[Gmecm] Failing Calif SMOG
Thomas Martin
n0dih1
Thu Sep 8 15:36:38 UTC 2011
You could add a gallon or 2 (or more if needed) of E85 to it and add some
additional Oxygen to drop the CO numbers down and get past SMOG check that
way. Then work on it later on. It WILL change your BLM numbers higher, but
as long as the integrator is under control it doesn't matter. You aren't
too far off from passing.
I always look at high CO is not enough Oxygen present to complete the burn.
High HC is A/F that had enough Oxygen, but not all was exposed to the flame
front. So it got hot, but not burned and just passed out the pipe. So
leaning the mixture out should help CO, but going to far to have the fuel
not burning completely will start to raise HC.
This is where adding some E85 works, PCM will compensate (BLM will go
higher) but Integrator will stay near 128, and the extra O in the fuel will
help complete the burn and drop CO. As long as Integrator isn't straying
from 128, HC should remain pretty safe.
Tom
On Sun, Sep 4, 2011 at 1:41 PM, Roger and Carol <rogerancarol at cox.net>wrote:
> Thanks for the comeback;
> I?ve completed your table?hope that helps. I' am aware that the more data
> supplied, the better the discourse. Should have included every thing my
> first post.
>
> idle readings : Std's
> ~2500 RPM Std's
> RPM 649
> 2635
> CO . 03 % 1.00%
> 2.06 % 1.00 %
> CO2 14.5%
> 13.3%
> HC 21 ppm 120 ppm 45
> ppm 180 ppm
> O2
> .3% .3%
> NOx
> na na (no load tests)
>
> I agree with all you?ve said, but would add that the BLM?s are the result
> of ECM base-line fuel mapping, plus INT adjustments for variances from
> optimum fuel control caused by either base-line fuel mapping or current
> changes in operating parameters. If they (BLM?s) are steady, it indicates
> the INT?s are averaging 128; mine were varying betwee 125 to 129, idle to
> 3000 RPM (2008 log). Latest log (Sept 2011) shows INT?s varying between
> 126.5 and 129.8, over the same RPM range. The conditions for both loggings
> were the same, and similar to the SMOG test runs---no load, two-idle speeds,
> sitting in the garage, same altitudes, etc. The BLM?s indicate current state
> of the fuel delivery system; meaning, if the BLM?s are steady between ~120
> and ~136 (by some people?s standards) action could be taken to improve the
> base-line fuel delivery system, but the ECM does have control as it is, and
> the resulting fuel-ratio is averaging 14.7, so it could be left alone. Since
> those parameters have been met with my system, it would indicate ?failed
> SMOG?, for whatever cause ?high HC, or high CO, the problem has to be with
> something specific to an individual cylinder; not the MAP, TPS, or CST;
> however, your point is well taken that a fuel distribution issue
> (injectors), or possibly one or more spark plugs failing at the higher RPMs
> on the monitored bank could cause the ECM to correct the problem on that
> bank, causing the un-monitored bank to run rich.
>
> I know I can't connect two O2 sensors in parallel. I?d like to have the
> option of selecting one, then the other (via switch), to compare affects on
> INT readings. If I can find room, I may install a second O2 sensor on the
> right bank, along with a switch.
>
> Your comment regarding ECM response-time due to the distance the exhaust
> charge would have to travel before the ECM would see it, if the sensor was
> placed after the cross-over pipe is interesting. I know the auto-trans
> equipped ?92-?95 Chevy trucks used a PCM, and placed the O2 sensor after the
> cross-over. As you know, the PCM operates at a much higher CPU speed, and
> has much more memory than the 160 BAUD ECM, that is used with the manual
> transmission trucks of the same years (my application is manual trans). As
> far as I know, all of the ECM equipped Chevy trucks had a single-wire O2
> sensor mounted directly in the driver?s side manifold. I?ve considered it
> may be an issue to move my O2 sensor from the manifold to the cross-over
> collector; I don?t know. GM sure seem to consider that.
>
>
>
>
>
> *From:* PERFormance DYNamics <perfdyn at att.net>
> *Sent:* Saturday, September 03, 2011 5:07 PM
> *To:* Roger and Carol <rogerancarol at cox.net> ; gmecm at diy-efi.org
> *Subject:* Re: [Gmecm] Failing Calif SMOG
>
> It appears to me that one of the quirks of Gmecm is not everyone seems to
> receive every post. You refer to info "*from previous posts*", yet in
> reading back through every post I've received, some of that info is missing.
>
> What about the CO2 and O2 readings ?? Combined they all tell the whole
> story. Individually they can be misleading. Still working half blind. A
> table form makes it a lot easier to piece together the picture.
>
> Idle readings : Std's ~2500 RPM
> Std's
> RPM 649 2635
> CO .03 % ??? 2.06
> % 1.0 %
> CO2 ??? ???
> HC 21 ppm 120 ppm 45 ppm 180
> ppm
> O2 ??? ???
> NOx na na (no load
> tests)
>
> Yes, a missfire results in unburned fuel(elevated HC readings) and OXYGEN.
> The ECM interprets this oxygen as a too lean A/F mixture and adds more fuel,
> resulting in an over-richened A/F mixture(elevated CO readings) in all
> cylinders. The Oxygen Sensor doesn't react at all to HC content, only O2. CO
> is typically formed when there is insufficient oxygen(rich A/F mixture) to
> complete the formation of CO2.
>
> *"It would seem that if BLM?s are steady, and near 128, that the resulting
> exhaust gas (post CAT) should read ?normal? emissions.".* BLM's don't have
> to be near 128 to be at stoichiometric or to achieve low emissions. The
> better indicator is the INT numbers. If they are near 128 and varying then
> the ECM is in control and the BLM's haven't hit an upper or a lower limit.
> The BLM's near 128 only indicate that the fueling calculations are in need
> of little adjustment. This of course is a good thing.
>
> Almost anything that effects fuel or air distribution in either side could
> be at fault. The fact that only one side is monitored will increase the
> error in the unmonitored side. If the average A/F mixture starts out correct
> but a distribution issue causes one side to be slightly lean, the other side
> will be slightly rich. With the monitored side lean, the ECM will richen the
> fueling to all cylinders, getting the slightly lean side correct and driving
> the slightly rich side richer yet.
>
> The new information of past emission test results and past datalog BLM
> numbers would suggest the ECM operation is unchanged yet the emissions have.
> That lends credence to the right bank rich injector theory. This assumes
> that the BLM readings are at similar conditions and similar to those when
> emissions testing. Otherwise it might be comparing apples to oranges. You
> could try swapping injectors side to side and see how it effects BLM numbers
> and/or CO readings. While you're at it, check the injector resistance in all
> injectors. Low resistance can cause somewhat unpredictable driver operation.
>
>
> As for the dual O2 sensor idea, this would be great to have if you could
> incorporate both readings in the datalog to observe side to side
> differences. To be able to use both O2 sensors for ECM control you need an
> ECM that accepts two O2 inputs. The sensor signals can't be combined into
> one signal input.
>
> Placing the O2 sensor where it sees both banks minimizes the maximum error
> in either bank. With everything being perfect this should not be neccesary.
> The down side is a slower correction reaction time due to the increased
> exhaust length between the cylinder and the O2 sensor.
>
> Carl
>
> ----- Original Message -----
> *From:* Roger and Carol <rogerancarol at cox.net>
> *To:* PERFormance DYNamics <perfdyn at att.net> ; gmecm at diy-efi.org
> *Sent:* Saturday, September 03, 2011 10:08 AM
> *Subject:* Re: [Gmecm] Failing Calif SMOG
>
> Thanks for the info?
> Original readings From previous posts, this subject, for SMOG measurements:
>
> ?---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 (past SMOG tests) .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.---?
> AND:
> ?----?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.-----?
>
> Wouldn?t a ?lean misfire?, or any ?misfire? imply no fuel burnt? No burnt
> fuel would imply no CO generated?which only occurs when the the fuel ratio
> results from a combination of too much fuel vs oxygen (air), resulting in
> an incomplete burn?not a misfire. A misfire results in an unburned charge of
> fuel, and air (O2), being expelled into the exhaust manifold; I?m not sure
> how the O2 sensor reacts to this combination of raw fuel VS additional
> oxygen simultaneously. It would seem that if BLM?s are steady, and near 128,
> that the resulting exhaust gas (post CAT) should read ?normal? emissions.
> The only way I can see high levels of emissions in the ?post CAT? exhaust,
> while at the same time the BLM?s are ?normal?, is either a ?false lean?, or
> a faulty O2 sensor that is heat sesitive, i.e.: reads OK at idle-speed
> exhaust temps, but reads a rich mixture as a lean mixture at higher temps
> resulting from higher engine RPMs. By the way, my O2 sensor is heated. Also,
> the EGR valve is inhibited from opening when the truck is not moving (needs
> VSS input).
> I think a stock ?87-?95 Chevy V8 would react differently to a bad injector,
> than my Edelbrock MPFI equipped engine. The stock TBI injectors affect both
> banks if one is dripping or has a diminished flow. While they are
> alternately fired by the ECM, they?re mounted above the manifolds plenum,
> allowing each injector to affect all cylinders. Obviously, the MPFI
> injectors are isolated to one cylinder. So I keep coming back to reasoning
> that if the ECM, which is only monitoring the left bank, is showing a BLM
> that is stoichiometric (14.7:1 fuel ratio), but the post CAT exhaust is
> saying there is elevated CO, and to some degree, elevated HC as well, then
> the problem lies (lays?) in the right bank, and has to be a problem specific
> to the right bank, that could effect high CO at high idle only, with also
> causing elevated (but not excessive) high HC at the same time. It?s my
> understanding that elevated CO is generally accompanied by elevated HC; this
> makes sense, since CO is caused by an incomplete burn, which also results in
> some unburned fuel being expelled from the cylinder post fire as well.
> As stated in another post, I?d love to put another O2 sensor in the right
> bank to make comparisons with the left bank, but space is at a premium,
> meaning I?m not sure I have the room. I?ll probably install the sensor in
> the collector after the cross-over pipe, and feed both banks to the ECM, and
> see what happens to BLM?s.
>
>
> *From:* PERFormance DYNamics <perfdyn at att.net>
> *Sent:* Friday, September 02, 2011 11:23 PM
> *To:* Roger and Carol <rogerancarol at cox.net> ; gmecm at diy-efi.org
> *Subject:* Re: [Gmecm] Failing Calif SMOG
>
> A right bank Injector problem that would cause high CO (leaking ?, stuck
> open?) would probably cause high CO at both idle and 2500 no load. It is
> likely it would effect the idle readings most. The same would hold true for
> a leaking fuel pressure regulator. Though not impossible, this seems
> improbable.
>
> A missfire in the left bank would cause excess oxygen at the O2 sensor
> driving the fueling richer(high CO). This of course also elevates the HC
> levels. The Catalytic Convertor then does its job combining the excess O2
> with elevated HC and CO, lowering both. In this case the HC levels could be
> low enough to pass with the CO levels still at a level that fails. Of course
> this is just conjecture. What are the HC levels? The O2 levels? The CO2
> levels?
>
> With the INT is varying around 128, then the ECM is controlling the A/F
> mixture at what it believes to be 14.7:1 in the left side. The high CO only
> at ~ 2500 RPM suggests either:
>
> 1] the O2 sensor is lying to the ECM
> a] a faulty O2 sensor, contaminated sensor (higher temperature at RPM
> could trigger the issue)
> b] exhaust leak allowing oyxgen into the left side
> c] missfire causing elevated oxygen content in the left side, drives the
> fueling richer
>
> 2] there is a difference in operation between the left and right banks
> a] fuel distribution issue (port FI with healthy injectors - this seems
> unlikely but worth mention)
> b] air distribution issue, restriction to flow in the intake or exhaust
> of the right bank
> (less air flow with the same amount of fuel = rich mixture)
> c] worn cam lobe (see b])
> d] the EGR gasses could be effecting one side more than the other
> (check CO readings with ERG disabled)
>
> 3] the engine operation changes between idle and ~ 2500 RPM
> a] weak/broken valve spring
> b] a restriction to flow in the intake or exhaust of the right bank
> c] EGR operation
>
> An exhaust leak that would effect O2 sensor operation would most likely be
> audible . . . using the right listening device. I use a length of 3/4"
> heater hose, 3 1/2 feet long. This is the best listening device I've used,
> and I believe I've tried them all. The best time to listen is just after a
> cold start when the engine is inefficient (lots of exhaust pulse).
>
> Carl
>
> ----- Original Message -----
> *From:* Roger and Carol <rogerancarol at cox.net>
> *To:* PERFormance DYNamics <perfdyn at att.net> ; gmecm at diy-efi.org
> *Sent:* Thursday, September 01, 2011 10:01 PM
> *Subject:* Re: [Gmecm] Failing Calif SMOG
>
> 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 <perfdyn at att.net>
> *Sent:* Thursday, September 01, 2011 2:56 PM
> *To:* Roger and Carol <rogerancarol at cox.net> ; 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 <rogerancarol at cox.net>
> *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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