Fuel Smell After Dp And Decat Install

lowforce

lowforce

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Hi @ all,
I am currently rolling a '98 AGU with a stage 1 map. It was running fine with the stock DP and cat, there was this bad smell outside the car only for several minutes after a cold start. I haven't observed any other smell issues. :D
I have installed a 3" downpipe and decat on my about a week ago and since then have this terrible smell issue.
When I stop at a traffic light with my window down, I could smell these fuel fumes, it feels like an old V6 with very rich A/F ratio. It is the same several feet behind the car and is very embarrassing. It doesn't matter if the engine is cold or at normal operating temps, the fuel smell is present. There is no issue with the windows up and the a/c running, fuel smell is not entering the cabin for some reason. :D
I am aware that it is common to have a little bit more smell after decat but this is a nightmare.
The whole exhaust was checked for leaks, none were found. Did a VCDS scan, no error codes related to lambda or mixture. Searched several threads but most of them were related to cabin smell issues.
Any ideas?
 
put the cat back on see if it cures the smell
 
Well you've removed the cat and increased the flow without letting the ECU know, what did you expect?
 
Don't suppose you have filled up and left the filler cap on the pump (the plastic lead snapped) like I did a few months back?
Dave
 
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@bez101, yes, this will be done asap and most probably the dp will be on the market. :D
@16Klappe, there are several 1.8Ts here running various configurations and no one has a smell issue. One has his cat guts drawn, other has welded a pipe instead of the cat, the third one has a 63mm straight pipe with an cheap muffler. Not to mention the fact that these cars only went through the quick procedure of uploading a new software to the ECU by unknown local companies, were not dynoed , no custom mapping to the hardware at all. This is why I'm a little bit confused.
 
Well it didn't smell before you fitted the decat.

And now it does.

You say there is no leaks in the system.

I say it's over fueling because the ECU doesn't know there isn't a cat. If you take that advice is up to you, if you don't...enjoy loads of fault finding.
 
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Thanks 16Klappe, it definitely makes sense to have the ECU/Lambda 'fooled' by this high flow dp and decat.
Will do some more runs tomorrow and check with VCDS. Surprisingly have done around 500 kms with dp&decat and no fault codes were stored, but apparently the eng is running too rich, since i need a gas mask when I'm aroung the car :think: Will install the stock dp & cat, at least it smells less distinctive with them (hopefully). My only concern is that they have done more than 450k kms. :)
 
Iv fitted decats to quite a few cars including audis before having them mapped and never had a problem with smells.
 
it's an AGU.

the ECU knows absolutely nothing about the presence of a cat at all, and won't ever throw any form of light or code from it's absence.

I'd suggest your issue is nothing to do with the decat really, and that it's running rich for some other reason. the decat has simply highlighted what the stock cat was somehow masking.
 
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Prawn, thanks for your suggestion.

Can the AGU lambda be checked if it is working correctly and how? No faults are stored but this does not mean that the probe is ok. I am aware that using a wideband would be maybe the best method but the nearest is some 400 kms away...
 
Agu has a single pre cat lambda, presuming you have a car with no faults, the ecu will trim fuel either way of lambda 1.0, regardless of cat or no cat, I have no idea what nonsense jardo is going on about.... :b
 
It seems that the exhaust smells less now, still very disgusting though. Hopefully it would smell even less at the next oil change. :laugh:
I've installed the old cat, there was this bad smell only for several minutes after a cold start, same as before. So I suppose that there the lambda/ECU is ok.:laugh:
I'm quite surprised with this 1.8T, had an mk3 golf 2.slow in the past. Also installed a decat but didn't have this fuel smell around it...
Did some research, and maybe I'm the only one to have these smell issues with a 1.8T 3" downpipe. Everybody else is quite happy with it and obviously not gassed. :D
 
Jay 01 s3, the fuel filter was replaced some time ago with a bosch unit. Still looks good, no rust or leaks from the fuel lines or the filter itself.
 
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I have the same issue with my AGU. 3"dp, decat and a horrendous smell, I've also been told today by a friend following me that I've got petrol streaming out of my exhaust :S quite concerning. Got a MOT coming up soon so stock dp and cat goes back on.
 
Are you sure it's not water/condensation?
If it's fuel streaming out, that's extremely dangerous for you catching fire and motorbikes skidding on!
Dave
 
I think it is normal to have more steam after decat install. Mine starts almost instantly and is a lot compared to what was before. With the cat it was less and started some time after cold engine start.
Here is a photo of my stock cat, you think it's clogged?
Cat
btw there was also a lot of smell the day I installed it. As its a catalyc converter, it smells like ammonia or sumthing, which is also very disgusting, but not as pugent as gasoline. Guess I should get used to it. :laugh:
 
After I had a sports cat fitted I could smell petrol for a little while on my old mk4 golf, but it did go after a short while
 
I think a 3" dp and decat is pointless without the correct remap. Car seems worse without a cat and mpg is definitely worse..
 
It's my daily car, so another slight mpg increase will not be welcomed.:laugh: But this could be confirmed after several more refills.
It does not seem worse. Maybe the turbo spools up a little bit faster since the 57mm restriction is after the decat, not after the turbo flange as on the stock DP. These are the only pros.:laugh:
The folks who did the remap said that it was a well known issue to have the original DP flexi or turbo flange restriction cracked after remap due to all the heat down there. This is why they recommended fitting a larger downpipe with a decat or sports cat.
 
Aaaaah I see. Well my car isn't remapped... yet.
 
It has been a month since I installed these bits, so here is a little update.
Sometimes it smells, sometimes it does not. It seems that it smells less when the exhaust temp rises. Don't know if this is normal. I was suspecting the lambda, so i did several VCDS logs. All of the recorded values are in tolerance as of the motronic diagnostics book that I have.
 
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