I have a 2001 4.6L with intake, exhaust, and Superchips Max. Performance program. I now have 47K miles.

I upgraded to the "max performance" from the "tow safe" tune at around 40K. At about 43K the clutch slave cylinder went out so I detuned the truck while the repair was being made. The truck was an absolute dog till I got home and re-tuned it. It was running better than ever until about 45K. It seems as though it takes longer to get the 3,500 RPM, and once it hits 4K, it takes FOREVER to hit 5K. On the highway in 5th, I almost have to keeo it floored to maintain 80 mph.

Finally a few weeks later I got a CEL. I pulled the code and found it to be the DPFE sensor which I replaced with the upgraded unit, and reset the computer. It didn't seem to change the performance at all, and now I'm getting PO'd. It's like something's holding it back, but I don't feel much drag when I coast in neutral. All I can think is maybe I damaged the pre-heaters or cats by running the max performance tune and loading up teh truck to it's rated payload in the hot summer months for 3 sometimes 4 hour trips. Any other ideas? Thanks.

 

What was the exact engine code?

JMC

 

P1400

 

Well, I drove 500 miles yesterday in 40 degree weather ALL highway with cruise set at 80 mph. I only got 14 MPG!!! WTF is wrong with my truck? Cats? Plugs? Coil packs? HELP!!!

 

P1400 - DPF EGR Sensor Circuit Low Voltage Detected. The DPFEGR circuit is shorted to ground, or the sensor is damaged or the VREF is shorted to ground. A scan tool that can read PIDs is required.

JMC

 

Are you saying it could be a shorted or bad O2 sensor? I don't have the rotten egg smell so I wonder if it's not running really lean? However it doesn't pop on deceleration even with my straight pipes. I wonder if I don't have one or more failing cats...???

 

Code 1400 refers to the Differential Pressure Feedback EGR sensor, not the O2 sensor. It is most likely a bad sensor.

It is the one on the driver side of the engine behind the power steering resevoir with the 2 rubber hoses going from it to the the EGR tube. It measures the flow of exhaust gas and the computer uses this to control the flow of the exhaust gas back into the intake manifold.

 

Darn...well, as I stated in the beginning of the thread, I replaced the sensor with the upgraded unit. The CEL hasn't been back since.

 

Ideas? 14 MPG highway is ridiculous!!!

 

With your tuner on a high perfomance setting your buring more fuel and putting out more exhaust especially with an intake kit, therefore putting more strain on your stock cats(which are very very restrictive to the engine). I suggest going and getting coils, boots,plugs first. If that doesnt do it replace your cats with hi-flow models, big improvements over stock. The rotting egg smell is from clogged up cats, I get it all the time at the shop. This will also bring up your mpg.

 

Thanks man, I may try that. This is completely opposite of what I've heard here though. They say the stock cats offer only a few pounds of restriction at best and are good up to something like 300 RWHP. Mine are probably shot though, I had a bad O2 setup when I first got the truck from the factory. Had to drive it this way for 4K mi. Can't the shop test the pressure between both O2 bungs or something?

 

Yep, I just ran a computer test on mine the other day to see the increased flow from my hi-flow cats. I lets a lot more through and lets the engine run cooler as well. Any diagnostic computer should show you the O2 flow from your sensors

 

Now I just need to find a willing shop in KS / MO.

 

Good Luck bud, let me know how things go OK?

 

I have an appt. tomorrow for some cat work. Will post back.