Minor Mods I Need Some Help Please

hvybrl

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May 10, 2015
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Hello Everyone,

I am new here and I hope you all don't mind me asking but I need some help.

I recently purchased my first mustang it's a 1991 lx notch with 120,000km and unmodified. The car ran fine and had lots of power. I installed full length headers (1-5/8" BBK), off road h-pipe (2-1/2"), flowmaster original 40 mufflers (2-1/2"), and stainless flowmaster exhaust pipes (also 2-1/2"). I changed the motor mounts just because I had them. I also added march underdrive pulleys. I changed the factory cap and rotor with an MSD cap and rotor set and also 9mm ford racing wires. I also changed the coil to an MSD coil. I had 3.73 gears installed also. I did clean the MAF of debris on the screen and used the proper cleaner for that as well as cleaned the little wires of the sensor. I also cleaned the throttle body and used TB cleaner on it. I was careful in doing all this to the car and took my time. Now for whats giving me a headache.

When I drive the car now and I get on the gas it kind of surges and is hesitant as it climbs through the rpm range. This all starts at about 3000-3500 rpm and up. I asked my mechanic to pull codes and it shows a Code 66 Mass Air Circuit. I assume this is the problem and am going to install a used MAF sensor to see if this will cure the problem. Vacuum on the motor was good and wires etc all checked out fine.

Am I on the right track with this diagnosis. Is the factory MAF big enough or do I need a bigger Mass Air like the BBK Mass Air calibrated for 19lb injectors? Sorry for a lengthy first post but I like to be thorough. Thanks to all for any and all help.
 
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mikestang63

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Welcome

Too often guys use too much cleaner or are not cautuous with the MAF. Did you remove the electronics from the housing? Check your MAF for broken power wires or you may have broken the sensing wire- it is very delicate. Do this first- disconnect the battery for about 30 minutes with the headlight switch on to totally erase everything from the EEC. Then reconnect the battery and see if that clears it up. If you want a nice cheap increase in HP, find a 70MM MAF from a 94 or 95 gt. You'll need to get a $15 adapter ring for one side but it is a great bang for the buck.

@jrichker for code 66 help...
 
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hvybrl

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May 10, 2015
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Thanks MikeStang63,

Originally I just cleaned the screen as that is all I thought was to be cleaned ( I didn't know better). I may have used too much spray to clean and I did use a little brush to completely clean the screen but it never touched the little wires attatched to the actual electronics. Yesterday I did take the sensor off and cleaned it with that spray. It appears there are two little fillament type wires which were in tact and I was extrememly careful when I sprayed it and in putting it back in.

I read about disconnecting the battery but not the headlight switch. Looks like I'm off to the garage to try something new. Hope it helps... I'll be back to let you know.
 

hvybrl

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May 10, 2015
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Well I turned the headlights on, disconnected the battery for 30+ minutes. Reconnected and took the car for a rip to find the same darn hesitation. My buddy was with me for the ride and he thought it felt like maybe a bad spark plug or wire. Im pretty sure that would show up when they scanned for codes not?

Anyhow I'm heading out in the morning to grab a used MAF sensor to see if that cures my problem. Hopefully that will do it.

P.S. If I find a MAF for a 94/95 i will grab it and do what you suggested MikeStang95
 

jrichker

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Code 66 or 157 MAF below minimum test voltage.

Revised 10-Feb-2014 to add 95-95 Mustang code 157 and 94-95 ECC diagram

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.

Computer connector for 88-93 5.0 Mustangs

Diagrams courtesy of Tmoss and Stang&2Birds

ECC Diagram for 88-90 5.0 Mustangs


ECC Diagram for 91-93 5.0 Mustangs
www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

94-95 Diagram for 94-95 5.0 Mustangs



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. Changes in RPM causes the airflow to increase or decrease, changing the voltage output.. 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.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

89-90 Model cars: 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. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.

91-95 Model cars: Measure the MAF output at pins C & D on the MAF connector light blue/red and tan/light blue) or at pins 50 & 9 on the computer. Be sure to measure the sensor output by measuring across the pins and not between the pins and ground.


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 wiring connector and pins A or B. Make your measurement with the MAF disconnected from the wiring harness.

Actually MAF pins C & D float with reference to ground. The signal output of the MAF is a differential amplifier setup. Pins C & D both carry the output signal, but one pin's output is inverted from the other. The difference in signal between C & D is what the computer's input circuit is looking for. The difference in the two outputs helps cancel out electrical noise generated by the ignition system and other components. Since the noise will be of the same polarity, wave shape and magnitude, the differential input of the computer electronically subtracts it from the signal. Then it passes the signal on to an Analog to Digital converter section inside the computer's CPU chip.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel pump, alternator, ignition & A/C wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Computer,. actuator & sensor wiring
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Fuse panel layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Vacuum routing
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg
 

smkshw

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Feb 12, 2010
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its not just the screen you clean,have to clean the sensors,just spray a bit of maf cleaner but dont touch it,also di electric grease in the plug connectors help....try that first
 

A5literMan

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And running the codes will not show an issue with the plug wires. Take a look around the wires. Make sure there are no melted,cracked,disconnected wires. Pull your plugs and check them also.
 

hvybrl

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Well I bought a re-manufactured Mass Air for the car from NAPA. I put it in and took the car for a rip and same old s#!%.
I did buy and already installed all new wires, plugs, and cap and rotor etc. I am going to try the old cap and wires to see if maybe i have a bad wire. If that doesn't solve it I'll check the plugs and call my buddy to come check if maybe somehow the timing is out. Not sure how cause it was fine before I started all this.

This is really frustrating me.
 

jrichker

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Did you check the voltages as described in the Code 66 test path BEFORE purchasing a replacement MAF?

After replacing the MAF, did you disconnect the battery to force the computer to relearn the sensor settings?

If you disconnected the battery, have you dumped the codes to see if you are still getting a 66 code?




Cylinder balance test: use this to find dead or weak cylinders:

Revised 25 March 2012 to add necessity allowing the KOEO tests to finish before starting the engine and the need for a properly functioning IAB/IAC to run the cylinder balance test.

The computer has a cylinder balance test that helps locate cylinders with low power output. You’ll need to dump the codes out of the computer and make sure that you have the A/C off, clutch depressed to the floor and the transmission in neutral. Fail to do this and you can’t do the engine running dump codes test that allows you to do the cylinder balance test.

Here's the way 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. You watch the flashing test lamp or Check Engine Light and count the flashes.

Be sure to turn off the A/C, have the clutch depressed to the floor, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.


Here's how 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. You watch the flashing test lamp or Check Engine Light and count the flashes.

Underhoodpictures007-01.jpg


Underhoodpictures010.jpg


If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and drivability problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, clutch depressed to the floor and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10




Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus Digital Ford Code Reader (3145) Equus - Digital Ford Code Reader (3145It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.


Cylinder balance test

If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1400-1600 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Let it finish the Key On Engine Off (KOEO) code dump. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. Remember to keep the clutch pedal (5 speed) depressed to the floor during the test. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure


Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder balance test. Low compression on one of these cylinders rules out the injectors as being the most likely cause of the problem. Look at cylinders that fail the cylinder balance test but have good compression. These cylinders either have a bad injector, bad spark plug or spark plug wire. Move the wire and then the spark plug to another cylinder and run the cylinder balance test again. If it follows the moved wire or spark plug, you have found the problem. If the same cylinder fails the test again, the injector is bad. If different cylinders fail the cylinder balance test, you have ignition problems or wiring problems in the 10 pin black & white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark plug hole. The other type leaks too much to get an accurate reading. Your local auto parts store may have a compression tester to rent/loan. If you do mechanic work on your own car on a regular basis, it would be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the throttle wide open with a plastic screwdriver handle between the throttle butterfly and the throttle housing. Crank the engine until it the gage reading stops increasing. On a cold engine, it will be hard to tell what's good & what's not. Some of the recent posts have numbers ranging from 140-170 PSI. If the compression is low, squirt some oil in the cylinder and do it again – if it comes up, the rings are worn. There should be no more than 10% difference between cylinders. Use a blow down leak test (puts compressed air inside cylinders) on cylinders that have more than 10% difference.

I generally use a big screwdriver handle stuck in the TB between the butterfly and the TB to prop the throttle open. The plastic is soft enough that it won't damage anything and won't get sucked down the intake either.

A battery charger (not the trickle type) is a good thing to have if you haven't driven the car lately or if you have any doubts about the battery's health. Connect it up while you are cranking the engine and it will help keep the starter cranking at a consistent speed from the first cylinder tested to the last cylinder.

See the link to my site for details on how to build your own blow down type compression tester.
 
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