I've got the tune down fairly good up to about 40% throttle snap, but anything over that and it's almost like I'm shutting the key off. No stutter or stumble, just instant "off" with the motor until I let off the throttle. If I roll into the throttle, it is perfect. The issue is present only with a throttle snap, making me think it's an AE issue. I just started playing around with that late tonight, but the instant lean is still persisting, only now I get a big puff of black smoke after the engine catches itself again.

Here is my initial thoughts: Run a monsterous amount of AE to compensate for the huge influx of air, and then run a very fast decay rate to avoid the rich spot. Some of you guys have mentioned this in some of my other posts, so I don't think I'm off to far here.

For testing something like this, am I better off making a huge change and then backing off to tune? That almost sounds better than making small incrimental changes so that I don't risk detonation.

Also, all the AE tables only go to 50% tps. Are the values scaled from 50% to 100%?

Please bear with me here if this doesn't make sense. I type this out on here not only to get your opinions, but it also helps me get my own thoughts straight

It's a 7730 ecm, running axxd code. The manifold is a vic jr with a 70mm monoblade positioned directly over the plenum.

 

Try upping/ lowering the VE tables at low rpm/ high map areas. I went through the same thing last year. Finally I used very little AE, and played with the VE table until it ran well, then I put some AE back in.

 

hmm, I just maxed my high load/upper VE tables yesterday. Is the best way to get the resolution back by fudging the injector constant? I'm gonna have to fix that anyways, figured I might as well ask now.

You still think it's the VE tables even though it's fine if I roll into the throttle? I can get to a very functional WOT if I roll into it. Just not if I romp on it.

 

Yes, as you roll into the throttle your probably hitting 70-80 kpa max right, and you won't hit the high map's at low rpm.


Your table tells it all, you need more fuel in the 90 & 100 maps.

I too had an injector constant that was off, and had the ve maxed out in some areas.

Change injector constant, scale your VE table accordinly, and then add 5% at 90kpa, and 10% to all 100 kpa's.

Can post your spark table, Sounds like it might need to be decreased in the same area your adding fuel. (low rpm/high map)

 

Decrease the decay factor of MAP AE and increase the actual AE multiplier. I had to do this with a zz4 running an edelbrock MPFI conversion kit (from TBI) which uses a single plane intake, very small plenum and a gutted 2 barrel TBI. It's great for a truck although I'd rather have had TPI on the thing for that extra grunt below 4000rpm... oh well.
I can be more specific but honestly, I didn't have to do what you did to your VE table, infact I decreased it by a bit from stock. That might have something to do with the zz4 cam but other than that, I just shifted the VE table to peak at 93% and at 4500rpm... engine loves it.
Is your problem during open loop or closed? If open loop, remember that the PE afr table is NOT used which leaves you with the open loop AFR vs map table and hence the relatively low AFR values in the 90-100kpa cells.

 

i just reduced the VE in all VE MAP that are greater than 30/40 map(idle/off idle) at 800/1200 rpms. and i added more AE/MAP at 0/20/40 map. AE/MAP and AE/TPS appeared identical in WB log and were about 11/1 or less in prior tune. that is what i thought that JP suggested i do? that is reduce VE as i stated. that will allow me the ability to bring in AE more so from AE/TPS and AE/MAP without a contribution from VE in upper map areas with hard accelleration at 5 mph or so. i had larger values in AE TPS 0% to 25% vs MAP in prior tunes. the result is inconclusive. SOP seems better but so many variables. i did some hard accell this morn in 1st and bog is reduced. yet there is some hesitation or AE lag. will review logs tonight.

ps AE tuning is a bitch.

 

Especially with large plenum wet flow like TBI . Oh well... makes tuning the other stuff a piece of cake.

 

What's the injector bias you are using or pump up the FP?

 

I too played alot with AE, and was able to make my combo run well under low speed accel, but in the end that was just masking my VE table being off.

For me the trick was too remove almost all AE then make it work by adjusting the VE tables. Then I brought the AE back in to finish it off.

Your problem sounds very similar, but it could be different.

 

What J said. Take a look at the multiplier/limit values in the constants area. If these are left unchanged, your AE tables aren't likely to do what you expect. I was able to get my 730 setup on either side of perfect (lean-pop, rich-dump). It got to where it was great when the engine was warmed up, but I never did get to do the lower temp corrections prior to changing combos again.

 

Wow, this is alot of good info to get me going

Spark values are still relatively mild since I haven't had a chance to adapt the MAF knock sensor to the new MAP ECM yet. Advance curve is taylored to estimated tq curve (compliments of DD2k), and scaled down proportionally as load gets lighter. Also want to note that the 7730 spark tables are on a 20.04 deg bias, so subtract that from the readings in the table. Not saying you don't know, I'm just not sure what your TBI ecm does

It is present O/L and C/L, but is actually more prevailant in C/L.

Tell me about it

They are LS1 28lb/hr injectors, but I am running 42psi instead of the LS1's 60 or so. I have my constant set to 25.5lb/hr. If this tinkering doesn't help out, I'm gonna have to tape a fp gauge to the windshield so I can see what the pressure is like under load. Maybe it is something as simple as a failing or weak pump.

Craig, I'll definately check that out too. If you don't mind me asking, why did you change setups? From what I remember, you had that thing running pretty well. Was it low 12's?

Thanks again for the help guys

 

Blinky, I hope that isn't YOUR SA table. If it is, well yeah, too much timing.
If you're not seeing any knock counts it's because it's being masked by too much fuel. I had this problem a while back and grumpy pointed it out too me. That was before I had much experience tuning.
First off, make certain initial SA matchs your base timing. I like 6-10 degrees, they should match! Then put the main SA table bias to 0. Now for some generic rules that I abide by; below 1000rpm and 90-100kpa SA shouldn't be more than 20 degrees, infact I like 4 at 400, 8 at 800, and 10 at 1000, then I ramp in the timing to a max of 32 all in around 2400-3400rpm depends on the combo. Also, idle area wants between 25-35 degrees. Cruising wants the most but I'd still stay below 44 degrees. If I were you I'd go back to a stock SA table. Look at how a normal SA table looks and you'll understand all of what I said and why your table is WAY off.
Also, your injector constant should be 23.5 if my calculations are correct.
Here's an idea of what I'm talking about.

 

****, I thought the BIAS was for the main spark tables

Luckily I had the max SA set to 36* total, or I could have been in trouble.

Base timing is 6*, and it's reflected in the program. I'm using your guidelines to revamp the spark table, I'll post it up for your review when I'm done. Thanks for catching that

 

Is something like this better?

Also, base timing is included in these numbers, correct?

I also noticed that I have a constant called "enrich power AFR enable min temp", and it's set to 119*C. Does the stock tune only use PE as a last ditch effort to help cool the motor down? I checked this on a few stock 8E tunes, and it's the same for all of them within a few degrees.

 

Back to the top

 

Man your first spark table was totally *** backwards. The second looks pretty good.

You'll see guys running lots of spark in the low rpm / high map, but usually with a big stall convertor, or with a stick and dumping the clutch at higher rpms (well at the track any way). I know when I had too much spark down low, my motor would almost stall out. You can just imagine that peak cylinder pressure is well before TDC with that much spark, and low rpm/high map.

 

Okay, here's how it works out to ruffly your final SA;
Spark Advance Initial (Distributor Setting) should be accurate. Don't assume anything, set your base timing and then set this value correctly.
Now the values in the main SA will make more sense and be what the engine is seeing (for the most part) under normal warm engine temps. There is more to be careful of, so don't skip this next part. There is a SA table vs load vs temp. There is a bias for THIS table. The stock bias is 20 so if you open the table, you'll notice values all above 0 and under the warm engine speed it should be 20 all across the load row. Now in your mind, subtract the bias and add that to your SA .
Now this is where the xdf file becomes useful. I'll be releasing an $8D xdf file that is "dumbed" down for practical purposes of making basic changes and not having to worry about the bias's. I'm a busy guy so don't expect it to be out until Mark starts hosting xdf files instead of ecu

 

I'd appreciate it whenever you get around to it. It's mistakes like the 3:00 a.m. timing table that have me wary. I've got some tuning experience, but with all the trouble this tune is giving me, I almost feel over my head at this point. I'm sure I'll work it out, it just gets so frusterating at times

 

LowC1500,

What do you consider "too much spark"? I'm running 28d in the idle area tailing off to 21d by 800rpm x 100kPa

 

What tranny u running? Maybe you never hit that area for any real length time.

It depends on your combo, poeple have posted before they like running high spark in that area for quick spooling of the stall convertors.

 

ZF-6 with 3.42:1 Dana 44. I've been playing with SA in that area to see if helps with a lean surge I'm experiencing. I read your comment regarding the motor stalling due to too much spark and was curious if that may be part of my problem. Mine has had an odd idle stumble and a lean surge when I elevate the idle speed at no load.

 

Try my rule where you start with 4 degrees at 400rpm, 8 for 800, 10 for 1000 and bring in the SA after that. Remember this; knock sensor doesn't work at idle on a stock configuration but at those engine speeds and just a tad too much fuel won't trigger a knock count seeing as it's not detonation, just pre-ignition.
I've never found a car that needed more than 10 degrees at 100kpa and 1000rpm... ever. I mentioned this a while back because some people just up and add 4-8 degrees to their WHOLE table forgetting that at low engine speeds the engine can't handle that... it's a fuel burn rate thing.
So take out timing in those area's and take out fuel, watch the tires roast as you stab the throttle. Another indicator of too much timing in those area's is having to roll into the throttle to get a burnout. Slamming it to the ground and it bogs might make you think it's an AE problem when it isn't.

 

OK: now i think that may be very helpfull with my chasing bog. will burn another chip tonight! i have been thinking AE=fueling when it may be equally spark.

Thank you!

 

Jon,

I'll try that tonight. However, I can tell you that I need to roll on the throttle to keep from frying the tires. At a 20mph roll in 2nd,
slamming the throttle could pirouette the car if the steering isn't corrected.

Ron,

How much spark are you running?

 

I tried running the new spark table, and the bog is nowhere near as bad. Now it is acting just like a rich stumble instead of complete dying out. I can't thank you guys enough

I'll keep an update going as I make progress, I'm sure I'll need some more help as I get the ve tables closer now and start with the AE.

What about the power enrich I mentioned above though? Why wouldn't gm enable it until such a high temp? Am I just reading the description wrong?

 

RE: "I also noticed that I have a constant called 'enrich power AFR enable min temp', and it's set to 119*C. "

Do you have a memory location for this? I looked through the code and couldn't find it. The $8D code does use two TPS% threshold for PE mode tables. One for normal engine temp and the other for high engine temp.

RBob.

 

Without checking on this, I could guess that it's a "go rich sooner when overheating" threshold, meaning be in power enrichment at a lower TPS threshold. Probably a corresponding TPS threshold to that number (maybe not in that .ecu yet). That, or just go PE full time.

 

onebinky,

I tried it too last night. Basically took 2d out of the idle area and the motor idled noticeably quieter and didn't stumble nearly as much. In fact, it hardly stumbled at all. I went back and dropped the timing some more and it seemed like it was a bit too much at that point. So tonight I'll be using last nights first chip and tweaking that.
Thanks Jon.

 

One thing that les IDLE timing (and I mean this for idle timing only) can do is let the engine idle with a little bit less vacuum and bring the pulsewidths up away from the inaccurate/inconsistent small PWs if the injectors are large.
Also less table idle timing will allow the idle spark stabilizer have an effect in both directions. If the table timing set to peak the RPMs, then less timing AND more timing will drop the RPMs, which is bad.

I have recently calibrated a few engines on a highly accurate engine dyno (but they are SMALL engines). They need about the same timing at low loads as JPrevost says. They also don't need much high RPM SA either for MBT.

Think of a mechanical/vacuum advance distributor. At low RPMs/high loads its basically base advance, no mechanical or vacuum adv. They seem to have pleased enough guys throughout history.

 

i changed all my low rpms all map. all map 400 rpms 4 deg, all map 600 rpms 6 deg, 800 rpms 8 deg. i am now idleing at 700 rpms 6-8 SA. cant really say idle quality is improved as that was never an issue. what i can say is that i drove car first this morn with those timing changes as well as removing VE at higher map 60-100 for VE cells 400-600-800-1000 rpms. the "tip in "bog/stumble" at moderate or hard accelleration is improved. my test of forcing a stumble in 2nd of 5 gears with a hard wach on go fast pedal produced a minimal stumble(much improved) and then car flies. i did a log with WB but have not yet read it. now here is the problem. i also added more AETPS at 0-20% TPS so i cant be sure which of the changes are giving me the result. WB log may show the AE results tps vs map as well as any lag improvement. i had as much as .50 sec delay prior. SOP shows that is gone.

 

8602

Here's what it looks like:

 

Maybe this one is just the high engine temp qualifier, and I'm missing the table for the high temp percent increase.

 

onebinky ,

That looks like Min Temp to allow PE. If that's the case it looks way too high.

 

Dom: maybe it was disabled? for unk reasons.

 

That location is the threshold to use the high coolant temperature TPS% for PE mode table. This is what it looks like in AXCN:

If the coolant is above the theshold at 8602 then the high coolant table is used. The value of 116°C seems to be reasonable.

RBob.

 

Thanks for the info, I just rebadged them so they are reflected accurately.

 

Jon/RBob,

Dropping the timing has really worked. I just burned a new bin with 26d at 800rpm but then dropping to 24d at 400-600rpm. Also dropped the timing at 30kPa up the rpm range and that seemed to help calm the decel and trailing throttle bucking.