New exhaust no theres an issue

[kingcat400]

So after Eagle got my truck running great I wanted to open the exhaust up a bit. Swapped out the turbo muffler for a free flowing Borla. I talked with him before I did the swap and he said that I would possibly see a rise in the wot shifts. But I got just the reverse.

Before the swap I could run the shifts out to 5200rpm with no issue. Now once it hits 4000rpm it begins to pop and sputter and maxes out at about 4500rpm

Do you guys think this could be something that is in the tune or maybe I need a better ignition?

[Hog]

A muffler shouldnt do that.

Sounds like fuel filter, fuel pump. I had a fuel filter start to clog and at 4000rpm it wuld start to stumble and not be able to rev over 4500rpm under load.

Stock ignition is fine for up to 5900rpm.

Assuming this is a 1996+ Vortec 350 L31.

peace
Hog

[EagleMark]

Couple times I had a good tune and shifted right where it was set (+ - a few hundred rpm)... when I opened up the exhaust it raised shift points a few hundred RPM = not accurate to what was set in tune. But was responsive to further changes. Gotta agree with Hog but it did change on me and shouldn't?

Sometimes people don't believe a change of plugs will make a change when they only have a couple thousand miles but I've had engines break up at the track at high RPM and a fresh set of plugs cured it.

That said I also have had issues with anything other then stock spark plugs, so I'd start there and because of the fancy Vortec distributor do a cap and rotor if the plugs did not cure the issue.

Hog, I'm leaning towards spark because of knowing his fuel pump etc... was new and had plenty of flow in data logs. But at this point we should be lookking at some WOT data logs! :jfj:

[Roadknee]

I went back and looked through the original thread where EagleMark helped Kingcat with his tune. Take a look at the Keezer6/20/13 datalog on post 54 here.

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?1326-TBI-Chips-com-help!-i-need-a-drivable-truck-soon/page4

Kingcat started a wide open throttle run at about 5:12. At the top of second gear and before the shift (5:22) the O2 voltage drops to nothing. At the same time the fuel pump voltage increased 0.2 volts. It is possible he has a fuel supply issue. 355Chev experienced the same problem with his 1995 K1500 recently. Through process of elimination he traced it to a wiring problem. To rule out all the 20 year old wiring he installed a new Dorman sending unit, hotwire kit and additional grounds from the sending unit to the frame. This solved his fuel supply issue.

I agree with Eaglemark; go collect a WOT datalog and post it up. I predict we'll see the O2 voltage drop and the fuel pump voltage increase when the engine falls on its face.

[kingcat400]

Sorry for takeing so long to reply. sema took up a week of my time.

I will try to get a log in the next week or so. It wont be hard to capture it.

[kingcat400]

What do you think? and of course i hook the computer up and it does not do it as bad.

[Roadknee]

I certainly don't see anything like what you describe in your first post. But you never held it at WOT in the datalog you attached either. The low rpm low map areas of the fuel table are a little rich and some areas of AE looked a lean. Neither of these would cause the motor to lay down at 4,500 rpm. Other than that I saw nothing out of the ordinary in my quick view. Curious, what intake manifold are you running?