My 2006 GT Premium Coupe w/5speed automatic developed an engine rattle upon acceleration (moderate, but not at WOT). The car performs very well. Brenspeed did the performance work and the modifications are GT-500 axle back exhaust, Roush CAI (with insert), accessory drive pulleys, and 87 octane performance tune for automatic. The AFR hovers around 14 during normal driving and I experience no over-heating. Called George at Brenspeed and he suggested a higher octane fuel or removing the insert from CAI and retune, but he said he thinks it could be a vibration caused by the insert. Anyone had a similar issue and what was the fix?

 

Somebody must have an idea or two!

 

Can you post a video? Hearing it would help

 

Thank you for your response! Yes, I will try to capture it on video or audio, so everyone can hear.


It seems I am not so technologically in the know. How do I load a sound bite or video here? Do I need to make a YouTube account?


Further complications; it is snowing and I do not like the precise handling in my 342HP toboggan!

 

Update: After several attempts to record this rattle on an iPhone, I have concluded that it is difficult to capture it on a device. People hear it, so I am not crazy, but road noise and wind noise seems more interesting to the iPhone. Additionally, this rattle seems to be confined to acceleration and only between 3500 to 4000 RPM. Brenspeed has consistently offered troubleshooting advice. Next step to burn off enough fuel to refill tank with 93 Octane and see if that if the rattle goes away. If not, a trip to North Webster, Indiana, will be in order (as long as there is good weather or winter is over!).

 

I also had a rattle (detonation) on acceleration. Mine was around 2000 RPM or so, and it didn't matter if it was WOT or not.


Switching to 91 seemed to cure the problem. (We don't get 93 here on the Left Coast).


What is interesting is that when I changed my spark plugs the detonation went away and I haven't heard it since, and I'm currently running 87.


At this time I am wondering if it was a bad plug? Excessive carbon build up?

 

Throw a bottle of octane booster in there and see what happens, I say. Can't hurt.

 

Finally, after the worst of the winter is a memory (I hope), I ran the 87 octane gasoline down to less than a gallon (.7 gallon to be exact) and refilled the tank with 91 octane top tier fuel. The rattle went away! Praise the Lord and ask WTF? Is there a cure other than running higher octane? I will be calling George from Brenspeed to inquire about a tune adjustment (either they make it run without rattle on 87 octane or give me a tune for 91 octane).

 

Brenspeed should be able to get you an 87 octane tune, but that may not solve your problem. I have a Bama tune 91 Torque, but when I was encountering rattles I was running their 87 Performance tune at the time (CA $4.75/gal gas will do that to a man). I needed to run the 91 octane gas *while still tuned* at 87 octane.


How old are your plugs?


Also, check your PCV hose to the intake plenum - my plenum intake had cracked, and the resulting air leak sounded like a rattle. I ended up lopping off the hose connector and just pushed the rubber hose onto the broken fitting (don't want to replace the plenum if I don't have to).

 

Brenspeed tuner says stale gas or gas with too much ethanol. Recommended only top tier and finding the freshest gasoline possible.


The plugs only have 28k on them.


Everything under the hood looks brand new and I can find no defects in the location you suggest.

 

Thank you Brent White! The owner of Brenspeed took on this issue and solved the mystery in a few short hours at no charge (The Indiana Shop). Apparently, there was too much spark advance (correctly predicted, but in practice...at least for my 2006 GT...proved to be too aggressive) and that caused the rattle/knock noise. No damage done. Brent had a 91 octane tune loaded (again, on the house) and I loved it so much I drove the car over 2,000 miles in 5 days. Had to get competition lower control arms to get the power to the road...wow!

 

Great news