This article originally appeared in the July 2017 issue.
If I’m being honest, I thought it would take a little longer to get to such a specific problem in this here monthly feature. It’s called “Common Problems,” after all. Not that this month’s subject isn’t common. It’s just one that has a pretty specific application that you might not necessarily think of right off the bat. Without further ado, what’s the deal with the throttle valve on a 6.7L Cummins?
The throttle valve sits between the intake horn and the rest of the truck’s exhaust gas recirculation system. When the computer wants to recirculate exhaust gases back through the EGR, it closes that throttle valve to force some of the air through the EGR valve. As you might guess, this makes your engine run significantly worse than normal. After all, would you rather breathe fresh, clean air or a bunch of smoggy, soot-infused air? Your engine feels the same way!
Now, it must be said up front that this is a huge liability for race trucks, which are doing far more work in shorter amounts of time than street-legal trucks. It’s for just this reason that Sinister Diesel came up with their throttle valve delete kit for 6.7L Cummins engines. There’s another issue with the stock throttle valve. Because so much sooty exhaust gas is moving through it, it can get clogged up with soot deposits. That’s bad enough on its own, but the special wrinkle here is that those deposits can make it so the “butterfly” valve gets stuck in the shut position. That means that even when it should be open and flowing air normally, it’s not.
Another disclaimer: this kit is strictly intended for off-road, non-street use. It’s part of the EGR system, which is obviously part of the emissions system. Messing with that stuff on street-legal trucks is bad news. Sinister explains how the throttle valve delete kit works. “When the EGR system is removed, there is no alternative source of intake air when the throttle valve closes. To get around this, the operation of the throttle valve is usually coded out entirely for most EGR-less tunes and the actuator itself is left unplugged. Sometimes the throttle valve can move unintentionally to a completely or partially closed setting which leads to cutting off the air supply to your Cummins and suffocating it. This can cost you power, shut your engine down entirely, or even cause catastrophic damage if it happens at higher RPM. Even when open and unplugged, the stock 6.7L Cummins throttle valve obstructs smooth airflow through your intake.”
Installation of the new throttle valve is a straightforward affair. The stock valve is relatively exposed, so you don’t have to dig into the engine bay to access it. Simply remove the hose clamp from below and take the four bolts out and you’re halfway done. The new valve is literally just a short metal tube that bridges the gap between the air horn and the rest of the exhaust system. You bolt it back on and hook up the hose clamp and you’re done.
One last step remains, though. To make sure that the truck will work without freaking out and throwing codes at you, new tuning has to be installed. Because so much has changed to the emissions system (you don’t have EGR anymore), you’ll get constant “Check Engine” lights if you don’t update your tuning. Also, one final note: this upgrade really isn’t going to do a whole lot for a stock engine. It’s designed to maximize the potential of a heavily-modified engine. Not that you should be discouraged; just know what you’re getting into if you choose to jump in.