Corvette Z06 Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
84 Posts
Discussion Starter · #1 ·
Like so many other members, I too am having a problem with LTFT's in the +20% range.

Modifications include a Vararam, Vortech Supercharger, 42lb Fuel Injectors, and Kooks 1-7/8" headers.

The following checks have been made:

1.) Verified: that all O2 sensors are wired correctly & functioning normally

2.) Verified: No exhaust leaks

3.) Verified: No leaks at any of the intake couplings

4.) Verified: No leaks at the fuel injectors

As a side note: Ether Starting Fluid is an excellent tool for locating vacum leaks since it will rev the engine nearly instantaneously. BUT CAUTION MUST BE EXERCISED, due to its flamability. It is similiar to using acytalene.

Anyhow, to compensate for the positive LTFT's, I am considering modification of the MAF table with my HPTuner software. I think that increasing the stock values by say 20% and then rechecking the LTFT's might get me close.

But after researching this site, it appears that some feel that it is better to adjust the IFR table, instead.

In my case, the PCM reprogramming that was included with my Vortech has already adjusted the IFR table (whether it is correct or not is debatible). However, the Vortech programming didn't make any adjustments to the MAF table which makes me wonder if that is the place to start.

Appreciate some advice from our members that have experience with tuning in this area.

Thanks,

Viper1
 

·
Premium Member
Joined
·
652 Posts
I have thousands of hours of scan time with centrifugal S/Cs.
This is with all kinds of variations mostly on my car. Two different cams, 3 different pulleys, and 3 different gear ratios in all kinds of combinations. For over 6 months when my car was moving it was being scanned. I would go out almost every night at 10 pm and until 3-4 in the morning just to scan and tune.
What does pulley size and gear ratio have to do with anything? Deceleration. You will find that when you let your foot off the gas in gear your LTFTs will go through the roof depending on what gear you are in and rpms and speed.
This is because the air produced by the S/C of course is dependent on the rpms of the engine but the MAF and PCM are programmed for practicly no air when you release the throttle. The PCM says hey the throttle is only at 7% so this is the amount of air I should have but the S/C is producing a ton of air because it's spinning at any giving rpm you decl. at.
This all changes drasticly with pulley size and gear ratio.
Now you think I'm really crazy, why does this matter?
Well when you go out and scan your car maybe you only decel in gear 10-15 times. Now this adds to your average LTFTs so you scale accordingly. The next time you go out you don't decel. in gear at all. This will have you scaling back towards the direction you were in.

Got to go eat. :D
To be continued:
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #3 ·
Hi Tom,

Thank you for joining in on this thread. :cheers:

Are you saying that adjusting the MAF would be better the the IFR, but that I need to consider the effects of in gear deceleration?

Hope you could elaborate some more on this. It seems that this issue has become very prevalent with our members who mod their Vettes. AND it is NOT always due to vacuum leaks, as I have discovered! :eek:
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #4 ·
Thought I would add some dimension to this thread:

Many of our members will likely read this and come to the conclusion that vacuum leaks are the cause.

Well, I thought so too and that is why I tried something else in addition to the "Ether" test.

I used my HPTuner software to backup my PCM prior to making the Vortech changes.

After recieving the P0171 & P0174 codes (lean banks), I went through my system and rechecked all intake connections. Using Ether, I was NOT able to find anything loose nor leaking.

So, I decided to reflash my PCM back to stock to see what, if anything, this would do to my LTFT's. To my surprise, the LTFT's went the opposite direction and I was now running too rich (P0172 & P0175)!!! :jawdrop:

This can be attributed to the changes that Vortech makes with the IFR tables to adjust for the larger (42lb) injectors.

IMOP, the LTFT's that so many individuals are getting could easily be due to improper tuning of the PCM for the given mod.

I'm hoping to shed some light on the "Best" place to make adjustments for this problem, the IFR or MAF tables.

Remember, if you change out the air cleaner sytem, fuel injectors, exhaust system, or even add forced induction, you are likely to encounter one of these conditions if a custome "Tune" isn't included in the package. :D

Just my 2 cents, but I think we have a lot of experienced "tuners" on our site here that could help develope this topic in greater detail. :mug:

Either way, I will be getting my setup "tuned" at A&A soon, so I don't expect these codes to haunt me for too much longer. :cool:
 

·
Premium Member
Joined
·
652 Posts
Got carried away. :D
Yes I scale the MAF vs. the injectors. This is why.
The injector table is scaled for the size injector you are using. Changing this of course changes the amount of fuel they will produce. This is fine for driving around town, infact great gas milage. But when you really step into it and you need fuel there's not enough because you scaled your 42/48lb injectors back to 38/40lbs to bring your LTFTs down. So if your going to scale them back why waste the money on them to begin with? This is also why so many S/C cars go lean and loose that #7 piston, it happened to me. This is why I bought HP Tuners because no one around here could tune my car especially with 20lbs of boost and a very unfriendly cam for S/Cers. 224/228 581/588 112 LSA.
OK, why I scale the MAF:
The MAF is calibrated and scaled for the LS engine with a restricted stock air filter. You change the air comming in you need to change the scaling on the MAF for the changed air flow. This is true for N/A cars also with aftermarket filters. The more air these filters produce the more negative the LTFTs will go. The filters that get alot of outside air at speed will also see neg. LTFTs on decel.
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #6 ·
Thanks again Tom for your expert advise. :jammin:

I was hoping that more of our members would be willing to contribute to this thread.

Come on guys ... I'm sure there are additional thoughts on this! :yeadog:
 

·
Registered
Joined
·
830 Posts
I'll leave the Tuning to Julio at Cartek
 

·
Premium Member
Joined
·
652 Posts
V1,
Here is the MAF scaling spreadsheet. I have the target LTFTs at -1.80 which has been working quite well for me.
Scan your car export the scan to a .csv file. Open the file with excel and copy columns Q & R, left and right LTFTs.
Paste them into the first to columns A & B of my spreadsheet and it will give you the multipier to scale the table at.
I'll also attach a sheet that scales the IFR table if you decide you want to go that way.
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #9 ·
Just wanted to extend my gratitude to FRC Tom. :guiness:

Tom confirmed the direction that I needed to go with cleaning up my P0171 "Lean Bank Codes" AND provided some very comprehensive spreadsheets for analyzing and adjusting the IFR and MAF tables.

Tom, I'm near "dead-nuts zero" on my LTFT's, but haven't had a chance to play with the "popping" on decel; however, that is much less now that I've applied the latest MAF tune.

The rest of the tuning can wait till Dyno day ... coming soon! :thumb:

Tom, if their is ever anything that I can do in return for you, don't hesitate to ask.

Viper1
 

·
Premium Member
Joined
·
652 Posts
Glad it's working out for you.
Maybe you would like to try my VE table spreadsheet.
I've also written one for the sparktable to get rid of any knocking and one for the PE table.
The PE table spreadsheet won't do you any good without a dyno though.
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #11 ·
Finally made it to the Dyno for a Tune, yesterday!

I took a trip up to A&ACorvette, in Oxnard, California, to meet with Andy to tune my car and dyno the results.

Before I go any further, I want to thank Andy and his crew for some of the best service that I have ever had! They are awesome! I've worked with many shops over the years and none have come close to the customer service at A&ACorvette ... bar none. :thumb:

Now for the details:

They started out with a quick road trip to do some data logging before making any changes. This impressed me because most shops won't take the time to "learn" your car's settings before tearing into it. :coo:

Next, they spent a couple of hours and a number of dyno pulls dialing in my VCM.

The results were amazing! Not just in the numbers, but in the seat-of-the-pants feel that put one "Hell of a Grin" on my face. :)

As for the numbers, you ask?

513 RWHP and 451 RWTQ

or if you prefer (w/15% drivetrain losses)

604 HP and 530 TQ (at the flywheel) :jawdrop:

In case anyone was paying attention, with the expertise of A&ACorvette, I came just short of making the same amount of hp at the rear wheels as the advertised (538 HP gain) at the flywheel for a Vortech setup!

Of course, I also have the Kooks 1-7/8" headers, Magna Flow Cats, and a Vararam intake system ... but who's counting anyway. :sneaky:
 

·
Registered
Joined
·
84 Posts
Discussion Starter · #12 ·
Tom,

If your offer is still good, I would appreciate a copy of the spreadsheets. Tuning has been a new learning process for me and I can use all the help that I can get.

I doubt that I will need to tweak much now that it has been dialed-in, but I still want to compare all the changes that was made to better understand the system.

After all, I have been toying with 427 upgrade for awhile. :)

AND now with a little temptation "seeded" by Andy @ A&ACorvette, I have a bad case of the "427 Fever".

I understand that there is only one cure, for this ailment. :D
 

·
Registered
Joined
·
1 Posts
Same here, if the offer is still good for the spreadsheets. I'm having trouble getting my +9 LTFT down closer to zero.
Thanks
 
1 - 13 of 13 Posts
Top