DirtyDaveW

The installation of the heads was okay but I'm getting weird Wide band O2 readings. There's no vacuum leaks. Gets -15psi at idle. Plugs look good.
It seems to run lean (15.x to 16.x) unless I give it a serious amount of pedal. Once into boost, the WB O2's are right where I want them(11.x).

Thinking that the heads are breathing better and that's why, I contacted Bryan Herter (PCM4LESS) about the tune but after looking at the flows, (he was impressed) he thought his tables were fat enough to be continued as-is.

The thing is, I'm using my narrow bands and it's going into closed loop fine. Why would the wide band show 15.x etc instead of 14.5 at steady cruise? Do you think that's 'normal' for a wide band to show different than a narrow bands normal operating level? My NB O2's are in two locations, the crossover pipe and one in the downpipe.

Also, it feels 'weak' in the 15.x to 16.x when given thottle. Almost stumbling at times so I think the wide band is telling the truth.

Have any idea where one effectively richens the tables/cells to correct this? And...., I thought it was pointless to modify the tables if you're going into closed loop since it's going to feed fuel based on NB O2 feedback. Am I incorrect?
Thanks,
Dave

DirtyDaveW

On a whim, I put in two new Bosch O2 sensors and initial driving seems to indicate an improvement.
BTW- ordering these Bosch 15703 sensors from Amazon.com cost $25 per. Ordering the same sensor from Autozone.com cost $56 per (!!!)

96capricemgr

You know the Bosch LT1 O2s are junk right? Never heard anyone who had good results from them. Now if using one of the widebands that is another story.

bobdec

I am OBD1 '94 Z28 and use these, Denso 234-4012 w/o any problems Amazon.com: Denso 234-4012 Oxygen Sensor (Air and Fuel Ratio Sensor): Automotive . From past LT1 forum threads, seems the Bosch O2 switching characteristics do not work well with the older GM PCM's and give erratic readings. Maybe the OBD2 (faster PCM processor) would act different not sure. In answer to you question..It is important you are sure about your AFR readings before starting, then richen the AFR by tuning the MAF tables (add X% to values in the lean air flow areas. This signals the PCM more air is entering the intake and the PCM will add fuel to maintain 14.7. If you are in SD mode then altering the VE tables X% does the same thing.

DirtyDaveW

Hi Dwayne I guess I should've fielded the question about preferences on these sensors first. I thought that Bosch had a good rep. I will try the Denso's that Bobs referring to next when I swap these out.
Thanks for the tips guys

DirtyDaveW

Thanks for the specifics Bob. It's appreciated

Injuneer

What "Gets -15psi at idle"?

DirtyDaveW

Hi Injuneer,
My AEM truboost shows -15 at idle. When it gets into boost and I have it set to 15psi, it shows "15" psi. Does the gauge incorrectly report "-15" ?

Injuneer

Normally 0 psi indicates standard atmospheric pressure =14.7 psi absolute. With a reference of 0 a perfect vacuum would be -14.7 psi. An automobile engine at idle will normally show about -10 psi (roughly 20"Hg vacuum). It is virtually impossible to have a pressue reading below 14.7 psi and you might see -12 psi with an engine under closed throttle decel from 5,000 RPM.

Are you sure the gauge isn't calibrated as "psi" on the positve side and "Hg on the negative side?

DirtyDaveW

Aha... it must be as you said, PSI on the positive side and Hg on the negative. Thanks for the clarification.

DirtyDaveW

The new O2's seem to have rectified my fueling issues. Thanks everyone.