Does the 5.7 tbi need back pressure to run correctly?

[Phr0stByte]

On my 94 there's only one O2 sensor, & it's before the cat & muffler.

Thats what i was thinking as well

 

[docstoy]

Went to garage to see what egr valve my wife's '94 c1500 5.7 k has on it, it has a negative back pressure valve, I do know that I changed the exhaust on her truck to make it louder ( less restrictive ) and it did change how it runs a little rougher and all I changed was muffler with dual pipes . The last light duty fuel and emissions manual by chevrolet (1993 ) that I have even states that if using shop air system ( so your not overcome by c02 ) that when ck'ing egr system that it could cause false egr valve operation to occur , that is on page 9-1 in light duty fuel and emissions manual. So if you want to change exhaust it could change what's going on and then have to deal with it . This is from personal experience and sure others here had similar experience

 

[docstoy]

And forgot to add, you need O2 sensor for original fuel system to run as designed or get someone that can tune system to modify parameters or have SES light on all the time. Sorry for to much information, just telling what happened to personal truck.

 

[Sean Buick 76]

All that matters functionally is that you have the pre cat 02 sensor and any muffler shop can add that for you no issue there. The post cat 02s can be deleted as you aren’t running cats and you won’t have any issues with how it runs but it could set off a check engine light. Not a big deal just have a tuner shut off the rear 02 sensors in the computer.

 

[2Grim4U]

All exhaust gasses are scavenged so the better they come out the better the engine will run. That being said you want non turbulent exhaust so a mandrel bent system with a good quality muffler will outflow a plumbers setup with kinks and wrinkles and no muffler. Summit had some good videos on where some mufflers actually made a little better hp than open pipes.

 

[PlayingWithTBI]

The post cat 02s can be deleted as you aren’t running cats and you won’t have any issues with how it runs but it could set off a check engine light. Not a big deal just have a tuner shut off the rear 02 sensors in the computer.

He's working on a 94, they don't have post cat O2 sensors.

IMO you'd have to have a pretty wild cam to reduce vacuum sufficiently where the EGR won't work properly. I'm running a 230/236° @0.050" duration without issues - before I eliminated the EGR and went to Hiwy Lean Cruise

Edit: with a 3" exhaust, cat, and Borla Straight Through muffler on a "383".

 

[Phr0stByte]

Cats and mufflers are cheap, and it's part of being a good neighbor and not making all us GMT400 guys look like dirtbags. Leave that to the Mustang guys running Pypes doing burnouts in front of the cops at Cars & Coffee. If you're running a stock cam, 3" is overkill. I'm running 2.5" with both cats and mufflers on a .515" lift Lunati cam and it's plenty. Any which way, you're not going to wreck your driveability by changing the exhaust so long as you put an O2 bung in it and run the O2 sensor.

Cats and mufflers are cheap, and it's part of being a good neighbor and not making all us GMT400 guys look like dirtbags. Leave that to the Mustang guys running Pypes doing burnouts in front of the cops at Cars & Coffee. If you're running a stock cam, 3" is overkill. I'm running 2.5" with both cats and mufflers on a .515" lift Lunati cam and it's plenty. Any which way, you're not going to wreck your driveability by changing the exhaust so long as you put an O2 bung in it and run the O2 sensor.

One, i dont need ethics lesson, thanks but no thanks. Two, my nearest neighbor is 5 miles away. Three, i have a 1969 Boss 429 Mustang my grandfather left me, and i burn it up just about every chance i get. Four, im running a roller cam in my truck. Appreciate the info though.

 

[Road Trip]

This truck is old enough it’s not required to pass emissions in Texas. Hadn’t thought about the O2 sensor. Maybe I can just cut a hole in the exhaust and welded in? Was planning to keep the TBI system for now

Despite being designed to monitor exhaust gases directly, O2 sensors should be treated
more like mom's fine china during maintenance. But check this out -- choose your favorite bung from the list,
weld *that* in, and then install that O2 sensor in like factory. (Some examples of O2 Sensor bungs)

Bonus points for upgrading to a 3-wire self-heated O2 sensor if your vehicle doesn't already
have that.