One O2 Sensor 11% Higher....Why ?

[Vcoat]

Trying to get through my shortblock build and its been one issue after another...Shorblock was assembled with the stock heads, whipple 2.3 etc. Went on the dyno busted a lifter in half (passenger side). Heads rebuilt back on the car. Fired it up, one side of the exhaust breathing normal the otherside barely coming out at all. Blown cat passenger side. The stuff was jammed in the pipe. I cant believe how it was breathing at all. Cleaned everything out...hollowed out both cats. Now the tuner is getting this 11% higher reading on the passenger side O2 sensor. Could the sensor just be bad ? from all the extra heat generated from the clogged pipe ? There is also a small header leak at the manifold(stage 8 bolts will be retightned). Anyone have other ideas what could be causing the higher reading ?...Thanks in advance!
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MMR 5.0 Stroker, 2.3 Whipple. Mono TB, ST Motorsports Intake, Steeda 10 rib, 16psi

 

[DirtyDogOfTheDesert]

O2 sensor going bad. Change both.

 

[SC boss]

yeah, after my build the car hit the dyno and the numbers didnt match side to side on the 02's. My tuner inspected and had a slight nick in one of the wires, got some new ones and they matched up awesome. could be that or just like DirtyDog and you said "going bad"

 

[Vcoat]

Thanks guys...will replace the O2's hopefully thats it...the header leak is pretty small ..not sure if that would cause the dramatic 11% difference ...

 

[lostsoul]

I think hawg had his pcm show one o2 higher then the other.. hopefully you dont have to go through that bs

 

[Wes]

Swap the o2s side to side to see if the difference moves with the sensor or stays on that side.

Wes

 

[Vcoat]

Thats a good idea...thanks!

 

[RRRoamer]

Header leak? If it's at the flange it will EASILY cause a 11% difference between sides. Remember, the CPU tries to keep the engine right at stoichiometric A/F at anything less than a significant portion of WOT. At stoich, there isn't much free oxygen available (by definition...). So even a little air leak at the flange will suck in enough O2 to have a very significant effect on the A/F as read by the O2 sensor. Especially given that it is an oxygen sensor...

That will also screw up the PCM's ability to properly fine tune the mixture, so it is definitely wise to fix that leak ASAP.

Oh, and the swapping idea is DEFINITELY a good one! Just because the leak is messing up the mixture, that doesn't mean the O2 sensor isn't going bad as well.

 

[Steedman07]

Hey Vic, how are ya? Who is doing this build on your car? Im just a little surprised that they havent figured this out for you yet..

 

[Vcoat]

Yea i know its been awhile and as I you can imagine very frustrating...i would radther not say who at this time... but hes doing the best he can and i am sure he will figure it out eventually.. everything checks out but one side is still running lean...injectors, cam timing, coils, everything seems to be ok...thinking now it might be a bad wire or something...when we switched o2s it was perfect...switched back and it was good...not sure whats going on...

 

[Wes]

We've seen differences in trims between banks on new builds due to erratic cam timing (think lifters/followers and TIMING CHAINS/TENSIONERS).

Just another angle to look at it from.

Wes

 

[Vcoat]

Thanks Wes ...but wouldnt the car be running rough if the cam timing was off ?

 

[Wes]

Thanks Wes ...but wouldnt the car be running rough if the cam timing was off ?

Maybe. Depends on how far off the trims are. I've had a couple come in with tensioner issues and they ran decent but the trims were off bank to bank. If you have any sort of a cam it can mask it.

These engines will run surprisingly "well" with cam timing issues.

Wes

 

[Vcoat]

I have the comp stage 2 blower cams...I will try to mention the tensioner issue to the guy..he was pretty confident the cams were installed correctly. What exactly about the tensioner should i ask him ? Thanks again for your help...

 

[Wes]

I have the comp stage 2 blower cams...I will try to mention the tensioner issue to the guy..he was pretty confident the cams were installed correctly. What exactly about the tensioner should i ask him ? Thanks again for your help...

Cams limited or locked out?

You should be able to datalog the actual vs commanded cam angle on each bank to see what is going on to an extent.

Make sure the tensioner is tight and the plunger holding pressure on the chain guides at low rpm - oil pressure should be strong and steady. We've had instances where the tensioner had an oil leak and wouldn't hold good pressure on the guide causing an erratic cam timing at idle/low rpm.

Wes

 

[Vcoat]

I believe they are neither...