[Diy_efi] [Gmecm] Failing Calif SMOG

Roger and Carol rogerancarol
Thu Sep 1 04:52:39 UTC 2011

Sorry about "reply", been a while since I posted on GMECM.
Swapping injectors from side to side would be interesting. Relatively easy. 
The Edebrock MPFI is a fairly standard set up, with injectors held in place 
by fuel rails; flex pressure line between banks.
The injectors were new ~5 years ago. Jeep sets a lot, so being gummed up 
would not be out of the question. Just seems inconsistent that an injector 
could cause a problem at higher RPM and not at idle.
I'm assuming the driver's side is at 14.7 (stoichiometric), and that the 
passenger side is excessively rich, causing the high CO. Swapping injectors 
from side-to-side should prove, or disprove that, if I can rely on INT/BLM's 
to be indicative.
I'm in Santa Barbara. We have bi-annual SMOG requirements here, with no dino 
I don't have anything fancy, just a scanner, and a laptop with WinALDL that 
I haven't used since "upgrading" to Windows 7 from Vista. I'm 
re-familiarizing myself with the WinALDL program in order to run some new 
logs. I'll run a new base line, then swap injectors, and then a follow-up 
logging session to compare the effects of swapping injectors. If the ECM can 
reach stoichiometric after swapping injectors, I'll try installing an O2 
sensor just before the CAT.

-----Original Message----- 
From: Avery Nisbet
Sent: Wednesday, August 31, 2011 2:57 PM
To: Roger and Carol
Cc: Do It Yourself fuel injection
Subject: Re: [Gmecm] Failing Calif SMOG

[Adding diy_efi back again please use reply to all.  There are a lot
of people on this list that know a hell of a lot more than I do about

Yes,  As long as you can also get high counts of the O2 sensor
crossings from lean to rich(at idle/fast idle and highway cruze). This
is the true test to see if your getting a solid 14.7 AFR.   Which Im
assuming you are getting right now.

Looking back at the CO numbers you were a little over 200% of the
allowed value.  I wish I knew what that ment in volume of fuel or
Air/fuel ratio.

How old are your injectors?  If you don't feel like running new wires
right now.  Try swapping all your injectors from the left bank to the
right bank.  Im not sure what intake you have so this could be pretty
easy or pretty hard.

This would cause the possible higher flowing injectors to be measured
by the O2 sensor.   If the ECU can still get good BLM's and O2 sensor
crossing after you do this you may pass smog or fail it based on a
lean issue.  Then moving the sensor to the collector will make it

What part of California are you in?  I'm in the SF bay area and I have
a wide band O2 sensor + an ostrich emulator.


On Wed, Aug 31, 2011 at 2:31 PM, Roger and Carol <rogerancarol at cox.net> 
> Avery;
> Is it your opinion that if both banks were being sensed by the ECM (O2
> sensor after collector), and if the ECM corrections resulted in a BLM 
> within
> the range of, let's say, 119 to ~137, then both CO and HC would be SMOG
> acceptable? In other words, can you rely on a BLM of 128+- to mean an
> air/fuel ratio of 14.7?
> The possibility of a leaky/drippy injector has been high on my mind, but 
> the
> fact that CO at idle is well within limits has me a little dubious; it 
> would
> seem a leaky injectors would result in a rich mixture across the RPM 
> range,
> not just at "high idle". It also seems unlikely that any of the sensors
> would be faulty, since the BLM's are not that far out, unless you can't 
> rely
> on BLM's to verify sensor operation.
> I could move the O2 down to the collector; I've already put a "bung" in
> there during the last iteration of exhaust mods. I would just have to 
> extend
> the cabling, and add a heater circuit.
> I'm trying to solve this issue analytically, rather than covering it up, 
> or
> throw parts at it. Without the "benefit" of the SMOG test (exhaust gas
> analyzer), I would be fat, dumb, and happy with my current PROM tune, 
> based
> on my current BLM's (otherwise bone stock 5.7L).
> -----Original Message----- From: Avery Nisbet
> Sent: Wednesday, August 31, 2011 11:26 AM
> To: Roger and Carol
> Cc: Do It Yourself fuel injection
> Subject: Re: [Gmecm] Failing Calif SMOG
> 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

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