testing the maf
Thread Starter
Racer
Joined: Apr 2005
Posts: 408
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testing the maf
Can anyone direct me or does anyone know how to test the maf on an 01 silverado? I know this does not pertain to a c4 corvette, but I have seen more extremely knowledgeable people here and I would appreciate anyone's guidance on where to find a diagnostic procedure. Thanks.
Race Director
Joined: Sep 2005
Posts: 13,269
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From: Sharpsburg Georgia
GA Events Coordinator
i can send you the tests, but the only real way to tell if you have marginal one that does not set codes and one that really does what it is supossed to is subtitute with a known good unit.
i do not know what kind of problems that you are having.
but if you will give me some more info i will see if i can get you what you need.
i do not know what kind of problems that you are having.
but if you will give me some more info i will see if i can get you what you need.
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
MAF problem should throw a code. However, an intermittent problem-could be caused by a marginally toasted relay (sticky)-and may not throw a code.My vettes an 87-so I suspect there are differences.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,062
From: altered state
St. Jude Donor '05
Originally Posted by blown87
i can send you the tests, but the only real way to tell if you have marginal one that does not set codes and one that really does what it is supossed to is subtitute with a known good unit.
i do not know what kind of problems that you are having.
but if you will give me some more info i will see if i can get you what you need.
i do not know what kind of problems that you are having.
but if you will give me some more info i will see if i can get you what you need.
Best way. Mine threw no codes, ran and idled smooth, even replaced it with a "known good one", ran the same.What I DIDNT know was it was making the car run dead lean.
A run on the dyno with the A/F readout told the story.$75 diagnosis.
Race Director
Joined: Sep 2005
Posts: 13,269
Likes: 0
From: Sharpsburg Georgia
GA Events Coordinator
Originally Posted by cuisinartvette
Best way. Mine threw no codes, ran and idled smooth, even replaced it with a "known good one", ran the same.What I DIDNT know was it was making the car run dead lean.
A run on the dyno with the A/F readout told the story.$75 diagnosis.
i went thru 3 of the old style bosch (remans from bosch) vane type mass air flow meters and still had the problems with a car. i finally got one from a junk yard and that cured the problem.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,062
From: altered state
St. Jude Donor '05
that is where you get to the point that you want to go shoot something
Its taken me a year and a half of fooling with it here and there (I seldom drive it), replaced EVERY FI, tuneup component, sensor, etc except that one. Like I said, car didnt give the typical MAF symptoms so I overlooked it. It just had a heating issue that would pop up at random, was beginning to think this thing was just "one of those cars that could never be fixed"
Back on topic
.
Thread Starter
Racer
Joined: Apr 2005
Posts: 408
Likes: 0
Thanks for the response guys. To give some more details, The truck seems to run fine, but has no power. When the throttle is pushed to around 4k rpm there is an engine knock. It is quite audible, and repeatable. I had the codes ran and all it gave was a maf malfunction, and a random knock code. The codes were cleared and the knock is still there, but not the maf code. We have replaced the plugs and wires, as the plugs had 120k on them. This has not fixed the problem. I am going to check the fuel pressure tomorrow to see what the pressure is doing when the engine clattering occurs.
Pro
Joined: Oct 2003
Posts: 506
Likes: 12
From: Savannah GA
On and OBDII car this may not work.... On a FWD olds we just un-plugged the MAF sensor we suspected bad. The car cleared right up even with the SES light on. From what I understand once the computer determines a MAF sensor is out of range it will fall back to TPS setting for fueling.
If you have 120k on your truck keep an eye on the fuel pump. Some head south in that range.
JS
If you have 120k on your truck keep an eye on the fuel pump. Some head south in that range.
JS
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Thread Starter
Racer
Joined: Apr 2005
Posts: 408
Likes: 0
Checked the fuel pressure at idle and under load and it went from 50-60 psi which seems right. We were running out of things to check when I remembered an article from many years ago when the new model chevys first came out that the catalytic converters were clogging pretty fast. We uncorked the exhaust and viola, the power was back!