[Gmecm] Failing Calif SMOG

[Roger and Carol]

Thanks for the reply;
INT is varying slightly around 128 (127-129), which indicates the ECM is in control. The BLM?s are steady, and within tolerance.
My understanding of what causes CO would imply a misfire would result in high HC, not CO. Co is caused by incomplete combustion, due to a rich mixture. 
A ?false lean? could certainly cause a rich mixture, resulting in high CO. Not sure what level of leak would be required, to cause the O2 sensor to read ?lean?. Would such a leak be audible? I?ve searched for reports of verified examples of such a leak without success. At any rate, I replaced the exhaust manifolds (but not to solve this issue), and gaskets without affect. I certainly do not here an exhaust leak.
No AIR used, so that?s not a cause. Remember, the high CO is only at RPMs above ~2300; idle HC is well within limits. If the INT and BLM?s are close to 128, that implies stoichiometric to me; HC?s and CO?s should both be ?good?, unless the O2 is sensing a false lean condition. 
I?m inclined to believe the problem is with the right bank, which is not monitored by the ECM, but is ?analyzed? by the SMOG machine.

From: PERFormance DYNamics 
Sent: Thursday, September 01, 2011 2:56 PM
To: Roger and Carol ; gmecm at diy-efi.org 
Subject: Re: [Gmecm] Failing Calif SMOG

Look at both the INT and BLM readings at 2600 RPM, warm, no load. Is the ECM in control under those conditions? At minimum the INT should vary some, even if the BLM seems stable.

If the ECM is in control and the CO readings are that high, check for anything that can cause the introduction of oxygen into the O2 side exhaust. Any additional oxygen will be interpreted as a lean condition and the ECM will drive the mixture richer in all cylinders. Exhaust leak? Upstream AIR air? Could you have any missfire for any reason on the side with the O2 sensor ? (a missfire contains not only the unburned fuel but also the unused oxygen)

If the INT is at 128 and not varying under those conditions, something may be disabling learn. 

Happy hunting.

Carl
  ----- Original Message ----- 
  From: Roger and Carol 
  To: gmecm at diy-efi.org 
  Sent: Tuesday, August 30, 2011 3:27 PM
  Subject: [Gmecm] Failing Calif SMOG

  ?94 Chevy 5.7L V8 with Edelbrock MPFI. ECM 16171199, with EPROM tuned by Edelbrock, based on broad cast code BDUY.
  The engine failed recent SMOG test with a CO reading on the ?high idle? test of 2.06% at 2635 RPM; max CO allowed is 1.00%. 
  CO at ?idle? measured .03%, at 649 RPM, which was well within the limit.
  My BLM?s at 2500 RPM read 130 on my scanner, which I believe means the PROM?s fuel map is biased ?lean?, and the ECM is compensating as it should. I?m confused as to how the BLM?s can indicate that the ECM has control over the fuel ratio but the exhaust gas (SMOG test machine) indicates a ?rich? condition, which results in high CO? Note that CO at idle was .03%, which is well within the limit, thus at idle fuel mixture is correct.
  This engine has only one O2 sensor, which is located in the driver?s side exhaust manifold (manual trans applications only). Does it make since that the cause for the rich condition is probably associated with the passenger-side only (not any sensor that affects all cylinders, like the MAP), and therefore not ?sensed? by the O2 sensor? Since I have Edelbrock?s MPFI, I think it could be an injector problem on the right bank only. Edelbrock?s system is batch fire, by the way. Inputs from ?fresh? minds would be appreciated.


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