four gas analysis

[candyredc10]

I recently had a four gas analysis done on my 84 c10. The results stated I had lots of hydrocarbons in my exhaust (unburnt fuel). I have a 4.1L 250 with 40,000 miles. I recently replaced my spark plugs and wires. I have the original distributor. Does anyone know what I could do to reduce these numbers? Are there any common problems with this engine that could cause this? I know that the distributors on these old Chevys are junk but mine seems to be in working order with few misfires.

 

[JoeR Jr]

Most common on older stuff with only high HCs is burning oil. There's a few other possible offenders though. Not enough timing is common too.

 

[candyredc10]

The smog technician told me that I might need new piston rings, The truck was a barn find and sat for many years, engine only has 40,000 miles. Could sitting have caused premature wear to the cylinders or piston rings.

 

[jake wells]

Run some engine restore or register it as a classic car.

 

[JoeR Jr]

The smog technician told me that I might need new piston rings, The truck was a barn find and sat for many years, engine only has 40,000 miles. Could sitting have caused premature wear to the cylinders or piston rings.

It might need rings. Might need something else. You're probably going to have to take it to someone that can diagnose it.
Joe

 

[shiftpro]

It might need i high compression BB.

 

[DoubleDingo]

I'd suggest running some MMO in the tank and the crankcase as recommended on the label. Change the oil, add the required amount of MMO to the crankcase, and drive the truck for a week, and change the oil and filter. Add the required amount of MMO to the tank, and run a few tankfuls of fuel through it. It should free-up any stuck items inside the engine, and also clean out passages, carb, etc.

 

[DoubleDingo]

I doubt it needs rings with 40k on it. But things are probably stuck some.

 

[DoubleDingo]

One more, the valve guide seals could need to be replaced. If they are no good it could be sucking oil past the seals into the combustion chambers. Much easier to replace valve guide seal than it is rings. Have you done a compression check on the engine?

 

[Bextreme04]

I would think definitely valve seals. Also, have you adjusted the carburetor? I would run through a carb adjustment and verify compression numbers are high and within 5% of each other.

 

[candyredc10]

One more, the valve guide seals could need to be replaced. If they are no good it could be sucking oil past the seals into the combustion chambers. Much easier to replace valve guide seal than it is rings. Have you done a compression check on the engine?

Thanks for the suggestions, I'm about due for an oil change and I'm going to put some classic motor oil in it with some additives. I haven't done a compression check yet, these integrated head 250s have notoriously low compression.

 

[candyredc10]

I would think definitely valve seals. Also, have you adjusted the carburetor? I would run through a carb adjustment and verify compression numbers are high and within 5% of each other.

I haven't done a carb clean or adjustment for a good while. I noticed it was idling a bit high today, so that might be in order. I haven't checked my compression yet, I need to get down to the parts store.

 

[DoubleDingo]

I haven't done a carb clean or adjustment for a good while. I noticed it was idling a bit high today, so that might be in order. I haven't checked my compression yet, I need to get down to the parts store.

Idling high can also be a vacuum leak

 

[DoubleDingo]

Thanks for the suggestions, I'm about due for an oil change and I'm going to put some classic motor oil in it with some additives. I haven't done a compression check yet, these integrated head 250s have notoriously low compression.

Conventional Oil and Marvel Mystery Oil.

 

[candyredc10]

Idling high can also be a vacuum leak

The engine idles high and a little rough. If I rev the engine it smoothes out and the rpms go down a bit but it eventually returns to the high idle. Does this sound like a vacuum leak?