Hey guys. Can't find my original "failed emissions" post, so here's another. At this point, I could get the waiver, but that means the truck's next owner wouldn't be able to get one in the future, and it's pretty hard to sell a truck that won't pass emissions.

Problem is CO emissions. Everything else is good. Limit is 25.00. Here's the rundown.

New plugs, cap, rotor. Timed correctly and vac advance confirmed functional.

TEST 1 - HC 2.64, CO 39.29, NOX 2.82

> Changed the oil, coolant, spark plugs, air filter, PCV, thermostat, & raised tire pressure to 35psi.

TEST 2 - HC 2.36 (-11%), CO 31.84 (-19%), NOX 2.71 (-4%)

> Changed O2 sensor (from hell).

TEST 3 - HC 2.54 (+7%), 29.15 (-8%), NOX 3.18 (+17%)

I need to get another 15% improvement to skate by on this one. Not sure what else to do. Truck feels like it's running better than ever. I thought about changing out the temp sensor, which never seems to get up to normal operating temperature, but after losing the alt/fan belt this past weekend, I watched the gauge climb nearly to redline, so I'm sure the engine is just running cooler.

Should I swap in a hotter thermostat?
Should I rebuild the carb?
Replace the cat?

Any ideas are greatly appreciated. Next test, either way, I'll have a bottle of alcohol in the tank and no air filter, but I'd like to get it honest, ya know?

Thanks.

The mikuni carbs are crap. Id say rebuild it and replace/check all vacume lines. Make sure everything goes to the right place and all.

I also liked your idea of a more modern cat.

When my 95 3.0 24V failed for NOX a few years back, I gave thorough Sea Foam treatment for starters (other things tune-up related had been recently done), and left as is until the gas tank ran down. Then chenged to fresh oil, filled the tank to 1/4 with super high octane, added a bottle of octane boost on top. It passed then. No idea how this might help with your CO...

I've got a rebuild kit. Hate the thought of replacing all those vac lines, though. This truck has more than my 92 VR4, and none of the diagrams - under the hood, in the service manual, or hand-drawn on this site - seem to be a sure thing. Shame I can't just throw a Weber on it. (No emissions connections means instant fail.)

Have to start thinking about a cat, I guess. Just strange that it would pass emissions with flying colors in 2012, but suddenly fail so bad I have to replace nearly the entire fuel/emissions system before I can barely scrape by this year.


I tested this last time with a bottle of Seafoam in the tank - which was below 1/4.

Not sure how running higher octane would help, though. If anything, it burns cooler due to reduced volatility. I think I need to lean it way out. And maybe replace the cat.

(sigh)

Thanks guys. Appreciate it!

The guy you need to talk to is PA_JERO, you've got his number. He's put more carby 2.6's through emissions than anyone using both Mikuni and Weber carbs. I wish i could help you but i just passed emissions at 2.1% opacity of 20% allowable in my 2 door 4 cyl <img src="/forums/images/graemlins/smile.gif" alt="" />

It should be a pretty easy thing to change the CAT for a new one, also how old in the O2 sensor, they are a wear item, like spark plugs. Also, I think there is a small lead plug at the base of the carb covering an adjuster screw to lean out the air/fuel mixture a bit. Alcohol in the gas tank helps NOX, but might help out on CO a little as well. (I've used the HEAT product found at many chain auto part stores)

-Jon

A quick and easy test to see if your converter is functioning properly is to measure the temps of the pipes at the inlet and outlet of the cat - if it's working properly the outlet temp will be higher than the inlet. No change means you need a new cat.

+10 on what RyanY said. It sounds like you need a new cat, but check with a digital infrared thermo.

John B.

Good point. The spare dizzy I've got came from him, actually. Borrowed a timing light yesterday and will be swapping in the dizzy without frayed wires just in case.

I'll keep you in mind when it comes time to smog test the Delica. <img src="/forums/images/graemlins/evil.gif" alt="" />


Hey Jon. Keith and I removed the old O2 last weekend. Had to go a little barbarian on it. Truck starts faster, idles smoother, accelerates more crisply, but the O2 was only good for an 8% improvement over the last test. Still need about a 15% improvement just to scrape by.

I'll look into the HEAT product.





I'm going to drive up to the shop this weekend to shoot it with the laser and see. Thanks, guys.

Fingers crossed. At least, with a problem like this, fixing it doesn't just mean I make a government agency happy. It means I'm reducing my truck's impact on the environment - and getting more miles per gallon! <img src="/forums/images/graemlins/kewl.gif" alt="" />

Bump.

Put an IR on it after some driving this afternoon at the shop. ~200?F inlet vs. ~350?F outlet. Seem about right to anyone here who knows? Google is full of wildly varying numbers, so I can't be sure.

I didn't think to smack it with a mallet to check for anything loose inside, BUT, I know running too rich could result in a melted catalyst, and the engine has always run-on when I shut it down, AND there's always soot on the rear window, so... [i]could it be the temp sensor for the gauge works, but the one for the carb doesn't, forcing the truck into enrichment more often than it should be (thus the reason the gauge never really gets up to operating temperature), and that enrichment is killing / has killed the cat?

Damn if these things aren't all related...