Hey,

I have a 03 3500 SO cummins that is a "California" truck with the cat on it, I pulled it off and piped where it used to be and immediately noticed all my Low End Torque was lacking and them drove it home (3 miles) and when I went to park it it started loping and running rough.

What the hell happened?? Any ideas?

 

My first thought is that you changed the amount of backpressure in the exhaust, and the computer is not putting in enough fuel to compensate for the increased airflow. Try resetting the computer and see if it relearns with a proper fuel curve. I'm not a long time diesel owner, so I could be wrong.

 

Did you do any welding on the exhaust pipe to replace it and not disconnect the batteries at least?

FYI, no sensors and nothing to do with back pressure. You changed something somewhere in the ECU.

 

Correct me if Im wrong, isnt that what the ground clamp is for on the welder? So you dont have to disconnect the batteries.

 

I have never had to disconnect the batteries when welding on mufflers, I have had a lot of trucks and had mufflers put on all of them and never had an issue. I am going to take it over to a Cummins certified truck shop tomorrow and have them check it out.

My real problem is I have been a loyal Powerstroke guy for many years and just got converted 3 days ago, so this is my first Cummins and everything is night and day compared to a PS. I can fix any powerstroke, I can usually just listen to them and know whats going on but now I feel like a short bus kid trying to figure this cummins out.

It runs strong just feels a little weird, more vibration and engine noise from 1900 rpm and up than seems normal, but then again what is normal to me is a powerstroke. Thanks you guys, I will let you know what the Cummins Guru says tomorrow.

 

Wait a minute, you SAID it was down on power and not running right in you first post.

Now it runs good but just more noise?

Of course its noisier, you removed 50% of the noise dampener in the CAT.

If you still have a funky idle and the motor is shaking, you probably hurt something.

NEVER NEVER NEVER weld ANYTHING on a computerized truck without disconnecting the batteries. Some will even tell you to disconnect the ECU bt generally the batteries are enough, BOTH posts, to keep the electronics safe.

 

Uh huh, just do a couple high frequency arc starts with electronics in the system and see what happens. I don't care how good your ground is you are gonna hurt some delicate pieces. These trucks have 6 to 7 processing units that can all take a hit.

All it takes is replacing one ECU and disconnecting them batteries is a small price to pay.

 

no 6 oh no don't get all butt hurt, I SAID it feels like it lost a little low end torque the engine runs strong otherwise, just different.

The idle changed from a constant smooth idle to a more loping V8 gasser type Idle.

Never knew you should disconnect the batts, will do next time, if you have fried a module that's no fun.

 

Removing the cat should not affect the engine at idle at all, should only change exhaust noise, same goes for driving it no power should be lost/gained. I can't comment on the sounds because my truck has no muffler either so my sound is a lot different then what you'd have. I don't know if you could of fried something but i've always disconnected both my batteries just to be safe.

 

Removing the CAT can increase lag time for the turbo under light throttle or normal driving.
The CAT actually acts as a barrier for the exhaust and will reduce spool time via back pressure in the turbo to a point....even though the CAT ends up being restrictive in the upper RPM's.

 

You misunderstand, just trying to correlate what seems to be conflicting info. Its not my truck so I don't have anything on the line.

I have noticed only a noise difference when pulling CAT and/or mufflers. If you get more vibration and a lopy idle it really sounds like electronics.

For the vibration, just make sure none of the exhaust pip or hangers are touching the body. That will cause some vibes and strange noise.