Aftermarket Custom Exhaust causing Higher Fuel Consumption

[R30WHO??]

Hi all,
Tried my best to search for a similar post to answer my question but unfortunately was unsuccessful. So here we are.

Car: ‘07 GTI FSI - BWA engine.
Tuned Stage 1.

I recently installed a magnaflow muffler where my res used to be and continued 3” all the way back to a rear muffler delete and then 4” tips. (Was done at highly recommended exhaust shop)

Since doing so my fuel consumption has skyrocketed. I have noticed the following L/100km readings are certain speeds.

Taking off from standstill with no considerable effort 75+L/100km sometimes maxing at 99.9

Cruising through suburban streets, 13L/100km

And then giving it a boot full will kick it back up to 50ishL/100km
—
Now my question is, could the reduced back pressure be causing an issue with the air to fuel ratio readings and therefore increasing the fuel input (car stinks when I stop, I thought this was initially new welds smell) or would it possibly be a faulty MAF/ 02 Sensor.

Couldnt imagine it would be a sensor. Would be weird to fail at that coincidental time period.

I have scanned with OBD11 and found a code for Evap Emissions Purge flow valve.
Recently got the same error and replaced with genuine Bosch part...

So in short.
New exhaust put on. Fuel consumption exceedingly high. Pls help me.

Pic for your troubles!




Sent from my iPhone using Tapatalk

[saabman]

If this has happened imediately after haveing work on the exhaust id check first any connections to the exhaust - make sure everything got plugged back in - Though I would expect to more faults.

I cant reccomend a genuine Ross Tech Hex CAN or what ever the current version is - Yep its about $400 but makes life a lot easier.

You will get a lot more information about the faults plus probably a whole lot more.

Your Evap fault could be Too much flow - Vacuum leak, or crud in the valve. It could be the valve not opening -faulty solenoid or blocked pipe.

I believe there is a filter in the Evap canister that can become blocked.

[saabman]

Here is one I pulled apart this week to see why it was leaking. Under a microscope it was quiet obvious



Un fortunately it wasnt just a matter of cleaning the particles out as it had held the valve seat on an angle for so long the face of the rubber seal had worn on unevenly and would not seal any more.

[Herbi3221]

definately check the exhaust place reinstalled the o2 sensors correctly. If the spacing is incorrect it could read wrong and cause all sorts of headaches

[Lucas_R]

Apart from the fuel consumption, does the car drive the same as before? Has the car given you any errors on the dash (check engine light for example)?

If it is indeed using that much fuel you must be able to see black smoke coming out the exhaust basically the entire time you are driving, and i imagine it must look like an old diesel 4wd when you put your foot down? Your rear bumper/hatch must also be covered in black sooty residue after a few days of driving?

If the downpipe hasn't been removed as part of this work (im assuming it hasnt based on what you have said) then there should be no need for the exhaust shop to either disconnect or remove either of the o2 sensors in the downpipe.

If by chance the downpipe has been removed then the shop would have had to remove your plastic engine cover and therefore would have unplugged the MAF sensor (back of engine cover near drivers side firewall). If this has not been plugged back in correctly it will cause issues and the car will run poorly. Also if the downpipe has been removed, the top 02 sensor plugs in to the wiring loom on the firewall just behind the battery on the passenger side. Check its plugged back in correctly.

Have you taken it back to the exhaust shop to ask them to put the car back on the hoist and check it over?

[brad]

The instantaneous reading doesn't mean much.

What are you averaging in L/100km? xxxkm per tank won't cut it.