Oil furnace smoke smell

I have a Bryant model 388E furnace with a model AFG oil burner installed under the house in the crawl space in 1993. The furnace has operated well until recently it has started giving off a slight smell of smoke when it fires off. After the fan starts the smell dissipates quickly until the next startup. A carbon monoxide detector mounted directly on a register reads zero so it is not dangerous, just annoying. The furnace has been serviced yearly since it was installed.
I have put off getting it fixed since the normal serviceman says he is very busy and my own opinion is that the repair might require the house to be without heat for a considerable time and this is a bad time of year for that. In addition the serviceman seems to have no idea how to proceed with a repair.
A likely cause for the smell is either a cracked heat exchanger or a bad gasket. I note from the papers that came with the furnace that the heat exchanger is removeable and is also warranted against defects for as long as I own the furnace. The installing contractor has gone out of business and I expect the small print in the warranty essentially voids it anyway.
Perhaps someone on this group can advise me if the heat exchanger for this furnace is still available from Bryant as a repair part. If it is not available or repairable it seems likely that a complete furnace replacement might be required and I would need to start thinking in that direction now.
Thanks
Rod
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Not good. It could be a simple thing, like a dirty exchanger...or a clogged stack...or a leaking gasket around the burner head...
Or...it could be a cracked heat exchanger.

WRONG. If you have a CO detector that came from Home Depot, Lowes...etc...its going to read zero until you get a reading that is high enough to be read, by the cheap unit, and, its a fact that none of the units sold there read until there is a possiblity of a dangerous level building. In other words, that is a false sense of security you have there.

And things break.

Then you need to find someone that knows what he is doing, and fast. Do NOT put that off any longer. If he cant figure out how to fix it, or how, or where to start looking, there is a damn fine chance that he didnt know how to service it right either. If thats the case, I would look real hard at a crack in the exchanger due to under, or overfiring, or a heat rise that was too high.

As stated before.

Not really. The installer means squat. He can install it today, and go out of the trade in the morning, and anyone that is licenced and insured in teh business can install a heat exchanger for you under warranty, PROVIDED the heat exchanger is bad. Labor is not covered under that warranty, so you are going to have to pay someone anyway.

Yes.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks for your reply.
I tested the CO detector with a candle and I found it would detect and register CO levels as low as 10 parts per million so I am confident the furnace is not putting dangerous levels of the gas into the house.
I observed the furnace operation for a few cycles. I found that it would ignite somewhat violently, slamming the draft regulator vane shut, then almost instantly a good draft was formed in the pipe and the vane opened about 1/3. I assume this is normal operation. I could detect no diesel or smoke smell around the furnace at all. I think the starting pressure forces a puff of exhaust into the air plenum somehow, and the smoke rises slowly up the heat pipes. After about 5-10 seconds this can be smelled at the registers. When the fan comes on this is completely dissipated in a second or two. When the furnace is opened so the heat exchanger can be viewed there may be a soot trail that will indicate where the smoke is coming from. I am, of course, not experienced in this and value your expert opinion.
It is good to know that a replacement heat exchanger is available. Buying a new one and paying for the installation is certainly less expensive than installing a new furnace. It is a major job maneuvering one in and out of that crawl space.
You may be right about the technical qualifications of the serviceman who has been working on the unit. However oil furnaces are kind of scarce around here (pacific northwest) and I doubt there are many really good oil furnace experts locally. I had some difficulty finding a serviceman 10 years ago. If I were to buy another furnace, I think I would go for a heat pump rather than oil, especially considering the price I paid for my latest oil delivery (yesterday).
Thanks again for your help
Rod
message

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Rod... It's possible that none of the answers have hit it. It sounds like you have a puffback problem or delayed ignition. What that means is that the burner doesn't light the second the oil begins spraying out of the nozzle and there's a slight "cloud" of oil in the chamber. Once that "cloud" comes around where the spark from the electrodes can touch it off...POOF! This would account for the slamming of the draft regulator. Once the fire has lighted it runs fine. Have a competant burner man check it. Although you've had it serviced regularly, it's possible something got in to the burner tip (nozzle) and is causing the pattern of the nozzle to be off center enough to cause this problem. If it was the heat exchanger, you'd smell burned oil all through you house and there would be soot near the registers too. A good burner man can check this out with a draft gauge. He places it in the burner area over the fire and when the forced air fan comes on, it'll usually peg the needle, indicating a force of air being introduced to the combustion chamber. Again...a good burner man can check this out. Good luck.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You are probably right about delayed ignition. I have had the furnace man out twice recently. The smell was more like diesel oil initially, but after he adjusted the burner it changed to more of a smoke like smell. I notice it is getting like diesel again now. In any event, there shouldn't be any transfer between the fire side to the air side in the furnace. So it is likely there is some sort of defect in the heat exchanger. That was why I wanted to know if replacement exchangers were still available.
The repairman never uses any instruments to adjust the furnace, so I expect he is not one of the experts you recommend. Most of the home heating systems in this area are either electric or natural gas and I expect the oil furmace experts have long ago gone into other trades or retired. The oil furnaces were replaced when the price of fuel oil went sky high about 15 years ago. I paid $1.66/gal for the last delivery. Diesel fuel at the pump with the road tax is cheaper.
I will look around for a competant repairman although I don't really know how to find one.
Thanks for your help
Rod

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.