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SOS EMERGENCY: 2004 Cherokee Burning Unidentified Substance

my Grand Cherokee is burning something WHEN MOVING, the burning subsides and goes away when idling.
THERE ARE NO LEAKS, and no apparent fluid loss of any kind. the truck is bone dry underneath. in the last 3 years I’ve replaced AC evaporator, AC compressor, exhaust manifold, cats, heater core, head gasket, radiator, battery, alternator, PSteering pump, rear engine seal. both differentials are resealed, and so is the transfer case. The smell is getting worse, and I can no longer drive with windows up, as the sulfury fumes are making me seriously lightheaded.
Having AC on makes it a lot worse.
The situation is desperate, I cannot afford a new truck right now.
I suspect a refrigerant leak, but no mechanic could find it.

Any help hugely appreciated.

A sulfur smell? Catalytic converter.

After a drive check to see if one wheel is hotter than the others.
That would indicate a dragging brake.

Im going to sound like a jerk here, but it sounds like you don’t have a whole lot of extra money, so why are you driving such an expensive vehicle that is expensive to fuel and maintain?

You say you can’t afford a new truck right now, whats wrong with a cheap economy car… You won’t impress anybody, but you will have some cash in pocket.

Drive a cheap car for a while and pay off debt and save some cash. You are broke and desperate, you need to start a monthly budget, How much money a month are you putting in that pig a month with gas and whatnot? I have been there, Im trying to help believe it or not.

Anyway an exhaust leak sounds likely…You better get to the bottom of it before you kill yourself.

How about an overcharging battery puking out sulfuric acid?

A battery shouldn’t be emitting this Odor unless it’s being over charged by a faulty or over-sized (in terms of amps) alternator. An old battery can begin to emit the same oder, but over many, many years.

Car batteries that emit this odor can remain odoriferous and warm for weeks, even months after discontinuing service. Many times people can smell the oder while they’re driving or when they get back into the vehicle after having let it sit all day, like after getting off from work. This is because the battery is located in the front of the vehicle and subjected to rearward air pressure which developes inside the engine compartment while driving. This results in the odor saturating the engine compartment, pushing the oder into the ventilation system, which leaks subtly into the cabin. BUT DONT BE CARELESS: if you’re smelling this oder, the risk of personal injury is VERY HIGH-- The smell derives from the battery changing chemical composition (for whatever reason), generally resulting in an extremely hot, EXPLOSIVE battery.

Power steering fluid and automatic transmission fluid is really stinky when it hits a hot exhaust manifold or exhaust pipe. So in addition to the above, check for leaks there. Power steering hoses esp tend to crack and leak at the ends of the hoses, at the connectors where they go into the steering box, so pay special att’n to that area.

I use the truck for work, and I have to cart a sizable toolkit around, so it is not a vanity issue. I live within 3 mile radius of most of my work, and I clock no more than 3K miles a year.
I would not be able to sell the truck in its condition (and it would have been immoral to try to).

The battery is 1 year old, and the alternator was replaced a week ago, as it was charging to 9v only. there is no regulator, apparently the battery is regulated in the computer. It is not hot to touch.

I had a leak in PS, and it had a different smell, taken care of.

Again the smell disappears when the truck is idling.

the 2 front cats were replaced in november on the warranty. the dealer refused to replace the rear cat, saying that there is nothing wrong with it, and stretched it long enough to get the warranty expired. in desperation I made my mech to pop it out and put a piece of pipe in.

the smell was weak until we’ve loaded new refrigerant last week. AC had been tepid previously this summer.

I’ll have the brake checked tomorrow, the smell does seem to be worse on the driver side.

however, putting AC on makes the smell 5x worse than with mere blower.

You say it’s 5x worse with the AC on. Does it matter whether the vent is set on “recirculate” or “outside air?”

yes, outside air is a lot worse. recirculate also accumulates fumes, but slower.

A/C refrigerant would not smell like sulfur, and your A/C would stop working pretty quickly if it was leaking enough for you to smell anything. Refrigerant doesn’t have much, if any of a noticeable smell, though some of the leak detectors that are put in are stinky. Not like sulfur though, more like stagnant water or stinky socks. Also, a battery that was overcharging enough that you could smell it wouldn’t last very long.

Some lubricants are very high in sulfur compounds–gear oils such as used in differentials and some greases, such as used in wheel bearings can stink if they get hot. You say the diffs don’t leak, and if the car drives well, the brakes don’t pull or grab, and there are no grinding sounds from the wheels, I doubt this is from oil or grease.

So really all that’s left is exhaust fumes getting in somehow. I’d look for a bad catalytic converter, as they really reek of sulfur when they overheat if you’re using high sulfur fuel. I’d also look for an exhaust leak, possibly near the air intake for the cabin, which would be on the passenger side I think. Check places that are hard to see, such as the manifolds near the firewall, the couplings to the piping, and any small pipes that may have rotted out, such as if there’s a bypass tube on the EGR valve. It may help to change your brand of fuel too–some are definitely higher in sulfur than others. Though in this case the stink may be doing you a favor in helping you notice you have a dangerous exhaust leak that’s getting into the cabin.

Good luck.

thanks! will try these.

another element worth noting:
after refilling the refrigerant the cab started accumulating perfume-like chemical smell parked cold overnight. that’s why I had AC compressor replaced, which seems to have taken care of that.

the newest suspect:
the foam firewall cover is soaked near the heater hose ports with sooty oil. no idea where from it may be.
I discovered this by accident, running my hand over every surface, as this is NOT VISIBLE AT ALL.
any ideas?

2004 Cherokee has no EGR valve.

previously fumes would start spewing after 15-20 minutes if driving,
but right now they come with every time I step on the accelerator.

no fumes at all stepping on it idling.

brake dragging - negative.

Ok. You say you smelled sweet perfume air. The only thing I know with a sweet smell is antifreeze. The hoses at the heater core could be leaking since there is residue on the firewall. If you step on the accelerator while the hood is up, look around. Maybe you can see what is leaking and then burning off. I had a Dodge with a ripped transmission seal and it would drip on the exhaust and stink only when driving.

did that many times, no problem whatsoever when idling.
will check tranny seal, thank you!
there is absolutely nothing visibly dripping there.