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How do you know if you have a bad map sensor and MAF??.. Help engine running bad

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Old 05-27-2012, 04:33 PM   #1
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Smile How do you know if you have a bad map sensor and MAF??.. Help engine running bad

My blazer is running crappy. I think my MAF is going out and I was told my map sensor is bad.. When the engine is running and I unplug the MAF it dies. When I was told that it should fall back to the map sensor and stay running?

I have bought new o2 sensor for it and tps and ignition control module.

The timing is off I know. Im not sure how much that has in play with it running as crappy as it is. I can't give it anymore than 1/4 throttle at times or it bucks n jumps or just almost dies.

The blazer has 192k miles so I was slowly just going to replace all the sensors. I just haven't gotten around to the map and MAF. I have tried a map sensor off my old 4.3 I have laying around and it didn't help the issue so before I buy one I was wondering if there was a way to check it. I also havent bought a air temp sensor not sure how often those goes out and i havent gotten a IAC either. I still need to hook it up to a scan tool and see what my cam retard is so I can zero it back out.

Any help would be awesome guys!

Thanks
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Old 05-27-2012, 05:42 PM   #2
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Quote: Originally Posted by 94s10cpi

The timing is off I know. Im not sure how much that has in play with it running as crappy as it is.
I would start there first.
Old 05-27-2012, 06:20 PM   #3
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

What are the codes in the vehicle self diganosis system ? Seems to me, those would be most helpful right now.
Old 05-27-2012, 06:23 PM   #4
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Let me go have autozone scan it real quick. Timing isn't off much. But maybe a few degrees.
Old 05-27-2012, 06:39 PM   #5
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Well it's throwing a lot of codes. Autozones scanner is junk and can't clear anything so ima go try oriellys to haw them clear it and see what ones pop on. But autozones read map sensor(had it unplugged it plugged in now before was scanner) tps low circuit, MAF threw one a few others he didn't show me much just said go have scanned by some place with better equipment haha.
Old 05-27-2012, 07:02 PM   #6
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Well oriellys read the same. But it saying throttle/pedal position sensor. And MAF then evap. Didn't read map sensor tho. I had him clear the codes. So far engine light is still off.
Old 05-27-2012, 08:50 PM   #7
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Well this is interesting. I guess everything is failing on this blazer haha my fuel pump just went out. Turn the key in it barely primes most the time it won't. Hooked up the gauge it does nothing. When it primes it goes to 50 or so then instantly drops after its done priming. When cranking it slowly goes up turn the key off instantly drops
Old 05-27-2012, 09:03 PM   #8
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

jeremy mine did the same thing when it went out
Old 05-27-2012, 10:14 PM   #9
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Jack up the radiator cap and replace everything under it ? Just kidding.
Sounds like you have quite a few codes to repair. I would be interested to know how it runs when you get every code repaired.
Old 05-27-2012, 10:31 PM   #10
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

New fuel pump is on its way. After that comes then I can get it scanned with a better scanner and start to get it on the right track! Hopefully it'll be running good soon.
Old 05-27-2012, 10:34 PM   #11
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

A "few" degrees timing can make all the difference in driveability. Is a few 1 or 2 or 5 to 10. Even 2-3 can be a big difference.

Seriously I would get that within spec first.
Old 05-27-2012, 10:44 PM   #12
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Yeah thats why im wanting a snap on scan tool to scan it to watch my cam retard. But now i need a fuel pump so once that's in, time to have it scanned and timing fixed then work on the what codes are thrown and i dont feel like paying 50 bucks or more to have a shop scan it when i could scan it if they'd let me use it. I know a guy that has one just finding time when he isn't busy. He works for a GM dealership and does side jobs besides that so its hard to catch him at a good time.
Old 05-28-2012, 01:17 AM   #13
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Quote: Originally Posted by 94s10cpi
Yeah thats why im wanting a snap on scan tool to scan it to watch my cam retard. But now i need a fuel pump so once that's in, time to have it scanned and timing fixed then work on the what codes are thrown and i dont feel like paying 50 bucks or more to have a shop scan it when i could scan it if they'd let me use it. I know a guy that has one just finding time when he isn't busy. He works for a GM dealership and does side jobs besides that so its hard to catch him at a good time.
Pull the distributor and look at the gear. If its worn replace it, then you will be within spec.

For the MAP sensor pull it out and look at the o-ring, they tend to fall apart, it may need replacing.

Since you dont have a scanner to read those sensors

How to test MAP:
http://troubleshootmyvehicle.com/gm_...ensor_gm_1.php

How to Test MAF:
http://easyautodiagnostics.com/gm_ma...tic_test_1.php
Old 05-28-2012, 01:38 AM   #14
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Ah thanks for the links! I changed the Map with one and the o-ring was good. and ill pull the distributor all the way out when it's hooked up to the scanner. The original map sensor that was in it had some carbon build up on it..
Old 05-28-2012, 01:53 AM   #15
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

My blazer is having symptoms of what both say are signs of a bad MAP or MAF except I haven't noticed any black smoke. But when I had it hooked up to a Matco scanner the o2 sensors weren't reading correctly and they were both brand new.

bad MAP

check - Rough Idle.
not that i know of - Black smoke coming out of the tail-pipe.
eh not really - Engine Stalls under load.
sometimes - Engine dies as soon as it starts.
yes if anymore than 1/4 throttle - Lack of power when you accelerate the vehicle down the road.
bad MAF

not sure autozone scanners suck - Lean and/or Rich code(s).
is throwing a fuel code forgot which code - Fuel Trim code(s).
at certain times yes 1/4 throttle or more - A tremendous lack of power upon acceleration.
once again not that i know of - Black smoke coming from the tail-pipe.
ides rough and stalls sometimes when trying to rev from idle - Vehicle may idle rough and stall.


But it did have a weak fuel pump.. So this could change once I get the new one installed..?
Old 05-28-2012, 11:44 AM   #16
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Quote: Originally Posted by 94s10cpi
My blazer is having symptoms of what both say are signs of a bad MAP or MAF except I haven't noticed any black smoke. But when I had it hooked up to a Matco scanner the o2 sensors weren't reading correctly and they were both brand new.

bad MAP

check - Rough Idle.
not that i know of - Black smoke coming out of the tail-pipe.
eh not really - Engine Stalls under load.
sometimes - Engine dies as soon as it starts.
yes if anymore than 1/4 throttle - Lack of power when you accelerate the vehicle down the road.
bad MAF

not sure autozone scanners suck - Lean and/or Rich code(s).
is throwing a fuel code forgot which code - Fuel Trim code(s).
at certain times yes 1/4 throttle or more - A tremendous lack of power upon acceleration.
once again not that i know of - Black smoke coming from the tail-pipe.
ides rough and stalls sometimes when trying to rev from idle - Vehicle may idle rough and stall.


But it did have a weak fuel pump.. So this could change once I get the new one installed..?
If you can capture some live data after you get the fuel pump done.
The MAF should be reading between 4-5g/s at idle.
The MAP should be reading roughly 32kPa at idle

Have a look at fuel trims. They should be no more than +/-10%

Most MAF problems can be fixed by taking it apart and cleaning it with MAF or electrical contact cleaner. Especially if you use a K&N oiled air filter.
Old 05-28-2012, 02:57 PM   #17
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Yeah I'll definitely try and video what it's doing once the pumps in. Ima try and check the map sensor today and MAF if the blazer will start. This way I can find out if the sensor are bad while I wait for the new pump to wait. If I can catch the guy im trying to have scan it on a day he's free the blazer should be running good that day.

And if the MAF is bad do you guy recommend a new one or refurbished?

And this may sound weird but before I started messing with the distributor the camshaft/crankshaft sensor codes popped up now those codes aren't I guess there's a chance I randomly somehow got it in the correct spot but I kinda doubt it.
Old 05-28-2012, 03:25 PM   #18
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Quote: Originally Posted by 94s10cpi
Yeah I'll definitely try and video what it's doing once the pumps in. Ima try and check the map sensor today and MAF if the blazer will start. This way I can find out if the sensor are bad while I wait for the new pump to wait. If I can catch the guy im trying to have scan it on a day he's free the blazer should be running good that day.

And if the MAF is bad do you guy recommend a new one or refurbished?

And this may sound weird but before I started messing with the distributor the camshaft/crankshaft sensor codes popped up now those codes aren't I guess there's a chance I randomly somehow got it in the correct spot but I kinda doubt it.
Much cheaper to get a MAF from a wreck yard. Expensive sensor to buy new.
The P1345 code pops up when the camshaft retard offset is out more than 27 degrees.
Old 05-28-2012, 03:31 PM   #19
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Yeah Ima try and clean my MAF today what all can you use to clean it? I know you mention something above but I cleaned a old one and forgot what my dad used but I know we has something around the house to use on it. When i got the blazer it had a fram air filter in it and i put a k&n in it but it disnt have much oil on it and it was running bad-ish before i put it in.

I see the timing is a pain hopefully I get it lined out. I wanna take it to gateway in stl just to get a time of it being all stock. Then the performance mods start.
Old 05-28-2012, 04:58 PM   #20
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Quote: Originally Posted by 94s10cpi
Yeah Ima try and clean my MAF today what all can you use to clean it? I know you mention something above but I cleaned a old one and forgot what my dad used but I know we has something around the house to use on it. When i got the blazer it had a fram air filter in it and i put a k&n in it but it disnt have much oil on it and it was running bad-ish before i put it in.

I see the timing is a pain hopefully I get it lined out. I wanna take it to gateway in stl just to get a time of it being all stock. Then the performance mods start.
ONLY use MAF cleaner, or electrical contact cleaner. Those do not leave any residue on the 3 wires. In a pinch you can use 99% Isopropyl alcohol

Here, do it this way:
http://easyautodiagnostics.com/gm_ma...f_sensor_1.php
Old 05-28-2012, 05:11 PM   #21
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

I've bought a maf sensor from a junkyard before with not much faith in it being good, but it ended up being fine thankfully. Definitely alot cheaper than going new from the auto parts store.
Old 05-28-2012, 05:12 PM   #22
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Alright I got some data for you guys. Will be posting it now. May take a little bit.
Old 05-28-2012, 05:56 PM   #23
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Here's some videos..



MAF readings:





MAP reading:
Old 05-28-2012, 06:49 PM   #24
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

These two are the same video.. I meant to upload this one..

Old 05-29-2012, 03:11 PM   #25
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

So if the map sensor isn't getting its 5 volts does this possibly mean my PCM is fried? Should I try and give it 5 volts else where and see if it works? Or would it still not function correctly since the PCM wouldn't be sending it the 5 volts?
Old 05-31-2012, 03:12 PM   #26
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Anyone?
Old 05-31-2012, 03:30 PM   #27
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

I would guess that the 5v could be shorted out. You could test for continuity against a ground. That or there is a break in the wire.
Old 05-31-2012, 04:08 PM   #28
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Might have a break not sure. I was using the battery terminal as a ground for it. I'll check into it more today. Try to trace the wires. So you don't think it's a PCM problem? That's my major concern. If its a wire that's a easy fix to me than needing a computer.
Old 05-31-2012, 05:08 PM   #29
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Did you follow this procedure?
http://easyautodiagnostics.com/gm_ma...tic_test_3.php
Old 05-31-2012, 10:10 PM   #30
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

Quote: Originally Posted by burned
Yep i did all the test on that. I can redo them but i tested the maf and map for 12v and ground then tested the MAF signal. I think that the maf is bad anyway i think it was going bad when i got the blazer.. Im just more worried about the map sensor not getting 5 volts. It was raining today so i didn't get to work on it any today. I ended up ordering a whole new sending unit so that should be here hopefully saturday then ima try a friends MAF and see if that helps.. Then im also going to be getting the timing back to where it should.
Old 08-25-2012, 03:44 PM   #31
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Re: How do you know if you have a bad map sensor and MAF??.. Help engine running bad

i am having the same problem with my 03 S-10 4.3L cant find the right test procedure for MAP sensor can only find procedure for model years under 2000 on volts test eng. running volts goes down when eng. is revved instead of going up to near 5.0volts cant clear code107
can anyone help
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