Can't pass emmissions!

cr55 · March 04, 2010, 04:23:38 PM

Hey, I know this isn't a hot rod but, I have a 94 Chevy Full size pickup with a 305 motor and high milage that won't pass the LOW speed emissions test. It passes the high idle or high speed part of the test with flying colors. Just the idle part has the problem. It fails the test miserably. I've tuned it up completely, but no luck, only down a couple of points. The truck has a sporactic miss to it, not all the time, but enough. I don't want to just start replacing parts because I'll be broke before i know it!

Any one have any suggestions? Thanks, CR

wayne petty · March 04, 2010, 05:00:15 PM

first... i would pull the cap and rotor...

take a bright flash light... look at the riveted reluctor wheel.. see if there is any play in the upper shaft... see if the ceramic magnet that is riveted under the the top plate is cracked...

you can see a ring of exposed magnet around the shaft... and around the outside of the upper part... if it has cracks... it will create random misfires..

this is what a replacement distributer from autozone looks like

http://contentinfo.autozone.com/znetcs/additional-prod-images/en/US/c11/30-1830/2/image/8/

it has a far superior design... costs a 100 bucks and a 23 buck core charge...

check the shaft for play... i had to replace one 2 days ago.. has almost a quarter inch of play at the top.... it was hitting the tip of the rotor on the cap terminals.. making all kinds of racket..

i also had to replace the coil.. it had a burned spot in the side.. where the high voltage was leaking from...

the owner got up under the passengers side dash.. disconnected the timing wire, with the air cleaner can off i used a screw driver to wedge the corner of a shop rag into the idle air control port.. this slowed the motor down to where i could set the timing.. set the timing to 0 .. 91,4.3 T10 blazer.4x.. it ran so good.. the owner was so happy.. he did not even scream about the price of the distributer.. the coil was only 22 bucks... i also made sure the coil wire was squeezed slightly so it held down tight..

you might also want to adjust the idle speed screw... so the throttle blades do not catch when you open them... and when you have the rag into the opening .. the engine barely idles at 500 rpm or so.. maybe less..

do open the throttle lever with the engine off... wiggle it around.. see if there is any movement in the throttle shaft bore.. worn TBI throttle shaft bores is a big problem on TBI motors..

freddrew · March 04, 2010, 05:13:36 PM

Just before you take the vehicle in for the next emmissions test, make sure the engine is warmed up and add a Quart of Methyl Hydrate to the fuel tank. That helps most engines pass the tests.
Fred

wayne petty · March 04, 2010, 05:16:23 PM

oh.... before i pulled the distributer... i had the cap off...

figured out which way the rotor should point when number one fires...

bring the crank around and line it up on the timing mark... and see where the rotor is pointing...

look at the pick up coil tips.. and the fingers on the reluctor.. turn the crank slightly till they line up... look at the crank timing marks..

now you can pull the distributer and put another in.. with the shaft pointing the same direction.. you can then put the new one in.. turn the housing to line up with the >< and the engine will start on the first try... usually you can get the timing so close.. you only may have to check the timing... but since you are going for a smog test.. it has to be exact...

Ed ke6bnl · March 05, 2010, 03:14:05 AM

Quote from: "freddrew"Just before you take the vehicle in for the next emmissions test, make sure the engine is warmed up and add a Quart of Methyl Hydrate to the fuel tank. That helps most engines pass the tests.
Fred

where would you get methol hydrate is this the same as methaol ED

cr55 · March 05, 2010, 07:55:20 AM

Guys, thanks for the help! I'll give it a try and see what happens...I hate DMV!

...CR

tomslik · March 05, 2010, 11:53:42 AM

i'd wanna see the co and hc numbers 1st.
what's not passing?hc or co? nox?

94, the cat's prolly dead....or the o2 sensor....

cr55 · March 05, 2010, 12:52:54 PM

The HC's are to high..way high for idle only...CR

tomslik · March 05, 2010, 04:28:24 PM

Quote from: "cr55"The HC's are to high..way high for idle only...CR

cracked plug,bad plug wire,vaccum leak,egr stuck open?

freddrew · March 05, 2010, 08:43:00 PM

I usually get it at a paint supply store
Fred

parklane · March 12, 2010, 11:14:08 PM

Methyl Hydrate is also called wood alcohol, and gas line antifreeze. Right Fred??

wayne petty · March 13, 2010, 12:55:50 AM

oh... by the way... i got a call from the guy with the S/T 10 blazer today.. thanking me for what a great job i did...

the truck it totally drivable.. gets better fuel mileage... starts easy.. has great power and no more weird misfiring..

the only thing i did was replace the coil, cap , rotor.. as they had a serious amount of burn marks... and installed an updated small cap hei.. with the new style reluctor and pick up coil that i linked a picture of above..

i posted what i did.. as you had mentioned that you had a small misfire..

i just tired to point you in a proper way to diagnose misfires that plague these motors...

why would a cracked reluctor make a difference..

this is do to the spark timing module looking at even wave forms.. then holding back the coil trigger signal a few MS... so the coil can fire before the actual base timing come up...

with a cracked reluctor or pick up coil magnets... the random/ghost wave forms that get created trick the ecm into triggering the spark at random times... this is the misfire... that you might be feeling..

this is the misfire that might be causing you to fail smog..

you don't have to replace anything... just examine the stuff i listed above...

this is why the internet was invented.. many heads are better than one..

inflamation sharing is swell