: Engine Knock?

07-26-07, 07:59 AM
I have a 2004 SRX V8 and have been noticing some engine knock at lower rpms. The vehicle is driven by my wife who puts 89 octane gas in it mostly.

Should I be hearing engine knock with 89 octane gas? I have heard knock can be very damaging for an engine long term. We have been hearing it off and on for maybe 2 months now. 93 Octane gas was tried for 1 tank and we didnt seem to hear it, but it could have been there just inaudible to us.

Should I take the vehicle in to the dealer?

07-26-07, 08:38 AM
Do you routinely use one of the brands listed at http://www.toptiergas.com/retailers.html

07-26-07, 11:32 AM
We do not use any of the ones on that list. Closest would be Sunoco. Dont know how close that is to "Sunoco-Canada".

07-26-07, 12:29 PM
I've been putting 87 in my N* V8 for 42,000 miles, and haven't had a bit of a problem.

07-26-07, 01:02 PM
I've been putting 87 in my N* V8 for 42,000 miles, and haven't had a bit of a problem.

Thats the reply I expected from somebody and was afraid of. We have had the vehicle about 2.5 yrs now and up until now, no problems and I am sure my wife dumped 87 in it on more than one occasion. I guess I will give my dealer a call. Maybe I have a bad knock sensor and it is not reducing timing to avoid knocking??

07-26-07, 05:14 PM
Knock or ping? Low pitched or high pitched clatter?

Some ping is ok if it occurs at light throttle. It not good if it's heavy at wide open throttle. The PCM will still pull timing and to get rid of it but that means less power.

I just want to make sure you aren't having a mechanical knock (i.e. a bad bearing).

You could also have some carbon build up and just need to cleaned out (like Top Engine Cleaner).


07-27-07, 01:30 PM
I use 93 octane always but even with the 87 octane the dealer filled the tank with I only experienced reduced performance and no noise.

07-27-07, 04:52 PM
If you are getting knock/ping/detonation, the knock sensor will start to pull timing to stop it. Running 93 octane maybe stop the knock but the main spark table in the PCM may not allow enough timing to get any more power.

GM usually runs really aggressive knock reduction not because of engine damage (which will occur if it's really, really bad under load) but because of customer perception. A slight knock freaks people out so GM just trys to limit it so the car doesn't wind up in their service department.


08-01-07, 09:50 PM
According to the manual, you can use 87 instead or premium. The only thing is you will lose some performance. And being I bought a Cadillac and not a Corvette, I don't mind the lack in performance.