Bad Idle Surge on '88 Fox w/Mods

Discussion in 'Fox 5.0 Mustang Tech' started by dangrego, Sep 12, 2009.

  1. He ran the codes with the car up to operating temp. Only one code came up.

    If the sensors not bad then it the way he has it mounted.
  2. What new computer? How could you hook it up funky? What was the code ?
    ????? Has what mounted?
  3. The ECT sensor!!!!!!!

    Only other reason its still throwing a code if the sensors not bad, is if the Sensors signal is not reaching the ECM, therefore it will always throw a code.
  4. I'll be back on tomorrow afternoon. I need more info . What your telling me is too vague? You need to check the sensors when the coolant is at ambient air temperature, from what was posted i thought you did.
  5. Then it's not the fault of the sensor is it, but the wiring. How can you mount an ect sensor wrong?
  6. I'll check back tomorrow.
  7. Correct, If the voltage at the sensor is the same as the voltage at ECM pin 7, then its not in the wiring.
  8. I originally said the way he has it should work, have you seen how it is mounted?

  9. Take a look at the pics on the first page
  10. No, I didn't see the picture of the way he has it mounted before I posted. All I'm saying is If the coolant is at ambient air temp, the act and the ect sensors should have the same resistance as measured on an ohm meter. Just to clarify the 2 resistance measurements were taken at the prongs on the sensor, not the harness, correct. (dangrego)

    My understanding is one wire ( on the harness ) is vref voltage ( between 4.5 & 5.0 volts ), the other is vsens, correct.

    I don't know if the sensor itself needs to be grounded or not. This would be easy enough to figure out with a piece of wire or some jumper cables. The sender for the gauge does, the sensor for the eec I'm not sure.
  11. Posted via Mobile Device

    The other wire on the Sensor is the SIGRTN.

    The sensor can fail in many ways. Just because the two sensors show the same resistance, doesn't mean they are operating correctly. That's what the self test does!!

    What if the resisitance at 50* was the same as 170*?.

    All code 21 is, is a sensor out of range. Be it too high or low.

    I've been around the block more than once.
  12. Posted via Mobile Device

    Also, measuring the resistance of a cold sensor has no bearing of what the sensor is actually doing on a engine at operating temperature.

    While the resistance of the 2 sensors may be the same at ambient, it doesn't mean its within the ECMs failure code range at Op temp.

    Code 21 doesn't mean the sensors reading is too low. Code 21 could mean its on the Low Side or High Side of out of Spec. Since resistance is going to build with higher temps, its possible that at Op temp, the resistance is through the roof, therefore still logging the same code.

    Thus the reason while all tests should be done at Op temp, to simulate what the sensor is actually doing while the car is running.

    Its possible that the way the OP has it mounted, that the coolant is flowing right past the sensor. I don't know how much pressure is in the Heater core line. But....if the OP could turn the T- fitting where the sensor is pointing down, instead of up, he may get a different reading. As this would surely allow the coolant to fall down to the sensor temp probe.
  13. liljoe07- I understand what you're saying about the code 21 and ambient vs. operating temp. I've never seen that be the case before, but just because It hasn't happened to me doesn't make it untrue. If dangrego gets his engine up to operating temperature and then checked the sigrtn wire at the sensor ( just to make it easier ) , do you know a voltage range the ect should be sending back to the eec? I'm not trying to give either of you a hard time, only trying to see if the sensor is actually bad without him spending money he may not have to. You're not 100% if it's the ect or the way it's mounted. You had him check the vref voltage why not check the sigreturn voltage as well.
    I've learned alot from reading "fords fuel injection manual" and from a guy ( I believe his name is Jeff Dunn) on ford's tech line. The questions I'm asking are some of the things we checked troubleshoot the same issues I had with my car. What I learned was just because there's a code, 21 in this case, doesn't always mean it's the sensor.
  14. Posted via Mobile Device

    Your correct, but for there to be 5v reference(which is what he got) at the ECT sensor( which is checked between the VREF and SIGRTN)
  15. Posted via Mobile Device

    Your correct, but for there to be 5v reference(which is what he got) at the ECT sensor( which is checked between the VREF and SIGRTN), would this indicate a wiring problem if the voltage was correct?

    If there was a problem in either circuit, the voltage would be off.
  16. Posted via Mobile Device

    Sorry Double Post.....Blame the Blackberry
  17. Posted via Mobile Device

    Also the SIGRTN is a sourced ground from the ECM, no voltage should be present, if there is it minimal.
  18. liljoe07 - I agree with what you're saying.

    BTW - these numbers are from the ford fuel inj. manual written By Probst

    At 86 degrees F. - 2.62 volts or 24.27k ohms
    122 -DF - 1.72 v. or 10.97k ohms
    194 DF - .61 v or 2.8k ohms
    212 DF- .47 v or 2.07 ohms

    dangrego - you can check your sensor off these numbers or replace it like liljoe07 wanted you to do along time ago. I was only trying to save you money. If the sensor checks out ok and I replaced it because somebody told me to I wouldn't be happy with them. I like to know something is broken before I fix it, and these numbers will tell you if it's good or bad. Either way I hope you get it sorted out.

    I assume these numbers should be K ( thousand ) ohms, if not then it is bad.
  19. Heres a good chart regarding ECT voltages. ACT voltages apply here also.

    Im having malfunctions with the graph, please bear with me......LOL

    Attached Files:

  20. If you haven't fixed the 66 code, you're going to be chasing rabbits for a long time...