Blowing white smoke/vapour, isn't coolant.

Sorta a repost to keep things on base.

Catalytic converter/emissions question:
I had to take my exhaust off at the collector for some welding. This required separating the downpipe from the cat (and muffler/tailpipe).
Before the teardown, I was getting 20/23 MPG (City/Highway). After putting it all back together, I'm getting 16/17 MPG and feels a bit sluggish on the pedal.
Also, since putting it back together, when I start it up cold, it blows a tonne of white smoke/vapour. Doesn't smell like coolant or fuel, and I'm not missing any fluids. White smoke blows out till the cat reaches 400F. Doesn't seem to matter if the Jeep is in open or closed loop. If I remove the upstream O2 sensor, no white smoke comes out the bung, but tonnes still coming out the tailpipe, which makes me suspect something going on in the cat.

Not throwing any codes, O2 readings both look good, checked most of the electrical and vacuum but really, the problem is there in open or closed loop so it's gotta be mechanical.

Also, I just happened to have to do AirCare the day after putting it all back together. Failed miserably. HC and HO were just over the limit, while NOx was around 5.0 (limit is 1.09).

All I can think is that I must have damaged the Cat internally when pounding the pipes back into place. This explains the sluggish pedal response and poor mileage, but I still don't know where all this white smoke/vapour is coming from. I understand the Cat takes HO/HC/NOx and breaks it down into H2O and CO2. Is it possible that somehow my cat is just producing a ridiculously amount of water due to some internal failure, or would this require higher HO/HC/NOx emissions from upstream?

I've also closely monitored my fuel trim but as I don't have another 4.0L to compare to, I'm sorta blind. LTFT is around 3.1 while STFT is around -2.0.

note - Tests performed (I did some electrical testing as well, but i'm sure it has nothing to do with the problem as problem is present in open and closed loop)
* Compression test was pretty good at 159,155,142,160,162,152.
* Leakdown was good.
* Injectors are all firing (full open/close verified)
* Spark plugs are clean, but not steam cleaned . Nice light tan colour on the isolators and no build-up. Number 6 had a very small amount of black crust, but barely noticeable.
* Spark leads. Found one spark lead that was not seated completely onto the distributor, and thus it had been burnt pretty bad. The spark plug attached to it though looked good (number 3) and the cylinder was clean. Installed a new lead and problem persists.
* Couldn't find any vacuum leaks. checked with propane. No change in idle anywhere.
* Installed new air filter.
* O2 curves look good. Swapped the upstream just to make sure, no change.
* Disconnected both O2 sensors for a cold start. Same white smoke until cat heats up to 400F.
* Induced a massive vacuum leak to see if there was any change. None.
* Injected low O2 readings to force a lean burn condition. No change.

I'm also going to open up the exhaust at the collector this afternoon to verify the problem only happens AFTER the Cat. I can't get the cat off the downpipe without cutting it off at this point, so collector will have to do.

Do an old fashioned vacuum test. If you broke up the matrix in the cat, you could have an obstruction now. That would show up as bad vacuum.

Yea, I'll run the vac test as well here, but that only really narrows it down to an obstructions SOMEWHERE. No idea where.

I did just pull the exhaust off at the collector again. Discovered something I didn't notice previously. The smoke doesn't show up immediately after startup. It's more like about 30 seconds after startup. Also confirmed that there is NO smoke coming out the collector. I actually sat under the heep with the downpipe in hand and held it in place to the collector, smoke comes out tail pipe. Pull back a bit so the exhaust comes out the collector instead, and no smoke at all.

So with this information, do we know anything? Whatever the smoke is, it doesn't smell like burning anything. Looks like thick water vapour but hangs in the air a while, but that may be due to the high humidity and cold weather.
Is there any specific type of damage to the cat that would cause higher production of water vapour, but still leave high NOx as well?

I'm just trying to figure out if there's any way the issue could be further down. Maybe the muffler instead of cat, or is cat really the obvious culprit at this point?

Maybe a plugged drain hole in the muffler and your muffler is full of water?

N8N_99xj said:

Maybe a plugged drain hole in the muffler and your muffler is full of water?

Click to expand...

Never did see a drain hole on the muffler. Checked now, and couldn't find evidence of one.


Did the manifold vacuum test. Looks good as far as I understand the test.
18" vacuum at idle. When I give it some throttle, the vacuum drops quickly then climbs back to a bit above 18". At 2000RPM I'm at around 22". When I let off the throttle, vac climbs up and then drops back down quickly.
Does this rule out exhaust restriction?

Stupid question but did you put the cat on backwards?

I left the cat attached to the muffler, so unless it was on backwards to begin with, it should be on the right way
This is making me insane. It looks, acts, and feels like a rich condition, but doesn't smell rich, and didn't touch anything other than exhaust, and when I take the cat out of the picture, the white smoke goes away. I'm seriously considering risking the massive fine to take it out on the highway with the cat/muffler/tail pipe removed to see what kind of mileage I get.

I figured it was a long shot. I know the intake side tends to get more clogged over time so if it was backwards you would see all the build up burning off.

N8N_99xj said:

Maybe a plugged drain hole in the muffler and your muffler is full of water?

Click to expand...

I drilled a small hole in the bottom of my muffler and put a sheet metal screw in there. I've been know to get in a little too deep on occasion and have had to drain my muffler. That sheet metal screw has been in there for years. Many mufflers come with a tiny drain hole.

Maybe you are blowing powdered ceramic out the exhaust? Hold a paper towel maybe 4-6 inches form the exhaust and then check to see what comes out, water, soot, coolant whatever, give it the sniff test also. If it is coolant you may even get a slight tint the same color as your antifreeze on a white paper towel. Most times when there is a lot of condensation in the exhaust it will actually drip, drip, drip, out the end of the exhaust pipe until things get way hot.

That's the thing. If the Cat is somehow damaged and creating the white smoke/vapour, that's fine, but it's not creating enough of an exhaust restriction for me to confirm it by vacuum gauge. If it's not creating enough restriction to measure, it probably isn't causing my mileage to to go hell. So then I've got two separate problems, or the cat is just doing it's job and making water from my massively rich mixture, which is being caused by seomthing else entirely.

Just grasping at straws here. But I'd be pulling a few plugs and checking the color. Six cylinders and you can be burning way lean is some and rich in others. Kind of a classic situation with a vacuum leak, wherever the vacuum leakage is in the intake (or into the vacuum inlet) it is likely off center.

I'm by no means an emissions expert, but when I hear high NOx I think lean burn, vacuum leak, not enough fuel or wrong plugs, maybe a faulty CAT.

Mileage isn't everything, too much air or not enough fuel into the cylinders raises the combustion temperature. If it gets high enough critical bits and pieces of the motor melt. I tend to run mine, happily, a little on the rich side for longevity. Lean motor damage here is pretty common, no speed limits on the autobahn.

Did pull all the plugs. 1-5 look absolutely perfect (almost suspiciously good, but not so clean that I'd suspect a water leak ). Number 6 was almost perfect except for a very small amount of black carbon deposit around the edge. While investigating the #6, I remembered that every so often, after a few hours of hard wheeling, when I let the engine cool down for a few minutes and start it back up, it'll ocassionally stutter for 30 seconds on startup and smells real rich. Suspected the N6 injector was leaking down as the cylinder cooled (also explains why my fuel pressure drops after 5 minutes being shut down), so I swapped it into the n5 cylinder to confirm, but now it's not doing it .

At any rate, an injector letting the cylinder pull some fuel in while cooling down wouldn't cause my current running problems (I don't think?).

Looked all over for vacuum leak, and picked up a vacuum gauge as well. Can't find a leak anywhere.
I'm stumped for now.

I've NEVER changed my fuel filter. I suppose that could be something, though that probably doesn't explain the white smoke from the cat. I suppose I'll check fuel pressure tomorrow, and maybe track down some newer (bigger) injectors as well. Saw a Neon at the wrecker the other day.

Just started my Jeep. It's cold and damp out.
FT = -9
STFT = -8
LTFT = +7.8
Fuel consumption at idle = 0.98G/h (gallon per hour)

Once it warms up, it'll show: (By warm up, I mean the post-cat temp is 450F).
FT = -2 to +2
STFT = -2 to +2
LTFT = +1 to +3
Fuel consumption at idle = 0.64G/h


What's confusing me is that my FT/STFT are always negative or closer to zero, while the LTFT is always around +3. I don't understand how this can be true if the STFT is never +3.

Anyhow, here's some pictures/video.

This is about 40 seconds after startup.


The smoke it's making.


Link to video:
http://www.youtube.com/watch?v=DKNq0SHuOGs

Just figured something else out.
When the engine is warm and not making any smoke, If I pull the #6 injector wire or spark lead, i get smoke again. Doesn't do this with any other cylinder.
So if it doesn't get spark and/or doesn't get fuel, it makes smoke.
WTF?