Failed emmissions test


Old 08-15-06, 10:31 PM
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Join Date: May 2006
Location: usa
Posts: 8
Failed emmissions test

I'm having a devil of a time passing our state DEQ test and am getting some conflicting advice from local garages. Hopefully someone on here can help shed some light on the situation.
Vehicle- 85 ford ranger 4 cylinder 2.0 liter

Test results
Hydrocarbons- passing 220 my reading 985 at idle and 621 at high idle (2500)

My CO was high but I leaned out the air fuel mixture and it solved that problem.

What I did so far-
Adjust timing, replace distributor cap and rotor, pcv valve, oil change, fuel filter. Plugs and plug wires changed last summer.

mechanic reccomendations- First guy says carburetor needs to be rebuilt. Says it's dumping too much fuel.
Second guy(carburetor rebuild guy) says that Hydorcarbon excess is not caused by carburetor. he says replace cat converter.
Third guy (muffler shop) says that cat converter has nothing to do with hydrocarbons. Says I adjusted the carburetor too lean.(adjusting the idle air mixture had little effect on HC although it did make my CO go way down) Says to replace spark plugs and maybe wires.

Anyone have any insight on this? I'm tired of throwing money at it especially in light of the bad advice I've been getting. thanks!!
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Old 08-16-06, 04:38 AM
Join Date: Dec 2001
Posts: 2,538
if the engine is not misfiring due to a bad wire or plug or other reasons like low compression etc.would suspect that fuel mixture is lean whether its due to a carb problem or adjustment or a vacum leak would probably check for vacum leaks using some carb cleaner and spraying around the intake gasket and base gasket and vacum lines to see if you can find any vacum leaks for a starting point should have a fire extinguisher handy when checking for vacum leaks this way.
the convertor can lower both hc and co but your hc is so far out of range that even a new convertor will not get you into specifications if the engine is missing your hc will be out of specifications until the miss is repaired if the engine is running good and smooth and you dont find any vacum leaks would suspect that it may need a carb rebuild due to it running lean not rich the idle mixture adjustment really will not have any affect on the 2500 rpm reading but can effect the idle reading.
Old 08-16-06, 08:41 AM
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thanks bejay. What in the carb would cause the excessive HC? I did a partial rebuild of the carb last summer. I'm no expert though I just replaced the parts with the parts that came in the kit. I didn't do any adjustments or replace the float. The carburetor rebuild guy was adamant that excessive HC could not be caused by the carb.
Old 08-16-06, 12:45 PM
Join Date: Dec 2001
Posts: 2,538
just deposits in the passages of the carb can cause it to not provide sufficient fuel you can find out if its lean very easily by dribbling a small amount of carb cleaner down the carb with the engine running at idle and at 2500 rpm if rpm increases much it is running lean, either do to a vacum leak or a carb problem.
hc is unburned fuel,co is carbon monoxide or partially burned fuel, just so you know what they are, any cylinder that is missing or not firing is obviously going to cause high hc and a lean condition will generally cause higher hc cause the engine is more capable of burning a slightly rich mixture versus lean mixture.
Old 08-16-06, 01:30 PM
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thanks again bejay. I took it to a different muffler shop. The old cat was completely dead. Replaced with new one. He says I should break it in for 100 miles or so before I test. Hopefully that's it. I did a test for a vacum leak and didn't see any. Carb was dissasembled and cleaned and gaskets replaced last summer. I replaced the spark plugs today. They looked OK. Engine running real smooth. I think I reset the idle air mixture a bit richer and give it a go after I break in the new cat.
Old 08-16-06, 05:13 PM
Join Date: Aug 2006
Posts: 6
A fresh oil change and a bottle of rubbing alcohol in the gas tank allways got mine to pass.
Old 08-21-06, 10:01 AM
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Thanks all. New cat was the trick. I am amazed at the level of incompetence I experienced at local repair shops. One guy charged me 60 bucks and all he did was turn the idle air mixture screw! That was all he knew how to do. Once that didn't cure the problem he was stumped.
Old 08-21-06, 11:41 AM
Join Date: Dec 2001
Posts: 2,538
alot of mechanics specifically younger ones doesnt know a whole lot about carburated vehicles and lets face it your vehicle is 20 plus years old they rarely get to work on them also, as most of the vehicles they repair are going to be fuel injected.

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