills and acceleration was absolutely horrible.. Once the exhaust leak broke out, it started going up hills easier. I could accelerate a little better. So I've kinda had the idea that the cats needed replacing for a long time. Especially since the guy before me told me they were messed up as well as the codes being there since I bought the truck.

I just bought the cats and the fuel pump.. but the truck won't start today.. It might putter a few moments, but then just shuts back off and wont start again. Just cranks and cranks

 

[Zach Smith]

Lots of possibility...have a vacuum gauge? A fuel pressure gauge? A multimeter? A 7/8 or 22mil wrench on hand? I would still try to narrow down the cats... Did you try pulling the o2 sensors?

 

[Chris Altizer]

Unfortunately, I do not have any of those tools except for the wrench. I also don't have anyone I know of that has those tools.

I haven't pulled the O2 sensors. The reason behind pulling them (At least what was given to me) was to see if the vehicle would gain acceleration/power. When the exhaust leak started it gained acceleration/power. So that says, that giving the engine more room to breath (Which was created by the exhaust leak) definitely helped to prove that the cats are backed up. I'm not sure why I'd need to double check that when its already been proven by the exhaust leak.

If someone could tell me why, then I'd put the double effort in. See, when the Cats get here, I have to do that anyway. I'm just trying to rationalize doing the extra work. See, I dont LIKE doing mechanic work. I CAN do the work, I CAN turn a wrench, but being under a truck kills my back. Its painful. If I dont have to do extra, I'd rather avoid it. If there is a different reason as to why I've been asked to remove the O2 sensors, other than seeing if the engine breathing more would provide more acceleration/power, then please describe said reasoning.

I'm not a sheep, I don't listen to instruction blindly. I ask questions first to get a broader understanding. Give a man a fish, or show him HOW to fish.. I prefer to be showed how (AKA given proper reasoning) than to just go "Oh Ok whatever you say...."

 

[Zach Smith]

I'm in agreement, it is very likely plugged cats - to an extreme. Your issue has worsened, When you posted I thought you may be looking for a way to get a More clear picture of what was happening prior to replacing parts. I misunderstood apparently and apologise for that. To answer why, with the issue worsened / it is quite possible that the leak that is there is now not enough for the engine to breathe, pulling the o2 sensors gives it just enough flow to run...although not well, helping to verify your issue is still the same - just worse. You have parts coming, slam them in...probably the issue.

 

[Chris Altizer]

I'm thinking the fact that it will stay running somehow, yet not let me accelerate, is the fuel pump/filter being clogged and needing replacement. When it does run, she runs smooth, but she'll just stop getting fuel out of nowhere as well. That says to me that the plugs should be good, as well as the wires. If they weren't I would assume that she would be running really rough. The exhaust leak made it run longer, but it just kept accumulating. That's why I'm thinking that the Cats being backed up for 6 mo's plus and being used regularly, and put well over 3000 miles on it since then, caused the O2 sensors to fail and making it so the truck has an issue running. The bad fuel pump, bad O2 sensors and backed up cats seem to make sense to me. I could be wrong. Before the exhaust leak, she ran smooth as can be. I could let her sit there at idle and rev the engine and she would sound super strong. As soon as she was in gear and accelerating, she responded super sluggish on the peddle. (Back pressure in the system with a failing fuel pump)

 

[xPosTech]

Back pressure in the system.

Ted

 

[Chris Altizer]

Back pressure in the system.

Ted

Dont know all the technical terms, sorry. I'd assumed it was called back pressure.. Am I the butt of the joke with the "Back pressure in the system" response?

 

[Zach Smith]

I don't think that was xtech's intention...more just a concise answer and vote...how I took it anyway... Don't mean to answer for anyone though.

 

[xPosTech]

Chris your last comment was "Back pressure in the system with a failing fuel pump." I dropped the failing fuel pump off to emphasize the (exhaust) back pressure. And no joke intended.

The easiest troubleshooting step for you to take was to remove the O2 sensors like you were advised. You refused to do that, instead relying on your guesses as to what could be wrong. An engine is an air pump. If air can't get out air can't get in. If air can't get in the PCM will cut fuel back to match the volume of air that can get in.

Good luck with your truck. If you listen to the guys still advising what to do you might get it fixed.

Ted