ve table adjustment question?
ve table adjustment question? I've been logging and reducing LTFT's to negative and locking at 0. As my Lterms went negative I started seeing more and more knock (1-4 degrees). I've looked at the knock and it occurs usually at 85-90 MAP in the 1700 RPM range. Not every time but quite a bit in that range. I'm considering making a change to the VE table but before I did I wanted to check in with you guys and make sure I was doing the right thing and how much to adjust it. Should I change both 85 and 90 MAP at 1600 RPM or change both those at 1600 and 2000? Would it hurt to change like 75-95 MAP in 1200,1600, and 2000 RPM? How much should I start out multiplying cells?
Yes, I used the IFR table and they are only slightly negative. I could stand to go a little further with the whole table but what I'm concerned with is the events of KR have been steadily climbing in that one area as I go negative with trims. 1400-2200 rpm at mid throttle. Like I said, I see most of it in the 85-90kpa range and in the neighborhood of 1700 RPM's. Am I looking at it wrong? Is there something else I should be looking to change? Timing never seems to be very consistent when the knock happens so I didn't want to change something that wasn't showing any type of pattern. Thanks for any info you can give me.
TECH Regular
Joined: Nov 2003
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From: Dallas
Are you giving it plenty of learn time on the new tune? Sometimes it takes 100mi. or so for the part throttle performance to stabilize.
I think its ok to play with your VE table. I have noticed that the part throttle cruise region of the VE table is particularly sensitive after adjusting the IFR table. I find that my most frequently used PT cruise cells (5,6,10) have the most negative fuel trims. Perhaps the fueling logic in the PCM works better when the fuel trims are positive (stock tune)?
I ended up reducing the VE table at a few points and increasing at others. I don't think scaling the whole trim cell or RPM range will help much. The way I see it, a modded engine will have a different shape VE curve, so the shape needs to change to correctly match. If you scale whole blocks of the table, you are not changing the shape as much as the offset.
When you see the KR at 85-90 map, is it usually following a throttle transition? Are you cruising along at 45 map, then push the throttle a little and get KR when it jumps up to higher map? If this is correct, then I would suggest increasing the VE table in the lower map range before the throttle transition occurred. Try adding 1% or so to the cruise load points only in that rpm range (example: 1600rpm/map40-50).
Hope this helps.
I think its ok to play with your VE table. I have noticed that the part throttle cruise region of the VE table is particularly sensitive after adjusting the IFR table. I find that my most frequently used PT cruise cells (5,6,10) have the most negative fuel trims. Perhaps the fueling logic in the PCM works better when the fuel trims are positive (stock tune)?
I ended up reducing the VE table at a few points and increasing at others. I don't think scaling the whole trim cell or RPM range will help much. The way I see it, a modded engine will have a different shape VE curve, so the shape needs to change to correctly match. If you scale whole blocks of the table, you are not changing the shape as much as the offset.
When you see the KR at 85-90 map, is it usually following a throttle transition? Are you cruising along at 45 map, then push the throttle a little and get KR when it jumps up to higher map? If this is correct, then I would suggest increasing the VE table in the lower map range before the throttle transition occurred. Try adding 1% or so to the cruise load points only in that rpm range (example: 1600rpm/map40-50).
Hope this helps.
At that MAP & RPM you must still be closed-loop
(WOT would be 100 kPa). So definitely want to
let the learning settle. You are also into PE at
that point and rather than fiddle VE (with no
big engine hardware changes?) messing the PE-
RPM table around surgically might be the better
choice. Or, pull timing if the O2s say it's over-fat.
Really need to observe from the different angles
(O2s, MAP, spark, KR, etc.) and see which of
them seems most out-of-bed.
(WOT would be 100 kPa). So definitely want to
let the learning settle. You are also into PE at
that point and rather than fiddle VE (with no
big engine hardware changes?) messing the PE-
RPM table around surgically might be the better
choice. Or, pull timing if the O2s say it's over-fat.
Really need to observe from the different angles
(O2s, MAP, spark, KR, etc.) and see which of
them seems most out-of-bed.
TECH Regular
Joined: Nov 2003
Posts: 434
Likes: 0
From: Dallas
jimmyblue, good point on the open/closed loop distinction. My suggestions for VE tuning are based on closed loop operation. I agree that PE table would be easier place to start to tune open loop operation.
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Now I'm confused. I will give it another log session before I change anything but that log was with roughly 75 miles put on it after the last IFR adjustment. What I was looking at was that at stock I had 3 KR events and the last time I logged I had 42. That number has went up as my Lterms went negative. I just wanted to get a handle on that too. My load cells are avg -1.6 and -2.0 and my O2's are 880 and 890. Seems like that part of it is on, just getting the knock at throttle transitions. My timing seems to be all over the place when the knock occurs. It can be as low as 14.5 or as high as 34.5. Where I'm confused at is the open loop deal. I'm not in open loop when the kr happens. I let the car warm up before I start logging and I'm in cell 14 usually when I get the knock. Definately in a load 6-14 cell. Is that map exceptionally high or something?
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9 Second Club
Joined: Nov 2001
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From: Bay Area, CA
ever consider this may be false knock? try running some higher octane fuel to rule it out.Also, if you are in closed loop the pcm will try to maintain 14.7:1 AFR which is what its suppose to do, if the knock is real pull some timing G/cyl cell your scanner says its suppoe to be in. as you said timing is all over the place which leads me to the false knock conclusion.
good luck
good luck
Are you all saying that adjusting IFR's for part throttle running will affect A/F?
As long as he's in closed loop it should not and should not cause knock. It is likely, timing, false knock or bad gas. Has the weather suddenly become hot?
It has here in NC and I had to pull timing.
As long as he's in closed loop it should not and should not cause knock. It is likely, timing, false knock or bad gas. Has the weather suddenly become hot?
It has here in NC and I had to pull timing.
TECH Regular
Joined: Nov 2003
Posts: 434
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From: Dallas
Another thing to mention. Those '98's are notorious for the false knock problems. Have you changed the KR sensitivity? I think the 98 PCMs have a table for knock floor or threshold or something like that.
