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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What sucks is I can't exactly go to a dealer and get them to do anything about my IAM dropping.

"Is the CE Light on?" - No
"Is the car running?" - Yes
"Does it make any weird noises?" - No

I have to wait until something bad happens to it....seems unwise.

Try using different brands. The fuels we have seen that work decently are 76 and Sunoco. I actually have found the worse offenders to be Chevron and Mobil. I know that might sound a little odd, but more marketing/advertising does not mean it is always better.

Cheers,
William Knose

If Bill's suggestion doesn't work, try using 8 ounces of Torco Accelerator in 10 gallons of gas. I had knock issues and that cleared it up. You can order directly from Torco or get it from one of their distributors.

I've also been adding a few gallons of 100 octane to every tank of CrAp 91 octane fuel we get here in Las Vegas. Here's a blending chart if anyone needs it.
http://i1299.photobucket.com/albums/...psfbpgwlcp.png

I had the best luck with 76 in my modded Forester XT...so it doesn't sound odd at all. However, I had the best luck quieting the crickets with Chevron which is why I stuck with it. That, and every convenient stop on my commute is Chevron....however, I'll give 76 a whirl if I don't just run e85 all the time.

would someone mind taking a look at my first log? sorry I did not run all the way to redline, but hopefully someone can tell me if things look normal or anything is out of whack. I am totally new to this and don't really have much understanding of what all the values mean, but this discussion of low adv multiplier has me worried, as I was down at the .5x range and now it seems to be climbing to .6-.7x range. I am running Vishnu OTS Stage 1, and on CA 91 gas.

http://www.datazap.me/u/pmok/stage-1...&data=1-8-9-12

Is your car stock other than the tune? Your AFR looks pretty rich...low 11s.

very close to stock... drop-in performance filter and a catless front pipe are the only mods. everything else is stock. stock headers with cat, stock exhaust.

afr at wot should be around 12.1 and 14.7 under normal load. adv mult should be at 1. the way i understand it is a smaller adv mult number means the tune is too aggressive and the ecu is lowering the numbers in the maps and visa versa for a number larger than 1. give it some more miles and itll get to 1.

long term fuel trims should stay within +/-10. If they go beyond 25 it'll throw a code. short term should be within that range too but once the ecu starts to learn it'll usually be +/-5 and 0 at wot.

I'd suggest taking some logs and try to pin point where and when it is knocking. I had the same problem with the stage 1 tune. took some logs and looked at the ignition map. Turned out that there was a peak where it was knocking, so I dialed back the ignition advance a little bit where it peaks. (at around the neighborhood of 0.70~.80 g/rev at 2000~2500 IIRC) IAM pinned at 1 after that on 91 octane.

There is also an issue on the cruise timing...up into 50deg adv on the stock tune.

I found if you tried to accelerate in 6th gear pretty much at legal speeds can cause knock.


I noticed this stock and stg1. I'm at 4k feet elevation with 91oct gas. (Others noticed similar issues with race gas)

Do you have logs showing this to share with the class? Let me find mine. :)

http://www.ft86club.com/forums/showp...&postcount=937

And above 2000rpm:
http://www.datazap.me/u/solidone/1-1...2&zoom=265-694

I was reading one of the other threads and noticed that mad_sb had mentioned that you might get more knock readings if you are low on fuel... I was running nearly on empty when I did my log. So I have tanked up and will try to do some more logging tomorrow to see what happens...

I have some logs showing the timing but it didnt happen to knock that time. I'll try and do some more when i have time off work.

Only have 2 logs.
It happened to me when watching real time...lowest i saw was .76. It was cold i live at 4500ft and my 91 oct isn't cali piss( correct me if i'm wrong)

I think I seem to have found the pattern. Around 3400RPM @ .9 engine load during cruise conditions (driving up a hill in this case). I'll dial back timing a tad and see how it goes.

so any drop in the IAM below 1 is a sign of knock and the engine will pull timing to compensate?

Yes. Any multiplier (DAM) below 1 reduces the timing.

still trying to understand what the KC learned value is and what it should be.

KC = knock correction?

Jamesm explained it to me

You need to look at the Engine RPM Vs Load table in tunepro/romraider ect and look at the value in the table for the given RPM vs Load. If that value is say 6 and your KC Learned is say 2 then it means its pulled 4 degrees of timing at that RPM/load point.

If the value in the RPM vs Load table equals the KC Learned then their is no knock retard at that rpm/load.

Hopefully I got it right.

so I did another run today on a full tank of 91, with similar results.

http://www.datazap.me/u/pmok/stage-1...og=0&data=1-12

Adv. Multiplier was around 0.52 when I started the car. As you can see it went back up a little during the run, but still nowhere near 1.00 at all. Thoughts/recommendations? Assume that I have no tuning skills at all and very little inclination to get too involved into it. Should I be worried enough to switch back to stock tune, or find a way to get higher octane gas?

Try recording some runs on the stock tune to see if u still have similar results.

Sorry to randomly chime in, but I also used to have a modded forester xt... were you on the sf.org forums?

+1

Be interesting to see if it was happening on standard tune

Pmok are you at significant altitude above sea level ?


PMok you could

Source some higher octane fuel
add octane booster to current fuel
Pull some timing in the problem area's (although you stated you don't want to get involved in doing that)
Run E85 and E85 tune

Yeah I will try logging at stock tune and see if I get similar results. Was wondering if anyone would say to let it keep learning a little more or what. I live in the hills about 1200ft above sea level but the logging and most driving is done pretty close to sea level.
Thanks guys!


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yeah, long time ago. same username.

i've fought tip-in knock with this thing since i started tuning it. I've tried all sorts of stuff, from the regular timing adjustments to throttle mapping and cam timing. Nothing so far has worked. Not even E85 lol. You can make it happen less often, and you can make it less severe (where you may see up to -2.1's you can get it to only ever pull -1), but I haven't found a way to eliminate it entirely. I've got it down to one or two instances in a 20-30 minute log at best.

My next plan is a custom map that'll pull timing based on throttle delta. If that doesn't work, i'll try the same thing with MAP delta.

The hack around the IAM dropping is just to make sure the value in the advance map where it happens is less than 3.9 (while keeping the same total timing).