MicroSquirt.com read only forum (Jan.15,2018)

Hi all,

I just took my 87 Landcruiser for a run at the emissions testing center here in lovely Denver Colorado. If you don't know, Denver loves to use a dynomometer with their emissions tests I'm writing not because I failed (42/30 for CO, 5/4 for HC), but because one of the culprits might be my overrun tuning on the VE table.

I've noticed before that my O2 sensor will go severely rich if I'm engine braking for an extended time. I have changed my lowest MAP VE values between 0 to 40% with no different results. My idle is at ~30 kPa at about 30%VE. By the way, MS uses the last value on the table without extrapolation if it goes off, right?

My engine sucks down to 12 kPa at the lowest, so maybe I'm getting so much exhaust contamination in the cylinders that ANY mixture will not ignite? But why would the "oxygen sensor" go rich if there was unburnt fuel with unburnt oxygen? It does this even with VE=0 (pw is still 0.1 ms).

The stock carburetter system used a fuel-cut solenoid for overrun. Stock motor is straight 6, 4.2L, exhaust headers to collecter (O2 is located here). Now it is TBI with water-heated intake manifold. I should probably try the code with true fuel cut (dual table?).

Thanks for the help, and please post emissions testing stories if you have them.

-Dave

I have noticed that on my car, the oxy sensor(NB) also starts getting rich as the length of time I'm engine braking increases.

At first I thought that it was because the oxy sensor was getting cold, but that will give a lean reading, not a rich reading.

I was looking at my exhaust tip last night and I was wondering, if the inside of my exhuast tip is black, and teh carbon in teh exhaust gases has had a chance to stick to a few metres of exhaust and a muffler along the way, what condition will the oxy sensor be in?

Is it possible that an oxy sensor can foul up like a spark plug and give a rich reading? If that's the case, even though on engine braking you've got a lean reading, there is a very good possibility that the air/fuel charge has not completely burnt and this carbon is clogging up the oxy sensor giving you a rich reading.

Of course, as soon as you get on flat land again, the oxy sensor will get hot enough for these carbon deposits to burn off and your oxy sensor will read normal again.

I guess the only way to test it is to go for a long run down a long hill and stop your car at the bottom, let it cool, pull out the oxy sensor and physically look at it.

Hi unclewoja,
My comments are embedded
Wednesday, December 1, 2004, 9:32:38 PM, you wrote:

u> Is it possible that an oxy sensor can foul up like a spark plug
u> and give a rich reading?

If lead, silicon or phosphor contamination damaged your sensor, it
will read rich. I have not heard carbon will do this, it typically
makes your sensor response sluggish. That would boot a self-diagnosing
ECU into open-loop which would likely be programmed rich.

u> Of course, as soon as you get on flat land again, the oxy
u> sensor will get hot enough for these carbon deposits to burn off
u> and your oxy sensor will read normal again.

I don't think the engine would ever get hot enough to burn deposits
off the o2 sensor. Otherwise o2 sensor life would likely be much
longer. The method used to clean o2 sensors is a propane torch
directly at the sensor head for an artful period. That is
significantly hotter than exhaust gasses at the sensor head.

u> I guess the only way to test it is to go for a long run down a
u> long hill and stop your car at the bottom, let it cool, pull out
u> the oxy sensor and physically look at it.

I don't think looking at it will tell you anything. When I replaced my
o2 sensor at 150,000 miles it looked worse than any sparkplug I have
seen. But it was still working, just sluggishly.

--
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Finally passed emissions I did more VE tuning and drove the truck really hard to heat up the cat before I got to the facility. My results were surprising compared to the first try. It was a very cold day the first test and was probably the main reason I failed. Its amazing to see my landcruiser stripped of emissions equipment (EGR, 2nd AIR) except catalyst pass with readings at half the limit!

At 10:13 AM 1/27/2005, you wrote:

>Finally passed emissions I did more tuning and drove the truck really hard
>to heat up the cat before I got to the facility. My results were
>surprising compared to the first try. It was a very cold day the first
>test and was probably the main reason I failed. Its amazing to see my
>landcruiser stripped of emissions equipment (EGR, 2nd AIR) except catalyst
>pass with readings at half the limit!

Other than the fact that in my experience most decently running stock vehicles have reading in the 1% to 10% of allowed. So while 1/2 is plenty to pass, it's nowhere near as clean as it probably was stock. Not that I care, I always figure that every time I take my truck to the store I make up for everyone in LA who bought a Prius. It's just for going to the hardware store but the neighbors insist on calling the parking nazis on me so I drive it a lot more than necessary.

Ira




(posted by email)

audifahrer81 wrote:

> test and was probably the main reason I failed. Its amazing to see my
> landcruiser stripped of emissions equipment (EGR, 2nd AIR) except
> catalyst pass with readings at half the limit!

Great to hear! Just goes to show how well a "modern" electronic fuel
system can clean things up.

--
Eric Fahlgren http://www.not2fast.com/



(posted by email)