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Old 08-27-2013, 01:25 AM   #1
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Default P0171, it'* been mentioned many times before, but...

Hi y'all peeps & geeks (just kidding, but seriously),

I know that much has been asked and well responded to about P0171, but I just have to clarify for my vessel is acting a bit different... it all started like this about three weeks ago: suddenly and out of the blue, I was hit with fault code P0102 (only, but shown as 2). Damn, my beast ran rough like next to impossible, but I managed to get 'er home to drop those perishable groceries & out to AutoZone for a quick reading.

After researching here and else where, I disconnected the MAF sensor and I was good to go, except for fact that if my rpm'* dropped below 1,000 she'd stalled instantly! Yeah, so I had to play games with down shifting this automatic, hovering the brake (left-footed) and playing the accelerator with the usual appendage to keep 'er above that 1,000 mark.

I didn't just succumb and throw a bunch of parts in, I looked for the obviously and found nothing suspicious, so I ordered the Duralast (limited lifetime warrantied, as opposed to the Dorman with awful reviews & 1 year warranty)... things were awesome for about a week, but then I sensed something wrong - at first there was this slight hesitation upon acceleration, yet within 2 or three days, it happened and I was right back to square one.

I came back here and explored further for now I had the illusive and deadly curse of the P0171, for as you may know can be quite variable in its diagnosis... checked the obvious first (and again) vacuum leaks and etc, but went onto bad grounds which were all good, crawled beneath her looking for something disconnected, rusted or broken for many hours, looked for exhaust leaks (nada/none).

As for scanning the O2 sensors, hZ'* at the MAF and checking the Lbs of the fuel pump, I've yet to do this yet for many of my diag tools were stolen a few years ago (sadly), but I do not want to surrender by just throwing various parts in, I want to diagnose this properly and intelligently, so I looking for clues and even possibly answers!

Please know now that as the MAF sensor has been disconnected, I can get by with keeping the rpm'* above 1,000, but this stuff is stressing me out and presently, I can not afford to throw bucks in aimlessly.

One more note, upon checking my grounds yesterday (with the key out of the ignition and upon my seat) I heard something cycling to the left of the MAF. Not sure what it is, but I inspected it and it wasn't to happy with me messing with those grounds attached to the body just above the horn on the battery side (opposite the driver side)

Any help or advise with this would be more than welcome & spectacular!

Many thanks in advance,
Dan - aka Motozappa
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Old 08-27-2013, 01:52 AM   #2
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First question is do you have a K&N style air filter on it? Because the oil will play hell on a MAF, second did you price out a AC delco MAF when you were shopping because in the past I have had no luck with using brand X engine management parts and always wind up going with the OE part. If you have a scanner that can look at live data you can look at the MAF info and determine if its calibrated correctly.
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Old 08-27-2013, 04:17 AM   #3
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Nope, only a dry "clean" filter. I'm sorry, but I thought I conscientiously opted for what I thought to be the better of my choices (2) in MAF'*. Guess I'll now know better next time. Thanks for your reply and for trying to help!
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Old 08-27-2013, 07:41 AM   #4
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its hard to trouble shoot without tools. i would say a live data scanner is necessary on anything after 96. if you have a smartphone thats the cheapest way to go. that way you can see if its the maf or something else. did you check with carb cleaner for a vacuum leak? check the vacuum line boot on the tb for cracks thats a common one?
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Old 08-27-2013, 12:25 PM   #5
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Yeah Justin you are right, it'* hard to diag w/o the proper equipment! I figure I'll have to surrender soon and lay out the bucks to have it evaluated (scanned) properly. I was sort of hoping that by the way I described my condition that something might click in somebody'* head. Like I've heard of people disconnecting their MAF sensor and it running better, but never heard of someone having my particular idle condition whereas I need to keep it above 1,000 RPMs to keep it from stalling.

I'm starting to believe that the MAF sensor is faulty and I'm going to exchange it because when I put it in the car was perfect for a week plus and now I'm back to having it run sort of OK with it disconnected. I've checked and checked and checked for Vac leaks visually with no evidence and with carb cleaner without any variance.

I appreciate your help and suggestions!
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Old 08-27-2013, 12:55 PM   #6
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Here is a procedure for testing the MAF:

TEST 1: Testing the Power (12 Volts) Circuit
Probe wire C with a multimeter (pierce the wire with the red lead, touch the black lead to the negative terminal on the battery). With key on and engine off you should read 12V. If you don't, the problem is power to the MAF, not a defective MAF.


TEST 2: Testing the Ground Circuit
Probe wire B with the black lead on the multimeter while touching the red lead to the battery positive terminal with the key in the off position. If your meter reads 12V go the the next test.


TEST 3: Testing the MAF Signal
With the engine warmed up, but turned off with the key in the off position, probe wire A with the red lead of the multimeter and touch the black lead to the battery negative terminal. PUT THE MULTIMETER IN FREQUENCY (HZ) MODE. Start the engine and note the hertz reading at idle. This reading may be stable (with only small fluctuations) or unstable with very extreme fluctuations. No matter what the instability in the reading, this will be your base reading. Manually accelerate the engine from the engine compartment as you watch the multimeter'* frequency readings. The Hertz Frequency readings should increase. When you let go off of the throttle and the engine returns to idle, the Hertz reading should come down to the base Hertz reading. Repeat this as often as you need to verify that the Hertz numbers on the multimeter rise and decrease smoothly every single time. If the MAF Sensor is working correctly, the readings on your Multimeter will not spike up and down crazily but will increase smoothly as you manually accelerate the engine and decrease smoothly as you let the engine return to idle.
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Old 08-27-2013, 04:57 PM   #7
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basically that will only tell you if you have a out put or not, you dont know if its reading the wrong cfm
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Old 08-27-2013, 05:01 PM   #8
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Quote:
Originally Posted by jwfirebird View Post
basically that will only tell you if you have a out put or not, you dont know if its reading the wrong cfm

A bad MAF will usually give you erratic readings rather than a smooth increase and decrease as RPM'* change.
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Old 08-28-2013, 12:58 AM   #9
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Roy and Justin, thanks for the input! I learned this nearly a month ago and thought it to be very interesting and informative:

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Old 08-28-2013, 12:59 AM   #10
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