Dirtoy4x4

Just failed emissions with excessive hydrocarbons at cruise 25mph.

Vehicle is 94 Truck 3.0 Auto - Cali emissions with high-flow cat & Downey headers. Truck runs and idles great. Changed the oil just before testing.

Had the following results.

At 25mph:
HC(PPM) limit 150 actual 195 - Fail
CO (%) limit 1 actual .43 - Pass
CO_CO2(%) limit 6 actual 15.63 - N/A (I guess this doesn't matter)
O2 (%) not measured but produced .35


At idle:
HC(PPM) limit 220 actual 55 - Pass
CO (%) limit 1.2 actual 0 - Pass
CO_CO2(%) limit 6 actual 15.8 - N/A (N/A again)
O2 (%) not measured but produced .18

Anyone with had similar results? Stuck open EGR maybe?

abecedarian

the co2 limit is tested but doesn't have a pass/fail yet because states are still arguing to some degree about limiting greenhouse gasses with the feds.
how many miles are on it?
possibly O2 sensor going south?

Dirtoy4x4

120k or so on the truck, but engine was rebuilt about 2-3k ago.

abecedarian

can't say for sure the O2 is the problem, but if it's never been replaced, 120k is about twice as long as they are expected to live. When they start to go, you may or may not get a trouble code but the typical result is a rich condition (high HC).

have the head bolt torque and valve adjustements been checked since the engine break in? (not that they're that relevant to the problem, just a curious question)

stormin94

Try driving it like hell before the test to get it hot, I know that works if it's just over...but that might be for NOX rather than HC.

abecedarian

thanks stormin94. you gave me an idea....

Dirtoy4x4:
check your timing...
and TPS: http://4crawler.com/4x4/CheapTricks/TPS/index.shtml

Dirtoy4x4

I had the front O2 sensor go a while back (cali emissions).. Didn't throw a code but caused a slow idle surge or fluctuation.. I read through some of the other post and found the FSM stating it should be 5.1 to 6.3 ohms at 68*

I tested the rear sensor after the cat today, its at about 15.5 ohms.. Front is at 6.5ohms (its about 90* out today). Assuming the front and rear sensors are the same, it appears to be the 02 sensor.


Haven't re-torqued the head bolts. They are torque to yield anyway, so I wouldn't mess with them. I belive they can only can be used once. Valves are fine as far as i know..

wardriver

Seafoam works wonders. RockAuto.com had good prices on o2 sensors.

abecedarian

seafoam may work wonders ... on an aged engine ... but I'd hesitate at least a year to use it on an engine with less than 5000 miles on it.
... unless I put a can in the fuel tank ....

Yoda

How far did you drive before the test. I used to work for a place that did tune-ups. A cust would fail at 1 station (it was only 1 mile from his house) We would "suggest" it was easier to pass at a different station that was 15 miles away up the freeway. They almost always passed there because they were fully warmed up.

I have been told seafoam in the gas tanks helps (any alcohol product....gas dry, seafoam, etc.)

The co-co2 at 6% is a minimum reading.

I test for a WA fleet now. We do our own testing.

JDMSLIK

With high HC your not burning all your fuel.

I''d suggest get your engine hot before showing up.
Adding methyl hydrate to your gas works wonders. It's in the paint section at any hardware store. I used to put about a litre or so for a full tank. It makes it burn hotter.
Was the air filter replaced with the rebuild?
Also what condition is your ignition system? New plugs, wires and rotors?

gte718p

Spend the 250 dollars on something emissions related and get the waiver. New O2 sensor, fuel filter, air filter, plugs, and wires never hurt anything. I ended up having to get my VW Passat waived. I passed emissions but could not get the check engine light to go off. Instant failure.

Dirtoy4x4

Thanks for all the help.

The plugs, wires, and distributor are pretty new. Airfilter is clean. The truck runs great. I'm guessing it is running rich, but its hard to tell with a 3.0 Auto on 35's, gas mileage is already terrible.

The testing station is a good 15 mile trip down I-5. The truck was plenty warm, I had been driving it for the day running errands before heading to the DEQ.

I'm going to order a new rear 02 sensor and see what that does.

scope103

Dirtoy4x4 wrote:
"I'm going to order a new rear 02 sensor and see what that does. "

It won't hurt to change it, but that probably isn't it. The rear O2 sensor is a "check" to see if the front sensor (or the catalytic convertor) failed. When running correctly, the front sensor will switch from about 0.25 volts to 0.9 volts about once per second as the computer drives the mixture ever so slightly rich then lean. Then, after the cat, the rear O2 sensor should NOT see the up/down (the cat oxidized the little HC left). If it does, it throws a code (because something upstream failed).

As others have pointed out, your are (obviously) running a little rich at 25mph. You could run a check on the front O2 sensor (which could cause your problem) through the diagnostic connector, but you'd need to wire it up so you could do it at 25mph.

Last, the resistances you measured on the O2 sensors are for the heaters, not the sensor itself (which you cannot test that way). The numbers you got are close enough; I don't see them as indicating a problem with the heaters.

Good luck.

Dirtoy4x4

hmm.. The front was in spec at 6.5 but the back at 15+?.

scope103

Like I said: it won't hurt to replace it. But if the rear O2 heater is out, it will not function properly until it gets up to temperature (and that might not ever happen at idle.) The mixture (and the resulting high HC on a smog test) is not affected by the rear O2 sensor. A dead rear O2 sensor might throw a code (indicating, incorrectly, a problem with the cat), but I can't imagine it would affect the mixture and therefore the HC.

But by all means, let us know what happens!

Dirtoy4x4

Well, I was sitting at idle for maybe 10 minutes in line at the testing station. I'll test some of the VSV's today. Not sure where else to look.

stormin94

Warming it up isn't the issue. I believe you want to drive it hard and get the block hotter than normal driving. Something with getting it hot lowers the HC levels. I did it with mine, and JDMSLICK confirmed that it was indeed the HydroCarbons, and not the NOX levels that fixed it.

I found out that simple fix after I tryed and failed numerous times.

JCM4x89pu

....i believe that your problem is the high flow cat... it's actually illegal to use one of those in california, but i doubt that anyone would notice and give you any trouble.
however, high flow catalytic converters are not designed to acheive a passing score on the california emissions tests.. do you still have your stock cat?? put it back on for the test!!.. and always drive around a lot to heat up the catalyst so it can burn up all the unburt fuel ..a hot, stock catalytic converter is what will reduce your HC and CO emissions.. even if it is running rich with a bad O2 sensor.. it will burn it all up (but your CO2 will still be high)

also... what are your NOX emissions?? that will tell you if your EGR is functioning properly or not. and.. do you have any check engine lights coming on?

so, replace your O2 sensor (you should only have 1 on the 3vze) .. put your stock catalytic converter back on (just for the test) .. and drive around for a while to get it heated up so it operates properly.

JCM4x89pu

oh, sorry... you said cali emissions.. and i live in cali.. so i didnt even notice that you're from washington.

but anyways... same thing.. it's the high flow cat.. and you probably are running a little rich.

O2 sensor & stock cat

GOOD LUCK!!