Just can't pass emissions

How rich is too rich? Whats the numbers from the printout? Whats your exhaust system and the condition/history of your smog equipment.

pour a few bottles of rubbing alky in the tank or a few bottles of gas line antifreeze in and it will lean out

Pull codes and note what parts of the test you had issues with and when (idle, rolling, etc)? The other numbers matter, as does knowing if you're barely missing it or off by a mile.

How to pass emissions testing:

High NO - high combustion temps - retard timing, check EGR for operation.
High CO – Rich condition - fuel pressure too high, check O2 sensors, replace air filter, Clean MAF element.
High HC – Lean misfire, vacuum leak, common misfire due to worn or weak ignition system components. On rare occasions, an overly rich mixture may be the cause. Do the ethanol/E85 fill up as suggested.
High CO & HC - Cat converters, smog pump, and smog pump controls.

How to pass emissions testing:

1.) Make sure all the emissions gear the car was made with is present and connected up properly. That includes a working smog pump and cats.

2.) Make sure that you have fresh tune up with spark plugs, plug wires, cap, rotor, fuel & air filters. An oil & filter change is a good idea while you are at it.

3.) Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical






If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.



89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.



Do not jumper anything to the single black connector. It is the power for the under the hood light. It is in another bundle of wires near the windshield wiper.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is less than $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/p-7208-equus-digital-ford-code-reader-3145.aspx– It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.


4.) Post the codes and get help to fix them. Don’t try to pass with codes not fixed. Clearing the computer just temporarily removes them from memory, it doesn’t fix the problem that caused the code to be set.

5.) Be sure to do the testing on a hot engine. Drive for 15-20 minutes prior to taking the test to get operating temps up into the normal range. Do not shut off the engine while waiting for your turn on the test machine. An engine up to full operating temperature puts out fewer emissions.

squekster said:

It burns so rich it brings tears to my eyes. A funny thing thought I pulled the plugs and they look good. I ran the diagnostic codes and the only one that came up was a fuel pump code only because when I did the mass air swap I didn't hook up the wire to the fuel pump relay.

Click to expand...

this could be a lean condition.

whats your base fuel pressure with the vac off?

and the only way to get a true fuel reading off plugs is WOT. at idle they air fuel is to up and down to get a true reading. if you have an infered temp gun you can measure EGT at each header tube and see if there is a big jump in temps between tubes... colder tube would be to much fuel ie: a stuck injector bad plug and so on... and hot tube would be a lean cylinder

What numbers did you get in the test?? I had issues with passing and I did the following and passed with flying colors

Put a couple gallons of premium fuel in it
Removed the spout so the timing did not advance during the test
Made sure that car was fully warmed up and the converters were HOT

I know this is an old thread but i used its information and information from other sources and managed to pass emissions after failing 12-15 emissions tests in a row. I have a 94 mustang gt with stock bottom end, 95 cobra gt40 upper/lower intake,1.6 roller rockers, cai, full mac exhaust (cai, o/r prochamber but swapped in cats for test, mac catback), egr delete, smog pump delete, and the gt40 heads have all the egr passages welded shut (somebody else did that before i bought the heads) 303 cam 24# injectors with pro m maf, 4.30 gears. after general tune up i used the denatured alcohol 1/2 gallon to 4-5 gallons of gasoline. passed for the first time after 12-15 consecutive failures over an entire summer where i was using regular fuel. this time i put timing to 6 degrees, ran 87 octane, and put in the above alcohol to gas mix. and bam...pass!
HC .0496 limit to pass 1.2
CO .9821 limit to pass 20.00
NOX .0236 limit to pass 2.5

Thanks Stangnet!

Old thread, so this is just informational too I suppose...

Do whatever it takes to get your engine coolant temp up near the highest temp you can imagine running it without damage to the engine. High temp thermostat, cardboard over the radiator, whatever... Have the engine very hot when you take the test, and you will usually pass. When you get out of the testing station, take the blockage out of your radiator, or go home and put in your usual thermostat.

I learned this when trying to pass a pickup that was burning oil on a massive scale. The truck owners couldn't afford to fix it, and needed the vehicle, so I got it passed. Since then I have got a few passed this way for cash strapped owners.