MAF Sensor regrounding

Fast Guy

Fast Guy

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View attachment 1641

The origional one seems to have gone, so here's a copy I found in a thread. All credit to whoever first posted it. :wink:

MAF Sensor grounding

First, you'll need a digital voltmeter and a small flat blade screwdriver.

The MAF sensor is located just past the air intake. You'll need to pull back the rubber cover to expose three wires. On mine, the outer two were orange, the middle one is white. The middle pin is where we need to get a voltage reading from (with the engine idling). Take the positive lead of the voltmeter and make contact with the middle wire. The negative lead should be pressed to one of the ground connectors on the engine block, near the firewall, right behind the fuel injectors. You might have to look hard to see them, just look for a bolt with several black wires running to it. Took me a while to spot it myself, several vacuum hoses in the way...

The voltage read should be less than 9mv (.009v), if it is above this value, the sensor needs to be reground. To do this, a wire needs to be run from the middle pin to the ground lug. You'll need to remove the connector from the MAF to get a good angle on it. On either side of the connector is a small opening for a small flat blade screwdriver. There is a wire that runs around the connector to hold it in place, you need to pry this wire outwards, and then move the connector back a bit. Do one side, then the other, and it should pop right off. I'd never seen this type of fastener before, once you have it off you'll see what I mean.

You'll want to solder a new wire to the middle pin, make sure you get a good connection. Then, run the other end to the ground lug. If you want to do the job right, you'll want to get a connector from Radio Shack or other electronics store that has a ring that you can crimp the wire to. I don't remember the size of the bolt, so I'm no help there. I just looped my wire around the bolt twice and put it back on. I may go back and fix it up nice some other time.

Once the sensor is reground, the voltage should drop significantly. Mine was at around 11mv, after the fix it went down to less than 2mv.
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hmmm

Member
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Had a look today at this today. The old middle wire stays in it's place right? You just have to solder a new wire from the middle pin to the ground lug. So now 2 wires are attached to the middle pin (the original white wire and the new wire which goes to the ground lug). Correct?

Has anyone got a pic showing where the ground lug is? I just couldn't find it. :(

Thanks.
 
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AJ4

Guest
Re: ...

hmmm said:
Had a look today at this today. The old middle wire stays in it's place right? You just have to solder a new wire from the middle pin to the ground lug. So now 2 wires are attached to the middle pin (the original white wire and the new wire which goes to the ground lug). Correct?
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Yes, you don't have to solder directly to the pin though, you can bare the ( white ) wire a little bit up from the pin and solder onto that ( much easier ) as long as you wrap it up well with insulating tape etc.
 
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Shaun

New Member
:D Just been out and bought a multimeter,switched it to 200mv and tested the white wire on the maff whilst the plug was connected and the car was running and got a reading of 57.3mv :shock: :? Is this correct :?: If i turn it to 2v it reads 0.054v :? Anyone shed some light on this please :?:
 
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RJC

Guest
Re: ...

Can't find where to ground the negative. Anyone help???

Pleeeeaaasssse
 
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AJ4

Guest
RJC - if you look at the plenum chamber at the back of the engine, you will see a bolt on it with some black wires attached, use that bolt to ground the negative. Alternatively, use the ground terminal of the battery, shouldn't make any difference which one you use.

Shaun - it should be less than 0.009 Volts ( 9 mV ), 57 mV is way too high :shock: I think you need to follow the good advice above and ground it :D


For anyone who is not very Voltmeter or electronics savvy, you will need to use a Voltmeter that can measure very low voltages. Some cheap and cheerful voltmeters only have a lowest range of 3 Volts. This can means that you dont have enough decimal places to measure thousands of a volt ( you are trying to make a reading of less than 9 thousanths of a volt ). A 3 volt scale means it will measure a voltage between 0 volts and 3 volts, but it will usually only be for one or two decimal places, ie 3.x or 3.xx. You need a meter that will read down to 3.xxx ( the third x is the thousandths of a volt x ).

Some voltmeters have a 200mV range, which means it will measure between 0 volts and 200 millivolts ( 200 hundred thousandths of a volt, which is 0.2 volts ). This is the range you want to measure with, your reading should be less than 9 mV ( 0.009 volts )

Sorry for the suck eggs and bad explanation, but just realised some people might not know how to use a voltmeter etc and what all the terms mean. Hope it helps anyway.

Cheers,

Ross.
 
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Shaun

New Member
Just an update,i earthed my MAF yesterday and it seemed a little smoother,but took it for a run tonight and it went really lumpy and the rev's seriously drop through the gear changes as though it was going to stall :shock: :? So i re-checked it and the millivolts had gone up :shock: :? It had gone from 57.3mv/0.054v to 69.4mv and 0.076v :shock: :shock: So i decided to earth it on the battery negative pole instead of a bolt and it now sits at 7.9mv and 0.008v :p :p :p So i'll see if there is any difference tomorrow :wink: Also just a question(aimed at Ross :wink: ) whilst i was checking the millivoltage i noticed that if i flicked the accelerator that the reading went upto 8.4mv..........is this supposed to happen :?:
 
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AJ4

Guest
yer, its not _supposed_ to happen, but it does if its not earthed properly :D

Btw, if you earthed it to the plenum chamber and it was still jumpy, I'd check out the rest of the earth wiring on the engine, sounds like its not too good. You need a good earth on the plenum for the injectors to work correctly etc. Try switching the ignition off and measuring the resistance from the plenum bolt to the battery negative terminal, it should be almost if not zero ( ie less than 1 ohm )
 
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jiw

Guest
i did mine yesterday as i was getting from 48-65mv, afterwards i got 1.2mv, i earthed it direct to the chassis with the main earth strap.

Has anyone got the correct readings for the earths on both the feed to the coil and the feed to the ignition amplifier? jeff
 
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Shaun

New Member
:D I originally earthed it to the wing by the standard boost pressure sender :wink: But thats where i was getting a higher reading :wink: So now its on the negative pole on the battery,cant see how it couldnt be earthed properly as it's soldered about 10mm from the MAF plug :wink: I'll have a go at cleaning all the earths on the engine and chassis tomorrow and see if that helps :? 8) Seems to run better where it is now though :lol: :lol:
 
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Shaun

New Member
:D Right,i still cant get it any lower than 6.2mv,i re soldered a thicker wire on the MAF this afternoon,cleaned the earths on the engine and plenum and it's only lowered it by 2mv :wink: :? Is there anything else i can try :?:
 
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Stoned

Guest
Out of interest the ohms reading between the white wire and ground is about 30 Ohms on my car. Surely even a dodgy earth wouldn't read this much ? Has anyone ever found where the white wires source is ?

Thanks
 
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gavmc18

Guest
just done this mod was reading 23mv before then when i earthed it it wentdown to 2.5mv. felt like it rana little smoother but not sure will have to see

gav
 
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