MAF to line pressure correlation

MAF to line pressure correlation

Postby konybravo [OP] » October 21st 2020, 8:27am

I accidentally came across this article, and figured I'd share it, since it was something I didn't know, and thought I might not be the only one :banana: Here's the article, itself, and on the bottom is the actual link:

Think cars are getting a little more complicated lately? How's a lot more complicated sound?!

This week I came across an article in a newsletter put out by one of the technical hot line service companies that we do business with. As I quickly scanned the article, I found it hard to believe what I was reading. This article seemed to hint that a faulty MAF, (Mass Air Flow), sensor was causing transmission failure. How could that possibly be? How could a MAF sensor input be the cause of an internal mechanical transmission problem?

In specific, the article stated that the tech-line specialist had received a call from a shop technician who had been working on a repetitive problem with a slipping transmission on a 2000 Chevrolet Suburban. The article went on to state that this vehicle's transmission had been replaced initially because it was slipping badly at steady throttle and that it exhibited very brown fluid. A short time after the Chevy was back with another slipping transmission and more brown tranny fluid. This time a different rebuilt transmission was installed. Again, a short amount of time went by and the customer was back with another slipping transmission.

Now, much more thorough testing was done, including line pressure tests. These tests revealed that line pressure was much greater than normal. Although most of the sensor inputs to the transmission appeared normal, the ‘calculated load' parameter in the computer's datastream was incorrect. This discrepancy leads to the technician disconnecting the MAF sensor. With the MAF sensor disconnected, the line pressure inside the transmission dropped to normal and the transmission stopped slipping.

This discovery also seemed related to information in Chevrolet Service Bulletin # 04-07-30- 013A, Titled: Automatic Transmission - Shift/Driveability Concerns/SES light on. In this service bulletin, GM states that use of an oil saturated aftermarket air filter can cause this condition. How? Too much oil applied to the air filter causes oil residue to transfer to the MAF sensor's sampling wire causing incorrect readings to the vehicle's computer. These incorrect readings are interpreted by the computer as actual data and the vehicle's computer adjusts transmission line pressure accordingly. With this incorrect information the computer forces the transmission to a constant internal high pressure state which wears out the transmission very prematurely. Technicians can either try to clean the MAF sensor sampling wire or replace the MAF sensor to correct the condition.

Several years ago I encountered a GM vehicle that I thought had a faulty transmission and the actual problem ended up being a faulty coolant thermostat. On that vehicle, the thermostat would stick open causing coolant temp to drop below 174 F. at highway speeds. As soon as the computer saw coolant temp at 168 F. it triggered the computer to remove the overdrive command to the transmission and the car would jump back to 3rd gear. Evidently that vehicle's computer strategy was such that it would not allow overdrive to engage at less than 168 F coolant temp. Sounds correct if you think about it as this is probably designed to prevent cold engine lugging or stalling problems. I caught it all happen while driving the car and recording the datastream. And to think, back then I thought "that" was an odd driveability problem.

Just another example of how difficult automobile diagnostics and repair continues to be
https://www.samscars.com/gf87.html
Aloha Kony
Image
Original Poster [OP]
User avatar
konybravo
Firing on 4 Cylinders (L1)
Firing on 4 Cylinders (L1)
Years of Membership: konybravo has been a member for 3 full yearskonybravo has been a member for 3 full yearskonybravo has been a member for 3 full years
Posts: 436
Topics: 16
Images: 56
Joined: May 2017
Location: Bulgaria
Gender: Male
Alias (AKA): Kony
Van Model Year: 1996
Van Make/Model: Chevrolet Astro
Extra Info: 4.3 AWD G80

  • Similar topics
    Replies
    Views
    Author
  • Fresh 4l60e low line pressure no 2nd or 4th
    by Bikley » January 17th 2021, 10:40am in Automatic
    14 Replies
    365 Views
    Last post by Bikley View the latest post
    February 17th 2021, 2:42am
  •  
    9
    23
    Last post by AstroSafari.com View the latest post
    April 11th 2021, 10:57am

Re: MAF to line pressure correlation

Postby Big_kid » October 22nd 2020, 1:08am

It makes sense. I had a cold engine driveability problem in my 1987 S10 for a while. I could leave my driveway normally, but when I got the the main road I had to floor it, and drive as aggressively as possible or it wouldn't be driveable. 2 miles later on the interstate all was well. It turned out I was low on coolant. Once I topped it off everything was fine.
95 Astro Conversion of unknown irrelevant lineage
We have enough youth. How about a fountain of smart?
User avatar
Big_kid
Team Leader
Team Leader
Firing on 8 Cylinders (L7)
Firing on 8 Cylinders (L7)
Years of Membership: Big_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full yearsBig_kid has been a member for 12 full years
Posts: 6816
Topics: 185
Images: 344
Joined: June 2008
Gender: Male
Alias (AKA):
Van Model Year: 1995
Van Make/Model: Chevrolet Astro
Extra Info: 2WD 5.7 V8

Re: MAF to line pressure correlation

Postby Jeffryscott » March 4th 2021, 12:56am

My transmission shop diagnosed the MAF as the problem with my issues. Under load I started having slippage and the speedometer would go crazy. Still working on sorting it out, but I had them drain and change transmission filter as I’ve been wanting to do that since purchase 10 months ago. Fluid was good and no signs of metal.
Jeffryscott
Fueling (1/8 tank)
Fueling (1/8 tank)
Years of Membership: Jeffryscott has been a member for 1 full year
Posts: 19
Topics: 3
Joined: March 2020
Location: Tucson
Gender: Male
Alias (AKA):
Van Model Year: 2002
Van Make/Model: Chevrolet Astro
Extra Info: LS AWD

Re: MAF to line pressure correlation

Postby Bikley » March 5th 2021, 8:00pm

Excellent information. Thanks.
Bikley
Firing on 2 Cylinders (L1)
Firing on 2 Cylinders (L1)
Years of Membership: Bikley has been a member for 2 full yearsBikley has been a member for 2 full years
Posts: 234
Topics: 23
Joined: June 2018
Gender: Male
Alias (AKA):
Van Model Year: 1994
Van Make/Model: GMC Safari
Extra Info: AWD Vin W

Re: MAF to line pressure correlation

Postby Rod's Trucks » March 5th 2021, 8:33pm

Thanks for posting that. :clap:
It is a somewhat obscure problem, and one that a poor diagnosis can be very expensive, for both a vehicle owner ( paying for a transmission overhaul) and for a shop replacing transmissions ( potentially having to do it again under a warranty).
Rod Johnson
Issaquah, WA
Rod's Trucks
Firing on 6 Cylinders (L1)
Firing on 6 Cylinders (L1)
Years of Membership: Rod's Trucks has been a member for 1 full year
Posts: 629
Topics: 35
Images: 57
Joined: January 2020
Location: Issaquah, WA
Gender: Male
Alias (AKA): Rod and/or WE7X
Van Model Year: 1998
Van Make/Model: Chevrolet Astro
Extra Info: Forest Green LS AWD


 
  • Related topics
    Replies
    Views
    Last post

Return to Automatic

It is currently April 11th 2021, 10:57am

Automatic Forum
AutomaticThe purpose of an Automatic Transmission is similar to that of a manual transmission, the auto tranny's primary duty is to allow the engine to operate in its narrow range of speeds while providing a wide range of output speeds.
To create a new topic in Automatic, click this button:
Previous topic Next topic
Recent Image Attachments
Attached by:
Bikley
in Automatic
Views: 260
Comments: 16
Date: Mar 29 '21
Time: 5:42am
» Read last comment
Attached by:
95AstroLT
in Automatic
Views: 351
Comments: 19
Date: Mar 06 '21
Time: 3:49am
» Read last comment
Attached by:
95AstroLT
in Automatic
Views: 351
Comments: 19
Date: Mar 06 '21
Time: 3:42am
» Read last comment
Attached by:
Attached by: Mmusicman
Mmusicman
in Automatic
Views: 260
Comments: 12
Date: Mar 01 '21
Time: 7:14pm
» Read last comment
Attached by:
AngryPunk
in Automatic
Views: 380
Comments: 15
Date: Feb 18 '21
Time: 11:47pm
» Read last comment
Sponsors

Who is online

Users browsing this forum: No registered users and 5 guests

cron