[getlost4x4]

My cats were plugged and I had knocked them out back in March.

As part of my goal to get my mileage back up from 9 MPG it was time to do a little exhaust work. Well, I paid a friend to do it anyway. I just don't have the time.

Anyway. Before this I got 14 MPG on the same straight of road I've been testing my modifications on. Now its up to 15 MPG.

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[getlost4x4]

hmm, i should have rotated those. just turn your computer upside down. :mrgreen:

The next part of the upgrade will be a new center muffler and maybe just convert it to single exit exhaust. Loose a little weight and make it sound a little better.

I'll try to get a sound clip. its still nice and quiet with the windows up. it sounds nice when you put your foot in it.

 

[bomana]

I deleted the rear muffler and have a Magnaflow high-flow center muffler. I really like the engine note, though I have heard from around the neighborhood that people know when I drive by...

I have been pondering deleting the cats.. Did you have any issues with the oxygen sensors?

 

[getlost4x4]

not yet. i coated the rear O2 sensors with anti seize. it hasn't burned off yet and it lets the O2 sensors warm up to operating temperatures without being able to read the gases flowing by.

if you delete the cats, do what I did and have it re-piped. having that whole area inside the cats open is really noisy and makes it not run as good.

 

[bomana]

not yet. i coated the rear O2 sensors with anti seize.

That is the copper type antiseize I use on my brake/wheel stuff to keep it from.. well seizing? You just covered the sensor with it?

if you delete the cats, do what I did and have it re-piped. having that whole area inside the cats open is really noisy and makes it not run as good.

Yeah for sure, I'm wondering if running a pipe through the cats could be the way to go...

Thanks!

 

[RRToadHall]

I am pretty sure he coated the threads with antiseize, not the sensor. Jsut a common sense assumption.

 

[getlost4x4]

No I coated the sensor with anti sneeze. The only use for that sensor is to tell the computer if the cats are working correctly. If you can keep them thinking the air has been "filtered" then it won't set off a check engine light. You can also use spark plug non foulers to keep the O2 sensors from reading the exhaust.

A lot of VW owners do this because the emissions system is overly sensative. I had a passat that kept throwing codes for bad cats even though there was nothing wrong with them. I put spark plug non foulers on both of the after cat O2 sensors and my problem went away.

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[jmason]

My cats were plugged and I had knocked them out back in March.

As part of my goal to get my mileage back up from 9 MPG it was time to do a little exhaust work.

My mileage is around 9mpg at the moment too, although the vehicle seems to be running well. How can one tell if the cats are toast? My check engine light has been on for the last couple of years at least, but once in a while it doesn't come up. I've had it checked out, but nobody seems to know what's causing it, and nobody said it's anything to worry about either.

I'm starting to think it could be my cats...

 

[LarryS]

neither of you guys are running stock any more so that has to be taken into consideration, backpressure measurements at the o2's compare bank to bank, IR (ideally) temperature bank to bank (i think they should be approx 50 deg. C hotter at the back of the CAT if the're working correctly) and a vac gauge shows blocked exhaust.

 

[getlost4x4]

you should get a code for the O2 sensors at the back. I can't remember the code.

 

[996TURBO]

Did you notice any loss of torque because there's less back pressure?

Because i did the same mod with a custom SS no cats Y.

 

[RRToadHall]

WOW! I just reread this thread and have to wonder about one thing... "...up TO 15 MPG." Seriously? My stock exhaust system, GEMS 265K miles and I get 17/18 MPG on a regular basis with mixed driving. The only thing NOT stock on my rig is the coils, wires and plugs. THen again I drive like an old fart on his way to the senior centre for bingo. :?

 

[jmason]

neither of you guys are running stock any more so that has to be taken into consideration, backpressure measurements at the o2's compare bank to bank, IR (ideally) temperature bank to bank (i think they should be approx 50 deg. C hotter at the back of the CAT if the're working correctly) and a vac gauge shows blocked exhaust.

Do you think removing the rear silencers would really alter it that much? Additionally, as far as I can recall, the check engine light has been illuminated since before I yanked the rear silencers. The better part of 5 years at least methinks

 

[LarryS]

the rear silencers...i doubt it, by that stage the exhaust has already lost a lot of energy, but it all adds up. Perhaps check your check engine light for what the issue might be, lazy/failing o2's could be just one of many, many reasons for mpg drop.

 

[Edable]

@996TURBO, did you notice any loss of torque when you did yours?

 

[desertdude]

WOW! I just reread this thread and have to wonder about one thing... "...up TO 15 MPG." Seriously? My stock exhaust system, GEMS 265K miles and I get 17/18 MPG on a regular basis with mixed driving. The only thing NOT stock on my rig is the coils, wires and plugs. THen again I drive like an old fart on his way to the senior centre for bingo. :?

Thats the key right there to better fuel economy than any mod, my friends keep complaining how their Rovers use gas while I on the other hand get very good milage ( for old V8s ) because I too drive like a granny.

 

[996TURBO]

@996TURBO, did you notice any loss of torque when you did yours?

Yes i've lost a bit of torque but gain better top end...and that muscle car sound!!!`)

 

[getlost4x4]

I think my gas mileage is mostly due to 150# wheel and tires on each corner. Its also lifted and a lot of crap has been trimmed off. I usually cruise down the interstate at 75 mph and I don't have to much of a lead foot.

 

[desertdude]

My cats have been cut off and dumped, I got it like this, I know it used to have cats because of the tubing welded in where the cats should be. Can't say for sure since just started driving a Range after a gap of three years but the mid range torque seems to be pretty beefy or maybe it has lost low end torque ?

 

[LarryS]

Whatever 'mod' has been done, usually nothing is done to the ECM/EMS so it doesn't know about it and certainly doesn't care as the ECM's [almost] primary function (other than the timing for fuel and spark) is to protect and keep the CAT working (where fitted). Without telling (altering) the fuel and timing maps your always going to lose the fight against the ECM. It's almost an exercise in futility.

You may have lost torque in removing the CAT (and altering the inherent exhaust timing, expected by the ECM) but it is not because back pressure is a desirable thing to have per se. Are the back pressure measurements particularly high to begin with?

IIRC there is a setting that can be done via the higher end diagnosics where the ECM can be told to ignore the o2's (market's where not fitted) but i think you still need to tell the ECM (via an external exhaust reading) an initially figure to give it a ballpark, and this may still only give so much.

Perhaps without a full on ECM rechip (with ideally further on road/dyno setting up) this is perhaps an option, if you've got rid of the CAT then you don't technically need the o2's.