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Engine smells like burnt plastic and black "soot" on the bumper.

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I searched and see discussions on both which I read through. Most were very old so I'm checking to see if there were any recent revelations.

Two symptoms, both may very well be benign.

1. In my 2000 NSX I have always smelled a burnt plastic smell out of the engine bay vent after driving (pretty much any speed, any distance). It has always done that (4+ years and 25k miles).
2. Today I had a person notice my rear bumper was "sooty". I always attributed this as dirt but upon closer inspection, it does appear soot like. It was also on the engine to some degree when I opened the bay.

Car specifics: Engine is stock except an intake. I have a ARK DTS exhaust but I do have CATS. I'm lowered a bit, Teins with Bilsteins (I believe 1.25-1.5"). The soot was more than normal today but I did just pull off my 18/19 TSW rims and tires and put the stock ones on (which are worn in the insides a bit and are making a bit of road noise especially the first few miles). The TSW's wore poorly, I will be getting a better alignment once I get new tires. I was on treads unknowingly as the inside was completely gone but the outside was like new. I am finding a better mechanic for that (driving to see Joe 2hrs away is a bit much for an alignment although it appears I paid the price).

Plan: I'm going to let the car cool overnight and double check the plugs. I never burns oil historically though. After that, I relay on Prime... I am doing a minor overhaul of the car this winter. Fix some paint issues on the bumper, pull off the clear bra and prep for a new one of more recent design. I could get more exotic on work if need be. Just bought a Shelby GT350 so down time doesn't drive me as insane as it did when the NSX was my only toy. First World Problem Solved...

Thanks,
Mike
 

LJSB

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I searched and see discussions on both which I read through. Most were very old so I'm checking to see if there were any recent revelations.

Two symptoms, both may very well be benign.

1. In my 2000 NSX I have always smelled a burnt plastic smell out of the engine bay vent after driving (pretty much any speed, any distance). It has always done that (4+ years and 25k miles).
2. Today I had a person notice my rear bumper was "sooty". I always attributed this as dirt but upon closer inspection, it does appear soot like. It was also on the engine to some degree when I opened the bay.

Car specifics: Engine is stock except an intake. I have a ARK DTS exhaust but I do have CATS. I'm lowered a bit, Teins with Bilsteins (I believe 1.25-1.5"). The soot was more than normal today but I did just pull off my 18/19 TSW rims and tires and put the stock ones on (which are worn in the insides a bit and are making a bit of road noise especially the first few miles). The TSW's wore poorly, I will be getting a better alignment once I get new tires. I was on treads unknowingly as the inside was completely gone but the outside was like new. I am finding a better mechanic for that (driving to see Joe 2hrs away is a bit much for an alignment although it appears I paid the price).

Plan: I'm going to let the car cool overnight and double check the plugs. I never burns oil historically though. After that, I relay on Prime... I am doing a minor overhaul of the car this winter. Fix some paint issues on the bumper, pull off the clear bra and prep for a new one of more recent design. I could get more exotic on work if need be. Just bought a Shelby GT350 so down time doesn't drive me as insane as it did when the NSX was my only toy. First World Problem Solved...

Thanks,
Mike

"Soot" on rear bumper could be from the tires. I get that sometimes too.
 
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In a previous century, I had another car that was a turbo with Bosch EFI, pre OBDII with no self monitoring function. Every once in a while under idle conditions the engine would run rich which would cause the catalytic converter to get really hot warming up everything around it including the undercoating which would them emit a wonderful aroma. It also left black residue on the inside and tip of the tail pipe. Turns out it was the fuel pressure regulator which every once in a while would stick raising the fuel pressure and causing rich operation (beyond the ability of the O2 closed loop control to correct).

Your car is OBDII so if the fuel mix was getting out of range resulting in soot, you should be setting an OBDII error code. A check of the spark plugs will confirm the fuel mix. If the soot is just on the bumper and not on the inside of the tail pipe or around the tips, I would go with Pbassjo' s suggestion.
 
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My back bumper gets soot on it too. I thought it was because I took out my cats.
I have Dunlop direzza ZII, maybe it is just rubber. It is always a pain, 200 miles and I have it.
Burnt plastic smell - can't help; are you sure it's not oil smell.
Then there could be a list - VTEC gaskets, head cover gaskets, cam plugs.
What does engine compartment look like?
See any suspects?
Let us know - Good luck.
 
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I'm no mechanic but I looked over the engine looking for any signs of a leak. Nothing yet. I'm going to lift it up today and check underneath. The plastic smell has been that way forever so I can't imagine it's anything critical but I will check the pipe routings in search of something plastic. I'm "hopeful" the soot is from tires. I suspect my alignment is a bit off and I just put on the old OEM wheels (not OEM tires). That would be a good reason for a step change. I have one of those "BlueDriver" OBDII readers (bluetooth to your phone with a bunch of stats). I'm going to plug it in and take a look at the air fuel ratio to see if anything looks off. I would have suspected anything serious would have been picked up by the CEL. I just need to get that tool back from my buddy...
 
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years ago, after a poor wheel alignment, I could write my name in the black soot on the back bumper, and after a good drive, I could smell it. New tires, and another "proper" alignment. the black soot is gone.
 
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As to the tire question, you specified the rims; but, you didn't specify the tires. If you are running around on tires with a UTQG rating of 120, that combined with a poor or very aggressive alignment and high asphalt temperatures would definitely contribute to the accumulation of tire shreddies on the back of the car.

I don't think the OBDII scanner can give you AFRs since the NSX uses narrowband O2 sensors. It may allow you to view the O2 sensor voltage and fuel trims which would tell you whether ECU is applying a lot of fuel correction which would indicate a problem.
 
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I've concluded it must be the tires. I didn't notice it until I put the old OEM rims on which have been sitting on a rack in my garage for 2 years.

Anyway, that's my story and I'm sticking too it... I'm working on some bumper repairs now so it won't be back on the road with new shoes and an alignment probably until next year.

Thanks for the help!
 
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Burnt Plastic Smell portion of the problem remains unsolved.

I'm re-booting this thread for a solution.

Item 2 is confirmed. "Soot" on the rear bumper was from old tires. I just got the car back on the road with new tires and the "Soot" is gone.

Item 1 remains a mystery. I still, as I have as long as I have owned this car, have a burnt plastic smell coming from the engine bay. I never had an issue, but it's still there. I just changed the CV boot and saw what appears to be some fluid weeping a bit (oil, not sure). These are the pictures I took. This would be on the back area of the engine toward the rear of the car. Sorry I didn't take a few shots a little further back to help locate. Any thoughts?

NSX Leak? by Michael Lohr, on Flickr

NSX Leak? by Michael Lohr, on Flickr
 
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I had a burnt plastic smell that was caused by the rubber exhaust hangers touching the pipes on my Pride exhaust. Burning smells are usually exhaust related to just start where the heads and headers meet and work your way back.
 
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I had a burnt plastic smell that was caused by the rubber exhaust hangers touching the pipes on my Pride exhaust. Burning smells are usually exhaust related to just start where the heads and headers meet and work your way back.

The seems like a reasonable approach. I have not tired that. I keep looking for a leak of some sort. I'll follow the pipes to the headers and see what we have. Thanks.
 
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It never dawned on me that the "soot" on the rear bumper was tires! (My car doesn't use oil best I can tell so it was a mystery.) I'm about to replace my OEM Bridgestone Potenza RE-010s that are date coded late 2015 on my '95 with "modern" Michelin Pilot Sport AS-3s. Very excited to drive on the new tires, expecting a much quieter ride and possibly better handling with 25 year new tech!
 
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