can bad o2 sensors cause idle surge and low maf voltage...

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blk92stangg

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I don't think the maf "tells", the computer to do anything, nor are any of the sensors linked in anyway, at least not in the way you are wondering. The MAF tells the computer how much air is flowing into the engine, and the O2's tell the computer how well the fuel was burnt (or how efficiently the engine is running). There are another slew of sensors that give the computer additional information on how much fuel and timing to run the engine at. While anything is possible, I would look elsewhere for your surging idle problems... like your IAC, vacuum hoses, TPS.
 

blk92stangg

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Sorry, didn't read your title better, but a faulty MAF sensor could cause a poor idle. Try cleaning the elements and testing again.
 

jrichker

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87'GTstang

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What method yould you possibly use for an 87' for codes, or am I still just stuck with the SOL method???
 

oz

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It's your underdrive pulleys - and usually is, when there is a surge problem... The underdrived don't allow the alternator to make enough power. The fuel injectors are directly effected by voltage - meaning if the voltage goes down, the pulse width of the injectors goes down, the fuel pressure goes down and the engine speed decreases (which forthur reduces voltage). When the computer realizes this, it goes into some panic mode where it 'juices' the engine. This causes the rpm's to jump - with this the voltage goes up, the injectors work properly and the fuel pressure goes up to normal.... the computer goes back to normal idle mode and starts the cycle all over again.
You can either:
1. Get rid of the underdrives (or keep the crank and ditch the others - this solved my problem - along with a 140A alternator)
2. Get a dyno tuned chip that will eliminate most (but not all) of this.
3. Get a idle bypass adjusting plate. I have heard good things about these.

Good Luck!
 

dastang2

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jrichker said:
Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html
can i use this info to check codes on a 95 v6 with loads of codes. hey it rhymes
 

jrichker

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dastang2 said:
can i use this info to check codes on a 95 v6 with loads of codes. hey it rhymes
I believe the 95's were OBDII and did not work with the paper clip or jumper wire trick. Maybe someone else has first hand experience.
 

91lxntch

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i have pulled codes but havent figured them out at all one is
95 fuel pump circuit
66 maf voltage low
bascially ive repalced everything i could think of tried diff maf units and diff electronice nothing worked i also got some good info from jricher but i am having trouble figuring it out i need to know what all it could be then go from there. im thinking it is my o2 sensors...everything was fine before i did all the work to the car....
 

86/92stang

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Typically I see low maf voltage as dirty elements or connector unlplugged or not fully plugged in (possibly rubber seal bunched up). I would try to clean if you havent and unplug and re connect the harness.

Edit: Just read the post above maybe dirty filter? If just clean maybe too much oil (if K&N style).
 

91lxntch

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heres what ive replaced
iab
mass w/electronics
upper intake gaskets
checked for vac leaks
cap/rotor/plugs/wires
cleaned 10 pin connectors
air filter
ect sensor
act sensor
etcetc......
so i gotta figure out why im getting codes 95 and 66 also got a code for my vss sensor...if someone could get me on the right track ...is it my computer.. or o2 sensors thats all i got left......also if someone could tell me what all it could be then i can at least try to figure it out right now there is too many possibilitys. like i said al i have left really is ecu or o2 sensors...this is really ****ty cause i dropped about 8 grand and have yet to be able to run the car much or take it to the track
 

jrichker

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Code 27 or Code 29 - Vehicle Speed Sensor (VSS) is an electronic sender mounted on the speedo pickup gear on the trans. It works the cruse control for both 5 speed and auto trans cars. On auto trans cars, it tells the computer to speed up the idle slightly as you slow down to a stop to keep the engine from stalling. Check to see if the electrical connector is plugged into it. Cost is under $30 and it is easy to replace.

Code 66 MAF below minimum test voltage.
Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables.

The MAF output varies with RPM which causes the airflow to increase or decease. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow. Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF and ground.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

To clean the MAF, remove the MAF element and gently spray it with electrical contact cleaner. You can also use non-flammable brake parts cleaner (same chemical in a bigger can & cheaper too). Let it dry and put it back in.

Code 95 is a fuel pump/fuel pump inertia switch problem. At sometime the fuel pump lost electrical power while the engine was running.
 

91lxntch

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ok so im starting to understand this info better and am going to try to take a stabe at it but i have a few more simple questions does the car need to be runnign in order to do this and would i set my digital voltmeter to 20k ohms or does it mattter what setting it is on...........what are the possibilitys it could be computer or wires thats all i can figure
 

jrichker

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91lxntch said:
ok so im starting to understand this info better and am going to try to take a stabe at it but i have a few more simple questions does the car need to be runnign in order to do this and would i set my digital voltmeter to 20k ohms or does it mattter what setting it is on...........what are the possibilitys it could be computer or wires thats all i can figure
What are you trying to measure the resistance of? Ohms is just for resistance, and is always measured with the power off.
 

91lxntch

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when you said to check the resistance of the maf signal wire......here is the funny thing now i am not getting code 66 anymore today i ran codes again and got for koeo code 11 then a long pause and a 1 then another long pause and then 29-34-95 which are memory codes the car runs really rich and surges bad im gonna try o2 sensors also is 40 fuel press with vac off too much for my setup....maybe its just to much fuel press im also running 21 base timing but i have tried 10-21 so thats deff not it either..im really gettign bummed out on this car
 
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