1995 Dakota SLT 4x4
263,000 miles

It's that time! Smog check time in California and the truck failed the first test, the second test, and now the third test. I'd like to document my California smog journey and hopefully, it will help others with similar problems.

Before 1st test
No work was done on the truck. I used 2 bottles of Techron fuel system cleaner about 2 weeks before the test and let it all burn out, filled with fresh gas, aired up the tires, drove the truck for 40 minutes before going to the smog station.
Results: failed for high HC and high NO

1st smog check fail


Before 2nd test
I did a full tune-up. Autolite plugs gapped to 0.35", wires, cap, rotor, air filter, PCV, crankcase breather element, and a fresh oil and filter change. Check out the pictures of the plugs. It's been two years since my last tune-up. White ashy deposits on the plugs look like we are running pretty lean. Ran the truck for about 100 miles before the next test.



Results: failed for high HC and high NO. Slightly lower numbers but not enough. At this point, I can't get much help as to why it is failing without paying a diagnostic fee of $300 for most shops. I called a few mechanics and one even said I should replace the engine because it is too old and worn out. I'm not giving up that easy. I also don't have the money to replace the engine.

2nd smog check fail


Before 3rd test
I'm a bit desperate at this point. After some research, I bought a vacuum gauge to check engine vacuum leaks. This link helped me verify my findings.
https://www.classiccarrestorationclu...oubleshooting/
The gauge stays solid about 20 at idle and snaps within a normal range when opening throttle quickly. So no major vacuum leaks. I'm suspecting lean running conditions, but that is hard to nail down and fix. Next, I need to check the fuel pressure with a gauge to see if I have a clogged filter or bad fuel pump that is starving the engine. More on this later.

Since the truck has so many miles and smokes a bit when I start it up or even during acceleration from idle, I decided to try some snake oil as a hail mary. I put a quart of Lucas oil stop-smoke/stop-leak in the engine. It's just really thick oil that helps with worn rings and valve seals. I also added two bottles of CRC "guaranteed to pass" in the 22-gallon gas tank. I followed the directions exactly; fill up with gas, drive until only 1/8 tank left, fill with fresh gas, drive for 30 minutes before testing.
I was certain this trick would do it. The truck smoke at startup diminished and the exhaust doesn't smell as rich.
Results: failed again! Higher numbers than the first test before the tune-up!

3rd smog check fail

At this point, I'm contemplating selling the truck or giving it to a scrap yard. For some reason, I never thought about replacing the catalytic converter. The existing cat is aftermarket and I think my dad had it replaced around....well who knows....maybe 160,000 miles. So in theory this cat has 100k on it! Another reason I didn't think to replace the cat was, oh I don't know, maybe because I'm getting quotes of $1400 for a replacement!
Also, the first smog shop said that I need to fix whatever is causing the exhaust smoke. So I never focused on the cat. I agree, this is something that should be addressed. It's likely bad rings and definitely bad valve seals. 263,000 miles of love does things.

Moving on.
I read somewhere that if the catalytic converter is suspect then you can check the temperature before and after the cat to check its operation. Using an infrared camera temperature gun, I read the temperatures of the exhaust pipe before and after the cat. Since this is a catalyst I should see a hotter/higher temp after the cat than before the cat. Check the images out. I'm reading 173C before the cat and about 102C after. Well, would ya look at that? My cat is completely F'd. Check out these pictures.

Exhaust pipe before the cat. Engine side.



Exhaust pipe after the cat. Tailpipe side.

The next fun part is finding a CARB-compliant cat at a decent price. Muffler shops are quoting anywhere from $800 - $1100 just for the cat and another $100 - $200 for install. I found that Napa, O'Reilly, and AutoZone all quote the same $1400 just for the cat.
After some more research, it turns out they are all quoting the entire exhaust from y-pipe to muffler. I looked up a CARB compliant catalytic converter (say that 3 times fast) from Walker PN 80906. Found it for $460 on Amazon.

I plan to update with fuel pressure readings and post-cat install. I hope this thread helps anyone out there with these beloved trucks.

 

How old/what brand are your O2 sensors?

 

I always did the tune up and oil change right before the test, like within the hour before the test if I could.

 

I had trouble getting my 95, 5.2 to pass smog. I found that f I drove for 20 to 30 minutes on the freeway, then went directly to have it tested, the Cat warmed up enough to pass smog.

 

Another problem I had was that my truck was stolen a few years ago. They cut off the CAT. My daughter’s boyfriend offered to put a new Cat on. I don’t know where he got the Cat. Thee years ago I failed smog because the model# had been filed off it. I took it to a shop and had a new California compliant Cat installed. Parts $274. Labor $300.

 

I would move out of that state as fast as I could.

 

NTK brand O2 sensor. It was changed 2 years ago when I last smogged it.

 

Also, I installed the Hughes intake manifold plate and new gaskets last year about this time. I know someone is going to ask! That will contribute to high HC with all the oil burning in cylinders.

 

From various reading, this seems to be either a lean problem, or, and egr problem. Might verify egr is working properly, and the passages aren't clogged.

Looking at the temps on your cat though.... That ain't right, it should be HOTTER on the exhaust side of it. (not the engine side....)

 

I find walker 80906 as a California universal cat for a 95 Dakota.

The truck is burning something looking at the plug. Does not look lean to me. The plug is not read by the porcelain. That should always be white and clean.

I would be trying a new catalytic converter, aftermarket do not last long. Walker has 50 000mile warranty, so they last a bit longer.