LT4 almost there but a bad MAF?
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,526
Likes: 104
From: Stafford Va
LT4 almost there but a bad MAF?
Ok I fixed the issue of the rough idle and no start with a new distirbutor cap and rotor and while I was there a new water pump since it was leaking. I cleaned the MAF sensor, hooked it back up then started the car up. Runs great then about 160 degrees it just quit. I pulled the MAF wire and the car started up ran great right up to 210 degrees and no issues. Idled very well. I did this a few times but with the MAF hooked it is erractic and when disconnected runs smooth.
I do not have any codes.faults. When replacing a MAF whether its new or not is there some procedure to reset the computer, I thought it would adjust itself. I know the answer but before dropping another $200 just thought I would ask. And with the MAF not connected it running off the speed density sensor info correct? So does the MAF have to go back on or inorder to do that the ECM needs to be reprogramed? I saw a few threads addressing burn off but did not see that in my shop manual????
Thanks
I do not have any codes.faults. When replacing a MAF whether its new or not is there some procedure to reset the computer, I thought it would adjust itself. I know the answer but before dropping another $200 just thought I would ask. And with the MAF not connected it running off the speed density sensor info correct? So does the MAF have to go back on or inorder to do that the ECM needs to be reprogramed? I saw a few threads addressing burn off but did not see that in my shop manual????
Thanks
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,526
Likes: 104
From: Stafford Va
False lead, no one around here can test the MAF with out it on the car and even then they are just running a test for codes, which I have none. Any last coments from the pro's from Dover or do we just let it go and say replace the MAF with only 20k on it>?????
Team Owner
Joined: Feb 2006
Posts: 23,186
Likes: 117
From: San Antonio Texas
I can't seem to get much help on my MAF either! I have no codes, but the LT4 won't rev over 5200rpm without what feels like ignition breakup. Had EVERYTHING that an electron flows through for the ignition replaced and still no high rpm. Runs great, strong and gets great mpg under 5k with no codes. Cleaned MAF and things got better for a couple of months and now the high rpm miss is back. 
Can't seem to find anybody that knows how to check this thing if it it's running with no codes.
I don't want to just buy another one unless somebody can really show me that it's the MAF and not the damned MSD opti.(I really don't want to have to deal with that bitch again!)
Can't seem to find anybody that knows how to check this thing if it it's running with no codes. I don't want to just buy another one unless somebody can really show me that it's the MAF and not the damned MSD opti.(I really don't want to have to deal with that bitch again!)
Melting Slicks
Joined: Jun 1999
Posts: 2,949
Likes: 23
From: Bowling Green KY
I think in the FSM there is a test for the MAF, you can test for a certain voltage but sounds like that's the culprit. And to answer your other question, yes the system runs on MAP if there is no MAF, and you can do that indefinitely if you want. But the car will never run "quite" as well with MAP as it does with MAF unless your tune is just absolutely dead nuts.
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
I can't seem to get much help on my MAF either! I have no codes, but the LT4 won't rev over 5200rpm without what feels like ignition breakup. Had EVERYTHING that an electron flows through for the ignition replaced and still no high rpm. Runs great, strong and gets great mpg under 5k with no codes. Cleaned MAF and things got better for a couple of months and now the high rpm miss is back. Can't seem to find anybody that knows how to check this thing if it it's running with no codes. I don't want to just buy another one unless somebody can really show me that it's the MAF and not the damned MSD opti.(I really don't want to have to deal with that bitch again!)
Can't seem to find anybody that knows how to check this thing if it it's running with no codes. I don't want to just buy another one unless somebody can really show me that it's the MAF and not the damned MSD opti.(I really don't want to have to deal with that bitch again!)If the car runs the same either way (MAF or no MAF), then it's your MSD opti.
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
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
There is no "re-set" procedure other than disconnecting the battery for 30 seconds or so to clear any store error code.
I've had a few MAFs fail on me over the years and none of them ever turned on the SES dash light.
When an 02 failed, all that told me was a Lean Mixture code. The 02 needs to reach a temp of about 600F before the ECM will begin to recognize its input. If the 02 temp remains too low, the ECM will ignore it.
My view is that your engine runs fine until it switches from Open Loop to Closed Loop. It's at that point that one of the sensors is out of range and causes the bad idle or shut down.
When the MAF is removed the system detects that and switches to a different mode, which I believe is Limp Home mode. This allows the engine to continue to run off pre-programmed look-up tables burned into the PROM.
I suggest you connect a scanner and see which sensor operates out of range when the system tries to switch to Closed Loop. You'd need to see the proper cycling of 02 voltage (.100 to .900 or so) quickly and repeatedly crossing the 450mv. causing the cross count number to increase.
A FSM will show what voltages should be present at the MAF connector points/pins.
Hope this helps.
Jake
West Point ROCKS!
I've had a few MAFs fail on me over the years and none of them ever turned on the SES dash light.
When an 02 failed, all that told me was a Lean Mixture code. The 02 needs to reach a temp of about 600F before the ECM will begin to recognize its input. If the 02 temp remains too low, the ECM will ignore it.
My view is that your engine runs fine until it switches from Open Loop to Closed Loop. It's at that point that one of the sensors is out of range and causes the bad idle or shut down.
When the MAF is removed the system detects that and switches to a different mode, which I believe is Limp Home mode. This allows the engine to continue to run off pre-programmed look-up tables burned into the PROM.
I suggest you connect a scanner and see which sensor operates out of range when the system tries to switch to Closed Loop. You'd need to see the proper cycling of 02 voltage (.100 to .900 or so) quickly and repeatedly crossing the 450mv. causing the cross count number to increase.
A FSM will show what voltages should be present at the MAF connector points/pins.
Hope this helps.
Jake
West Point ROCKS!
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,526
Likes: 104
From: Stafford Va
Just ran the codes again, as I mentioned on the other post and had a code 48 MAF sensor. I am running a PCM For Less reprogramed ECM. Not sure why it took so long to pop, Will change it out and see what happens. Advanced Auto has a reman CARDONE MAF for $125 with a one yr warrenty, anyone use one of these? Looks like case closed
Melting Slicks
Joined: Jun 2000
Posts: 3,215
Likes: 6
From: Tampa Florida
Klondike: If you are having 'high' rpm missing...I would suspect your MSD Opti. My experience was from mile one...a ~6000 rpm 'limiter' after install of the MSD. Installed a new OEM Opti...pulls cleanly to 7200 rpm.
MSD warrantied it...replacing several parts. I did not reinstall-got money back.
Good Luck!
MSD warrantied it...replacing several parts. I did not reinstall-got money back.
Good Luck!
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
I bought a replacement MAF for my 86 off a wrecked 'F' body at a wrecking yard. Installed and fired the engine before I left the yard. That was in 2004 and it's still going strong. Cost me $50.
Many MAFs are interchangable across different model cars. I just took my bad one with me and found one with the same numbers stamped onto it. BINGO!
By the way, my O'Reilly's has a cross reference book that shows which MAFs were common to which make/model/year cars. I just went through it, wrote down the make/model/year of the cars using the same MAF as mine. Then, when I went to the yard, I knew which cars to look for; made finding one a lot easier.
Jake
West Point ROCKS!
Many MAFs are interchangable across different model cars. I just took my bad one with me and found one with the same numbers stamped onto it. BINGO!
By the way, my O'Reilly's has a cross reference book that shows which MAFs were common to which make/model/year cars. I just went through it, wrote down the make/model/year of the cars using the same MAF as mine. Then, when I went to the yard, I knew which cars to look for; made finding one a lot easier.
Jake
West Point ROCKS!
Last edited by JAKE; Mar 15, 2009 at 04:53 PM.
Melting Slicks
Joined: Jun 1999
Posts: 2,949
Likes: 23
From: Bowling Green KY
There is no "re-set" procedure other than disconnecting the battery for 30 seconds or so to clear any store error code.
I've had a few MAFs fail on me over the years and none of them ever turned on the SES dash light.
When an 02 failed, all that told me was a Lean Mixture code. The 02 needs to reach a temp of about 600F before the ECM will begin to recognize its input. If the 02 temp remains too low, the ECM will ignore it.
My view is that your engine runs fine until it switches from Open Loop to Closed Loop. It's at that point that one of the sensors is out of range and causes the bad idle or shut down.
When the MAF is removed the system detects that and switches to a different mode, which I believe is Limp Home mode. This allows the engine to continue to run off pre-programmed look-up tables burned into the PROM.
I suggest you connect a scanner and see which sensor operates out of range when the system tries to switch to Closed Loop. You'd need to see the proper cycling of 02 voltage (.100 to .900 or so) quickly and repeatedly crossing the 450mv. causing the cross count number to increase.
A FSM will show what voltages should be present at the MAF connector points/pins.
Hope this helps.
Jake
West Point ROCKS!
I've had a few MAFs fail on me over the years and none of them ever turned on the SES dash light.
When an 02 failed, all that told me was a Lean Mixture code. The 02 needs to reach a temp of about 600F before the ECM will begin to recognize its input. If the 02 temp remains too low, the ECM will ignore it.
My view is that your engine runs fine until it switches from Open Loop to Closed Loop. It's at that point that one of the sensors is out of range and causes the bad idle or shut down.
When the MAF is removed the system detects that and switches to a different mode, which I believe is Limp Home mode. This allows the engine to continue to run off pre-programmed look-up tables burned into the PROM.
I suggest you connect a scanner and see which sensor operates out of range when the system tries to switch to Closed Loop. You'd need to see the proper cycling of 02 voltage (.100 to .900 or so) quickly and repeatedly crossing the 450mv. causing the cross count number to increase.
A FSM will show what voltages should be present at the MAF connector points/pins.
Hope this helps.
Jake
West Point ROCKS!
Melting Slicks
Joined: Jun 1999
Posts: 2,949
Likes: 23
From: Bowling Green KY
If you look in an LT1 computer you'll see 4 calibration tables that control what voltage the MAF puts out based on a given airflow. When running in Closed Loop w/ a MAF, you can adjust these tables to reach 128 for your block learn, but you should only need to do that if you have made major changes to the airflow coming in to the car. Adjusting these tables is somewhat similar to adjusting the VE tables for a MAP car.
