Cold air tuning ?

[FTA1995]

Just got my LEGALLY PURCHASED
tunercat software.
Looking at the MAF tables they seem a bit shallow.
I hooked up a granatelli maf not too long ago, idle is a bit wacky.
Any suggestions for adjustments?
Thanks

[Injuneer]

What do you mean by the MAF tables look "shallow"?

Best thing you could do is put the stock MAF sensor back in. The Granatelli intentionally miscalibrates the MAF output signal to make it look like the engine is flowing less air at high air flows. That leans out the power enrichment (PE = WOT) mode A/F ratio. Since the stock programming is too rich in PE mode, typically producing a targer A/F ratio of 11.7:1, you want to use the stock MAF sensor and correct the PE mode A/F ratio by using your tuning software, not some poor quality aftermarket MAF sensor that is attempting to fool your PCM. Leaning out the PE mode A/F ratio is worth up to 15HP.

What do you mean by the idle is a bit "whacky"? Wrong RPM, erratic, rough????? If your car is close to stock, there's nothing in the stock tuning that would make it run "whacky", whatever that means. Sounds like you may have mechanical or electrical problems with the engine that have to be fixed before you can tune it. You don't use tuning to put a band-aid on those kinds of problems.

Can we assume you have a 1995 LT1? Can you give us some idea of what modifications have been done to the engine? Why not use a "signature" with basic info about your car - year, model, engine, tranny and any major mods? That way people have the info up front that they need to help you. I know its difficult to set up a signature, becasue of problems with the board software, but it is possible, using the "Quick Links" tab.

Have you ever scanned the PCM and produced a data log of the engine running under various operating conditions? That's usually the first step in tuning.

Describe your problems more accurately, using terms that people will understand. Describe your car more accurately so people will know what you are starting with.

There are some online tuning guides "stickied" at the top of the "Computer...." forum on CamaroZ28.com that will give you a basic understanding of the initial tuning steps.

[FTA1995]

Thanks Injuneer,

We figured out what the problem was, it was a bad bit in the idle underspeed advance (5 deg x 25 rpm err instead of 2), just an input error.
Fixed that, idle is much better now.

The internals of this engine are questionable because we got it from a private seller, DOES have a hot cam, and a forged bottom end, but the heads are stock

Talked to the grantelli guys too. we talked briefly about adjusting the freq on the ecm to read an appropriate intake mass. I GUESS i could do this, but it seems to me that going back to an OEM sounds like a better idea. Could the uncalibrated sensor be to blame for n oversensitive burst knock? I've heard that because these heightened flow sensors, the ecm reads more/less than it's actually getting, and from the unstable flow, hits the burst knock threshold much easier. Not sure, stll learning the whole EFI tuning thing, most of my experience is with with late model engines.


Thanks for the info, it really helps.

[FTA1995]

and yes, i have been dataloging,
getting a lot of knock counts and knock retard (non audible, maybe false) low rpm MAP at 80-100
about an average of 20 deg (peaked at 125 deg last test run ).I think it might be on the DFCO period.... If thats the case, there sholdnt be a problem.
IT seems ok, power is up and balanced, but sill that sensor readout bothers me. A bit worried about it, i might just ease the timing back to where it was until im not getting anymore knock, but im only advancing a max of 38. maybe its the CR being higher than it should be for the overlap... I'm jut doing what I can right now to get the most power outwithout bending rods or blasting holes through pistons.


Its frustrating, but what learning process isn't...

[Injuneer]

and yes, i have been dataloging,
getting a lot of knock counts....

The knock count by itself means nothing. Its how fast the number in the field changes, and whether the PCM uses it to set knock retard. The knock count field starts at "0" and the PCM increases it when it sees operating conditions that "MAY" cause knock. It isn't unusual for it to add 3000 counts on startup. The field just keeps incrementing up until it reaches the maximum number that can fit in the field, then resets to 0 a nd starts over again. A knock count of 23,456 is meaningless. The PCM will not use the knock count to set knock retard unless it sees signs of true knock from the knock sensor.

....and knock retard (non audible, maybe false)....

You should never hear knock in an engine equipped with a knock sensor. The sensor picks up the knock and the PCM retards the timing way before you can hear it. Being "non audible" does not indicate false knock.

.... low rpm MAP at 80-100....

Even a huge cam won't cause that problem. Only WOT will do that, and it doesn't matter what the RPM is.

about an average of 20 deg (peaked at 125 deg last test run ).I think it might be on the DFCO period.... If thats the case, there sholdnt be a problem.

What number are you talking about... 20 deg, 125deg??? And what do you see as this numbers link to decel fuel cut off?

[FTA1995]

What number are you talking about... 20 deg, 125deg??? And what do you see as this numbers link to decel fuel cut off?

I noticed that i get this 125 deg of retard when the decel thresh is met,
even if i change it... maybe because it leans out for the dfco condition?
I thought it was a bit strange,
I really don't understand that one, once again still learning.
The PCM will pull out about 20 deg under the conditions i said before...
As long as I leave the max knock retard at the right area I shouldn't have a problem?
Thanks again for your patience and help

[Injuneer]

Stock programming limits knock retard to 15deg. Most tuners reduce that amount. If you retarded the timing 125* it would be firing more than 90* ATDC...... not likely.