Normal Scan Values MAF, BLM etc
Thread Starter
Heel & Toe
Joined: Aug 2005
Posts: 16
Likes: 0
Normal Scan Values MAF, BLM etc
I have been searching this forum and was hoping that someone could point me to some expected or normal values for MAF, BLM, IAC and etc. I understand that these change depending on conditions but I am hoping to find a range of normal values or even a detailed review in a publication for my 1985 C4 with the 4+3. Some example questions that i have a re what is a normal MAF value for a given RPM, the same for IAC and how to interpret BLM values. Thanks
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Another forum member (Morley) had posted this link in a thread a few months back. It is a page he created, and IMHO gives a very well rounded and easy to understand overview of GM EFI tuning.
(I don't want to speak for him, but I think it is still a work in progress)
http://home.comcast.net/~khiester200035/index.html
It answers a lot of the questions you are asking. The stickies on this page over at Thirdgen.org also carry a lot of information:
http://www.thirdgen.org/techboard/diy-prom/
(I don't want to speak for him, but I think it is still a work in progress)
http://home.comcast.net/~khiester200035/index.html
It answers a lot of the questions you are asking. The stickies on this page over at Thirdgen.org also carry a lot of information:
http://www.thirdgen.org/techboard/diy-prom/
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
MAF values are very hard to give an answer for, there are many variables that will affect a MAF's reading. I can say that at idle your MAF should be reporting around 9-12 gms/sec flow.
For BLM's you want to see 128, but 125-134 is very acceptable. As the BLM goes lower it indicates you are running on the rich side, and as they go higher you are running towards lean.
The IAC counts really only come into play at idle and you'd want to see them as low as possible, but here again there are many variables that will affect the IAC counts (ie. fan request, alternator load, A/C clutch engaged or not....)
For BLM's you want to see 128, but 125-134 is very acceptable. As the BLM goes lower it indicates you are running on the rich side, and as they go higher you are running towards lean.
The IAC counts really only come into play at idle and you'd want to see them as low as possible, but here again there are many variables that will affect the IAC counts (ie. fan request, alternator load, A/C clutch engaged or not....)
Heel & Toe
Joined: Jan 2006
Posts: 16
Likes: 0
I have numerous data logs of my LT1 if you want to look over them to see what mine runs for typical data.
I see around 7-8 GM/sec idle air flow, which ends up around 1.9 to 2.0% calculated duty cycle (rpm*PW/1200 for calculated duty cycle), MAP around 40-42 (0.4 to 0.42 as Freescan logs it), 4 mS PW on the injectors, around 29-38 for idle IAC counts.
Again that is for an LT1, which shouldn't be very far off.
If that helps any.
I see around 7-8 GM/sec idle air flow, which ends up around 1.9 to 2.0% calculated duty cycle (rpm*PW/1200 for calculated duty cycle), MAP around 40-42 (0.4 to 0.42 as Freescan logs it), 4 mS PW on the injectors, around 29-38 for idle IAC counts.
Again that is for an LT1, which shouldn't be very far off.
If that helps any.
Thread Starter
Heel & Toe
Joined: Aug 2005
Posts: 16
Likes: 0
Thanks for the offer, for now I am just researching trying to get a better feel for the numbers. As noted there are differences between MAF and MAP systems. Anyway, the car runs well at this time and I am going to scan again soon to see how the long term fuel trims (BLM) change with the pink top injectors that are in it. That's the only non-stock thing about the car-
Drifting
Joined: May 2003
Posts: 1,730
Likes: 1
From: Charlotte NC
St. Jude Donor '05
Originally Posted by 85C-4
I have been searching this forum and was hoping that someone could point me to some expected or normal values for MAF, BLM, IAC and etc. I understand that these change depending on conditions but I am hoping to find a range of normal values or even a detailed review in a publication for my 1985 C4 with the 4+3. Some example questions that i have a re what is a normal MAF value for a given RPM, the same for IAC and how to interpret BLM values. Thanks
Maf is going to vary with how much air the engine is pulling in.
BLM's should AVERAGE around 128. That doesn't mean they will sit there.
IAC should read around 30-50 counts at a fully warmed idle in gear.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
