Engine 11 Mpg?

Discussion in 'Fox 5.0 Mustang Tech' started by Landon116, Aug 13, 2014.


  1. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Do the diagnostic thing first, you may find other problems beside the MAF...

    Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

    Dumping the computer diagnostic codes on 86-95 Mustangs

    Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

    Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

    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.

    Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

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

    [​IMG]

    [​IMG]

    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.

    [​IMG]

    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.

    [​IMG]

    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 driveablity 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, and clutch (if present) is pressed 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
    [​IMG]



    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 www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW 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.

    Swapping the MAF sensors between different MAFs is a big no no. The MAF body and sensor are designed to match each other. Therefore you can't swap sensors between different part number MAF bodies and maintain proper calibration. The assembly is designed to match the computer’s internal program, and swapping a different MAF can upset the computer's calibration. In other words, your monster MAF probably won't match the calibration of your 5.0 Mustang computer.

    The OEM Ford MAFs are not calibrated to injector size. The injector sizing is done in the computer’s internal programming. Aftermarket MAF’s “lie” to the computer in an attempt to fool the computer into changing the injector pulse on timing to match the increased airflow.

    The only other MAF that is a one for one swap for a 93 and earlier 5.0 Mustang is the 94-95 Mustang MAF.

    94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

    Once your replacement 70MM MAF is in place, disconnect the battery for about 10 minutes. When you reconnect the battery and start the engine, the computer will relearn the settings for the new MAF.

    *1.) Metal flange adapter http://www.kustomz.com/cat3.html Buy the TR70 for $44.95. Or spend some time on eBay looking for one that may fit.

    *2.) MAF & sensor interchange
    The 94-95 Mustang 5.0 MAF & sensor is also found on:
    1995-94 Mustang 3.8L F2VF-12B579-A2A,
    1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
    1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
    1994-92 Town Car 4.6L F2VF-12B579-A2A,
    1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
    Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.
     
    #21
    Last edited: Aug 20, 2014
  2. mikestang63

    mikestang63 Mustang Master

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  3. oldskolbus

    oldskolbus Founding Member

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    did you fill it up a second time or are you going off the fuel gauge? Fill it up/push the mileage button, drive that tank out, then fill it up at the same pump. use that mileage and gallons to get your mpg. The gauge is just a float in the tank, they aren't the most accurate.
     
    #23
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  4. Landon116

    Landon116 Member

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    Thanks for the info. Received the maf and installed after battery disconnected for 10 minutes. Car runs better. I filled up the tank to check my milage again. I have another issue now. The car gets to around 4000+ rpm it loses power, misses and hesitates bad. 0-60 is something like 11 seconds.. it is lacking power through the complete rpm range but worst at high Rpms.I checked the fuel pressure. At idle no vacuum on FPR: 38-39 psi
    FPR plugged in: 30psi
    When reved with FPR plugged in : dives to 25.
    Injectors will hold pressure when engine is off. Some plugs show white on the part under the electrode , where it should be a toasted -like color. Leading me to believe it's lean at or around WOT. Also looked at engine bay at night in the dark and it was light up like there was lightning bugs flickering around my engine bay. Plugs arching at boots and plenty of other places. Cheap AutoZone wires to be swapped with 9mm ford racing wires. IAT and 02's to be swapped just for maintenance. If you think I should check something else let me know ! I need me car running right !
    Thanks guys
     
    #24
  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    What were the results of the code dump? You should have at least gotten an 11.
     
    #25
  6. Landon116

    Landon116 Member

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    I will pull codes again when I get back from school. I recently pulled codes before the test and received all emissions related codes and passed cylinder balance test. I will post up the codes. What are your thoughts about fuel pressure diving when revved? Normal? Can't get a solid answer for anyone else.
     
    #26
  7. stykthyn

    stykthyn Commander of the snuggie cultists

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    one thing at a time. post the codes you pulled. no 11 code means the ecu still hasnt given the all clear and you will be going in circles trying to figure out what is wrong.
     
    #27
  8. stykthyn

    stykthyn Commander of the snuggie cultists

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    and please for the love of god tell me you didnt put a filter directly onto the maf meter.
     
    #28
  9. Landon116

    Landon116 Member

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    For the KOEO test I received :
    81, 82, 84, 85, 33, 96

    Engine dies EVERY time a KOER test is attempted shortly after test it initiated.
     
    #29
  10. Landon116

    Landon116 Member

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    Ran KOER test and received : 94 , 44 , 23, 81 and 29

    Didn't realize I had to wait for KOEO test to finish before moving on. And yes I have a filter in the engine bay on the Maf. I'm gonna get scolded right ?
     
    #30
  11. mikestang63

    mikestang63 Mustang Master

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    That is a no no. All you are doing is sucking in hot, turbulent air into the MAF. Either put the stock airbox back on, or get an aftermarket fenderwell CAI.

    @jrichker for codes
     
    #31
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  12. 89llx

    89llx Member

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    I dont want you to feel bad ,but, We drove my wifes 89gt aod mustang to the Woodward dream cruise.
    The car has edl heads ,stock cam with 1.7,s headers, cobra intake 70mm throttle body and 70mm mass air, stock 19lb injs,s
    2800 NON lock up converter and 410 gears.
    The car was turning 2800 rpm at 70 mph, and may God be my judge it got 25mpg

    it is a 30 thousand mile car, also the car goes mid to low 13,s
     
    #32
  13. Landon116

    Landon116 Member

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    That sounds great.. And yes that does make me feel bad. lol
     
    #33
  14. stykthyn

    stykthyn Commander of the snuggie cultists

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    A 5.0 in good running shape should see low mid 20s on the highway. In town 12-16 depending on conditions abd driving habits.
     
    #34
  15. Landon116

    Landon116 Member

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    Could a MAF setup like I have it cause really THAT bad of mpg? I understand the issue and i have a cold air kit on the way already. I am just curious though.
     
    #35
  16. Landon116

    Landon116 Member

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    Posted up the codes. Only concerning code I saw was code 96 which I believe is in the continuous memory. It stopped cutting out with plug wire replacement. Just fuel economy! I think it has dropped to 9 or 10 and I barely drive it..
     
    #36
  17. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Code 96 causes & tests 91-93 models. – KOEO- Fuel pump monitor circuit shows no power - Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits. The fuel pump circuit lost power at one time or another.

    Revised 07-apr-2013 to add check for corrosion and damage in fuel pump relay socket

    Clear the codes by disconnecting the battery and turning on the headlights for about 5 minutes before reconnecting the battery. This will clear any remaining codes. Drive the car for several days and dump the codes again. In many cases, this clears the 96 code.

    Look for a failing fuel pump relay, bad connections or broken wiring. The fuel pump relay is located under the Mass Air Meter on Fox bodied stangs built after 91. On earlier model cars is under the passenger seat. On Mass Air Conversions, the signal lead that tells the computer that the fuel pump has power may not have been wired correctly. See Mustang Mass Air Conversion | StangNet

    Diagram of the fuel pump wiring for 91-93 cars.
    [​IMG]

    Look for power at the fuel pump - the fuel pump has a connector at the rear of the car with a pink/black wire and a black wire that goes to the fuel pump. The pink/black wire should be hot when the test connector is jumpered to the test position. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. No voltage when jumpered, check the fuel pump relay and fuse links.

    [​IMG]


    Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92 or later models the fuel pump relay is located under the Mass Air meter. Watch out for the WOT A/C control relay on these cars, as it is located in the same place and can easily be mistaken for the fuel pump relay.

    Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed, or there is a broken wire in the relay control circuit. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.

    [​IMG]

    91-93 Models:
    Using the diagram, check the dark green/yellow wire from the fuel pump relay: you should see 12 volts or so. If not the relay has failed or is intermittent. Check the inertia switch: on a hatch it is on the drivers side by the taillight. Look for a black rubber plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the power feed to the fuel pump. Good voltage there, then the fuel pump is the likely culprit since it is getting power. No voltage there, check the Pink/black wire, it is the power feed to the fuel pump relay & has a fuse link in it. Good voltage there & at the dark green/yellow wire, swap the relay.

    All testing is done with the ignition switch in the Run position. Do not forget this crucial step.

    The pink/black wire s should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the fuel pump has opened up.

    With the test jumper in place the green/yellow wire should be the same voltage as the pink/black wire +/- 0.25 volt.

    If not, look at the red wire: should have the same voltage as the battery positive terminal +/- 0.25 volt.
    If not, then check the yellow wire on the EEC relay located on top of the computer. This one is hard to get to. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the computer has opened up.

    If the red wire does not have the same voltage as the battery positive terminal +/- 0.25 volt and the yellow wire on the EEC relay does, then check the red/green wire on the EEC relay. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the ignition switch is defective or the fuse link in the ignition wiring harness has opened up, or the EEC relay is defective.

    All testing is done with the ignition switch in the Run position. Do not forget this crucial step.

    The pink/black wire s should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the fuel pump has opened up.

    With the test jumper in place the green/yellow wire should be the same voltage as the pink/black wire +/- 0.25 volt.

    If not, look at the red wire: should have the same voltage as the battery positive terminal +/- 0.25 volt.
    If not, then check the yellow wire on the EEC relay located on top of the computer. This one is hard to get to. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the computer has opened up.

    If the red wire does not have the same voltage as the battery positive terminal +/- 0.25 volt and the yellow wire on the EEC relay does, then check the red/green wire on the EEC relay. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the ignition switch is defective or the fuse link in the ignition wiring harness has opened up, or the EEC relay is defective.

    Diagram courtesy of Tmoss & Stang&2birds
    [​IMG]
     
    #37
  18. Landon116

    Landon116 Member

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    Okay have a new problem- but I think it's related. I was driving home from school and it sounded like an injector went out or I had a miss fire. Then my car revved on its own, I messed with the pedal and it went higher. Throttle was not stuck ! I think something went haywire. I had to turn the car off while driving because the engine rpms were increasing to like 4500+ This could be a good hint to my problems. Help!! This is getting dangerous I think.

    I played with the gas pedal to see if it was stuck but it wasn't.
     
    #38
  19. Landon116

    Landon116 Member

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    Thanks for the great information!!
    I cleared the code 96. Probably a past issue. Anyways did you read my other post? I have a lot of backfiring when letting off the gas. Like the computer is dumping too much fuel. It smells awful rich too. What can cause the computer to think it needs more fuel ? I checked my grounds. Can removing and unplugging my emissions cause this ? I left the EGR plugged in but capped off all vacuum locations and removed the TAB and TAD solenoids because they weren't even hooked up. I made sure I had no vacuum leaks. Also is it normal to see fuel pressure drop when the engine is revved? Thanks jrichker!
     
    #39
  20. Landon116

    Landon116 Member

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    My situation hasn't improved after fixing my arcing issue and installed a proper intake. So far Ive gotten 50 miles with half a tank.. and calculating amount of fuel pumped I got about 10 mpg on a full tank. This is my daily driver.. I need to figure out what the problem is.. can you suggest anything at all ?
     
    #40

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