failed emmissions
Thread Starter
Heel & Toe
Joined: Sep 2006
Posts: 19
Likes: 0
failed emmissions
I need help. I failed a smog check and it shows that my 90 vette is running way to rich. ( like twice the calif. maximum)I have already replaced fuel and air filters,plugs and wires, oil, egr valve, knock sensor, O2 sensor fuel pump and ECM. The only other thing I have done is put in a 160 degree thermostat. I am not throwing any codes. I do have some stumbling on acceleration after the car warms up. I haven't a clue on how to lean the motor out so I can at least pass smog. any help would be greatly apprecciated.
Last edited by michaelparola; Jan 26, 2007 at 04:31 PM.
Burning Brakes
Joined: Sep 2004
Posts: 869
Likes: 1
From: Bradford Pa
I need help. I failed a smog check and it shows that my 90 vette is running way to rich. ( like twice the calif. maximum)I have already replaced fuel and air filters,plugs and wires, oil, egr valve, knock sensor, O2 sensor fuel pump and ECM. The only other thing I have done is put in a 160 degree thermostat. I am not throwing any codes. I do have some stumbling on acceleration after the car warms up. I haven't a clue on how to lean the motor out so I can at least pass smog. any help would be greatly apprecciated.
Burning Brakes
Joined: Sep 2004
Posts: 869
Likes: 1
From: Bradford Pa
injector or injectors may be old/worn out/stuck open/leaking - there is also a method to test this but it eludes my mind at this point. you can read across the injector terminals on the injector itself to measure the resistance of each one. this is a start and easy to do...
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
First, you probably need to go back to a stock thermostat. Fuel delivery is a function of Coolant Temp with the Coolant Temp Signal replacing the choke. Colder - more fuel - warmer - less. Emissions certification/requirements are at operating temp in the 200's - not start up or warm up (or with the a/c on for that matter). So you might replace the thermostat, then look at your BLM's once it's up to designed operating temp. If deadon, you might try another test and if it fails that, you probably need a new CAT. Otherwise, if the BLM's are lean, the O2 probably has air flowing past it that isn't part of the exhaust stream and that causes the ECM to add a bunch of fuel it doesn't need. The cause can be a vacuum or exhaust leak or an air pump that's putting air into the Headers instead of the CAT plus some other things, so get some more data to see what you need to start looking at.
Pro
Joined: Mar 1999
Posts: 678
Likes: 0
From: Oslo, Norway
Running a little rich?
I have no requirement for a cat but the measurements do a little rich at the idle. When increasing the rpm it get better which idicate a hotter than stock cam which is right. I want to take away the cat due to better sound.Will that make the hydrocarbons go dramatically up and the co too???.
I have thought that it might be that I get airleakage into the exhaust system via the airvalve at the headers in the air system. The valves are my original 1985. Have there been problems with leaky valves( I have not read about it). I have only one O2 sensor on the passenger side I think and I have a needlepoint thin leakage in the drivers side headers. I don't think that would have done the rich mixture. I think that the headers have good gaskets and do not leak but how can one measure that?
Will appreciate some good comments
JAn-Erik
I have thought that it might be that I get airleakage into the exhaust system via the airvalve at the headers in the air system. The valves are my original 1985. Have there been problems with leaky valves( I have not read about it). I have only one O2 sensor on the passenger side I think and I have a needlepoint thin leakage in the drivers side headers. I don't think that would have done the rich mixture. I think that the headers have good gaskets and do not leak but how can one measure that?
Will appreciate some good comments
JAn-Erik
Thread Starter
Heel & Toe
Joined: Sep 2006
Posts: 19
Likes: 0
First, you probably need to go back to a stock thermostat. Fuel delivery is a function of Coolant Temp with the Coolant Temp Signal replacing the choke. Colder - more fuel - warmer - less. Emissions certification/requirements are at operating temp in the 200's - not start up or warm up (or with the a/c on for that matter). So you might replace the thermostat, then look at your BLM's once it's up to designed operating temp. If deadon, you might try another test and if it fails that, you probably need a new CAT. Otherwise, if the BLM's are lean, the O2 probably has air flowing past it that isn't part of the exhaust stream and that causes the ECM to add a bunch of fuel it doesn't need. The cause can be a vacuum or exhaust leak or an air pump that's putting air into the Headers instead of the CAT plus some other things, so get some more data to see what you need to start looking at.
Thread Starter
Heel & Toe
Joined: Sep 2006
Posts: 19
Likes: 0
injector or injectors may be old/worn out/stuck open/leaking - there is also a method to test this but it eludes my mind at this point. you can read across the injector terminals on the injector itself to measure the resistance of each one. this is a start and easy to do...
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Burning Brakes
Joined: Sep 2004
Posts: 869
Likes: 1
From: Bradford Pa
however, if one of them are firing irratically or something of that nature...that could cause an issue...
as far as what ohm they should be...i believe around 16 for high impedance injectors which is what the TPI's came with - i'd consult a service manual or perhaps someone else will chime in with the correct number
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
You will not pass without a CAT or if you do, you will be a very rich person and probably own a couple of Z06's and be posting on another Forum.
Stock Thermostat is 195.
Air Valves at the headers can be checked by removing and making sure that air only passes through them in the direction of the Headers.
The Block Learn Multiplier is simply a mathematical representation of Long Term Fuel Trim - Rich or Lean or ideal (128). Above 128, it's Lean and the ECM increases injector on time to richen it up. Below that number is just the opposite. Whatever it is leads to an easier diagnosis. Hook up a scanner to find out.
Stock Thermostat is 195.
Air Valves at the headers can be checked by removing and making sure that air only passes through them in the direction of the Headers.
The Block Learn Multiplier is simply a mathematical representation of Long Term Fuel Trim - Rich or Lean or ideal (128). Above 128, it's Lean and the ECM increases injector on time to richen it up. Below that number is just the opposite. Whatever it is leads to an easier diagnosis. Hook up a scanner to find out.
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
I live in California. I run a 160 thermostat and have passed a smog with it on. I installed an adjustable fuel pressure regulator. I set it at about 35 psi. I set the timing to 4 degrees. I run the engine at idle with the AC on just before the test. Get it hot and then bring it in. I passed with flying colors.
Drifting
Joined: Dec 2003
Posts: 1,344
Likes: 0
From: Conyers Ga
I failed mine earlier this month for the same reason. My mechanic adjusted the timing to where it ran so lean, it almost stalled. That and a can of sea foam and I passed by wide margins. Afterwards, my mechanic set the timing back to where it was.
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
Have you pulled the plugs and checked them for heavy carbon deposits or wet with fuel? also, do a leak down check, hook a fuel pressure guage (i think you already have) and it should take about 5 mins for it to leak down, anything less may indicate leaky injectors.
Tom
Tom
