mass air flow sensor / unplugging to test

mass air flow sensor / unplugging to test

Postby subsailor592 [OP] » December 6th 2009, 7:21pm

I have a 99 astro 147k runs fantastic. Recently - since november I've been using it to travel (500 miles) 1000 round trip between home in Ohio and work in South Carolina every two weeks. After work one evening I sensed what many in this forum have described when dealing with a bad mass air flow sensor. I Had the codes read. I hope they all lead to simply replacing the sensor? (I'll list them below) and was hoping someone could tell me how to unplug the MAF so I can take a test run to see if the problem goes away. I think astro355 said in a thread somewhere this could be done. Also if I find out it is the MAF and I have to replace it does anyone know what tools I'll need because I'll have to buy what I didnt bring. Thank you for any help.

P0101
MAF or VAFACKT
Range / Perf

P0300
Random / multiple cylinder misfire detected.

P0442
Evap Emission control system leak (small)
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Re: mass air flow sensor / unplugging to test

Postby astro355 » December 7th 2009, 7:05am

Hello,

you can find the MAF sensor in series with the air intake ducting. There will be one connector that plugs into it and you can simply unplug it. What that will do is force the PCM to run off of a default table and set another SES. Here is a pic of the maf not connected to the duct work.

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You will need no tools to unplug it but a flat-head screwdriver to R&R if you need to replace it.

What I would suggest first though is starting with that random misfire. What is the history of this vehicles's maintenance?
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Re: mass air flow sensor / unplugging to test

Postby subsailor592 [OP] » December 7th 2009, 4:38pm

I’ve owned this Astro five years now. It was under 70k then. Since there was no documented history of past maintenance I don’t know what was done prior to me. When I took over I have it tuned once a year (this past October). Guy that does my work is chief mechanic of a pretty big Post Office motor pool by day. The only thing I did different was had him use a rotor & cap (new but at least a year old I had in the garage subjected to seasonal temperature changes). So I take it the misfire is not dependant on the MAP? If I unplug the MAP and see no change maybe a look at the cap, wires is in order? How do you suggest I proceed? Thanks again.
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Re: mass air flow sensor / unplugging to test

Postby astroturf » December 7th 2009, 4:53pm

subsailor592 wrote:I’ve owned this Astro five years now. It was under 70k then. Since there was no documented history of past maintenance I don’t know what was done prior to me. When I took over I have it tuned once a year (this past October). Guy that does my work is chief mechanic of a pretty big Post Office motor pool by day. The only thing I did different was had him use a rotor & cap (new but at least a year old I had in the garage subjected to seasonal temperature changes). So I take it the misfire is not dependant on the MAP? If I unplug the MAP and see no change maybe a look at the cap, wires is in order? How do you suggest I proceed? Thanks again.


Hey sub, Welcome to the forum. It sounds as though you've found your own answer: Cap & Rotor. I would ask what brand of parts you are using for cap, rotor, plugs, and wires? Why an annual tune-up? These things can go for 100,000 miles on GM parts, and do very well. Out of curiosity, what kind of mpg are you getting? And, Again welcome to the board. Jim
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Re: mass air flow sensor / unplugging to test

Postby subsailor592 [OP] » December 7th 2009, 6:49pm

Thanks. I did the math my first 500 mile trip from Ohio to S.C. / I was amazed that I didn’t have to refuel the entire trip. The brand rotor and cap was Napa. I don’t know what wires and plugs he used. When I say tuned once a year, I have it looked at with more experienced eyes than my own plus being a 99 there’s always something in need of fixing. I know the plugs, wires, rotor & cap were replaced in October – the old ones were in use about three years but not over 100k. I’ve got to drive the 500 back this Friday. I’m not an expert but I’m thinking tonight when I head home from work I’ll unplug the MAF and see how she responds. If my logic is correct, and I get a normal ride I’ve got to replace the MAF. If I don’t get a better ride I’ll suspect a gremlin somewhere with my wires, cap, or rotor. How long can you test by running with an unplugged MAF before doing harm to the engine?
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Re: mass air flow sensor / unplugging to test

Postby astroturf » December 7th 2009, 7:40pm

Sub, I suspect, that you can run it until you are out of gas. To the best of my knowledge it defaults to a base program in the pc. But your mpg will take a hit in the process. Jim
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Re: mass air flow sensor / unplugging to test

Postby astro355 » December 8th 2009, 1:50am

If you get a better ride with the MAF unplugged, you might want to try cleaning it first before you spend the money on a new part. What kind of air filter are you using?

But still, I'd look into that misfire first. The misfire would give you more pronounced symptoms than the MAF would.
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Re: mass air flow sensor / unplugging to test

Postby subsailor592 [OP] » December 8th 2009, 3:41am

Astro355 I've got a Fram filter from my home town Pawtucket R.I. in there. I think you're right about looking into the misfire. The unplug made things worse. It bucked more and on the high way it let me know 50mph was tops. After plugging it back in I could get 60 70 without much trouble.
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Re: mass air flow sensor / unplugging to test

Postby Leeann_93 » December 8th 2009, 4:06am

First thing I'd do is replace the NAPA cap & rotor with AC Delco. Second is replace the oil filter with Fram.

I've had terrible experience with NAPA on caps & rotors on this engine and Astro355 has had bad experiences with Fram oil filters on his (and we're not the only ones).
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Re: mass air flow sensor / unplugging to test

Postby webcat » December 8th 2009, 4:24am

I was buying some oil today and the guy at autozone asked me if i wanted to save some money , he said i get a free Fram oil filter with the purchase of the oil , I said no thanks and told him that i heard that they use cardboard inside the frams oil filter to filter the oil and it makes your oil psi go low sometimes.
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Re: mass air flow sensor / unplugging to test

Postby subsailor592 [OP] » December 9th 2009, 9:12pm

I’m going to clean the MAF sensor tonight. I bought a can of MAF cleaner at the auto store but then I did a general search on the web for “cleaning mass air flow.” Something caught my eye: It’s either genius or insane, probably the latter. This one mechanic advises getting a freezer size zip lock bag and a bottle of isopropyl rubbing alcohol 70-30. Stick the MAF in there and seal her up for twenty minutes gently moving its placement around to dislodge the crud. If I didn’t think this was a recipe for having to buy a new sensor it sounds tempting and then after the alcohol bath hit it with the MAF spray. Any opinion on this?
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Re: mass air flow sensor / unplugging to test

Postby astroturf » December 9th 2009, 9:28pm

I've always just sprayed the snot out of it with the MAF cleaner. The alcohol bath sounds risky to me. Jim
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Re: mass air flow sensor / unplugging to test

Postby Tygre II » December 10th 2009, 5:34am

I vote for the insane... :shock:

Alcohol in high percentages eats rubber seals and does damage to plastics. Most of our vehicles weren't designed to have contact with more than 10% alcohol.

That mechanic probably has people coming back to him later to replace the MAF sensors that were just cleaned.
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Re: mass air flow sensor / unplugging to test

Postby subsailor592 [OP] » December 10th 2009, 10:34pm

Cleaned it. Reconnected it with a new air filter… like magic. Amazing how something so easy can make such a difference. It didn’t appear very dirty and I did use rubbing alcohol 70/30 taking care not to soak the plastic box or female connector. I used a toothbrush that’s bristles poked nicely through the small impingement holes on one side of the MAF. Inside I clearly saw the filament-like bands and very small (look like miniature transistors). They were so small they seemed like it wouldn’t take much to break so I was very easy-going. My SES light is still on but the rough ride is over. One point of interest I discovered: The ring-clap that secures one end to the MAF to the air box cover was not tight. So loose it is as if the person who replaced my filter forgot to even tighten it at all. It ran crappiest when it was raining now I think I know why.
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Re: mass air flow sensor / unplugging to test

Postby astro355 » December 11th 2009, 10:16am

What does a new MAF cost? I'll send you a bill for let's say half of that. :mrgreen: Good job!

What codes is it setting?
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Re: mass air flow sensor / unplugging to test

Postby chefred112 » February 2nd 2011, 11:44pm

hmmm...will try cleaning my maf as well... have a P0305 and P0442 mil. I changed the distributer last weekend so i 'll try the maf and maybe new gas cap next...
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Re: mass air flow sensor / unplugging to test

Postby fast68 » February 3rd 2011, 6:56am

avoid fram oil filters those are pennzoil cheap cardboard garbage filters


clean the MAF screen etc with electrical cleaner

that usualy fixes them, does for me anyways

i just went through this exact thing on a 20003 silverado it was spitting out MAF code

cleaned it real quick and the code never came back

cap and rotor we always use auto zone one and actually they work fine really


none will last 100k miles

i replace them once a year or two at the most they wear quickly and will cause all kinds of running issues

sputtering bucking missing not wanting to go in gear, especially when cold



among other issues.

so change them often

its about the most common wear item to replace on these engines, TBI and others as well.,
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Re: mass air flow sensor / unplugging to test

Postby worldtriad » September 1st 2011, 7:39pm

So how much does a new MAF sensor cost and how long do they usually last? My 1999 Astro Van is having those codes. It ran a little rough for a few seconds and then smoothed out, but my SES light is now on. Had the code checked, came back to MAF sensor. That code came up before I had my fuel injection spider fixed, and went away after that for a few weeks, but now is coming back.

Can I figure out how to remove and try to clean it? I'm trying to save a little here if I can. My old Ford is getting a new fuel pump right now, and that was not an expected repair.

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Re: mass air flow sensor / unplugging to test

Postby Leeann_93 » September 1st 2011, 9:22pm

Pop the air filter housing off the upper shroud. Unscrew the hose clamp that holds the air intake hose to the plenum. Remove air filter assembly from the van.

Now, right behind the air filter box is the MAF sensor. Unscrew the hose clamps holding the intake hose to the back and the filter to the front. Use MAF cleaner only. Spray on the elements inside - do not use any tools as those elements are really fragile. Spray the hell out of them until they look like metal again.

Reinstall to filter box and intake hose, then reinstall air filter assembly on the van. Clear the code if you have that capability; if not, drive to where you can have it cleared.
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Re: mass air flow sensor / unplugging to test

Postby worldtriad » September 2nd 2011, 9:30pm

Thanks, I got a can of MAF cleaner and the guys at the shop helped me out and it was all cleaned out, and put back on. Code was clearing itself after car turned off and back on again on the second or third start. It looked pretty darned clean when it came off of there and I'd say he used about 1/3 to 1/2 of the can to spray it off really good. The SES light is still off but I only drove it to parts store to get a new Wix air filter and then home again.

If that isn't enough to do it....how much am I looking at for a new one? And since I know how it goes on and off, I can probably do this myself, right?

Thanks!

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