02 silverado fuel mileage went down ALOT!!

[J-Ri]

To really look at the injectors, you need to look at the waveform with an oscilloscope. With 100k, they are probably in need of replacement, so I would replace them anyway. I don't remember the exact frequency, but the waveform won't even show up on a 2.5mS scope. Looking at the datastream will tell you to replace one if the voltage is 450mV and doesn't move, but being slow on a scan tool doesn't necessarily mean it/they are bad.

If O2 sensors dont get the mileage back to where it was, you may want to get an induction flush done. Your numbers were right at the top of the range, so you could easily get an increase.

[AaronIROCZ]

The cats were replaced 200 miles ago, passenger side wes plugged. Now what is an induction flush?? Is that something I can do at home or something the local dealer would have to do??

[j cAT]

because your cats were bad i new that at 100,000 mi the o2 sensors were off. now after replacing the o2 sensors and you confirm your hopefully improved mileage , clean your maf sensor with CRC maf cleaner.

[mbumgua]

If you haven't resolved your milage problem you might check your fuel regulator . It has a vacuum line on it that will suck fuel into the engine if the regulater leaks. It does not leak externally, only internally. Pull the vacuum hose off and see if it is wet inside. It is located on drivers side of engine in middle of intake manifold. about 50-75 bucks. Good luck

[AaronIROCZ]

That was actually the first thing I checked, everything was dry. Thanks.

[72chevelleOhio]

Originally Posted by j cAT

I suspect the new exhaust system has much less back pressure, and this is the problem, as this will effect the pcm control on mixture and timing. I get 19 hwy and about 14-15MPG around town I still have stock exhaust. this is a stupid question but, the o2 sensors were replaced when the cat's were replaced ? I hope so............

I got my 02 z71 with 21k on it, I got 15 mpg. I bought a programmer, a cold air kit, cat back exhaust, and a throttle body insert. then I got 17 mpg. I now have over 128k on it, now with 3" straight pipes...still adverage 17 mpg

[j cAT]

Originally Posted by 72chevelleOhio

I got my 02 z71 with 21k on it, I got 15 mpg. I bought a programmer, a cold air kit, cat back exhaust, and a throttle body insert. then I got 17 mpg. I now have over 128k on it, now with 3" straight pipes...still adverage 17 mpg

with this mod that you have done on 02 sil 5.3l what octane of gas do you use to get this mpg ? what pcm programmer did you use?

[mbumgua]

Back to the fuel regulator--Did you check it right after driving the truck or after it sat for awhile? Sometimes they only show gas in vacuum line right after driving. Good luck!

[72chevelleOhio]

Originally Posted by j cAT

with this mod that you have done on 02 sil 5.3l what octane of gas do you use to get this mpg ? what pcm programmer did you use?

I almost always run 87 octane, I used a hypertech programmer set to use 87. I had 2 1/2" duals, 3" duals, and now a 3.5" single stainless exhaust setup that belongs on a diesel. (it was free) I'm running a cat but no muffler. the 2.5" and 3" had a muffler...the exhaust being my only mod that changes, I thought it was strange that you wrote the lack of backpressure caused the fuel mileage to drop, when mine has not.

[AaronIROCZ]

After it sat for a while and while running, all dry. I just got my o2 sensors and I am going to install them tomarrow and see what happens.

[AaronIROCZ]

Well I just replaced the o2 sensors today. The passenger side seized and stripped the 02 bung out. I got lucky and was able to retap the bung and now they are in, I will let you all know if this helps out the fuel mileage.

[72chevelleOhio]

Originally Posted by AaronIROCZ

I will let you all know if this helps out the fuel mileage.

Did it?