[Diy_efi] [Gmecm] Failing Calif SMOG

[Avery Nisbet]

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.
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>>
>>
>
>