Howdy All,

I have quiet a problem with exhaust soot on the back of my car (mainly the boot lid front and bumper), it only takes a day.. 2-3 days and it's fairly bad.. noticeable black build-up... still in lots of dotty bits but

Here's a picture from 5 days - half wiped away to show the difference:
http://gallery.me.com/lathiat/101214/IMG_8632/web.jpg?ver=12735618160001


I've done some reading, and it seems the most common causes are

(1) Fueling/AFR not right - O2 Sensor
(2) Burning Oil


I was wondering if anyone has had experience with this on Magna's (This is for my 3.5L TL) - and if there is a more common cause.. car has done 125,000Ks no idea if the O2 sensors have been changed at any point I am guessing not. Hoping to save on just replacing them for no reason if it might be something worse (oil) - or replacing random bits of oil related stuff until it's fixed - if possible.

Last oil change was 3500Ks/2months ago (HPR10) - I just checked now with cold engine (theory was the most oil would be in the bottom) and it is about 4mm off full - so has dropped a little bit, 99% sure it was properly full when we serviced it... went for a couple drives got back, checked warm.. basically the same.



Any advice from experience or things to look for would be appreciated.

Regards,
Trent

o2 sensor could be the cause, but black exhaust suit is usually it running really rich, you'll notice alot of modified cars have this...id say due to crappy tuning...will run rich all the time....Had this happen to the TR.

Could also be a coolant temp sensor faulty, wouldnt hurt to test them, new ones are pretty expensive.

But yours doesnt look THAT bad........Might be worth checking to see if the ecu is throwing any faulty sensor codes.

;1250806']o2 sensor could be the cause, but black exhaust suit is usually it running really rich, you'll notice alot of modified cars have this...id say due to crappy tuning...will run rich all the time....Had this happen to the TR.

Could also be a coolant temp sensor faulty, wouldnt hurt to test them, new ones are pretty expensive.

But yours doesnt look THAT bad........Might be worth checking to see if the ecu is throwing any faulty sensor codes.

Thanks yeah.. I presume the Coolant sensor is due to the automatic choke never coming off? I currently get around 14-15L/100K but it's a manual, and I don't exactly putter around most of the time although I generally drive more putter-y until it warms up... it really is that bad it gets like that every-time I clean it within 2-3 days max its driving me NUTS loll.

Would it do that without the CEL being on?

Automatic choke? Dont think EFI cars have that dude...while cold the car runs off a map on the computer till its warm then the oxy sensor comes into play

CEL? Possibly mate when did it come on?

;1251080']Automatic choke? Dont think EFI cars have that dude...while cold the car runs off a map on the computer till its warm then the oxy sensor comes into play

Well that's sortof what I meant.. the equivalent of an old school choke being the car running a bit differently :P Was wondering if that meant it might run a bit rich hence your reference to it maybe being an issue.


;1251080']CEL? Possibly mate when did it come on?

Nah it's never come on at all, thats why I meant... I wouldn't of thought there was any errors if the CEL hadn't been on.

May be one for one of the more technically advanced members to answer. Or is it only under WOT it goes black?
I'll keep an eye on this thread in the hope you find a resolution but yes that's all i can suggest

;1251159']May be one for one of the more technically advanced members to answer. Or is it only under WOT it goes black?
I'll keep an eye on this thread in the hope you find a resolution but yes that's all i can suggest

OK thanks for the info [TUFFTR].. TBH I'm not sure a few days go past where I didn't find WOT somewhere, which might not be helping lol

I had this problem once. Turned out the muffler had holes in it, Instead of the wet carbon flying harmlessly out the exhaust pipe on startup, it was covering the outside and inside of the bumper bar, as well as the boot lid. Worth a check. Do you perhaps have an aftermarket exhaust system with pipe tips that stick out less than the original? If you do a lot of town driving the exhaust system never really heats up enough to burn off the carbon, a lot of it builds up in the system and can be dislodged when you fire it up next. Shouldn't end up on your bumper though. If everything at the back of the car is ok perhaps change the oxygen sensor, might improve your fuel economy, although yours is OK provided the car is used on short town trips only.
Coolant temp sensor should throw up an error code, if I remember correctly, so check the codes, if any. Thermostat being jammed open can cause this too, without any error codes. Does it reach normal temperature reading on the dash gauge after a couple of Km of driving?

I had this problem once. Turned out the muffler had holes in it, Instead of the wet carbon flying harmlessly out the exhaust pipe on startup, it was covering the outside and inside of the bumper bar, as well as the boot lid. Worth a check. Do you perhaps have an aftermarket exhaust system with pipe tips that stick out less than the original? If you do a lot of town driving the exhaust system never really heats up enough to burn off the carbon, a lot of it builds up in the system and can be dislodged when you fire it up next. Shouldn't end up on your bumper though. If everything at the back of the car is ok perhaps change the oxygen sensor, might improve your fuel economy, although yours is OK provided the car is used on short town trips only.
Coolant temp sensor should throw up an error code, if I remember correctly, so check the codes, if any. Thermostat being jammed open can cause this too, without any error codes. Does it reach normal temperature reading on the dash gauge after a couple of Km of driving?

Exhaust system is standard.. VR-X system.. I -did- have some big holes in my exhaust up until the other day, see here:
http://gallery.me.com/lathiat/101214/IMG_8630.jpg?derivative=medium&source=web.jpg&type=medium&ver=12735604110001

Part of the reason I got it fixed (And dropped 20dB from my car, lol).. is I was hoping it would help with this issue.. if anything it's worse.

I do lots of longer trips up big 100K roads, with some messing around at each end.. I do a few shorter trips but longer trips is probably more common.



Might just look at the O2 sensor was just worried it might be oil burn related but yet to hear from anyone on that I guess.

I do lots of longer trips up big 100K roads, with some messing around at each end.. I do a few shorter trips but longer trips is probably more common.

Might just look at the O2 sensor was just worried it might be oil burn related but yet to hear from anyone on that I guess.

There are a number of posts I've read on here where the oxygen sensor has gone between 110000 & 120000km. I would have expected that you should be getting under 10km/l with mostly highway trips in a FWD, so your 14-15km/l sounds way high even with spirited driving. Poor fuel economy is a strong indicator of a bad oxygen sensor from what I've read.

If it is the oxygen sensor, and its been like that for a while, the rich running won't have done the cat coverter any good either.

Andy.

Pull the oxygen sensor. If it is covered with soot, it is stuffed. Simple! As above, on a longish trip you should get about 10 L/100 km. (or 10 km /L, same thing. Wifey's 2L Lancer gets 15 km/L or 6.6L per 100 km on a country trip)

I do get around 7-9L/100K when cruising.. its all the inbetween stuff that shoots it up.

Oops... :facepalm I did actually mean l/100km in this case, even though I still think in km/l (well mpg really...). :ninja:

Yeah but I mean my dash average is usually 13-15 .. but if i look at instant when i am cruising it reads 7-9-ish.

Hmm... while the trip computer's fuel consumption is often not particularly accurate, that is still a fairly large disparity. In my TJ2 AWD, on highway trips under cruise control the instant readout usually "averages" in the low-mid 8s while the average consumption figure will be just under 10. Around town, at constant speeds from 60 to 80 km/h the instantaneous readout will "average" high 7s to low 8s, while the average consumption figure will be around 13.5.

While the car has only just ticked over 100000km, I've got a new genuine sensor ready to go in the next time the car visits the mechanic as I will be doing an extended road trip soon and I don't want the fuel economy to go to pot in the middle of it.

Andy.

When my oxy sensor went I had a big hole in the power range between 2500-3500 rpm. Above 3500 it picked up again. Fuel economy wasn't really affected.
I average around 9.5L/100kms 3.5 manual and like to give it a bit so your 14-15L/100kms does seem high.
Could be a few things, I'd start with cleaning the AFM especially if you use a oiled K&N filter.
Check exhaust for restrictions. Disconnect before the cat. Look at the cat to see if it's blocked or collapsed, then look forward and inspect the merge collector, part of it has a tendency to break off and could be blocking the exhaust.
Other than that check general wear items, spark plugs, HT leads, distributor cap and rotor for wear. Cleaning the throttle body wouldn't hurt.

Thinking outside the box what's your wheel alignment & tyre wear like? My fuel economy improved by over 1L/100kms with a proper alignment.

Thanks for the extra info mitch.. I do use a K&N filter.. only went on about 6000Ks ago though... sounds like my consumption is definitely up though... since I'm hearing alot more about oxy sensors and the likes I think I'll just bite the bullet and replace it.. and see how it goes... as I understand it there is actually -2- oxygen sensors?

Spark plugs and throttle body have been done, had a plan to look at doing the leads, cap&rotor at some point when I had some cash to spend on that when it's mostly "unnecessary" just as a matter of maintenance etc.. will look in the exhaust as well and take a peak.. the car is fairly "new to me" in terms of <10,000Ks.. so this problem fairly sure pre-dates that... I did have a giant hole in my exhaust to the point my rear muffler was mostly useless up until the other day, dunno if thats gonna have hurt things previously in terms of AFR and fouling up the cat/sensor.. will take a peak.