Jump to content

My Truck Keeps Failing The Emmision Test

rudegirl

Recommended Posts

rudegirl New Member

rudegirl

Posted
Posted

my 1991 GMC 1500 wont pass the emmision test. I have replaced egr valve the whole muffler and someone at the garage said it could be the computer so i replaced with one from the wreckers..Its failing the HCppm the limit is 90 and my truck is reading 177 . can anyone give me any advice on what to do next so it will pass.

ironhead3fan Enthusiast

ironhead3fan

Posted
Posted

If your catalytic converter has never been replaced, replace it. I had to do it last year on my 1990 Chevy K1500 to get it through emissions, along with the EGR valve.

fbachman Senior Enthusiast

fbachman

Posted
Posted
my 1991 GMC 1500 wont pass the emmision test. I have replaced egr valve the whole muffler and someone at the garage said it could be the computer so i replaced with one from the wreckers..Its failing the HCppm the limit is 90 and my truck is reading 177 . can anyone give me any advice on what to do next so it will pass.

 

Not sure this will help, specifically, but HCppm is heavy, unburnt, hydrocarbon. This means you have unburnt fuel in there, beyond the acceptable limit. This means that for some reason you are rich, or, that the cat is not running efficiently or is "used up".

 

O2 sensors can cause this... if they are sending a bad signal/reading to the ECM, and throwing the wrong amount of fuel in based on the reported wrong amount of O2 in the exhaust, that could be the issue as well (makes you run rich).

angelic0- Enthusiast

angelic0-

Posted
Posted

hmm, try putting in 2 liters of Isopropanol with a full tank of gas before going through inspection 8)

 

are you sure your ignition timing is correct ?

HawkScot Enthusiast

HawkScot

Posted
Posted

back when I was several years younger, I made the mistake of putting a "performance" thermostat in my 1992 Suburban w/5.7l engine. I was satisfied, it seemed to have a bit more power, ran cooler, but the mileage was off a bit... I also put the K&N airfilter in at the same time... I figured the mileage was off a bit because I liked the way it sounded and ran....

 

Long story short.

 

The 160 thermostat never let the engine get to full operating temperature (that the computer expected) so it was running a bit rich all the time. I figured this out when it failed emissions with high HC. After doing a full tuneup (like you should have done, you did right??), I still failed emissions...

 

Had a emissions certified shop check things and they indicated I needed 3 things. Correct Thermostat (192), new catalytic converter and new O2 sensor. I had them do all three and they guaranteed it would pass emissions. It did with flying colors. I have over 250,000 miles (original engine) on this rig and it passed emissions last year with flying colors and gets good mileage too!

 

Bought a 84 Fiero back a few years, the previous owner had removed the thermostat because it was overheating... I put the correct thermostat in, replaced the water pump (cause of overheating), but it was too late for the O2 sensor and catalytic converter. I ended up replacing them also to get it to pass emissions.

 

My story and I'm sticking to it,

 

Run the proper thermostat or you will end up replacing O2 sensor and catalytic converter sooner than normal. BTW, I did not have any codes ever.

Draenor Senior Enthusiast

Draenor

Posted
Posted

Have you been keeping up on maintenance? When is the last time the plug and wires were changed? Are you getting a check engine light?

Z45 Senior Enthusiast

Z45

Posted
Posted

It could be just that the injectors are gummed up and the engine carbonized and not burning fuel efficiently. I would try running a strong fuel additive for one tank before having it tested.

 

Here is a good fuel additive that claims to help you pass emissions by cleaning the fuel system for peak performance.

 

api_bottle_300pxh.jpgP.i. Additive helps pass emission tests by running one tank of treated fuel through the engine prior to testing

 

Friend claimed his car was running like crap and after he put a bottle of this thru the tank it was running like new again.

Flyingbrian Enthusiast

Flyingbrian

Posted
Posted
... SNAKE OIL...???

 

 

agree the truck is running rich it doesnt have clogged injectors. Dont waste money running that junk through your engine :thumbs:

WilliamBos Senior Enthusiast

WilliamBos

Posted
Posted

Probably time for a cat. If you can afford it, get an OEM cat. We bout the aftermarket cheapies for my Dad's 88 GMC, and by the nest e-test, we had to replace it. The aftermarket ones seem to burn out real fast. (e-tests every other year up here.)

C. Charles Hahn Senior Enthusiast

C. Charles Hahn

Posted
Posted
Run the proper thermostat or you will end up replacing O2 sensor and catalytic converter sooner than normal. BTW, I did not have any codes ever.

 

Agreed, though if you re-tune the computer so that the vehicle is calibrated for the thermostat, those problems won't happen.

WilliamBos Senior Enthusiast

WilliamBos

Posted
Posted
William, which aftermarket cats are you talking about? Performance ones, like Summit and Jegs sell? Just curious.

 

Can't remember which one, but it cost less that $100.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.

  • Forum Statistics

    250.4k
    Total Topics
    2.7m
    Total Posts

  • Member Statistics

    342,840
    Total Members
    8,960
    Most Online
    appletrav
    Newest Member
    appletrav
    Joined

  • Who's Online   2 Members, 0 Anonymous, 356 Guests (See full list)

  • Latest Articles

  • Posts

    • newdude
      2 speed transfer case optional now?

      By newdude · Posted

      This is a 1/2 ton thing ONLY.  All HDs 2020-2026 have the two speed transfer case, with Autotrac as an option.     1/2 tons 2019-2026, regular 4x4s come with a single speed case (no 4LO!), and trucks with Z71 ordered, or all Trail Boss trucks come with the 2 speed case.  2 speed case is also an option on WT, and is also standard on High Country.  
    • newdude
      Different requirements for oil filters?

      By newdude · Posted

      2013 5.3 still to this day calls for the PF48 filter.  Which as a 15psi bypass pressure.     There is a TSB, 17-NA-157 that talks about the PF-63 and PF-64 filters which have a higher bypass rating of 22psi.    TSB HERE - temp.xml   "Beginning in 2012, the oil pumps began to regulate main gallery feedback instead of pump out pressure. This means that the oil pump now does not begin to regulate until pressure is built up to the main gallery. This change reduces the amount of time it takes to provide oil to the engine bearing and lifters during extreme cold start conditions.  Main gallery feedback oil pump control systems are present on the following engine families which use Spin-on oil filters: Small Gas Engine (SGE), Large Gas Engine (LGE), High Feature (HFV6) Gen2 and Small Block Gen5 gasoline engines. These engines with the main gallery feedback oil pump control systems are factory built with an ACDelco® oil filters"   It also calls out what engines use those filters.  The gen 4 small blocks were not on that list (LMG, LC9, L9H, L92, L94, L20, L96).  Gen 5 small blocks use the higher pressure filter.          That all said...   Your 7045 Napa filter is the PF63 equivalent, with 22psi bypass.  You are already using the higher bypass pressure filter.  You CAN keep using it, you don't technically have to use it though.  
    • Grumpy Bear
      Different requirements for oil filters?

      By Grumpy Bear · Posted

      Do you know WHY the filter relief setting was increased to 22 psig?    When the new system goes into the second stage the pump volume ramps up considerably. It was found that the 15 psi filter bypass setting put the filter in bypass on a warm engine when the second stage was activated. Raising the filter bypass setting forced the filter to do what it designed to do. Filter. Preventing debris from circulating during high load, high rpm operation.    So next question is how did GM find this out? VLOM/lifter failures and a deep dive by Melling Corp.    Last question. Is it required? Look at it like this; a motor may be equipped with a rev limiter. But it only works if the set point in reached. That 22 psig setting only matters if the pressure differential across the filter media exceeds 15 psig during normal warm operation. Second stage kicks in around 3000-3500 rpm.    I can't answer your question because I don't know you and how you use the truck. But I think there is enough information here to let you decide for yourself. 😉
    • Coastie05
      give me some tips to make my truck look better

      By Coastie05 · Posted

      Go back to OEM wheels. 
    • newdude
      2020 Trailboss 6.2 replacement

      By newdude · Posted

      Probably not their first rodeo, so it should go as planned most likely.  Typically the service manager or tech doing the swap will put some seat time to shake it down after they get it all put back together.  We usually put 50-100mi before we hand them back so if something happens, its not after you get it.  A coolant leaks, oil leaks, a ground left off or loose, vibration, etc.     The new engines so far have been good?  There's been a couple that have popped out there again (the replacement engine) but most have been okay.  

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...