CEL flashing, bad idle, severe misfire, P0302 P0316, compression test results

Discussion in 'SN95 4.6L Mustang Tech' started by evolucion311, Aug 18, 2011.

  1. Hey Bullitt, that is a great call.


    It makes sense. I didn't understand how the fuel pressure could be so high and yet the LTFT values were not big negative values as would have been expected.

    Learned to pay more attention to the coolant and IAT settings as when far out of wack, this can cause other issues.
  2. HOLY FUDGE. My cats are glowing.

    This is after about 3 minutes of idling in my garage trying to troubleshoot my misfire.

    Check it out:

    Clogged cats?!?! - YouTube
  3. Cats normally overheat for two reasons. Clogged or excessive fuel in the exhaust. This also includes exessive oil in the exhaust (possibly from blow by).

    Misfires is a ready source of excess fuel. In this case, the misfire is mainly on bank 2. So this does NOT explain the hot right hand cat.

    A clogged cat can be diagnosed by looking at engine vacuum. When the exhaust is clogged, the vacuum will not be a large as expected and it will be slow to recover. Check the Ford service manual.

    I don't see any way that clogged exhaust could cause a misfire in a specific cylinder. Nor do I see how clogged cats can cause random misfires.

    My vote is that the red cats have the same root cause as the high fuel pressure.


    Because the PCM doesn't know the true operating temperature of the motor. I suspect that the PCM is making the AF rich because it thinks the motor is cold. This is the source of the extra fuel.
  4. Burns, if you recall my bad exhaust valve in cylinder 2, the unburned fuel mixture was going straight out of the cylinder and getting into the right side cats. I think this might explain why the right bank cats would get clogged from running so rich.
  5. Ok, so the theory is the right hand cat is clogged from previous overheating and the left hand cat is overheating from the misfire on #5?

    IMO, this might be reaching just a little (unless you are looking for excuse to do an exhaust upgrade).


    While your theory is possible, it does ignore the high fuel pressure issue. Where as the "cold motor" theory does tie up the symptoms and the measurments all under a common root cause.

    You have an ODB2 scanner. IMO, you should use it to eliminate a bad IAT and/or engine coolant sensor, stuck open T-stat before moving on. These are easy fixes that if true are needed anyway.

    A vacuum gauge can help answer the clogged cat question. Then we can turn the theory into repairs.
  6. Burns as always thanks for the quick replies.

    My 02 GT doesn't have an IAT sensor, unless I'm mistaken? I thought that was a feature of the 96-98 GT engines and all SN95 V6 engines. Please correct me if I'm wrong.

    What would the procedure be for troubleshooting a bad coolant temp sensor? I can swap out a thermostat easy enough but following your philosophy, I'd like to troubleshoot and diagnose before throwing money at the problem.

    I'm not looking for an excuse for an exhaust upgrade but after 150,000 miles and this glowing, I am going to guess my cats are done for.
  7. The 02 does have an IAT sensor. It's integrated inside the MAF. The other MY Mustangs have a separate IAT sensor located in the intake tube. Further proof there is an IAT sensor is right inside the ODB2 scanner.

    The toubleshoot, cross check with reality. For example, if it's 70 degrees outside and the PCM says the IAT is -48, then you know something is wrong. Note, because engine bay temperatures are normally higher than outside air, it would be normal for the IAT to read slightly higher than air temperature.

    As for the engine coolant sensor, it's a matter of cross checking the the values that the PCM has with reality. For example, if the motor is at full normal operating temperature but the PCM says 160 degrees, then we can conclude the sensor is wrong. Note, air in the coolant crossover can cause the ECT to read low.

    If the motor is actually cold, then focus should be on a stuck open T-stat. The actually motor temperature can be determined by using an infrared scanning thermometer. Just point it at the T-stat housing.

    I do agree that the cats maybe indeed toast. I'm just trying to push a slightly different trouble shooting path. IE, Test. Think. Start simple and work up. Working up can include staring with cheap/easy repairs just because they are cheap and easy. Then it makes it easier to justify the more expensive repairs when the other "possible" causes have been ruled in/out.
  8. I use a Mac and can't load the Ford repair manual ISO I have.

    I tried to use BootCamp to load up Windows XP and since I have Mac OS X Lion I can't use XP anymore. Argh. It only works with Windows 7 now.

    Could one of you wonderful gentlemen with access to a shop manual post what the test procedure should be for testing the wiring for the MAF/IAT and coolant temp sensor?

    Also, can I check for a bad thermostat manually?
  9. Alright. The thermostat is OK, i boiled it in water and it opened and closed just fine.

    I get 4.6 volts on one of the wires going into the temp sensor and 4.6 volts on one of the wires going to the MAF.
  10. Burns, if you check out the video at the end of page 5, I took the car out for a drive on a 90 degree Georgia day. The 100-110 IAT sounds reasonable. The coolant temp is 208 or so. That also sounds reasonable.

    It is not as if the motor was cold when that video was taken. The motor had been warmed up and driven for 80 miles or so that day.
  11. Odor — described as a sulfur or rotten egg smell

    Rich fuel conditions
    Miss-fire conditions
    Excessive sulfur content in fuel
    REFER to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.

    Attach a vacuum gauge to the intake manifold vacuum source.
    Monitor RPM with scan tool or tachometer.
    Observe the vacuum gauge needle while completing the following:
    NOTE: The vacuum gauge reading may be normal when the engine is first started and idling. However, excessive restriction in the exhaust system will cause intake manifold vacuum to decrease with the engine at a steady/constant idle speed.
    Start the engine and gradually increase the engine speed to 2000 rpm with the transmission in NEUTRAL.
    Decrease engine speed to base idle rpm.
    Key off.

    Did manifold vacuum rise above 54 kPa (16 inches-Hg) with the engine speed at 2000 rpm?

    Yes:go to HF11
    NO: Manifold vacuum did not reach an acceptable level. GO to HF12 to check for excessive restriction in the exhaust system.

    Key on, engine idling.
    Increase the engine speed gradually from base idle rpm to 2000 rpm with the transmission in NEUTRAL.
    Observe the speed the vacuum gauge needle rises, while maintaining the increased engine rpm.
    NOTE 1: On a non-restricted exhaust system, the vacuum gauge needle will rise quickly to the normal range as the increased rpm is maintained.
    NOTE 2: On a restricted exhaust system, the vacuum gauge needle will rise slowly to the normal range as the increased rpm is maintained.
    NOTE 3: The rate of speed the vacuum gauge needle rises to the normal range is slower on a restricted system than on a non-restricted system as the increased rpm is maintained.
    Decrease engine speed to base idle rpm.
    Key off.
    Is the rate of speed that the vacuum gauge needle rises back to the normal range (above 54 kPa (16 inches-Hg)) much slower than that of a non-restricted system?

    Yes:A moderate restriction may be present. GO to HF12 .
    No: No indications of restrictions or leaks have been detected in the exhaust system.

    NOTE: An intake manifold gasket leak can also cause the vacuum gauge needle to remain well below the normal range.

    Disconnect exhaust system immediately after the exhaust manifold.
    GO to HF10 and repeat the vacuum measurement.
    Did the vacuum needle QUICKLY rise above 54 kPa (16 inches-Hg) with the engine speed at 2000 rpm?

    YES:There is a restriction in the muffler/tailpipe assembly. REPLACE the muffler/tailpipe assembly. COMPLETE Catalyst Monitor OBD Drive Cycle to verify repair (Refer to Section 2
    NO:There is a restriction in the catalytic converter. REPLACE the catalytic converter. NOTE: On vehicle applications where their is more than one catalyst, REPLACE only the damaged catalyst assembly. INSPECT the muffler to be certain converter debris has not entered. COMPLETE Catalyst Monitor OBD Drive Cycle to verify repair (Refer to Section 2

    Disconnect muffler/tailpipe assembly from the catalytic converter.
    GO to HF10 to repeat the vacuum measurement.
    Did the vacuum needle QUICKLY rise above 54 kPa (16 inches-Hg) with the engine speed at 2000 rpm?
  12. Hmmm. Where in the world does a vacuum gauge attach to my intake manifold. Maybe at the PCV port on the intake plenum? Not sure how I'm going to do that....
  13. If it were me, I would use the EVAP purge line (rear of TB). Don't have to worry about adding a tee. Just disconnect the EVAP line and use that TB port.
  14. So here's an update: I put an off road H pipe on the car and am now getting P0300, P0305, P0307, and P0316.

    Car runs better but it is still misfiring.

    I should mention that I can NOW hear a "ticking" over the radio that perfectly matches when the motor misfires.

    Tick tick tick tick PAUSE (misfire) tick tick PAUSE tick tick PAUSE tick tick tick tick


    Bad computer?
  15. The ignition system has two capacitors, one on each bank, located near the timing cover and rocker cover area. They look like little black cubes. You can see one on this Cobra motor. The 2V parts look the same.


    If they are not connected, connect them. If they are, you might try disconnecting them and seeing if there's any improvement. Perhaps you've got a cap that's got an intermittent internal short causing misfires.
  16. One of the causes listed is a stuck open EGR valve. What was done with the EGR system during the new exhaust system install?

    One of the other causes listed is low fuel level. Of course this could be a clogged fuel filter. How's the fuel pressure?

    Have you removed the radio interference capacitors?

    The Ford PCM pinpoint tests (JD) for the CKP sensor has a 9 step procedure to trouble shoot the CKP sensor, wiring, and PCM. A misfire has been the common theme from the start. Perhaps it's time to run that series of pinpoint tests.
  17. :nice:
  18. Ok... I finally got Windows 7 installed on my Mac so I can use the Ford shop manual. I will do a CKP troubleshooting procedure and see what is what with the black ignition capacitors. I always thought those things were simply ground connections to the engine block.
  19. Burns, I ran JD pinout tests without success, all looks to be correct.

    I have not messed with the EGR system aside from putting vacuum on it and hearing it click-cycle.

    Where are the radio interference capacitors located?