I have an '04 CTT with the Fabspeed secondary cat bypass and otherwise everything else is stock. I love the way it sounds. Has a slightly louder idle but really comes alive around 3500 - 4500 vs the nearly dead silent stock exhaust. I think I also noticed a modest throttle response improvement and just overall slighly more power throughout the band (but this could just be audible improvement).

Reason for my post is after the install, literally the first day after driving about 50 miles I got a check engine light. Engine was running pretty rough. No stalling or anything but just running like it had a really bad tune. Next time I got in the car it was 100% fine. No light, no rough running. Over the past 6 mos since I installed the Fabspeed bypass (and not making any other single modification) the rough idle/run has come back about 5 or 6 times - always lasts for about 20 mins or so, usually until I stop the car turn it off, let it sit for a few mins, and then restart and the problem is gone.

Has this happened to anyone else with the Fabspeed bypass pipes? Fabspeed says you are not supposed to throw any codes or get any lights, but I would be really surprised if it was something else considering the first time it happened was minutes after installing the Fabspeed bypass.

 

Your post caught my eye as I have been thinking of doing the same thing you have done: secondary cat by-pass only.

QUESTION: Did you have to add brackets or bars or anything to reduce rattle, especially at idle?

These cars are computers and they require re-booting when there are significant updates & upgrades. Since the problem wnet away after you restarted it, I assume that the emgime computers reset themselves according to your new hardware and issue may be solved.

 

The bypass pipe is not in anyway a mod that would affect your engine like that... maybe its your gas quality

 

I have had this on my CTT... was not the exhaust but the coilpacks. They were all mostly cracked and would cause intermittent issues like misfiring and poor idle. Have you checked your coilpacks lately?

 

No brackets were required. Zero rattles at idle or any speed. The Fabspeed is a beautiful pipe, very well made. I also thought it would go away the next time I started the truck but its now happened about 6 or 7 times in 10,000 miles. Just had a service done and all error codes checked (there were none). Clearly not the end of the world, but just a bit annoying and if its something I can fix I'd like to because other than this issue the truck runs flawlessly.

Thought it could be the gas quality because that is exactly how it sounds but strange because it happens so infrequently and it doesn't happen at startup usually. I also only go to Exxon or Shell stations and have never put anything but 93 o 94 in the truck. Most of the times it has happened I had just shifted into reverse or I'm just sitting at a light and go to pull away when it happens then goes away after about 10 miles of driving completely on its own or occassionally needs to sit over night then its perfect on next startup.

 

This sounds exactly like what I am experiencing. Thanks for the advice. I will have the coilpacks checked on the next oil change. Can I look at them myself, what would I be looking for? Just some small cracks around the plastic casings?

If you had them changed was it an expensive job?

 

I always change coil packs when changing plugs, simple, as easy as changing the plugs so while your there. The cost of the coil packs are about the same as the plugs depending who you get them from. A visual inspection for the cracks, easy to see, big difference once changed if there cracked.

 

That is good to hear, thanks. Was hoping it was a fairly inexpensive replacement.

 

I had one coil pack changed when the plugs were changed. The dealer said it was cracked and in a very difficult place to change. He said he repaired that one cracked coil "under CPO warranty" and that he saved me "$200."

My gas mileage was so HORRIBLE (8.9 mpg in town and 12. 8 mpg highway) that I took it in and they went over it. I also has them check for electrical trouble because my turning signals no longer made any sound and my radio presets were often lost.

Turns out that there is 'nothing wrong mechanically' but my lousy gas mileage is likely due to our lousy gas. We only have 90 octane max available at the pump unless I want to spring for AVGAS. This is Alaska and the best gas in a measely 90 octane.

I almost always used Chevron except when it wasn't available on the Alcan Highway last fall. I tried Shell nitrogen enriched and I thought on highway driving at speed I saw 14.8 mpg but driving conservatively I observed 20.2 mpg! followed by 19.2 mpg after I had to get on it for safety.

These are all PCM read outs.

My SUV seems to hesitate just slightly when starting out cold (garaged at 55F but just started in the AM. And there are times it runs a bit rough. I think it mat be due to my short trips in town, insufficient octane in Alaska, build up in the engine due to babying it so much, and maybe that immense running gear needs some miles (2-4) to get the gear oil up to normal.

I appreciate your thread.

Maybe an ECU tune might help resolve your rough idling?