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.

Failed e-test. High HCO and CO

malignd1

malignd1

Registered Member
Joined
Aug 13, 2010
Posts
43
Reaction score
0
Location
Lakewood, CO.
I just bought my 1990 K5 at the end of July and immediately gave her a tune-up. Put a brand new Falken performance distributor cap and rotor with wires. Replaced the plugs with those super expensive pulsars, and changed the oil putting valvoline high mileage synthetic. Just received my certificate in the mail from military families org. so I can get my support the troops plates. Took her down to get e-test and she failed with super high HCO and CO levels but passed everything else. I did notice that when I fired her up in the morning she was spewing white smoke out of tailpipe, which eventually went away after engine warmed up, but my sniffer tells me the exhaust reeks of unburned fuel. I am also convinced there is a slight miss at driving speeds but have asked several others who say they can't hear it. I have been searching for resolutions and am going crosseyed trying. Any assistance will be greatly appreciated
 
How far off is it you should have a printout?90 should be FI so would check for codes.Also If I think there's a chance of failing Ill do a fresh oil change right before I get to the station and remove the pcv from the valve cover to have it suck fresh air rather than crank fumes.If everything checks out for spark and fuel could be a bad cat or a thermostat out of range.Should have a 195 and if it runs cooler it will run a little rich.
 
reading was hc 18.6995, limit is 3.0000 and co 54.6355, limit 25.0000. I just changed oil less than 800mi ago. The cat passed. As far as the therm goes, I just bought one as a spare but haven't installed it yet. How can I check for a vacuum leak? Does almost have a blower sound when running. Could this be a vacuum leak?
Prior owner replaced stock breather with edelbrock. Could this mod be creating issues? Filter looks good. Could tbi need adjustment for too much fuel?
 
One way I use to check for leaks is use carb cleaner. Have the truck running and spray a bit on the hoses. It should change idel if you have a leak.

Have a fire ext. ready... yes I have lit my truck up.
 
The TBI gaskets commonly leak and would cause a vacuum leak resulting in higher HC numbers.

Do a CK5 forum search. It has helped me with numerous issues. There are a lot of guys on here that know what they are talking about.
 
I had a similar problem on my 89, it ended up needing the EGR valve replaced, passed with flying colors after that.
 
Thanks,
I appreciate all the info. Now if i could just find est wire to try my new timing light.
 
EST wire should be on driver's side of firewall under brake booster.

The oxygen sensor is the most common thing I see that causes high CO and high HC, just install a new one they are pretty cheap. I also occasionally see the vacuum hose disconnected from the throttle body especially after someone has done work on the throttle body or distributor as the hose is easy to knock off and/or split the rubber elbows on the ends. Also having the timing way out will cause emission failures and overheating issues. At your altitude I'd set the timing @ 3-4 degrees instead of 0.
 
malignd1 said:
reading was hc 18.6995, limit is 3.0000 and co 54.6355, limit 25.0000. I just changed oil less than 800mi ago. The cat passed. As far as the therm goes, I just bought one as a spare but haven't installed it yet. How can I check for a vacuum leak? Does almost have a blower sound when running. Could this be a vacuum leak?
Prior owner replaced stock breather with edelbrock. Could this mod be creating issues? Filter looks good. Could tbi need adjustment for too much fuel?
Click to expand...

Bingo, that is the sound of a vacuum leak for sure. Find that leak and either take your chances and try for another test and hope that alone makes it pass or replace the CAT as well then try another test. A NEW CAT will clean up HC's no problem (assuming no vacuum leaks).
 
4X4HIGH said:
Bingo, that is the sound of a vacuum leak for sure. Find that leak and either take your chances and try for another test and hope that alone makes it pass or replace the CAT as well then try another test. A NEW CAT will clean up HC's no problem (assuming no vacuum leaks).
Click to expand...



Vacuum leaks will definitely cause the HCs to go high but not CO; in fact it will cause the CO to go low because CO output has a direct correlation to the air fuel mixture. A rich mixture will cause a high CO reading and inversely a lean mixture will cause a low CO reading.
 
Today I replaced the oxygen sensor on "Gertrude"(working title) today and alSo I found that a hose connecting to my "vacuum advance"?...at least that is what the guy at napa called it, was falling apart and i replaced it with new hose and a new port and the idle seems to have dropped a little but exhaust still smells rich. I decided to do a jumper test and was given a code 42. I did disconnect my est wire earlier today just to check the timing and the idle dropped significantly when i did. Timing appears to be right on . I also decided to try and check for vacuum leaks using carb cleaner method and didn't seem to be able to locate any leaks. Only 3days left before free retest expires. Any insight would be most appreciated as frustration looms and visions of my dream ride being road ready for winter fade ever so slightly with each additional moon that rises.
 
Ok, im surprised no one else has said it. so here goes...

you just bought the vehicle. My advise would be to put the truck in factory operational condition, with factory parts, before you started using any "as seen on tv" parts. gotta have a base line to work from, and we all know the factory setup gets the job done. Id head on down to the parts department at chevy and get good ol ACDelco parts for that tuneup, and possibly given the code 42, and the way the vehicle is operating, a new ignition control module (small part on bottom of distrubutor housing) just to be safe.

High HC is caused either by a rich condition (how's your air filter look?) or incomplete combustion. hence my questioning the "as seen on tv" stuff. If you have a vacuum guage, You can try setting your timing by vacuum, the engine may have a stretched timing chain throwing off valve timing causing these concerns.

also, never hurts to get a high quality fuel treatment (aka BG 44k or similar) and put that, as well as fresh high test fuel in the tank. May even want to get a fuel induction service done in case there is carbon build up in the intake manifold.
 
also, on a fuel injected system, a fuel flow restriction can cause both high HC and CO, so id replace your fuel filter, and possibly check your fuel pressure at the same time.
 
So I just got back from the re-test and now the levels are even higher than they were before by about 1/3. Can anyone recommend a mechanic or shop in Denver that I can take this to and have it checked out and repaired who will not over charge me. I would like to continue to do it myself but I do not have a garage or space to do more extensive work. Are my non delco plugs and rotor/cap the likely culprits?
 
You must log in or register to reply here.

Latest Posts

Top Bottom