How long for ECM to recognize cat back exhaust?

Ridersfan · February 19, 2016

Yesterday, I installed MBRP 3" catback exhaust on my 5.3 6 speed. (It was a very simple and quick install by the way, less than 20 minutes I was done) but I find the performance to be a little underwhelming. It seems to idle higher and be a tad gutless compared to factory exhaust. No other performance enhancements yet.

So, I'm thinking that the ECM needs to realize that the truck can breathe better before I'll see any improvement. Admittedly, I left my shop and drove home last night and only drove back to work this morning... so no real miles put on to speak of as I'm <12 blocks to work.

How long before the truck will wake up?

Exhaust sounds great by the way! Can definitely tell when AFM kicks in, but doesn't bother me. Will eventually buy a tuner and shut it off at some point.

http://mbrpautomotive.com/index.php?page=products&part=S5080AL is the exhaust that went on... cheap kit too

07Softail · February 19, 2016

I don't think the ECM will make any adjustments...A tune will do the trick though and highly recommended.

RT

Ridersfan · February 19, 2016

I've read in different threads where folks will disconnect their battery for a couple of hours so it starts from there and then others chime in saying it doesn't have to be done so you don't have to reset clock, etc and will learn itself. I do hope to do a tune... but sneaking exhaust under the radar so my mrs doesn't give me "the look" won't bode well if I buy a tuner right away too ;)

Willshire · February 19, 2016

After the rear O2 sensors i don't think the truck knows what exhaust is on it. unless there is a backpressure difference from your new vs old exhaust

MikeNH · February 19, 2016

Dual exhaust will often trade a small amount of low end power for high end gains. No exhaust will affect idle speed. The ECM won't learn anything, the real world gains from exhaust are essentially nothing. It's a sound gain, nothing more.

krdeal · February 19, 2016

Dual exhaust will often trade a small amount of low end power for high end gains. No exhaust will affect idle speed. The ECM won't learn anything, the real world gains from exhaust are essentially nothing. It's a sound gain, nothing more.

I disagree on the idle level with a full exhaust. Mine starts off higher upon initial start up and then dies down after a while. Even the tune did not change that. I thought it was just the extra noise causing it, but mine idles at about 800-1000 RPMs upon initial start up and then finds it's way down to the normal 450-500 RPM.

Temp does not seem to be an issue as I am in South Florida.

MikeNH · February 19, 2016

The RPMs sound normal. They always start high to get the cats to light off. There is no way exhaust changes that.

SILVER SLED · February 19, 2016

Welcome to the world of modifying a stock engine. With all the technology GM has, do you think they would put an exhaust on that would loose mileage or horsepower? The stock exhaust will flow plenty, the aftermarket cat back is just for sound.

Ridersfan · February 22, 2016

Welcome to the world of modifying a stock engine. With all the technology GM has, do you think they would put an exhaust on that would loose mileage or horsepower? The stock exhaust will flow plenty, the aftermarket cat back is just for sound.

Pretty well anyone that markets exhaust systems, headers, air intakes, etc. all make claims for gains in power &/or mileage. So, yes, with all the technology that GM has... it can be bettered... otherwise why would the market for these things exist? Your own signature line shows that you bought into a cold air intake and a tune... and nobody is calling you gullible.

Just asking my question since there are several other threads that talked about unhooking the battery to speed up the "learning".

Maybe it's all in my head, but I did put some miles on over the weekend and can see an improvement in throttle response now.

SILVER SLED · February 22, 2016

Pretty well anyone that markets exhaust systems, headers, air intakes, etc. all make claims for gains in power &/or mileage. So, yes, with all the technology that GM has... it can be bettered... otherwise why would the market for these things exist? Your own signature line shows that you bought into a cold air intake and a tune... and nobody is calling you gullible.

Just asking my question since there are several other threads that talked about unhooking the battery to speed up the "learning".

Maybe it's all in my head, but I did put some miles on over the weekend and can see an improvement in throttle response now.

I "bought into" the tune because it did in fact get rid of the top speed governor and did in fact adjust for the change in tire height and did make the trans shift/down shift tons better. I bought the intake only because it sounds good, just like a cat back.

joshc64311 · February 22, 2016

Cat fight

FishinJ · February 22, 2016

I put a GM Borla on mine and I would say it made 0% increase in performance but it sounds much better and that's all I was looking for. After install the truck ran exactly how it did a couple hours before installing it.

joshc64311 · February 22, 2016

If no performance gain than how is GM claiming 10 HP gain on the new silveraydo with their exhaust?

SILVER SLED · February 22, 2016

Well, for example, if I added a "cold air intake" that was advertised as a 20hp gain, a cat back for 10hp, headers for 20 hp and can't forget the famous throttle body spacers for 15 hp, that would bring my 355hp 5.3 up 65hp, to 420hp, and it should get me about 5 mpg better mileage, according to the sellers of these products.