CEL lights, fuel trim issues...it seems to be the MAF, correct?
#1
Instructor
Thread Starter
Join Date: Nov 2002
Location: Atlanta, GA
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
CEL lights, fuel trim issues...it seems to be the MAF, correct?
Over the past few months, I have small issues with my fuel trims (typically only the Short Term Fuel Trims are affected). I suspected the MAF to be the problem, so I cleaned it and things "appeared" to return back to normal for a few months (less hesitation and no CELs). I had the previously mentioned "bucking" and hesitation under low speed, low rpm throttle. Recently, the CEL has come on a few times; perhaps once a week or so.
Looking at my fuel trims today after my drive to work (36' F) while the car was cooling down at idle:
- my LTFTs were both: +3% (left and right bank)
- my STFTs were both -3 to 0% as they cycled (left and right bank)
Now, this doesn't look too bad and is easily w/in the range of values. As I am sitting there, I get my famous CEL:P0175 System Too Rich (Bank 2). Sometimes I get P0172 (System Too Rich Bank 1), but not this time as I typically clear the code before it has a chance to throw the other bank as well.
So, I clear the CEL and look at my fuel trims:
- upon resetting a CEL, your LTFTs go back to: 0 (left and right banks)
- I look at my STFTs, at idle, with the LTFTs at 0 as they zero-out when you clear a CEL like that: -22 to -18% (cycling - both left and right banks)
It appears as if my STFTs are what trip the CEL light as they are approaching -25%. They were just at -3 to 0% before I got the CEL, when the LTFTs were +3% each. I never saw them get below -3% or so when my CEL came on as I was watching it when it happened, yet the light still came on. Any explanation?
I am still thinking that this is my MAF as your system will typically run positive corrections under throttle/load and negative corrections under idle if the MAF is bad (if I am wrong, please someone correct me).
Any ideas?
Looking at my fuel trims today after my drive to work (36' F) while the car was cooling down at idle:
- my LTFTs were both: +3% (left and right bank)
- my STFTs were both -3 to 0% as they cycled (left and right bank)
Now, this doesn't look too bad and is easily w/in the range of values. As I am sitting there, I get my famous CEL:P0175 System Too Rich (Bank 2). Sometimes I get P0172 (System Too Rich Bank 1), but not this time as I typically clear the code before it has a chance to throw the other bank as well.
So, I clear the CEL and look at my fuel trims:
- upon resetting a CEL, your LTFTs go back to: 0 (left and right banks)
- I look at my STFTs, at idle, with the LTFTs at 0 as they zero-out when you clear a CEL like that: -22 to -18% (cycling - both left and right banks)
It appears as if my STFTs are what trip the CEL light as they are approaching -25%. They were just at -3 to 0% before I got the CEL, when the LTFTs were +3% each. I never saw them get below -3% or so when my CEL came on as I was watching it when it happened, yet the light still came on. Any explanation?
I am still thinking that this is my MAF as your system will typically run positive corrections under throttle/load and negative corrections under idle if the MAF is bad (if I am wrong, please someone correct me).
Any ideas?
#4
Instructor
Thread Starter
Join Date: Nov 2002
Location: Atlanta, GA
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Oak
what kind of mods?
'01 w/ 34k on the clock
Last edited by Ruiner; 01-18-2006 at 03:42 PM.
#6
Instructor
Thread Starter
Join Date: Nov 2002
Location: Atlanta, GA
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Dock
I'd have to say it's the MAF.
Trending Topics
#8
It's strange that the STFT would suddenly go from 0 to -20 while you're just sitting and idling. Maybe some oil or lint got on the MAF or maybe the MAF is failing with an intermittent electronic fault. If your datalogger is working correctly the ECU should move the short trim gradually towards zero and the long trim towards -20 if you drive around slowly.
#9
Instructor
Thread Starter
Join Date: Nov 2002
Location: Atlanta, GA
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by ebaker
It's strange that the STFT would suddenly go from 0 to -20 while you're just sitting and idling. Maybe some oil or lint got on the MAF or maybe the MAF is failing with an intermittent electronic fault. If your datalogger is working correctly the ECU should move the short trim gradually towards zero and the long trim towards -20 if you drive around slowly.
The problem is that I never get my LTFTs to hit the extreme +25 or -25. I typically throw a CEL before that happens (I have seen them as high as +7 or 8). When I clear the CEL, the LTFTs zero-out. I do know that a symptom of a bad MAF is LTFTs (STFTs as well) in the positive range under throttle and STFTs in the negative range at idle.
#10
Instructor
Thread Starter
Join Date: Nov 2002
Location: Atlanta, GA
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Dock
If I were you, I'd drop by J. Ellis and bend Craig's ear on this issue before springing for a new MAF.
#13
Instructor
Thread Starter
Join Date: Nov 2002
Location: Atlanta, GA
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Woodster
Take it to your local dealer and have them diagnose your problem,
time is money also!
good luck!
Marty K.
time is money also!
good luck!
Marty K.
#14
Addict
Rennlist Member
Rennlist Member
Ruiner........heck of a deal on that MAF.
But hey, what are you going to do for a hobby after you get this solved
........seriously, please come back and let us know if this solves the problem.
But hey, what are you going to do for a hobby after you get this solved
........seriously, please come back and let us know if this solves the problem.
#15
Instructor
Thread Starter
Join Date: Nov 2002
Location: Atlanta, GA
Posts: 201
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by GreggT
Ruiner........heck of a deal on that MAF.
But hey, what are you going to do for a hobby after you get this solved
........seriously, please come back and let us know if this solves the problem.
But hey, what are you going to do for a hobby after you get this solved
........seriously, please come back and let us know if this solves the problem.