Good morning
Reaching out for viable input
I own an 85 c10 pick up that has just failed emission
Hc side of test. Reading was 898 ppm pass limit is 220 ppm
Before testing. This is what was done.
Complete tune up
Oil change
New cat
New smog pump
Replaced all vacuum lines
Was disappointed to see it fail at such a high number on the hc side
What in the sam hill should i do or look at next?
Any input would be great.

 

My self personally I would first look at the plugs and possibly pick up a set of hotter plugs as well as checking fuel pressure.

I've read that an improperly adjusted carb can cause this too as well as a faulty smog pump among others. If the first two causes don't get you sufficient results then go back to the smog pump it self and make sure your new pump is not faulty.

 

Is this a 2-speed test?? Idle and cruise. If so at what speed did it fail?

HCs are the result of a misfire.

Misfire: bad plug, bad wire, bad dist cap, stuck open EGR valve, crossed plug wires (check 5&7 first), bad compression or an extremely lean air fuel mixture. Over advanced ignition timing can also cause high HCs.

First thing I would do it try to determine which cylinder or cylinders are misfiring.

Using insulated pliers (available at most auto parts stores) pull each wire off the plug and listen for a drop in RPM. Find the cylinder that does not change the RPM when the wire is removed.

You could also have a bad vacuum leak - possibly the power brake booster diaphragm or booster shaft seal.

Heat range of a spark plug refers to the actual temperature of the white porcelain that surrounds the center electrode of the spark plug - it does not affect the actual spark itself.

 

Its a 2 speed i guess they checked at idle and at 2500 rpm
Didnt say when failed. Just that if failed

 

did it fail at both speeds??

 

Seems odd...my friend who registers his vehicles in Tennessee every year says there is no emission testing...not even the OBDII plug in.

He lives and works in NC yet keeps vehicles registered there for now and has for the last 4 years.

Even California waives vehicles 25 years or older for emission inspection and your truck's an 85???

Why your HC's are high has been answered above,but seems odd they would expect a vehicle that old to be held to those standards.

 

post the results for all 5 gases.


if it was a misfire condition, the 02% would also be high. if its running rich do to blowby or fuel trim issues the hc will be high and the CO high also