Detonation??!!??!

[kodiakz]

Hey all. Need a little help. Had to go out of town suddenly yesturday to attend to a family matter. Went from Denver to some little town in Nebraska. When I got to Nebraska, I filled up @ a local shell with 91 octane. Later, had to get onto a small highway quickly and as I hammered it, sounded like bb's were let loose in the motor and the check engine light came on. Pulled over immediately as I thought the blower blew or I took out a ring. MOtor then ran absolutely fine for the 300 mile return trip. When I got home and checked the dtc code with the predator, it said something about the maf sensor malfunction? I have never heard detonation before and was wondering if that is what I experienced, and, if so, why and what could have been damaged.

A little side note: the local smokies were so impressed with the black rocket that they gave me a good driving award What bums me out is that I clearly saw him waiting on the side of the road so I clearly slowed while passing through his little speed trap. He must have seen this and decided to ticket me anyway!! He followed me for about 20 miles and then ahuled ass up on me and gave me a ticket for 97 (he gave me a break and didn't write it for 100 so I didn't have to go to jail--what a swell fella). So much for the preferred insurance rates

 

[jgwatsonjg]

Detonation also Sounds like Marbles in a Coffee Can. (That's how I usually see it described and its accurate) If the Maf Sensor Freaked out, you probably Ran way to Lean and that was your detonation. I'd probably get a New Maf Sensor just to be on the Safe Side.

Also, Checked any cables/plugs/wiring ETC ETC

Agent M.

 

[jonboyNY]

ususally you should run 93 octance for no detonation issues, also the best gas to use is BP/Amoco or Sunoco.

Gas from Mobil Shell etc having denotation issues on FI engines.

 

[kwinsor]

Here's my .02

The MAF codes I've read on mine said the MAF was giving a reading that differed from what the computer expected based on MAP and throttle position. If you still have a 1bar MAP sensor you are likely to get a MAF code under hard acceleration depending on your setup. I've had them.

My second issue also has to deal with the MAP sensor being 1bar instead of two. It's my understanding that the PCM uses a lookup table for quickly setting the air fuel ratio when there is a quick change in throttle position. Shortly thereafter the O2 sensors update the short and long term fuel trims. This look up table stops at 1bar! When we go into boost there is no lookup table. I've seen very lean readings on my wideband O2 analyzer on sudden acceleration. Back off and hit it again and everything is fine.

I'm waiting for an RPM pickup for my wideband. When I get it I will record some data. I'm hoping to be able to scale the volumetric efficiency table so it will have a 2bar range. I have a 2bar sensor from MSD so that part is ready.

GM uses 2 bar sensors on their supercharged vehicles. There must be a reason.

kw