Why does my Advance Multiplier keep dropping?
 

Details: 60-70 degree ambient temps (rough winter in So-Cal), completely stock engine, intake, and exhaust. 91 octane.

Running OFT stage 1 (various different maps) my AM will stay near 1 at times, but commonly drops to .88 - .9. That I don't worry too much about. However, it seems at times it drops to .45 - .5 (which I do worry about). I can't find a pattern in driving scenario that causes this drop. I can get the AM back to one doing some high gear, low RPM, WOT.

It has fresh oil (Redline 0w20) and doesn't burn a drop. Gas mileage is always pretty good and the car runs fine except when the AM drops low enough it feels like a turd.

Running the stock map the car exhibits the same behavior. The only difference is I have one of those oddball ECUs that resets my AM to .7 after the car sits for a bit rather than keeping whatever value it was at when the car was off.

I have 28,000 miles on the car. Mostly street, some autoX, no track.

Any ideas? Is CA gas really THAT bad? When I ran e85 for a while I had no trouble keeping AM of 1, and I'm not sure what my AM was like before that because I didn't have a way to log before then. So it's possible the car was like this from the get-go. But I'm a bit leery of running e85 now, in case the car has some actual engine problem...since e85 would most certainly void the ol warranty.

Yes, CA gas really is that bad. I would log and see if the iam drop is due to tip-in fbkc, which is quite common. If it is, reshape the ignition base and advance tables such that at low load where you're seeing the problem the value in the advance map is less than 3.9 degrees, while keeping the same total timing. This will effectively disable coarse correction in that range while still allowing the ecu to pull timing if significant knock occurs anywhere else.

Also look in fine learning to ensure that the values are being written into the lower load buckets and not up top where it would matter. You can't drop the iam without having significant flkc.

Remember there are three distinct modes of operation in the stock knock control logic, which never operate at the same time. It is entirely possible to have values in flkc while having not seen any fbkc.

You probably don't have an engine problem.

Have you tried different gas brands and/or stations?

I had the same problem as you with an otherwise stock car, AM dropping and staying at around .4 or .5 running OFT stage 1. It would start dropping slowly almost immediately after flashing (resets to 1.0) and going for a drive. Switching from my local Chevron to Mobil has kept it at 1.0 for the past few days, gonna keep my eye on it.

I pretty much exclusively run Chevron because back when I had fuel pump chirp issues, I found Chevron kept the car the quietest. However I have tried a number of different Chevron stations (40 mile commute makes this easy to do) and have seen the same pattern.

thanks for the advice. I'll do more logging and see if I can find the bad spots. Or just say fuggit and run e85 since it seems to fix all the problems, lol

That Chevron station next to McDonalds on Nobel and Costa Verde was pretty much my only gas station for 2 years when I went to school in SD :)

Knock.

Shortly after I flashed to the 1.4 tune (yes, I had been running the 1.3 version for some time) I noticed that my AM was not stable at 1. At one point it eventually dropped to .65. I gave it to over 50 miles and monitored daily. It eventually got to .85 where it bounced in the range for 20 so miles. At about 70 miles after my reflash I was due for my oil change which took place at 7500k on the car. The day after I noticed the AM was holding at a rock solid 1 and it has been at 1 to date (maybe 100 miles?)

Do you think an oil change can effect AM? what if your due for one like I was at over 7k miles?

No. Generally speaking, changing your oil will not make your car stop knocking if it is.

Just flashed to the 1.54B and went for a run. First time running it and my AM stayed pegged @ 1.0

My vote is Cali gas as well.

Yes CA gas is bad. The dropping Advance Multiplier indicates the tune is too aggressive for the fuel you are running.

I have a customer who mixes 100 octane fuel with the CA 91 to bring it up to 93 to prevent having to de-tune the car. E85 is certainly an option if you can get it.

The AM dropping to .45 should be addressed.

-- Bob

Even stock tune it does this...that's what has me concerned.

It could be other issues as well. Nelsmar told me a few days ago that he discovered that the injectors from the factory could be out of calibration by a significant amount (I think he said something like up to 10%).

Not sure if something like that could contribute to knock, but I doubt that the DAM acting the way it is on the factory tune is entirely due to acn91.

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