How do you test a MAF?
Thread Starter
Instructor
Joined: Mar 2002
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From: Brentwood Essex
How do you test a MAF?
I've read a lot of posts on the subject of surging in idle, and many times the MAF has been the cause of the problem. I'm currently installing a new engine (spec in my sig), and have reused all the ancilliaries from the original engine.
The original engine suferred from surging at idle, and I wonder if the MAF is suspect. How best to check it?
TIA Steve
The original engine suferred from surging at idle, and I wonder if the MAF is suspect. How best to check it?
TIA Steve
Team Owner
Joined: Sep 2001
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From: Athens AL
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Re: How do you test a MAF? (steveelsbury)
If the MAF is totally bad it will throw a Code and your SES light will come on. Sometimes you can disconnect it and see if the idle improves, but that trick doesnt always work either. Only surefire way is to put a new one in and see if that fixes it. If it doesnt, its usually the TPS voltage or the IAC.
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From: Glendale, AZ
Re: How do you test a MAF? (vader86)
If the MAF is totally bad it will throw a Code and your SES light will come on. Sometimes you can disconnect it and see if the idle improves, but that trick doesnt always work either. Only surefire way is to put a new one in and see if that fixes it. If it doesnt, its usually the TPS voltage or the IAC.
a buddy of mine was having problems with his MAF he was getting TERRIBLE flow readings (no codes) so we swapped MAFs and low and behold, he got MUCH better readings with mine than with his, and on the flip side, i couldn't even keep my car running with his MAF...but got NO codes! terrible idle, backfire, etc. try swapping the MAF with someone who has no problems....this is the best test, and it beats spending a couple hundred bucks on a part you may or may not need??!?!
Team Owner
Joined: Sep 2001
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From: Athens AL
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Re: How do you test a MAF? (85_togo)
well, it might throw a code, but as i said the only way to be sure is swap it with another that works fine.
Thread Starter
Instructor
Joined: Mar 2002
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From: Brentwood Essex
Re: How do you test a MAF? (vader86)
This is the very reason I started this thread. My baby was showing no codes, yet I'd read a post which said the MAF was bad with no codes shown. My problem is that in the UK, Vettes are as rare as Hen's teeth, so swapping a MAF with a buddy just ain't gonna happen!
Clearly, I don't wanna buy a new MAF on the off chance the old one might be dud. Guess I'm gonna hafta assume it's fine, unles the rebuild doesn't run sweet - in which case buying a new MAF will be part of the diagnostics.
The problem is this still makes no sense. If the MAF can be 'bad' enough to throw out the ECM, then surely there must be some way of (say) monitoring the output from it and seeing this is the case?
Help me, Obi Wan (any Obi-Wan!)
Steve
Clearly, I don't wanna buy a new MAF on the off chance the old one might be dud. Guess I'm gonna hafta assume it's fine, unles the rebuild doesn't run sweet - in which case buying a new MAF will be part of the diagnostics.
The problem is this still makes no sense. If the MAF can be 'bad' enough to throw out the ECM, then surely there must be some way of (say) monitoring the output from it and seeing this is the case?
Help me, Obi Wan (any Obi-Wan!)
Steve
Le Mans Master
Joined: Jul 1999
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From: Maryland
Re: How do you test a MAF? (steveelsbury)
I've had an intermittent idle issue for quite a few months now. Had it at the shop and they didn't find the problem yet either (of course it didn't act up at the shop). Anyways, they said that next time it does the idle dropoff thing (mine sets the MAF code) to tap on the MAF unit lightly with the handle of a screw driver or something. usually if it's going bad it's the hot wire anomometer which is on the way out. It will cause an erratic signal and erratic idle & sometimes the SES light will go on / off or set a code. The one time since then my car acted up it was pouring rain so I said to heck with that, I'll just drive with rt foot on gas, left on brake and ignore it again. ;) That was about 2 months ago. I can't say if it works or not, but at over $500 a pop for a GM MAF I'd be darn sure that's what's dead before just throwing parts at the car! ~Juliet
Le Mans Master
Joined: Nov 2000
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From: Chandler AZ
Re: How do you test a MAF? (85_togo)
a buddy of mine was having problems with his MAF he was getting TERRIBLE flow readings (no codes) so we swapped MAFs and low and behold, he got MUCH better readings with mine than with his, and on the flip side, i couldn't even keep my car running with his MAF...but got NO codes! terrible idle, backfire, etc. try swapping the MAF with someone who has no problems....this is the best test, and it beats spending a couple hundred bucks on a part you may or may not need??!?!
Pro
Joined: Jul 2001
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From: Taxahoma
Re: How do you test a MAF? (billreid1@***.net)
I think I paid @ $130 for my MAF. I got it at bumper-bumper. The dealer wanted in think $350-$400 for one. The way those things seem to go out getting a rebuilt one seems just as good as a new one. It was a Bosch part.
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Joined: Apr 2002
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From: Silverdale WA
Re: How do you test a MAF? (steveelsbury)
unfortunately i don't believe pulling it off the car will help you determine the problem (it didn't in my case). the car ran the same with the damn thing on or off. as far as the pigtail that ecklers and mid america vette sells, there are no valueable instructions included. according to the haynes manual the maf should produce ~0.5v at idle to ~4.7v at wot. this is taken from pin c (center) to ground.
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Joined: Jul 2001
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From: Glendale, AZ
Re: How do you test a MAF? (billreid1@***.net)
a buddy of mine was having problems with his MAF he was getting TERRIBLE flow readings (no codes) so we swapped MAFs and low and behold, he got MUCH better readings with mine than with his, and on the flip side, i couldn't even keep my car running with his MAF...but got NO codes! terrible idle, backfire, etc. try swapping the MAF with someone who has no problems....this is the best test, and it beats spending a couple hundred bucks on a part you may or may not need??!?!
:D ;) :D ;)... and that friend of his had a laptop with Diacom software and a little help from 85_togo (borrowed MAF) and Craig Marcho to determine the MAF was bad. Basically at WOT in the 4k RPM ramge the MAF should supply the ECM with somewhere around 200g/s. The bad MAF was only putting out a MAX of 160... not good. Now, I know not everybody has access to diagnostic software but there are other ways of testing the MAF. I know Ecklers and I think Mid America sell a little pig tail you can plug into the MAF, and using a DVM, checking for functionality. I would think if they sell such an animal they also provide instructions on how to properly troubleshoot the MAF using their item. Further there are people talking about using the Wells MAF which I take it is only about $160... a far cry from GM's asking price for a new unit. Juliet is right... my price for a new unit (my wife works for a Chevy dealership) is $315-330 :eek: ... not cheap. By the way, Jeff Kopp (18carfan), has the best prices on new GM parts if that is the route you want to take.
:D ;) :D ;)... and that friend of his had a laptop with Diacom software and a little help from 85_togo (borrowed MAF) and Craig Marcho to determine the MAF was bad. Basically at WOT in the 4k RPM ramge the MAF should supply the ECM with somewhere around 200g/s. The bad MAF was only putting out a MAX of 160... not good. Now, I know not everybody has access to diagnostic software but there are other ways of testing the MAF. I know Ecklers and I think Mid America sell a little pig tail you can plug into the MAF, and using a DVM, checking for functionality. I would think if they sell such an animal they also provide instructions on how to properly troubleshoot the MAF using their item. Further there are people talking about using the Wells MAF which I take it is only about $160... a far cry from GM's asking price for a new unit. Juliet is right... my price for a new unit (my wife works for a Chevy dealership) is $315-330 :eek: ... not cheap. By the way, Jeff Kopp (18carfan), has the best prices on new GM parts if that is the route you want to take.
Melting Slicks
Joined: Jun 2001
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From: Sarasota, FL
Re: How do you test a MAF? (85_togo)
My car just crapped out last Wednesday. Was running awesome down this great canyon here in Co and when I got to the bottom the scanning software I was running showed a VERY lean condition. I got home and the engine got rougher and rougher. When I cooled down I couldn't start it at all. It wouldn't idle. I could get it to fire and maybe kinda-idle for a few seconds with heavy throttle input. I tried all the multi-tester methods described in the shop manual, all the methods in my TPI tuning book, all the methods in my Haynes manual, unplugging and running car, etc, etc. All these tests seemed to show an operating MAF. Scanning software showed what seemed like reasonable gm/sec numbers coming from the MAF. I went over to a friends house and swapped his MAF onto my car and it ran perfect.
In retrospect there were some occasions (about 3 over two months) when I would try to start my car and it wouldn't "catch". It would fire and rev to 1100 rpm or so and then just die. I could get it started with some throttle and if warmed up at about 1700-200 rpm for about 3 mins it would run fine. I bought a new MAF from Autozone for 153 and change including tax. This was a rebuilt Bosch unit with a three month warranty. Good luck.
In retrospect there were some occasions (about 3 over two months) when I would try to start my car and it wouldn't "catch". It would fire and rev to 1100 rpm or so and then just die. I could get it started with some throttle and if warmed up at about 1700-200 rpm for about 3 mins it would run fine. I bought a new MAF from Autozone for 153 and change including tax. This was a rebuilt Bosch unit with a three month warranty. Good luck.
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Joined: Jul 1999
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From: Maryland
Re: How do you test a MAF? (BobMachus)
I bought a new MAF from Autozone for 153 and change including tax. This was a rebuilt Bosch unit with a three month warranty.
