Check Engine Light Help

Discussion in 'Fox 5.0 Mustang Tech' started by SFC_R0CK, Nov 1, 2008.


  1. SFC_R0CK

    SFC_R0CK Member

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    I have searched all the forums and maybe I just did not use the right keywords or phrase but I could not find an anwser to my question. And sorry if this is not posted to the right spot. Also sorry for the length just trying to provide enough information.

    I have another good technical question for the 5.0 Mustang Forum. First a little background on the situation, I picked up a four cylinder 89 Notch for 600.00 minus the motor and trans and performed a V8 swap (AER manufacturing 306 long block, FRPP E-303 cam, FRPP 1.6 rockers, FRPP 24 lb injectors, 70 mm TB, FRPP Tubular intake, BBK shorty headers, H-pipe, MSD billet distributor, MSD A6L, MSD coil) replaced the computer with an A9L, complete engine wiring harness, fuel injector harness, headlight wiring harness with a 3G alternator upgrade, all were from an 89. None of the harnesses have any splices or repairs made to them other than where I adapted the alternator upgrade, all sensors, switches were installed new.

    And now the Question, I get a check engine light coming on after driving it 10-20 minutes, if you shut the car off and start it right back up it does not come back on until after 10-20 minutes again and the local auto shop is unable to pull any codes because they cannot communicate with the computer. I switched the computer out from 89 notch with my 89 convertible and they can read it there fine. The car runs fine until the check engine light comes on then it runs sluggish. I drove the car for about 300-400 miles before check engine light problem started.

    Any help on this is greatly appreciated.
  2. FrankenStang

    FrankenStang Mustang Master

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    Moved to tech.
  3. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    There's info here for pulling codes. Let us know what code(s) are being thrown.

    One other thing that is probably covered but I didnt see noted in your post:

    Do you have a means of letting the EEC know you have 24 pound injectors?
  4. MuDDuQ

    MuDDuQ New Member

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    My best guess would be change the EGR valve
  5. SFC_R0CK

    SFC_R0CK Member

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    I forgot to mention the 70 mm TB is a C&L with the tube for 24 lb injectors. The problem is I took it to a shop to have the codes causing the check engine light pulled and they can not communicate with the computer. I swaped the computer from the 89 notch to an 89 convertible and they could read it fine. They could not tell me why they could not pull codes from the 89 notch. So right now I can not get any codes. But the car runs fine until the check engine light comes on then it runs sluggish after that.
  6. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    So what you're saying (I think) is that you have some wiring issue keeping you from retrieving codes in your notch. You have confirmed that the EEC itself can spit codes if it's put into your vert. Correct?

    Have you tried using a test light to pull codes? This removes some complexity/variables.

    Additionally:

    Here's some info for if you cannot retrieve codes
  7. SFC_R0CK

    SFC_R0CK Member

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    Yes, I believe it is a wiring issue but had no idea exactly how to check the harness. No, I never tried a test light since the shop could not get their scanner to work, plus I never used a test to get codes before. Thanks for the link it will probably take me a couple of days to check that list completely. I will post what I find.
  8. SFC_R0CK

    SFC_R0CK Member

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    Ok here are the results of the tests I have done so far, I am not that good with electrical stuff.

    Battery voltage : 12.7v
    Battery Connections: All new and clean, and tight.
    Alternator output: between 13.5 and 14.5 volts
    Any recent voltage irregularities: No
    Make sure pin 30 on the computer is hooked up correctly: factory 1989 wiring harness no mods.
    Check aftermarket devices: None, No chips.
    Disconnect computer and inspect for damage: None found
    Visually inspect the ENTIRE engine and computer wiring: All new sensors and harness was retaped when installed less than 300 miles ago.
    Check Self-Test Input circuit on Pin 48: shows OL on mulitmeter.
    Measure resistance between battery negative post and pins 20, 40, and 60 at the computer harness: pin 20 = 5.9; pin 40 = 5.0-5.2; pin 60 = 5.0-5.1
    Turn key to ON with engine OFF and computer removed. Measure voltage on pins 1, 37, and 57: pin 1 = 12.08v; pin 37 = 12.10v; pin 57 = 12.10v
    Measure resistance between Pin 46 and Pins 40 and 60 at the computer harness: pin 40 = OL; pin 60 = OL
  9. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    I dont think some of the tests were done correctly. When doing resistance testing, the device is divorced from power supplies. For instance, when you check Pin 48 (STI), you set your meter to read resistance and then put one lead on each end of the wire. One meter lead would go to pin 48 on the EEC connector (with the connector disconnected from the EEC) and the other goes to the STI terminal itself.

    If you did that correctly and still read infinite resistance, you have found an issue and should address it.

    The test between 46 and 40/60 also appears to have failed.


    What was the reading between 26 and 46?

    This diagram should be close to your vehicle's circuitry and might help.
  10. SFC_R0CK

    SFC_R0CK Member

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    Ok I retested these

    48 to 48 = 0.00

    26 to 46 = 5.03

    Where do I test 46 to 40/60?

    Thanks
  11. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    Does 48 to 48 read 0.0 or open circuit? I have the feeling it's the latter.

    You check resistance between 46 and 40, and then between 46 and 60. 40 and 60 are power grounds.
  12. SFC_R0CK

    SFC_R0CK Member

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    Pin 48 to 48 = 0.00

    Pin 46 to 40 = OL
    Pin 46 to 60 = OL

    Thanks
  13. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    Something is probably up with your 48 to 48 continuity. I haven't had a meter show 0.0 OHms of resistance for a run of any sort (copper conductors intrinsically have resistance).

    Have you made sure that 40 and 60 have less than 5 ohms when checked between each individually and their other end (the sheetmetal ground near the battery)? You can see the sheetmetal ground in front of the battery. The ground for these wires has a cylinder-looking connector on it. Check the resistance of 40 and this grounding point. Then check 46 and this ground point.

    If 46 and 40, and 46 and 60 cannot achieve continuity, the issue is likely inside the EEC (power was applied to the circuit and the board burned).
  14. strtrcr50

    strtrcr50 New Member

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    My car will not pull codes with a scanner but will with a test light..:shrug:
  15. SFC_R0CK

    SFC_R0CK Member

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    Pin 48 to 48 = 000.1
    Pin 40 to GP = 000.0 had to use an extender wire and its not copper
    Pin 60 to GP = 000.0 had to use an extender wire and its not copper
    Pin 46 to GP = OL had to use an extender wire and its not copper
    Pin 46 to 40/60 on the connector = OL

    The computer can be read if it is in another car with no issues.
  16. SFC_R0CK

    SFC_R0CK Member

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    I just ran the KOEO test using a test light and this is what I got

    67 = Neutral safety circuit failure (Car only starts in park or Neutral)
    85 = Canister Purge Solenoid circuit failure (Not installed)

    Would these 2 codes account for my orginal problem with the check engine light coming after driving it 10-20 minutes, if you shut the car off and start it right back up it does not come back on until after 10-20 minutes again. The car runs fine until the check engine light comes on then it runs sluggish after that.

    I am gonna go drive it till light comes again then run another KOEO test and see if I get anything different.

    Thanks for all the help so far.
  17. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    Neither code should affect performance.

    I would do a KOER test. You might need to remedy 67 first. Be sure the HVAC selector is turned off.
  18. SFC_R0CK

    SFC_R0CK Member

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    Ok just drove the car and redid the KOEO test and these are the codes it came up with this time.

    22 = MAP/BP sensor out of self test range.
    35 = PFE or EVP circuit above the maximum limit of 4.81 volts.
    51 = ECT sensor signal is greater than the Self-Test maximum of 4.6 volts
    53 = TPS circuit above maximum 4.5 volts
    54 = ACT sensor signal is greater than the Self-Test maximum of 4.6 volts
    67 = Neutral safety circuit failure (Car starts only in Park or Neutral)
    85 = Canister Purge Solenoid circuit failure (Not installed)

    ECT, TPS, ACT all are new and have less than 300 miles on them.

    PFE or EVP I am not sure what it is.

    Thanks
  19. SFC_R0CK

    SFC_R0CK Member

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    HVAC selector was turned off, I do not have AC installed.
  20. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    It would seem you still have an issue with the sig rtrn (pin 46).

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