[Shotimes] Re: MAF Voltage signals

[Adam Parrott]

Carl,

Was the 0.5v to 2.8v range with the Pro-M 77mm?  Are you running a chip or
LPM with the MAF?  How the EEC will respond depends on the MAF transfer
curve that it is using, the latter being determined by either the factory
program or by a chip, LPM or tuner.  For a 55mm MAF, a 0.5 - 0.6v idle
reading is somewhat low but not uncommon.  IIRC, Josh has said that a
typical 55mm MAF on a NA V6 should idle around 0.8 - 1.0v at idle.

Adam


----- Original Message ----- 
From: "Carl Prochilo" <gr8sho@prochilo.myserver.org>
To: <TechSHO@topica.com>
Cc: <shotimes@autox.team.net>
Sent: Tuesday, March 09, 2004 11:47 AM
Subject: Re: MAF Voltage signals


One more question about the observed measurements I mentioned below.
 Given the range of 0.5V to 2.8V on the MAF signal, how will the EEC
behave in terms of controlling the engine?  It certainly seems that
engine is running rich and wanted to confirm that this is the
expected behavior.
-- 
Cheers,
Carl Prochilo
1992 Ultra Red Crimson

Carl Prochilo said:
> Alan, yes, I never bothered to see if the CEL was on when unplugging
> the MAF.  Verified that it does come on when removing the connector.
> And I
> wasn't probing the correct wire either as you guessed.
>
> I never mentioned this in the previous post, but the MAF in question
> is a
> Pro-M 77mm unit from circa 1998.
>
> Here's some more information.  To probe, I carefully exposed a small
> area of
> wire by scraping away some of the insulation so I could get
> alligator clips
> on the wiring harness.  Using the EVTM schematic, I verified the MAF
> is
> receiving the correct voltage, about 13.77Vs.  These are the thick
> Red wire
> for power and the black/green wire for ground, and are right next to
> each
> other.  I then probed the light blue and tan wires.  These are the
> signal
> wires back to the EEC.  The readings here were not what I expected.
> At
> idle, I'm seeing somewhere between 0.53V and 0.6Vs.  At WOT, the max
> I'm
> seeing is about 2.7V to 2.8V, and SHOULD be close to 4.5V.  (If the
> signal
> goes over 4.7V, I understand the CEL will come on again.)  Assuming
> the
> wiring harness is good, I probably should try a stock 55mm MAF and
> see what
> readings I will get.
>
> To do serious troubleshooting, the PCED refers to a breakout box
> that I now
> wish I had access to.
> --
> Cheers,
> Carl Prochilo
> 1992 Ultra Red Crimson
>
> Don  Donelson said:
>>
>>
>> Correct .. your car will run with the maff unpluged ... the EEC
>> when it
>> detects the maff not connected will run in whats called " open
>> loop mode"
>>
>> The EEC will default to a stragity that by passes your 0 2 senors
>> ( the EEC
>> wont read them ) and will create its own default fuel table.
>>
>> dond
>>
>>
>> ---------- Original Message ----------------------------------
>> From: Alan Fanning <awfanning@earthlink.net>
>> Reply-To: TechSHO@topica.com
>> Date:  Mon, 08 Mar 2004 20:06:42 -0800
>>
>>>She';; run without the MAF, but should throw a CEL. This happened
>>> to me
>>> this
>>>weekend when I needed to move my parts car - I forgot I had swiped
>>> the MAF
>>>to use on my other car for smog testing. Started and ran fine (in
>>> driveway).
>>>But the CEL was a giveaway that I had forgotten something.
>>>
>>>Sounds like, in your case, you may not be measuring the wire that
>>> has the
>>>information you're seeking(?)
>>>
>>>    Alan
>>>
>>>> I finally got around to the task of probing the wire mentioned
>>>> in the
>>>> attached note.  The way the voltmeter behaves it appears that
>>>> the signal
>>>> is
>>>> open to the PCM.   I've observed that when removing the
>>>> connector from
>>>> the
>>>> MAF meter, the engine doesn't behave any differently.  I also
>>>> connected
>>>> up a
>>>> spare 80mm Ford MAF and still no difference.
>>>>
>>>> I would have thought the car wouldn't work that well, or at
>>>> least rough
>>>> without the MAF signal.
>>>>
>>>> The other item of note is that the fuel consumption of the car
>>>> is high.
>>>>
>>>> Does this sound like a bad MAF connector?
>>>> --
>>>> Cheers,
>>>> Carl Prochilo