Another failed CO emissions thread (1 Viewer)

Joined
Sep 25, 2014
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Henderson, CO
Yup, sorry. I've read through everything I can find in search and haven't found an answer yet.

The subject: '97 LC, 248k, stock gears, 285 Duratracs.

Before 1st test was done I did:
- Oil change, 5w30 Mobil 1 & Toyota filter
- New plugs (Denso), wires (NGK), cap (Denso), rotor (Denso)
- New air filter, Toyota washable.
- Recent EGR work including: clean passage in intake, clean throttle body, replaced all vacuum hoses for EGR and under intake, replaced EGR modulator (new blue top). This fixed my P0402 CEL.

Results #1: 1/9/17
HC: 0.8266 Limit: 1.2 Pass
CO: 28.3386 Limit: 15 FAIL
CO2: 709.1657
NOx: 1.7091 Limit: 3.0 Pass

Changed engine temp sensor (this helped last time), checked timing, & decided to try the "easy" way out and added 2 bottles of Guaranteed to Pass to the fuel. Due to dealing with some driveshaft issues I didn't get back to test the truck with the next tank of fuel after I ran out the additive like the product recommends. 4 weeks and 5 tanks later I went back.

Results #2 2/10/17
HC: 0.4346 Pass
CO: 18.3501 Limit 15 FAIL
CO2: 680.4616
NOx: 1.6221 Pass

Replaced all other vacuum lines I could find, tested TPS, and cleaned MAF sensor.

Results #3: 2/14/17
HC: 0.5068 Pass
CO: 20.2299 Limit: 15 FAIL
CO2: 707.0228
NOx: 1.9111 Pass

I started to suspect the downstream O2 sensor after seeing some high voltage readings on my ScanGauge. Tonight I checked both O2 sensors per the FSM and both are within spec (upstream is 14.4 ohms, downstream is 14.0 ohms, FSM range 11-16 ohms). Is it possible for them to still be bad and causing the rich condition? I have two new Denso sensors sitting here just in case but I'd rather not throw $ at somthing that tests OK and may not fix the problem. What else am I missing that could cause high CO?

I did replace the charcoal canister with the vatozone one recommended here, due to pressure at the fuel cap at fill ups. Could that have anything to do with it? Could it be pulling more fuel vapor from the canister than intended?

I can post the graphs from the tests if that would be helpful.

TIA!
 
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Joined
Sep 25, 2014
Messages
133
Location
Henderson, CO
A little more info: I programmed the ScanGuage to show long & short term fuel trim, and O2 sensor voltage. Long term fuel trim is usually in the +1 to +5 range, and short term is usually in the -2 to -8 range. Upstream O2 sensor voltage oscillates per the FSM in the range of .1 - .9V. I have seen the downstream voltage as high as 1.25V but that was at idle, and the FSM says the range is .1 - .9V @ 31 MPH.
 
Joined
Feb 6, 2002
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OC, CA
It is an air fuel ratio problem and most of what you have done has nothing to do with air/fuel. Either too little air, like a clogged air cleaner, bad maf or too much fuel, like leaky injectors, bad pressure regulator, bad O2 sensors. There are more things listed in the order of their liklihood in the FSM.
 
Joined
Sep 25, 2014
Messages
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Location
Henderson, CO
Just to close out the thread for any future searches....

Changed O2 sensors and oil last night and passed emissions today with CO below 13.

EDIT: I switched motor oil from Rotella T6 5w-40 to Mobil 1 5w-30 last fall. With this oil change I went back to the Rotella T6. I also suspected leaking exhaust valve seals because every now and then I'd notice a puff of smoke at start up, and I also have a small rear main leak. I don't know if the leaking valve seals can elevate CO emissions but in effort to slow the leaks I added a quart of Lucas engine oil stop leak.
 
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Joined
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North Front Range, CO
When using HDMO like Rotella T6 the levels of ZDDP (zink) are higher, thus why Rotella doesn't recommend for use in cars with O2 sensors and cats. The ZDDP coats the O2 and cats. I have used T6 (and old T, old formula T6) I had luck 2 years back cleaning the O2's and cats to get my 80 to pass. Tried again but either or both the cats were just wore out at 460,000 mi and the O2's were changed in 2011 with 364,000 mi on the ( 100,000 mi on them).
 

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