1992 suburban not passin emission testing

Can you remember how many miles you have driven since the engine was installed? What I mean is that if you have a good running engine and have a new converter, sometimes the easiest things are the ones overlooked. Check your air filter to make sure it isn't dirty and restricting air flow. Also check your spark plugs to see what kind of shape they are in and if they are burning clean. Spark plugs can tell a lot. If you had transfered any emission related parts from the old engine to the new, maybe one of those items has an issue or is clogged. I hope this helps. Good luck.

what did it not pass for .

Retarding the timing will cool the combustion which will lower the Hydrocarbon number,it will run bad but after a passed e test put the timing back to an advanced state which may help with the stumble.

have the obd codes checked, once they get checked, post the results here, and we will be able to better help you in a solution, I can assist you in defining what the codes mean, and how to repair your vehicle so that your emissions will drop below the required amounts so that you will pass the test

Using BIO-Fuels can often reduce the smoke emissions which will help passing any tests.

You can locate bio-fuels near yourself using google.

if it's slightly above the limit.. you could try putting in premium gas or an octane additive as that will lower your emissions slightly..

everthing effects the reading. pedal position, rpm load engine temp. air temp. all that stuff you added was just a waste of time and money. What you should of done wa diagnosed it correctly so your not cheating an emission test. Since barley failed the first time I would of recommended a tunup if not done in 40,000 miles. I would have looked at the scanner data to see if the inputs were correct. Iwould have serviced the oil if its been awhile. If everything checked out i would of recommended a catalytic converter. But there are 3 test to determine if the cat is dead we do first. If your car was barley failing and you needed a tunup and the cat was still good the need for a tuneup could toast the cat within a couple weeks.

theres 3 things ur emisans fail on 1 spark plugs 2 air filters need changing 3fuil filter so yes a full service should do it change ur oil fuil filter air filter oil filter and oil

check vacume pressure at carb. diaphram had sim. prob. with 78 caprice

Your vehicle came with a smog pump. It may have seized up (probably breaking the fan belt) and my have simply been removed by a mechanic at an earlier time. It is located below the alternator on your vehicle.
If there is no pump but a bracket to hold it, it has definitely been removed. Vehicles will often pass a state smog test without the pump. It only works during engine decelleration (when you lift your foot off of the gas pedal)
Charlie