[Diy_efi] [Gmecm] Failing Calif SMOG

Wed Aug 31 18:26:14 UTC 2011

I have never herd of not testing for NoX.  I thought it was the great
evil that the EPA said caused smog.

But yes you have another 4 cylinder that ECM is not correcting for.
Putting the O2 sensor before the cat will average the signal between
the two banks.  The now un-sampled side will become more lean but not
perfect.  The current sampled side will run richer but not a lot.
Think of them just balancing each other out.  As long as there are no
terrible problems such as an injector dumping 75% more fuel in than it
should, The average will get you to pass smog again.  Your numbers
being close to passing shows that you probably don't have a big issue
the ECM is just not seeing that other bank.  One or two of the
injectors on that side are probably flowing a small percentage higher
than expected.   Which the ECM could compensate for if it could sample
that air..

-Avery

On Wed, Aug 31, 2011 at 11:13 AM, Avery Nisbet <anisbet at gmail.com> wrote:
> Adding Diy-efi back to the CC line.
>
> -Avery
>
> On Wed, Aug 31, 2011 at 9:49 AM, Roger and Carol <rogerancarol at cox.net> wrote:
>> Sorry about not including my HC numbers. Also, NOX is not tested in my area,
>> so none to report.
>>
>> HC at idle measured 21 ppm, well within the limit of 120 ppm. HC at "high
>> idle" (2635 RPM) measured 45 ppm, also well within the limit of 180 ppm.
>> In past years, CO has averaged .00% at both idle and high idle., and HC has
>> averaged 16 ppm at both idle and high idle. Looking at old logs I've made of
>> BLM's show an average of 130, depending on RPM/MAP. Again, confirming that
>> the engine has been biased slightly lean since the install, but corrected by
>> the ECM.
>>
>> My exhaust uses a cross-over, converging on the passenger side, just in
>> front of the CAT. My O2 sensor is located in the driver's side manifold, per
>> requirements of my SMOG Ref (this is an engine conversion into a Jeep); the
>> configuration equals a 1995 Chevy 1500, with manual trans.
>> I've contemplated a second O2 sensor in the passenger-side down pipe, but
>> access in that area is extremely limited. Placing it in the collector below
>> where the two banks come together would most likely change my "symptoms",
>> causing all cylinders to be leaned-out due to something going on with the
>> right bank.
>> To me, this raise the question regarding PROM tuning for older cars/trucks
>> that have only one O2 sensor mounted on one bank. If you tune for the bank
>> with the sensor, what ever base data you log could be in error, causing your
>> tune to incorrect, as far as the engine goes.
>>
>> Anyway, obviously the "engineers" thought that as well, since most OBD II
>> vehicles use two, or more, O2 sensors. In fact, in my case, the '94 Truck
>> with auto trans uses one sensor in the collector after the "Y" pipe
>> connection. But the PCM has a much higher baud rate than the ECM. Don't know
>> if that affects whether you can put the ECM's sensor after the "y" pipe, or
>> not.
>>
>> I'm thinking a lean misfire on one cylinder, or any kind of misfire would
>> result in high HC, not high CO. CO is "incomplete" burn, meaning fuel is
>> left over after burning. This left over fuel gives an indication that the
>> cylinder did fire, but was too rich for a complete burn. An increase in HC
>> would be expected (as it did in my case), but was not significant (in SMOG
>> terms). The increase in CO was significant, causing SMOG test failure.
>> Thanks for the replys
>>
>>
>> -----Original Message----- From: Avery Nisbet
>> Sent: Tuesday, August 30, 2011 10:29 PM
>> To: Roger and Carol
>> Cc: gmecm at diy-efi.org
>> Subject: Re: [Gmecm] Failing Calif SMOG
>>
>> What kind of exhaust are you running? ?H,X, or Y pipe?
>>
>> Can you move the O2 sensor to the other side or after the exhaust's
>> join? or get a wide band and log some runs compared to the ALDL
>> output.
>>
>> Could the tech give you numbers on HC's HydroCarbons? ?Also how were
>> your Nox? Those will tell us a little more about rich or lean. Over
>> advanced or under advanced.
>> Carbon-monoxide is more of a incomplete combustion thing(a few things
>> can cause it).
>>
>>
>> How did the Tech put the engine into "fast idle"?
>> -Avery
>>
>>
>>
>> On Tue, Aug 30, 2011 at 3:27 PM, Roger and Carol <rogerancarol at cox.net>
>> wrote:
>>>
>>> ?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.
>>> _______________________________________________
>>> Gmecm mailing list
>>> Gmecm at diy-efi.org
>>> http://lists.diy-efi.org/mailman/listinfo/gmecm
>>>
>>>
>>
>>
>