Cold Start And Koer Help

Discussion in 'Fox 5.0 Mustang Tech' started by Keith5.0GT, May 31, 2017.

  1. Hello, this is my first attempt using this site. I have been going through the extensive idle guide on this site. I'll cut to it. 1990 gt 5spd. Cold start the rpms go up and drop to 500 then stall. I have to rev it while it stumbles to keep it running. Once warm (in a few minutes) I have no trouble. I have no koeo codes now. Koer codes now are 21,33,41,91. I have tps adjusted, timing set, new plugs/wires/ect/iac/thermostat/egr/egr sensor. Egr sensor I had to shorten the rod to get proper volts and get rid of a koeo code. Also did clutch and other unrelated things. So the cold start is my problem. Koer codes to help. I also cleaned the 10 pin connectors. They were good but the prongs for the "VREF" and "o2sensor heater ground" looked a little darkened. One last note, when I tried to start with iac and spout unplugged it wouldn't, but I unplugged the MAF and it fired right up. I have since re-set the idle after removing the iac spacer plate to see if it helped but the lack of plate made more adjustment needed. This has been a 4 month pain in the butt for me and I'd greatly appreciate help. Thanks!
     
  2. Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.

    Revised 6-Apr-2017 to add diagrams and resistance check for ECT wiring.

    Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error. Warm the engine up until you get good hot air from the heater and then dump the codes again.

    The computer Engine Coolant Temperature sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the passenger side front of the engine in the water feed tubes for the heater. It has two wires that connect by a weathertight plastic connector.

    The water temperature sender for the temp gauge is located in the driver's side lower intake manifold. It has a single wire that connects by a push on connector on the temp sender.


    If you have replaced the ECT sensor and are still having ECT like problem symptoms, check the ECT wiring .

    [​IMG]

    See the graphic for the 10 pin connector circuit layout.
    [​IMG]


    Check the resistance of the green wire on the ECT connector to the green wire on pin 7 of the computer connector. You should see less that 1 Ω (ohm)

    The ACT & ECT have the same thermistor, so the table values are the same

    ACT & ECT test data:

    Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate readings.

    Pin 7 on the computer - ECT signal in. At 176 degrees F it should be .80 volts

    Pin 25 on the computer - ACT signal in. At 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer.


    Voltages may be measured across the ECT/ACT by probing the connector from the rear. A pair of safety pins may be helpful in doing this. Use care in doing it so that you don't damage the wiring or connector.

    Here's the table :

    50 degrees F = 3.52 v
    68 degrees F = 3.02 v
    86 degrees F = 2.62 v
    104 degrees F = 2.16 v
    122 degrees F = 1.72 v
    140 degrees F = 1.35 v
    158 degrees F = 1.04 v
    176 degrees F = .80 v
    194 degrees F = .61
    212 degrees F = .47 v
    230 degrees F = .36 v
    248 degrees F = .28 v

    Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

    50 degrees F = 58.75 K ohms
    68 degrees F = 37.30 K ohms
    86 degrees F = 27.27 K ohms
    104 degrees F = 16.15 K ohms
    122 degrees F = 10.97 K ohms
    140 degrees F = 7.60 K ohms
    158 degrees F = 5.37 K ohms
    176 degrees F = 3.84 K ohms
    194 degrees F = 2.80 K ohms
    212 degrees F = 2.07 K ohms
    230 degrees F = 1.55 K ohms
    248 degrees F = 1.18 k ohms

    Diagram courtesy of Tmoss & Stang&2birds

    [​IMG]



    Code 33 - Insufficient EGR flow detected.
    Look for vacuum leaks, cracked vacuum lines, failed EGR vacuum regulator. Check to see if you have 10” of vacuum at the EGR vacuum connection coming from the intake manifold. Look for electrical signal at the vacuum regulator solenoid valves located on the rear of the passenger side wheel well. Using a test light across the electrical connector, it should flicker as the electrical signal changes. Remember that the computer does not source any power, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.
    Check for resistance between the brown/lt green wire on the EGR sensor and pin 27 on the computer: you should have less than 1.5 ohm.

    Backside view of the computer wiring connector:
    Computer wiring harness connector, wire side
    [​IMG]

    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


    EGR test procedure courtesy of cjones

    to check the EGR valve:
    bring the engine to normal temp.

    connect a vacuum pump to the EGR Valve or see the EGR test jig drawing below. Connect the test jig or to directly to manifold vacuum.

    Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).


    apply 5in vacuum to the valve. Using the test jig, use your finger to vary the vacuum

    if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.

    if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.

    if engine stumbled, connect EGR test jig to the hose coming off of the EGR Valve.
    Use your finger to cap the open port on the vacuum tee.
    snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
    did the vacuum gauge show about 2-5 in vacuum?
    if not the EVR has failed

    EGR test jig
    [​IMG]

    The operation of the EGR vacuum regulator can be checked by using a test light applied across the wiring connector. Jumper the computer into self test mode and turn the key on but do not start the engine. You will hear all the actuators (including the EVR vacuum regulator) cycle. Watch for the light to flicker: that means the computer has signaled the EGR vacuum regulator successfully.



    Code 41 or 91. Or 43 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

    Revised 11-Jan-2015 to add check for fuel pressure out of range

    Code 41 is the passenger side sensor, as viewed from the driver's seat.
    Code 91 is the driver side sensor, as viewed from the driver's seat.

    Code 172 is the passenger side sensor as viewed from the driver's seat.
    Code 176 is the driver side sensor, as viewed from the driver's seat.

    Code 43 is not side specific according to the Probst Ford Fuel injection book.

    The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

    The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
    "When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

    When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

    Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

    Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

    Testing the O2 sensors 87-93 5.0 Mustangs
    Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear.

    Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor , you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.

    Backside view of the computer wiring connector:
    Computer wiring harness connector, wire side
    [​IMG]

    87-90 5.0 Mustangs:
    Computer pin 43 Dark blue/Lt green – LH O2 sensor
    Computer pin 29 Dark Green/Pink – RH O2 sensor
    The computer pins are 29 (L\RH O2 with a dark green/pink wire) and 43 (LH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

    91-93 5.0 Mustangs:
    Computer pin 43 Red/Black – LH O2 sensor
    Computer pin 29 Gray/Lt blue – RH O2 sensor
    The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


    Testing the O2 sensors 94-95 5.0 Mustangs
    Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


    Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

    Testing the O2 sensor wiring harness
    Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer. Using the Low Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.

    87-90 5.0 Mustangs:
    Computer pin 43 Dark blue/Lt green – LH O2 sensor
    Computer pin 29 Dark Green/Pink – RH O2 sensor
    Disconnect the connector from the O2 sensor and measure the resistance:
    From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
    From the Dark Green/Pink wire on the RH Os sensor harness and the Dark Green/Pink wire on the computer pin 29

    91-93 5.0 Mustangs:
    Computer pin 43 Red/Black – LH O2 sensor
    Computer pin 29 Gray/Lt blue – RH O2 sensor
    Disconnect the connector from the O2 sensor and measure the resistance:
    From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
    From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 29

    94-95 5.0 Mustangs:
    Computer pin 29 Red/Black – LH O2 sensor
    Computer pin 27 Gray/Lt blue – RH O2 sensor
    From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
    From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 27

    There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged and the contacts are clean and not coated with oil.

    The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

    Check the fuel pressure – the fuel pressure is 37-41 PSI with the vacuum disconnected and the engine idling. Fuel pressure out of range can cause the 41 & 91 codes together. It will not cause a single code, only both codes together.

    Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

    Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

    Code 41 can also be due to carbon plugging the driver’s side Thermactor air crossover tube on the back of the engine. The tube fills up with carbon and does not pass air to the driver’s side head ports. This puts an excess amount of air in the passenger side exhaust and can set the code 41. Remove the tube and clean it out so that both sides get good airflow: this may be more difficult than it sounds. You need something like a mini rotor-rooter to do the job because of the curves in the tube. Something like the outer spiral jacket of a flexible push-pull cable may be the thing that does the trick.

    If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.





    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
    (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

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

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

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    Vacuum diagram 89-93 Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg
     
    #3 jrichker, May 31, 2017
    Last edited: May 31, 2017
  3. Thanks a lot for the response. I've been going through your checklist. It just gets intimidating for a noob but I'll try to deal with the wire tests and everything. I've learned a lot about the car over the past 4 months. I'm impressed that you have been on here helping people for this long. Lots of good info here.
     
  4. He is the merlin of mustang information, he sits at an old desk with books covered in cobwebs stacked up and waves a magic mouse all while wearing a pretentious hat. :jester:
     
    Keith5.0GT and jrichker like this.
  5. If youbran the codes with engine cold, the code 21 could be false. Generally engine needs to be hot before running codes. That will eliminate a false 21.

    Code 41/91 are o2 sensor codes meaning lean conditions on both sides. If could be the sensors, or a huge vac leAk.

    What are the mods on this car? Has the intake been changed? Any chance one of the lower intake gaskets slipped
     
    Keith5.0GT likes this.
  6. Thanks for the response. I did check for codes cold and when i checked today after driving and warm, code 21 was gone. just had 41,91,33. so ill list my few mods, but i will say first, the lower intake did leak so i changed the gasket and used black rtv in the front and back like they show in the lmr video. unfortunately its leaking oil again! could that cause any problem? that is my only leak.....right now. so mods are cold air intake, trick flow upper and lower intake,mac headers and exhaust, adjustable fpr, pulleys.....thats about it i think. but I've been learning and working on it for the 4 months since i bought it.
     
  7. When you use the rtv on the front and back walls you have to make sure its very clean and let the goo flash, a little extra in the corners where the intake gasket tab meets the wall. 1/4 inch thick and I run my finger along the edge to smooth it to kind of a crown in the middle of the wall, it also makes sure the rtv 'sticks' to the wall.
    I've used the new style blue rubber ones that have ears that hold them on the wall with a skim cote of rtv to hold it still, again letting it flash before installing the intake, I also use 2 threaded rods to guide it on straight.
     
    Keith5.0GT likes this.
  8. If there is a vac leak on the lower intake, it could be the source of your issues and causing both o2's to read lean due to drawing in air from the lower to block seal area.

    You can try and do a check with carb cleaner for vac leaks.
     
    Keith5.0GT likes this.
  9. one thing id like to run by you all that I'm interested in. If i cold start it, it dies. but if i cold start it with the maf unplugged, it starts and runs fine. if its running for a bit with the maf plugged in and i unplug it, there is no change. so i don't have an engine code for the maf but could it be bad? or maybe a sensor that depends on it?
     
  10. I think you need to look for a vacuum leak, I don't think the maf is malfunctioning without a code show'n up
     
  11. Cold start is open loop computer operation with a minimum sensor input. The computer relies on preset tables to calculate the air/fuel mixture.

    Once the engine coolant temp rises above a preset point, it switches over to closed loop and uses data from all the sensors to calculate air/fuel mixture.
     
    Keith5.0GT likes this.
  12. ok thanks guys. this car has been a pain. fun. but a pain. i'll get back to messing with it soon.
     
  13. When you unplug the MAF, it's running in s sort of "safe mode" that tends to be richer. This is prob why it runs.

    I'd troubleshoot for a vac leak around the intake seal. Could also be a slipped intake gasket drawing air from inside the engine through the PVC system
     
    Keith5.0GT likes this.
  14. That makes sense. I'll take the intake back off in the next few weeks. Hate that it's leaking all over my hard work. But I bet it's easier the second time!
     
  15. Alright I'm finally back to the stang. My ect with coolant temp at 75 degrees shows 4.5 v in back of plug and 29.5 ohms on sensor. The volts seem off from the chart so I'm not sure where to go from here....
     
  16. Replace the sensor, it isn't expensive or difficult to do.
     
  17. It is a new sensor I just put on. But maybe defective? Got more data at 114 degrees 1.7 volts at plug and 6.4 ohms at sensor. Gotta check chart but I think the ohms I'm getting are a good bit off but volts are ok.
     
  18. Y
    yeah the ohms are too low.... Hmm
     
  19. What is the scale on your meter? It should be set to K ohms, KΩ or Kilo Ohms

    Some meters autorange, they set the scale for you. In that case it probably has something like KΩ on the display.
     
    #20 jrichker, Jun 12, 2017
    Last edited: Jun 12, 2017