I posted a poll in tech/performance I hope someone will vote on.

http://forums.corvetteforum.com/zerothread?id=681620

As the post states I have new polished Fastburn heads, MiniRam, 30lbs Ford inj, Old stuff: hot-cam, accel 300 ignition, headers. I over tightened the valves, but since fooling with the ECM, I am making improvements and am hoping that these engine changes are so dramatic that I just need to power through the confusing TunerCat tables and get the ECM sorted out.

If you guys could give me a vote at the link or any opinion, I would appreciate it. So far- backing off timing and leaning low MAP values has helped, but intermittent backfire still there.

As another issue my O2 readings are way extreme 982 down to 26. Wow, never saw anything below 100 before. Low values are usually at de-acceleration.

thanks,

 

There are 4 decel fuel cutoff constants that are a function of Kpa and RPM. If your mods were significant enough to change the MAP at idle you may have to change the point where the fuel C/O's. If your not getting knock counts I personally wouldn't reduce spark advance.

Is the backfire at decel conditions only? These are stock 91 values used for example:

1.) Decel fuel C/O MAP enable =20 kpa
2.) Decel fuel C/O Map disable =28 kpa
3.) Decel fuel C/O RPM enable =1400
4.) Decel fuel C/O RPM disable=1100

I don't remember exactly what I changed them to on my 396 but I think the first two were 30 and 35 Kpa. You need to look at your data and see what your MAP is during decel. You need to cut off the fuel during decel. I don't know what the stock idle MAP was on my 91, but now it's 60-65 Kpa!

Beth

 

I have been fooling with the spark advance numbers in C/O. You have just given me a good hint. I noticed I had up to 55Kpa at idle. I didn't even know that was possible. Anyway, I'm going to move the C/O Map constants up. And experiment with some other constants.

thanks

 

The contants I mentioned are only active when TPS=0 (or very close to it). Typical MAP values for stock motor at idle are 30-40 Kpa.


[Modified by Beth396, 3:45 PM 11/4/2003]

 

Thankyou Beth296 - Yes, I understood that C/O stands for cut-off. Now if someone could please explain all the new values in TunerCat 2.0 to me, I would be indebted for life. Which at my age - ain't too long.

I removed most of the backfire by moving the Decel C/O to 30 Kpa and the Decel C/O disable to 35 Kpa. Injector pulse is now 0 at 0% throttle.

Where does the Decel C/O RPM Enable/Disable come into play? If the Map constant works at any RPM - what do these values effect?

My timing is still off. I have increased the advance which helps lower RPMS (below 3200) but is hurting 3/4-full throttle and higher RPM. I haven't been above 6K yet. I don't want to fire anything that hot until I am sure I am not lean up there.

 

The decel C/O rpm is enabled when your not meeting the MAP C/O enable. For example, you let off the gas (TPS=0) and MAP does not reach the disable value (MAP=30 Kpa) but the rpm drops to 1100. In the corvette world this isn't going to happen.

I looked at my bin file after I posted my response to you and found that I haven't changed these values (1100, 1400) from stock. In my case this doesn't make sense because I've changed my gear ratio significantly also. These values should be increased. What is realistic? I'll have take a real close look at what is happening in my case, but it's probably going to be increased by a factor of two.

I have a paper that I can email you that gives some information on EMC tables. It's written for ACCEL's Calmap program but it's very similar to your system. They also give a graphical representation of spark advance that shows what happens when you have too much or too little advance.

Please keep me informed on your "problem" because I'm still getting a little popping in the exhaust at low (<10%) throttle. Going from a 48 to 58 mm TB didn't lean out the mixture like I thought it would. I need to lean out my fuel table at low MAP. My engine is still work in progress. I've spent the last 4 months fixing things other mechanics screwed up. I only work on it and test drive it and have stopped keeping track of how much cash I've spent and threw the schedule out the window....now it's fun. The boyfriend stopped complaining about how much time I spend on the car now that I let him help.

..and I thought I could just pay someone to give me more power...boy have I learned my lesson. I'm paying for the power in number of hours in my garage...at least it's cooling off and I don't have sweat pouring in my eyes. I'll go back to my "Barbie" image once the project has stabilized! Beth

 

Me too! Only I'll have to bleach my hair. And my eyes are more green than blue. Hey, what forum is this, anyway? :jester

I would greatly appreciate any info. Thanks in advance. Here is what I have "sort-of" figured with the decel backfire: It just isn't flexible enough.

Example: If at a given rpm your spark advance varies 8 to 10 degrees, the closed throttle table has only 1 value at a given rpm. So if you come off throttle there can be an 8 to 10 degree difference instantly. The fuel and spark are a mess. At first I lowered the decel numbers: Logic- backfire = too much advance. Not necessarily so. If there is fuel left over from P/E and or the advance is 32 degrees total then you need alot more advance in the C/O table. Pain. If I had any idea what the P/E Delta tables and the PW Deltas did, I would try more fine tuning there in relation to Decel.

I don't think the basic tables or even moderately modified tables are in anyway close to anticipating the huge amounts of air and fuel that a heavily modified engine can produce instantly. Example: My Map tables are starting to look a little strange. At low Kpa the VE is really low, but above 50 Kpa they are much higher. I like graphs with nice sweeping mounds - they look pretty. I don't like these spikey things. :jester :D

I'm not even close to figuring out Map, advance and P/E for even "street" acceleration. I have a huge "flat" spot WOT above 3200 RPM to 5200 RPM. Ridiculous - this sucker should scream to red-line. I suspect it will take a ton more fuel with the right advance to speed up that tach.

Thanks again.

 

Skippy, I emailed you the paper, let me know if you didn't receive it. The following are my responses to your issues:
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Skip: If at a given rpm your spark advance varies 8 to 10 degrees, the closed throttle table has only 1 value at a given rpm.
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Yes, only one value per RPM cell because your generating max vaccum (low MAP) at TPS=0, so it's just 2 dimensional table.
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skip:So if you come off throttle there can be an 8 to 10 degree difference instantly.
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There is only a large difference if you have it setup that way: between the spark advance vs MAP table and the 2-D spark adv table for TPS=0. I don't have the numbers with me here at work but I've increased the spark advance at TPS=0 a bunch and don't have any knock counts. There is also a max spark advance constant that needs to be increased. My base timing is set to 9-10 degrees and my spark advance table has tons of advance (33-53 degrees).

When I got the Ed Wright chip, my headers glowed bright red due to not enough spark advance. It took me a few header gaskets and a lot of time before I figured this out. The $350 I paid him didn't get me much and he was not helpful at all. His idea of fuel tuning was changing the injector constant. I can't blame him completely because he could only do so much with the data the mechanic was giving him. That's why I don't trust anyone with my engine anymore.

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skip: The fuel and spark are a mess. At first I lowered the decel numbers: Logic- backfire = too much advance. Not necessarily so. If there is fuel left over from P/E and or the advance is 32 degrees total then you need alot more advance in the C/O table. Pain. If I had any idea what the P/E Delta tables and the PW Deltas did, I would try more fine tuning there in relation to Decel.
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I have not optimized my engine for PE yet. At the beginning there's is enough parameters to experiement with without getting confused on the WOT tables and corrections. My fuel tables are mature enough (rich enough at high rpm/MAP) that I set my PE to 100% TPS (at all conditions) so that I DON'T go into PE and I can just optimized the fuel, spark and decel tables.

Another method I've found useful for optimizing the fuel table is to lock the long term fuel trim upper and lower values to 128 and 127 respectively (locked BLM method). I only recommend this if your fairly close on your fuel table. Then you only monitor the short term fuel trim and make your adjustments to the table based on what STFT is reading.

I export my datamaster file to excel and plot each MAP curve on a graph of RPM vs STFT value. When you look at the 2D version of the 3-D matrix the discontinuities become obvious...I smooth out the curves. If you still have questions about the PE deltas after you read the paper we can talk about these tables but I don't think they are your biggest concern right now.

Make sure your knock sensor is working and turn up the spark advance. Beth

 

I received the email. Thanks for the information there and here.

Here is what I "think" I "know", maybe.

A. Yes you can blame him. I have read a couple of expensive EPROMs and this is what all these guys do. That's when I said enough. I can do a better job. Imagine a 20% increase in performance and better gas mileage when you reprogram your $600 "custom" chip. That's what happened to me.

B. I can't do this programming with an XRay anymore. I am posting a poll on monitoring software.

C. I re-introduced a backfire/stumble at low RPM. OOPS, back to last burn. At this point, I need to keep advance very low.

D. My torque stinks - old set-up would blow me away. However, at 90 to 100 mph in 3rd, this L98 runs and sounds like a race car instead of a suped-up V8.

E. My custom intake tube collapses because this combo sucks so much air. When I have it dialed in, I am going to get a 58mm TB and compare dyno tests.

F. Where is that jerk BMW that made me do all this in the first place? I was going down a straight at Laguna Seca and at 120 mph in 4th, this "suckar" was right on my bumper. I couldn't shift to 5th because of the ZF gear ratio (.75), he would have either passed me on the straight or at the next corner under braking. That's when I set some goals - one is a minimum 130 mph shift point for 4th gear.

G. I am willing to post any and all useless information that I have. I just want everyone to promise that if it works, they will only beat-up on Japanese and German cars, oh and Fords are okay, too. And vipers, I guess.

.

 

Skip,

Will you list a summary of your mods under your bio section? Without going through individual posts, I don't remember what modifications you've done. I know they don't give you much room, but if you could come up with a short list it would be helpful (i.e., induction, heads, cam specs, displacement).


quote:
________________________________________ ______________________

Where is that jerk BMW that made me do all this in the first place? I was going down a straight at Laguna Seca and at 120 mph in 4th, this "suckar" was right on my bumper....
________________________________________ ________________________

Puleez! Sure, blame your attachment to raw unadulterated power on Barbie (or Ken) in her beemer.

Beth