Failed Colorado Emissions - P0401/high CO only (1 Viewer)

[lazy]

I just bought my '97 LX450 and when driving back to Colorado the CEL came on. I decided to roll the dice getting it passed through emissions with the CEL, but I failed due b/c of 1) gas cap and 2) high CO. Limit on CO is 15 gpm (grams per mile) and I blew a 20.8 gpm.

The truck was taken to autozone and had the code pulled down and it showed up as P0401. I passed on the new EGR valve the guy tried selling me, but did pick up a new gas cap.

What's perplexing, and as I understand it, high CO means I am burning "rich." P0401 should raise my NOx and I should be running lean, but I am well below the NOx levels based on my emissions test the other day.
I plan to tackle the CEL later and reverify the code this evening, but assuming nothing changes, I plan to clean the air filter, change the distributor cap and rotor, spark plugs and wires. Then pour a thing of seafoam in the gas tank, get the truck nice and hot and go back in for my retest. I don't want to mess with the EGR and what not if I am not coming in hot on my NOx.

Anything else I should do? or should I approach differently?

 

[Parsnip]

https://forum.ih8mud.com/threads/p0401-defeated-with-pics.363575/page-7#post-8957362

Read that whole thread.

Your 401 code is one or more of the following:
failed vacuum line, EGR VSV, EGR Modulator, EGR temp sender or crud in the intake.

You were wise to pass on the new EGR valve as those are rarely failed.

IMO start with popping the top on the modulator and look for the stain in that last photo. (after reading that whole thread, naturally)

 

[lazy]

Thanks. Just out of curiosity....can the 401 cause me to have high CO levels during my emissions test? If so, I'll tackle the problem. I just don't want to fiddle with it and cause another problem for the emissions test. I'll have 2 years to get the kinks worked out of the CEL. Just need to get my CO levels down a bit.

 

[ChiTown]

You are correct about the 401 code and NOx. A basic tune up should help depending on the age of your current components.
Second guess would be old O2 sensors or dirty MAF sensor.

 

[gerg]

I just ran the emessions test guantlet and had persistant high NOX. Do your tune up and hunt for high octane (94) ethanol free gas as the ethanol burns hotter than regualr gas and you could also retard your timing. I did mine to about -5deg. Make sure your egr is working perfectly and eliminate all vacuume leaks. I had a huge one from my valve cover gasket that was very hard to diagnose. Hope yours goes easier than mine. Took me a long time.
g

 

[lazy]

Thanks, I ordered denso o2 sensors from amazon yesterday. I'll replace those and get the "performance kit" from CDan coming as well. Looks like there isn't much to "service" or clean on the MAF w/ high potential to FUBAR. And expensive to replace. I get a "free" shot at the retest, so I'll do the performance kit, o2 sensors and some seafoam to see if that doesn't get me by....

Anything else?

 

[Pin_Head]

The P0401 is unlikely to be related to high CO. Go through the emission troubleshooting guide in the FSM for P0401 and high CO. There are lots of possibilities.

 

[gerg]

Sorry meant to say ethanol burn hotter and will raise your nox. Forgot to mention I also yanked my thermostat and tested in the morning. There was a lot of prayer in there too. Why do these engines make such high nox?

 

[lazy]

Still haven't gone back to get the vehicle emissions tested, but a couple questions and wanted to bounce off some ideas I have.

Revisiting college chemistry class 13 years ago, high CO would be an indication of not enough oxygen. More O2 would help to make more CO2 and water (and less CO). Correct?

My vehicle is leaking a fair amount of oil, mainly with what I thought to be the external distributor seal. When I pulled the distributor, there was a little oil on the inside of the cap. My research has shown changing the internal seal of the distributor is unknown. It is probably enough oil not to worry about it for another couple 10k miles, but I'm in there and would prefer to get it fixed now (especially since my wife views the truck as unreliable). So, "new" rotor on order (used from CDan).

New spark plugs and wires have been installed.

New o2 sensors.

New air filter, replacing the aftermarket version.

I've switched from premium, which the PO claims he ran in it, to the stuff us commoners put in our vehicles. I have also developed some pinging around 2k+ rpms. Not sure if the pinging is related to the octane rating, but everything I read has shown the 1fzfe should be fine with commoner grade gasoline. I removed the throttle body and cleaned up "the port" and inside of the throttle body - something I read can contribute to pinging and the 401 code (hoping for 2 birds with one stone!). I wish I could trust a can of seafoam throttle cleaner would take care of what I spent 90 mins scrubbing and scraping, but remain skeptical on the "spray and pray" throttle cleaning method. I left the intake plenum on, and will remove if I have to. Hopefully, I'll pass emissions and if the 401 is still around I'll go down that road.

My vacuum modulator fell apart when I moved it out of the way to get at the throttle body. It had the stain on the filter parsnip alluded to upthread. So, I'll be replacing that.

Where is the VSV for EGR? I'd like to pull that and test to ensure it still works. The FSM drawing might as well have been bowl of spaghetti noodles dumped on the page. It appears all the VSV's are under the intake plenum?

Anything else to get the truck blowing less CO?

 

[ChiTown]

The vsv solenoid is under the upper intake manifold. Make sure you clean out the vacuum port on the back side of the manifold. (Follow the vacuum line from the brake booster side of the egr valve)

 

[Parsnip]

BTW I found that a small bottle brush fit well into the hole where the temp probe lives. The brush can go through the intake and into the lower part of the EGR valve easily. I used one with some intake cleaner spray and used some 0000 steel wool to make the temp probe shine like a new penny.

 

[lazy]

Made it to the emissions testing place 20 mins before they closed today (I'm sure they loved me). Got the "2nd chance," but it looked like the vehicle passed with flying colors. CO went from 20.8 gpm to 1.8 gpm. Everything else stayed the same, maybe slightly lower. Also, looks like the new vacuum modulator and some vacuum hosing may have fixed my P0401 code as well (probably need a few more driving days to confirm).

Glad to be able to put this behind me! Onto "work" which yields much more fun!

List of things done in case anyone else is having a similar problem:

• New O2 sensors (both of them)
• Cleaned throttle body
• New EGR vacuum modulator
• New vacuum hosing (around modulator)
• New wire set
• New PCV hose
• New Spark plugs
• "New" distributor (mainly to fix my oil leak problem)
• New rotor
• New Distributor cap
• New air filter
• changed oil to synthetic mobil1 10w-30
• cleaned MAF
• cleaned throttle body (replaced throttle body gasket as well)
• can of seafoam in gas tank

 

[englaneato]

Crazy here in cali a cell is an auto fail. Having made that mistake as a teen I always clear codes before heading in.