smoke at idle

I searched and most results I found deal with smoke on acceleration, but what I have is smoke at idle after warmup. I first noticed it about a week ago and thought the rings were gone it was so bad. I checked the oil and it was a little low, but not enough to cause any issues. When I got it home I pulled the plugs and found alot of carbon buildup, so I changed the plugs and ran a couple cans of seafoam through the intake. I thought this had cleared up the problem, but it is still smoking.
It only happens after prolonged driving and then a period at idle. I believe it is runnning rich, but I'm not sure why. It has been running a little cooler than normal since the weather has been colder. I am going to check the thermostat and make sure it is not stuck open and replace it (195*).

This does not appear to be a head gasket leak because I am not losing any coolant. I thought it might be valve stem seals, but that should not smoke after prolonged driving. I've heard the MAP sensor causing smoking and a rough idle, but my idle is smooth. The o2 sensor is about 1.5 years old and I haven't noticed any huge mpg drops (it usually only gets about 13.5 city).

Anybody have any ideas?

Thanks

what color is the smoke?

blue = oil

white = condensation or coolant, if coolant it'll have a bit of a sweet smell

black= too rich (gasoline)

What year/ engine?

As long as the engine is not symptomatic and exhibiting any driveability issues and if there is no check engine light (depending on your year), I would just continue to monitor the levels of coolant and oil closely.

Also, in colder weather, there may be a bit of condensation burning off which is just the byproduct of combustion. Don't want to confuse that for a problem.

If you're concerned about it running rich, finding a tech. that understands exhaust gas analysis can be helpful and not too expensive.

birchlakeXJ said:

What year/ engine?

As long as the engine is not symptomatic and exhibiting any driveability issues and if there is no check engine light (depending on your year), I would just continue to monitor the levels of coolant and oil closely.

Also, in colder weather, there may be a bit of condensation burning off which is just the byproduct of combustion. Don't want to confuse that for a problem.

If you're concerned about it running rich, finding a tech. that understands exhaust gas analysis can be helpful and not too expensive.

Click to expand...

94 model 4.0

There appears to be no driveability issues, however this amount of smoke is not normal. It is not the typical smoke after startup burning condensation from the exhaust. It appears to be a gray/black color which lead me to believe it was carbon. I used the seafoam to aleviate the large carbon buildup in the intake and on the plugs.

I call it the BurgerKing syndrome. You drive around, then wait in line at the drive through. By the time you get to the window, people are looking to see who's on fire.

It is caused by shot valve guides or leaky valve seals. The vacuum is highest at an idle and it sucks the oil down the intake valve stem/guide.

A new set of seals may help, otherwise you need a valve job which includes sleeving the valve guides. NEVER let anybody knurl the valve guides. It will lask 10k miles, then be even worse. Never buy a rebuilt head because they always knurl the guides (cheaper).

IIRC, around here if you pull the head and take it to the machine shop, boil the head, sleeving the guides, grinding the valves will run you about $200 or so.

when my front o2 sensor went bad, i'd get carbon coming out of the tailpipe. It would actually leave a black spot on the ground if it was idleing there. Might want to check that.

old_man said:

I call it the BurgerKing syndrome. You drive around, then wait in line at the drive through. By the time you get to the window, people are looking to see who's on fire.

It is caused by shot valve guides or leaky valve seals. The vacuum is highest at an idle and it sucks the oil down the intake valve stem/guide.

A new set of seals may help, otherwise you need a valve job which includes sleeving the valve guides. NEVER let anybody knurl the valve guides. It will lask 10k miles, then be even worse. Never buy a rebuilt head because they always knurl the guides (cheaper).

IIRC, around here if you pull the head and take it to the machine shop, boil the head, sleeving the guides, grinding the valves will run you about $200 or so.

Click to expand...

That sounds like exactly my problem....thank you. Is it possible to replace the seals without pulling the head? If it is possible, should I go ahead and do that or is it worth my while to go ahead and pull the head and take it to the shop? Is it possible to tell which is bad without pulling the head....what do I look for?

Thank you again for your informed answer.

i have the same issue. built a 4.6 stroker, ran out of money/time and ended up using the only head i had laying around, a '95 model with +250k on it.

engine runs great, just smokes at idle. Planning to build a head for it and change it this spring

Does anybody know how to tell what I need to replace (seals or head work?) and can the seals be replaced without pulling the head?

Changing valve seals without pulling the head can be done by a couple of different methods. The root problem is how to hold the valve up while you remove the valve spring. I made a device from an old spark plug. I broke out the ceramic so the spark plug was hollow, then I brazed a air fitting to the plug. I then screw it in the spark plug hole and connect my compressor. It forces the piston to the bottom of the stroke and applies air pressure against the valve to hold it in place. I believe some specialty supply houses have a "store bought" version, along with a special pry bar to push down on the valve spring while removing the retainer.

I have seen people take a different approach where they pull the plug and insert a carved dowel to hold up the valve.

You only need to replace the intake seals. That is where your oil is being sucked through.

Personally, I would pull the head. It isn't all that much work and then you have a chance to clean all the carbon and gunk. Check prices with your local machine shops on a simple valve job and sleeving the guides. The prices vary greatly around here. If you don't have to have one or two day service, you can usually negotiate a cheaper price.

old_man said:

Changing valve seals without pulling the head can be done by a couple of different methods. The root problem is how to hold the valve up while you remove the valve spring. I made a device from an old spark plug. I broke out the ceramic so the spark plug was hollow, then I brazed a air fitting to the plug. I then screw it in the spark plug hole and connect my compressor. It forces the piston to the bottom of the stroke and applies air pressure against the valve to hold it in place. I believe some specialty supply houses have a "store bought" version, along with a special pry bar to push down on the valve spring while removing the retainer.

I have seen people take a different approach where they pull the plug and insert a carved dowel to hold up the valve.

You only need to replace the intake seals. That is where your oil is being sucked through.

Personally, I would pull the head. It isn't all that much work and then you have a chance to clean all the carbon and gunk. Check prices with your local machine shops on a simple valve job and sleeving the guides. The prices vary greatly around here. If you don't have to have one or two day service, you can usually negotiate a cheaper price.

Click to expand...

Thank you.

If I understand this correctly, it will do no damage to leave this the way it is for a little while. The Jeep is the wife's DD, and I don't think she would appreciate transporting the kids in my trail rig while I do the work.
I think I will get a head at the salvage yard and set it up for a quick swap. I assume while I am in there it would be a good idea to replace the lifters. Is there anything else I should do while I have it apart?

Do not change the lifters. Putting new lifters on an old cam can cause lifter failure. Especially with the new oils, you should change the cam and lifters together.

Make sure and clean the valve cover well. There are a couple of baffles on the vent holes that clog up and cause pressure buildup in the crankcase. This alone has been known to push oil past the seals.