I have a Flowmaster 50 Series Delta Flow muffler installed on my 97 4WD Blazer. Before I installed it with the stock muffler, I was getting 16 MPG, after installing the Flowmaster it dropped to about 12 MPG. I believe factory exhaust line for my Blazer is 2.5". The stock muffler was 2.5" in and 2" out. When I had the Flowmaster installed I went with 2.5" in and 2.5" out.
I thought I'd give you a heads up on this. I'm almost positive the problem is that the PCM and sensors are not accepting the change. I have tried many other things as well, email me if you'd like more info.
I tried this a couple of times already. I started from a complete "cold start." I disconnected the battery and left it off overnight and still no change. I really was hoping this would work too. I have my own scanner tool and there are no trouble codes or even pending codes and all sensors are working correctly. I figured the culprit was the O2 sensors, however, I've had all of them checked out and there also working properly. There is black carbon build up on the exhaust tip which almost proves that too much gas is being sent into the mixture.
Thanks for your reply
Hey, one thin too remember when your dealing with the GM comptures is that they can take up too two weeks to relearn, once the power has been cut. You may not notice the learning curve as much later on but it is still learning.. I have been talking with the tech dept at JBA headers, and the test's that they have run on the variuos 4.3's have resulted very little difference in duals to singular exhaust the single exhaust has actuallt proven to be better for the 4.3 the problem people run into is what they call over evacuating the motor this means your getting to much out.. bad for performance.. The other thing they said was that they tried different Y-pipes etc and the only HP gain from another Y-pipe came when they schrunk it down to something like and inch and 7/8. I run a 1992 GMC Jimmy, 4.3 bored .30 ever 10.5- 1 pistons, head work intake work roller rockers. I have the factory pipe from the manifold top the rea with the exception of a high flow muffler. These sytems have been tested by JBA and proved to be the best in power gain. Their headers flow 30% more then stock enough to gain power but not too much to kill it. I think you might have over did it just my 2 cents worth good luck.
I tried the cold start over a month ago and see not even the slightest change. You may be right about the over evacuating the motor. However, I have spoken with the techs at Flowmaster and they are the guys who recommended the Series 50 Delta Flow muffler for my Blazer because they had done tests on 4.3L s-10 and this muffler performed best. I would think that better flow IN and OUT would make things better for the engine and it probably does....now I just have to convince the PCM of that.
Not sure what else to tell you about the computer, however you really have not increased the amount of airflow through your engine unless I missed something in your info, you have the K&N filter system right but factory manifold and cam etc? The problem is that you are still only flowing factory spec's once you get in the intake, but you are taking way more out make sense? I'll try to post the number for the JBA tech line if I remember to write it down.... I'm not sure but I think most would agree that ifthe problem started after you installed the muffler system, then that is the problem you know what I mean? Good luck