What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Need Help, failed emissions! 1991 k5

M

Messenjah

Registered Member
Joined
Apr 21, 2013
Posts
23
Reaction score
0
Location
Portland
I failed emissions terribly bad. My k5 has 143k original miles. The HC was 731 and CO 6.2 CO2 was 9.8

As you can see the results are far beyond standards HC 220 CO 1 CO2 6

I am wondering if this means it's a bad cat. It probably is time for a tune up on it. Everything on it is fairly original except the muffler, fuel pump, fuel tank, and hubs. All of which I replaced with new. The truck runs really well. Any advice is appreciated as always.
 
Even without a cat fuel injection should burn pretty darn clean if it's working right.

Plugs and wires would be my first inspection/replace, along with cap/rotor inspection (I never replace unless they are actually in bad shape).

Does your check engine light work correctly? If so, any codes?
 
Most of the times my trucks failed emission tests when we had them here (now they dont test vehicles 20+ years or older),I failed them mostly because I was forced to sit idling in the parking lot a half hour,before I got my turn in the bay to be "sniffed"...when I was lucky enough to go for a blast down the highway and floor it several times,then pull right into the inspection bay,I passed with flying colors..
There are tricks to passing emission tests,like adding dry gas (isopropanol) to the fuel to lean the mixture out more,advancing the timing sometimes helps,and on one of my older trucks the guy pulled the pcv valve out of the valve cover and laid it aside,and it passed,after failing for excessive hydrocarbons...

It never hurts to have fresh plugs,cap,rotor and wires,and air filter when you go for an emission test,but getting the engine HOT is the key...idling sitting still wont get the combustion chamber hot enough..
 
Is it burning oil? If so, how many miles since you changed the oil?
 
It's been a few years since I had to do an emission test to my '82 but the last year it was required for me was a PITA to pass. At the point all the EGR stuff was gone and it was failing miserably.

Failed a couple of times initially and then I wound up buying a couple of gallons of methanol racing fuel from a specialty place and ran that on a near empty tank during the test. The truck passed with flying colors. Smelled pretty awesome in the process as well! Good luck.
 
Old oil can make it fail an emissions test real quick. As others have said I would start with a FULL tune-up including an oil change then try again.
 
Thanks for all the replies! I had just changed the oil after using amsoil flush. So the oil was great and I had just used their fuel additive p.I. performance in the tanker
tank too. The truck runs great, don't think I burn any oil. I do get the blue puff of smoke on occasional starts ups, but very rarely.

I did sit in line awhile. I think I am going to give the crc guaranteed to pass a try and get the engine really hot before I go and test it. I live in Oregon so the testing centers are not very close to the freeway. I don't have any check engine light indications. Not sure how to change the timing on my truck but I am going to research it on here and learn. I am trying to learn as much as I can about my rig and this website has been amazing in the learning process.

I am ordering a.c. delco plugs with a summit rotor wiring and cap kit, as well as a new summit air filter. Not partial to summit or anything,they just have it for a great price and seem to be a reliable product.

I did put a flowmaster super 40 on it with my friends help but I doubt that would have anything to do with my test score. I am having another mystery issue with my truck that my mechanic couldn't figure out even but I can start a new post for that. It's a rubbing noise that comes and goes periodically. As soon as I try the tune up and test again I will post my results. Thanks to everyone for the help.

Any thoughts on the crc stuff???
 
If I were to try the racing fuel, do I just run the truck to empty and then put like 3 gallons in before testing? The racing fuel won't harm the truck at all?:confused:
 
Messenjah said:
Any thoughts on the crc stuff???
Click to expand...

If you need to "cheat" with fuel additives to get around emissions, there is something wrong with the truck.

Not saying I personally care whether people do it or not, just that there is something causing the failure, and fixing the problem may result in more MPG, power, better driveability, etc.

Have to admit, I haven't had to do emissions for a long time, but I know back then you only got so many tries to pass before you had to start paying again, and it would be frustrating having to go back every time you change or fix something, having no idea whether you'd pass or not.
 
Most smog places can give you an idea of what is wrong. For me, my EGR valve was bad.
 
Messenjah said:
If I were to try the racing fuel, do I just run the truck to empty and then put like 3 gallons in before testing? The racing fuel won't harm the truck at all?:confused:
Click to expand...

I looked back through some old notes and seems like I added 2 gallons of methanol to a mostly empty tank and then immediately had the truck tested. After the test I immediately filled it up with gas.

Don't have exact info, but I recall that the NOx was reduced the most by adding the methanol.
 
Thanks greyhoundjc, I might give it a shot.

They gave me a list of possibilities, all of which I do not know how to even begin fixing. I have to register it by the 21st though and am running out of time. I am not trying to "cheat" the test and forget about any issues. The problem is that I do not have very much money or time right now. I am a grad student and working, so my days consist of work then hw. Even during the summer. I want to fix what is wrong as best I can and pass DMV too. The registration fee and doing emissions here comes out to $150. That's not even including the money I gotta spend getting it to pass.

CO possibilities:

Dirty air cleaner or filter (filter looks ok)
contaminated oil (fresh change)
stuck choke
Carburetor
mal fuel injection
Thermostat (I just changed for new 6 months ago)
cat issues
air pump
computer

HC possibilities:

Plugs, wires, rotor, cap
Vacuum leak
Exhaust recirculation system
Spark timing
CAT
Air pump
Worn valves, seals, guides, piston rings
Fuel injection system
 
My thought process was since it failed in all categories then maybe it was something from the list that was present on both lists. That's what led me to think it was the cat. My exhaust doesn't sound or perform all that great until the truck gets hot and it begins to flow real nice. I figured maybe this was the crud in the cat heating up and being forced out. Purely speculative guess by me though.

I am starting to wonder if I have an issue with the injection. The truck seems pretty good. Maybe the throttle response is a little sluggish and I don't know it (I drive like a grandma mostly). I avg 13 miles to the gallon city and 15 highway, Not sure if that info helps at all.

What is the EGR valve? NVM, I just researched it. So if I were to disconnect the valve would that help in passing? Have to be tight with my money and they're expensive to replace. I was thinking about doing a courtesy test with it unhooked to see if it is the issue.
 
Last edited:
Not sure, how do I check it? Is my truck scanable for codes? I know the mid 90s trucks were but mine is a 91 k5. If so, could I do it at AutoZone?
 
You must log in or register to reply here.

Latest Posts

Top Bottom