91 Mustang... smoke from back seat


Old 06-02-04, 05:54 PM
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Join Date: Aug 2002
Location: Northeast Louisiana
Posts: 159
91 Mustang... smoke from back seat

Sunday my 17 yr old daughters 91 Mustang LX 2.3L got hot enough over in the back seat area to actually start the foam in the back seat to smoldering and smoke. Maybe too much information below but I'll post what I can think of in case it's helpful.

...The hot area is directly over the muffler which was replaced in Oct 2003 by a local muffler shop.
...I looked under the car and there is no shield over the muffler area but I don't know if that is normal or not.
...I've seen catylitic converters get really hot but don't know if mufflers will heat like this if clogged. The catylitic converters are forward somewhat of the area that got the heat. The rear catylitic coverter was replaced Nov 2003 by a different muffler shop but the front converter is probably original to the car.
...The engine had a very bad miss. I replaced both ignition coils Nov 2003 because the front one would drop out entirely at times then start back. The front ignition coil was NOT firing at all when I checked it Sunday by pulling the wire loose at its base while the engine running. Just checked that earlier today and both coils firing and engine running smoothly... EXACTLY same problem I had in Nov 2003. This has not occurred since changing the coils last year. I purchased the less expensive ones at AutoZone @ $41.99 ea. Maybe mistake?
...The engine temp and fluids were normal and no hot smell at all coming from the engine area. Oil on the dipstick looked clear and although very warm not more than usual for an engine just turned off. I could lightly lay my hand on the radiator without discomfort.
...Can the timing being off enough for engine to crank well but cause excessive heat in the exhaust system?

Any educated guesses?... Does this sound like something could be caused by ignition coil failure? The ignition coils are easily enough for me to replace if necessary but I don't fool around with welding equipment around gas tanks so if sounds like exhaust system will just tow to a shop.
Thanks for any ideas...
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Old 06-02-04, 07:54 PM
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Was the smoldering area under the seat cushion or the seat back? Also, was a hole burned through the fabric or other seat covering?
Having done a few dumb things in my youth, I would question whether any smokers were in the car that day.
Old 06-02-04, 09:00 PM
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
There is no muffler shield on this car and one should not be needed unless you have modified the exhaust
The timing on this engine is computer controlled so if it was off, the comp would correct for it (except at Wide Open Throttle)
It doesn't sound like youre engine is hot, just your exhaust
Probably not a coil prob.
To heat up the seat foam to the point of smoking...that would have to be really hot
I'm thinking Goldstar may be on to something...
Old 06-03-04, 06:05 AM
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Join Date: Aug 2002
Location: Northeast Louisiana
Posts: 159
First thing that came to my mind when I saw smoke coming from under the back seat was something under the seat had started the fire but there was nothing there when I looked. My daughter doesn't smoke and is avid about no smoking in her car and when I removed the rear seat there was no evidence of anything either so I feel certain it wasn't that.

The smoldering was under the seat cushion just off center on the drivers side. Only the under side of the cushion that is against the floorboard area was burned not the top seat covering itself. The area on the floor under the seat was hot enough to melt the black tar looking stuff away and discolor the metal somewhat and the foam under cushion next to the floorboard was black and smoldering in about a 10-12inch area. This burned area is directly over the center of the muffler.

The exhaust system as rest of the vehicle is completely stock no modifications of any kind.

Can a muffler get this hot? I don't doubt catylitic converters can because I've seen one hot enough it was almost ready to turn red but don't know if a muffler can heat that much.

When my daughter called she was having problems I met her, swapped vehicles and drove hers. The longer I drove the worse the burned smell became. I kept stopping and checking under the hood and under the dash for the burned smell because I never thought it would be from the back seat. I didn't find the burned area until I got home and by that time it was bad enough inside the vehicle I had to let the windows down because it burned my eyes. I could then see the smoke coming from the back seat area when I got out of the car.
Old 06-03-04, 07:33 AM
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Bent or a leak

Check to see if maybe something has made the exaust to be pushed close to the floor, something may have hit the exaust or maybe a hanger somewhere broke making that part of the exaust to raise. If there is plenty of clearance check to see if there is an exaust leak that is pointing toward the floor.
Old 06-03-04, 07:45 PM
Join Date: Jul 2002
Location: corona Ca.
Posts: 471
I'm going to step out on a limb and say it is likely not related to the 4 cylinder design, yet could be something inherent on both the 5.0 v8 platforms and the 2.3L platforms.

I deal with a lot of mustangs, and parts, and was at the junk yards a while back and saw a 91 convertible mustang that had EXACTLY the same damage you describe, I couldn't figure it out. the rear seat cushions were burn on the bottom side badly, and the damage went all along the trans tunnel where it scorched the center console, and went up to the dash where part of the dash had warped too. I've never seen that before until you mentioned this.

-I know for a fact that there are no wires under the carpet that stretch from the dash to under the rear seat

-the damage was worst under the rear seat, so perhaps it started their?

-the mustang in the yard was a v8 model, yet it was a convertible. Is yours a convertible? THe top motor is electrical, and is placed dead center behind the rear seat. It is possible that that motor had a short that could have burnt the seat which spread straight line up to the front of the car

-sometimes a transmission can leak, spraying fluid all over the inside of the transmission tunnel. I'm thinking it's possible that oil/tranny fluid could have been coated all over the inside of the trans tunnel. the muffler can sometimes get close to the spinning driveshaft right about where that rear seat is. It is quite possible the muffler rubbed on the driveshaft, causing a spark, which ignited the oil under the car, which would heat up the rear seat. The seat belts bolt on via a male stud which goes through the floorpan right in that area, and it all could have heated white hot which would start smouldering in that area

Hopefully this helps somewhat. I am very, very curious too, so if you find out what the culprit was for sure, please do tell!
Old 06-04-04, 06:41 AM
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Join Date: Aug 2002
Location: Northeast Louisiana
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Jeremy, thanks for the info. What my daughter drives is a hatchback. It's been quite perplexing and cannot find anything that looks wrong in the exhaust when I inspect it. You're right about no wiring in this area and I can see nothing top or bottom of the floorboard that could create heat electrically or otherwise except the muffler. The burned spot is directly over the muffler which makes me suspect it.

What I'm going to do when I get off this evening is crank it and watch very close and see if it duplicates the problem.
Old 06-04-04, 06:53 AM
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Let us know what you find. This is a real head scratcher.
Old 06-04-04, 05:09 PM
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Join Date: Aug 2002
Location: Northeast Louisiana
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Okay, I ran the car today to see if I could replicate the problem of last Sunday. It cranked fine but would also do that Sunday and ran great, no miss. Sunday it was missing very badly and it seemed to be the front ignition coil was not firing. I say this because when I unplugged the main cable going into this coil it did not change anything at all. I also unplugged the spark plug wires and they were not firing.

Finally after driving for about 15 minutes today it started the missing again. Same thing, no fire at all from the front ignition coil. Also when missing started the exhaust from the tailpipe was very irregular and seemed to be hotter that when I checked it before the miss. The missing came at went for about 5 minutes then straightened out and I could not get it to repeat even though I drove for about another half hour.

The temp of the muffler and the rear catylitic converter seemed to be about the same to the feel all through the process or if any difference maybe converter slightly hotter. This converter is further away from the floorboard a little bit and also has the drive shaft between it and the floorboard so it doesn't seem to heat car as much.

The floorboard area over the muffler did get warm but never got hot enough to be anymore than uncomfortable to the touch from inside the car. I think though if the missing had continued it would have got much hotter.

Again this brings me back to my original notion that the front coil going in and out seems to be involved in this somehow. Any thoughts???
Old 06-05-04, 09:20 AM
Join Date: Dec 2003
Location: Indiana
Posts: 312
This is not necessarily a theory, I saw it happen - once - years ago. I think it was a Toyota. The muffler exploded into small pieces. A dead miss on the ignition side equates to pumping raw fuel into the exhaust. It should affect the converter more than the muffler I would think, but the entire system will still have raw gas settling in it. Gasoline vapors go off at a very low flashpoint. Fix the miss first, I'm guessing no more problems with a smoking rear seat.
Old 06-05-04, 01:54 PM
Join Date: Apr 2002
Location: Pittsburgh,Pa
Posts: 2,417
Most modern cars have shielding for heat the entire length of the exhaust system.They also run hotter than the older cars.So when you were having a misfire the exhaust system went into a superheat mode from burning the fuel the engine did not burn this heat scorched the underside of the seat.The misfire needs repaired pronto.Be aware that the heat and burning of raw fuel has damaged the converters.I would check with Ford to see if the oe muffler had a heat shield I think they did from the factory.

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