Cargo Commando

Well-Known Member
Cummins ISX Egr Problems

I think my EGR valve is on it's last leg. I have a'05 Cummins ISX 400 ST motor. Is this valve electrical or vacuum? Can I replace it my self? I figure if I can block off any coolant lines and have some o-ring/gaskets on hand it might be a DIY job. I'm somewhat mechanically inclined, and prefer not to spend 1k on something I can do in a few hours. Or how about bypassing it and using a few jumper wires to offset the codes encountered w/ bypass? The truck still runs well (no codes) but idles rough. Trying to be prepared, ya know?


Active Member
rough idle probably isn't the fault of the EGR valve. If the EGR starts to malfunction you will get a yellow "check engine" light and usually causes low power during hard pulls. On the EGR note, there have been several ECM calibration revisions since '05 that dramatically increase the life of the EGR valve so you should have the shop (Cummins dealer) check next time you're in as most are warrantable and will be free.
You can't bypass the EGR valve with jumper wires, the computer is smarter than that. It is electrically (mechanically) operated and plumbed to the cooling system. You won't be able to pinch the lines off as they're steel coolant lines. They can be a bear to change. They take about 2 hrs in the shop. My first one took about 4hrs.
The ISX like other engines occassionally wears a cam lobe or has injector issues but the most common idle fluctuation issue will be caused by either failing timing or injection actuators. They're expensive and there's 1 of each for the front 3 cylinders and 1 of each for the rear 3 cylinders and very difficult to pinpoint the problem one, so most shops will typically change both of whichever set is causing the problem. Just be happy you aren't having to deal with DPF or DEF systems yet on your engine. Good luck.

Cargo Commando

Well-Known Member
Thank you for your reply. I already feel more educated and willing to challenge my mechanic on his accessment of my problem.
I had ny egr go out once. It registered as a dash fault and a check engine light. At first it was periodic where it come on for a bit and eventually clear its self out. Nothing happened. Was like that for a few months. Eventually it'll be steady and you will lose power in general. Might want to check your dpf filter too if you actually start having egr issues. Mine seemed to have clogged alongside the egr going out. Not sure if they were related issues.

Sent from my htc DNA


Well-Known Member
I had an ISX in a '06 International ('05 build date). Shortly after I got it, I unplugged the EGR. Sure, got a fault code and CEL, but the engine ran great and oil stayed a lot cleaner. Later, I installed a 1/4" steel plate between the intake manifold and the EGR tube. Plugged the EGR back up and could have given a rip if it worked or not. Later, around 600,000 miles, the EGR went bad. No problem. Ignored it. Still had original EGR valve on it when I sold the truck with almost 900,000 miles on it. It passed me a couple of weeks ago on my way to Indy. They still haven't done anything to it. Still runs fine. I sold it to get a 2013 FL glider with a PRE-EGR engine in it. Factory rebuilt. Didn't want to fiddle with any of that emissions stuff and newer high priced engines.


When my EGR went out on my ISX, there was no censor light, just a trail of thick black smoke, didn't have to worry about anybody tailgating me. They had to take a few things off to get to it which you could do but it needed to be calibrated.


New Member
If you want to bypass egr and fool the computer take it off, weld the valve closed, disconnect the control rod from the motor. Welding closed fixes the stuck open issue. Disconnecting the rod that opens and closes the valve allows the computer to activate the motor normally its just not connected anymore.