please help at end of rope!!!

[mikemedic3]

Well I know it's been discussed and I have searched extensively, but. My truck 03 Yukon 5.3 not flex fuel, a while back threw the maf code and started to idle rough while in gear, so with a 140000 on her I changed it, for it to come back with intermittent 304 and consistent 161 171! so after research I changed the intake gasket, checked intake itself, barely in spec for warp. After which maf code gone but bank 2 o2 161 171 still there with rough idle still there in gear!!! So I changed the o2's both after cat with no change, both still throw code, (heater malfunction). So I checked pcm1 fuse ,good, checked wires from o2 sensors and found the pink wire was broken on bank 1 sensor2, so I respliced. Went down road for about 5-6 miles and check engine light came on!!!!!!!! po161,171 still with rough idle. I am at a loss, I can't afford to send to a garage, I don't have a scan tool to read anything other than codes!! Really need help with this it is also throwing a 304 code too (lean cylinder 4) no bank given. What the hell can this be?????????

 

[mikemedic3]

Anyone? Anyone?, Bueller?, Bueller?

 

[kschumake83]

my 2000 silverado threw a code for bank 2 sensor 2 so I threw a new o2 sensor in. It didn't work, so I did a little research there and I was told that where the rear o2 sensor wire goes around the trans they tend to pinch. I never verified this as I only have to pass an emissions test once a year, and if you drive it like you stole it for a couple miles it will heat up the sensor and the code will go off. So I would immediately drive to my inspection mechanic and get it inspected, then I would return to driving like grandpa with the check engine light on.

 

[JennaBear]

O2s after cat don't do anything with fuel, P0304 isn't lean cylinder four it is misfire.

cylinder 4 is on bank 2
1357 on bank 1
2468 on bank 2

Could very well be fuel pressure that is causing rough idle.
P0304 and P0171 Check fuel pressure, if low, start from there...at idle it should be about 50psi.

 

[2005SnowKon]

Try cleaning your mass airflow sensor. .

Sent from my SPH-L710 using Tapatalk 2

 

[mikemedic3]

Thank you all for the replies, will try fuel pressure end of it. Seeing I replaced Maf it shouldn't be that! Not that it couldn't be bad already. but that code went away after i replaced the intake gasket.

I heard about the wires getting pinched and tried to follow them. But after it goes over the trans I can't see until it comes around by rear of engine, what I can see the loom is ok with gentle bends.

This is the problem, I have checked, replaced all that I could think of and the damn thing is still acting up. I will get a pressure guage today and try that, I have to replace the water pump on the wifes blazer today, cause of course that is giving me trouble too, just did the intake gaskets on that, because it was old faithful on the top! Get that done and now the pump is leaking. It just never ends!! I told her I am getting her a new truck one part at a time! The blazer I have done over the past 3 yrs the alternator, bothfront wheel bearings, master brake cylinder, then of course broken rear brake line! thermostat, intake gasket and yesterday the idle pulley and today the water pump. Still need to do the rear pinion bearing, and fuel sending unit! Really wish I had the money for something new!!!

 

[JennaBear]

MAF is unrelated to fuel pressure. Your pump might be going out.

Sent from an ice cream sammich.

 

[mikemedic3]

Here's another question for those that think it's the fuel system IE pump or such. What does that have to do with a heater circuit malfuntion code for the after cat sensor's? I don't see how a weak fuel pressure/lean condition would trip that code? I am just tring to learn.

 

[saltygq]

MAF is unrelated to fuel pressure. Your pump might be going out.

Sent from an ice cream sammich.

X2, my truck was giving rough idle and in gear plus the random cylinder misfire. From what you explained I would change the pump, I banged on the tank a couple times and it started working again. Maybe try that and see if it runs better, if so you will know for sure its the pump. Or better yet rent a fuel pressure tester from autozone and test the pressure at the rails. Should be over 50/55 IIRC.

Hope you get it fixed soon.

 

[mikemedic3]

checked the fuel pressure and it's spot on at 50. So doesn't seem to be fuel. I am really at a loss here.

 

[mikemedic3]

Finally found the problem!

Well took the truck to the garage, I was at a loss. To recap;
Check engine light came on and had MAF code, changed the MAF and still had code with a lean code also. The truck also began to have a rough idle while in gear. So after research determined it was the intake gasket, so I changed that.
Now no more MAF code but was getting a 171,161 if memory serves correct which was bank 1,2 sensor 2 heater circ. malfunction, and still had rough idle in gear, and occasional 304 code for misfire cylinder 4. So I checked fuel pressure, which was ok, changed after cat o2's with no change, checked fuses which were ok. Climbed underneath to search wires and did find bank 1 sensor 2 pink wire broken, so I respliced, still to get heater malfunction code and rough idle when in gear. At this point I gave up and took it to the garage.
Well they found the fuse to the o2 sensors blown, and a bad plug in cylinder 4. Now I checked the fuses, removed them and retested them, so only thing it could be is that it must have popped ofter I respliced the pink wire. Now with all the other codes that I was getting and seeing it more or less happened all at the same time I did not check the plug believing it was a lean issue all along. I figured initially the lean and misfire codes for that cylinder were from the vaccum leak in that area.
Having a vaccum leak, bad plug and broken wire for the o2 sensor all within a short enough time to overlap cost me 150 in labor!!!! However it is real nice to have the truck running smooth again!!!!
I post this for anyone else having similar issues, so you are sure to always start with the basics, and don't rule out two different issues that happened simultaneously!!!!!

 

[madmike]

Been in the same situation Mike, I replaced the intake gasket and o2 sensors and MAF and still misfiring. Fuel pressure fine here also. Regulator also working fine.

Just a couple of items for anyone checking this thread... a hole/crack in the cold air intake duct between the MAF and throttle body will also cause a misfire code and condition as well as still show bad MAF code at times or have a vacuum sounding leak. Something I learned to check also, from another mechanic but it didn't solve my issues.

Also for those saying heater codes are not related to engine misfire, what Mike was referring to was the o2 sensors in the 2003 yukon have heating elements in them and that was what he was referring to, not the heater inside the cab of the truck.

Thanks for the info on the o2 fuses. Will have to check those to see if that is part of my problem on my misfires. I did see that my open loop went to closed loop when I replaced the o2 sensors, but still showing lean condition one the left bank. Will check that next.