Pre-detonation on 91 octane???
 

To the California C63ers out there, do you guys have issues with your C63's detonating under load, even with quality 91 octane? I only use Chevron 91 octane in my baby and I continually hear pre-detonation happening when I have all the windows down driving next to a k-rail or a curb or something. I have a Weistec catch can that I left off when I did the head gaskets because I lost the clip that I need to put back on to help catch the aerated oil that's reducing the effective octane of the fuel, but I'm wondering if anyone else is having the same issue or if I have a genuine problem. Sorry if this subject has been beat to death, I couldn't find anything using the search language I tried. Thanks in advance gents.

Yup. Drives me nuts.

Do you have a catch can and if so, does that help? When I had mine on, the head gasket was leaking so it was knocking, but I haven't had it on since I fixed the head gasket.

I know we have bad gas here, but have never heard it. If you hear it, normally it's too late.

That's exactly why I'm concerned, if I can hear it detonating, it's bad.

This makes me sad. I am moving to California in December.

I'm sorry.

Here in Hawaii, we have 92 octane and I'm pinging also. My car is bone stock non-pp.

Has anybody tried running a cooler plug? I know the weistec supercharger kit comes with a plug that's at least a few heat ranges colder, I wonder if that would help bridge the gap between our high compression engine and California ****ty gasoline? Anyone have any thoughts? At this point, it's either that or I start running the 110 I run my Charger, in my C63.

Check your PMs.

Weistec actually does not recommend the colder plugs for non-sc applications.

I do have the catch can. I can't really tell for sure if it helps bc I have also been using Techron once a month and occasionally using octane booster. My pinging isn't as bad as before but it's def still there.

i doubt you're having Pre-detonation from 91 octane ...something else is wrong with your cars, probably the tune if you have one. I've ran 89 once (I kinda had too was in the bush with no other gas stations for 100's of miles) and the car ran no different then it does with 94 ..no detonation or anything.

check your fuel pumps or fuel rail ..that'd cause the random detonation you're hearing

This is a timely thread as I have experienced pinging on three occasions recently. I also live in Southern California and use Chevron gas almost exclusively in all of our vehicles. The AMG is the first one to experience pre-detonation so I'm wondering if the gas has been further cut with an oxygenate such as ethanol to comply with state mandates. Fortunately, the engine only did this in C mode shifting into third gear at low rpm, the first time turning left on to a road with an incline from a stop. My car is a '13 sedan with the P31 package and only engine mod is the ROW air boxes and AFe filters. The pinging I heard only lasted for a moment but it's still worrisome.

I'm going to try Shell gas on the next fillup and see if that helps.

I'm going to try 76 this week and see what happens. My car is literally bone stock with the exception of fabric air filters and the catch can. I spoke to one of the other forum members this morning and he thinks the issue is due to carbon buildup in the combustion chamber causing an effective increase in compression ratio and that once he was able to clean out some of that buildup, the problem went away. I will say that after I did the head gaskets and had clean chambers and clean piston tops, I had no pre-ignition at all. It's probably been 6 months since I put everything back together and my commute is all of 5 minutes on 45 mph roads, so I'm sure there's a fair amount of buildup in there. I release the hounds as often as I can, but with the speed limits in my area, there really isn't a good place to let the big dog eat. At any rate, I'm going to start running seafoam in every other tank and try using 76 and see what happens...

Yeah but did you go WOT when you had the 89 in your tank? Probably not

Doubt it detonating. Engine has knock sensors that would retard the timing. It's likely lifter or cam adjuster chatter.

It is retarding the timing, that's why I hear it briefly and randomly. Lifter chatter is highly unlikely since the lifters have less than 10k miles on them and also because this is happening at 3k rpms during acceleration. I could see the cam adjuster clatter being possible, but I've heard a lot of timing chain clatter in my time and this doesn't sound like that. Also, since the fuel cap says right on it, the minimum acceptable RON is 93, and I'm using crappie California 91, I'm guessing my problem is fuel related.

This is much more plausible. If most of you guys are hearing something, it's likely not detonation because you are all still driving. The knock sensors would retard the timing and if you can hear it as much as you think, your engine would be toast.

Agreed. Hearing knock is unlikely as computer would adjust timing to counter it.

Computer is adjusting timing 100s if not 1000s times a second... hook a scanner to it and check your timing, see if it's retarding. I run 91 Oct with 10lbs of boost, I can feel it pull some timing power wise but never heard any knocking.

Ps, knock (detonation) and pre ignition are two different terms.

What your describing is knock or detonation. Pre-ignition destroys engines in no time. Knock is the fuel mixture lighting up too far advance, as the cylinder pressure keeps increasing too much other pockets of fuel outside the fuel kernel start popping off causing that pinging noise.