97 Cobra Imrc Issues (please Help Thanks)

Discussion in 'SN95 4.6L Mustang Tech' started by ppartain, May 10, 2013.


  1. ppartain

    ppartain Member

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    I bought a 97 cobra a week ago with a few bolt on mods. It has been a garage queen with 48k original miles. 93 octane and mobile 1 synthetic its entire life. Now that being said I drove it a few days ago and it suddenly acted, sounded and ran like a V6. I thought I sprung an exhaust leak (sounded funny) so after driving it to the muffler shop and realizing it wasn't that it got its first CEL come on. Hooked a hand held up and realized it had a 303 & 305 misfire. I assumed coil pack being that it was on the same half. I bought new ones but figured out how to test them and realized they test like the new ones. I cleared those codes and realized I had a 1516 IMRC code. I ran fresh 93 through with NOS octane boost and lucas fuel treatment. I also sprayed a little seafoam through the TB. Still same issue. I carried it to my local oil change place and they had larger computers and said the IMRC was stuck closed. It is off and on or sometimes its for several miles. From what I gather its the plate sticking closed that's throwing the misfire codes. I also understand ford doesn't carry the IMRC controller if its the issue? Anybody with some thoughts or links on repairs please chime in. Ive heard of a delete kit but with 410 gears and 19mpg I hate to lose more gas mileage. I hate to remove the entire upper and lower and not have needed to. I guess ford can diagnose a little deeper im not sure. Does these open all the time? I thought they only opened at 3250? Also they didn't want to do a fuel system flush because neither vacuum line looked to atomize to all ports. thanks guys
  2. wmburns

    wmburns SN Certified Technician

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    FWIIW, a stuck IRMC isn't going to cause a misfire. Always focus first on the misfire DTC codes before working on any other DTC codes.

    If the IRMC is stuck closed, this will cause power loss at higher RPM.

    If the IRMC is stuck OPEN, this will cause poor throttle response at low RPM's.

    Also remember that a bad/clogged/stuck fuel injector can also cause a misfire. Use a "noid" style test light to confirm a firing "pulse" on the fuel injector.

    My vote is a coil pack issues since for the V8, #3 and #5 share a coil pack circuit.
  3. ppartain

    ppartain Member

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    well maybe its stuck open at times. it was idleing low/rough has no throttle response ar low rpm. just like a v6. I figured the ports acting up would cause a misfire. So does the IMRC stay 100% closed until 3250?
  4. ppartain

    ppartain Member

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    sounds like a V6 with flowmasters when its acting up. Runs like it too.
  5. ppartain

    ppartain Member

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    I tested the primary and secondary resistance on my factory packs. they were in spec and matched the new ones. I took them back thinking that wasn't the problem.
  6. trinity_gt

    trinity_gt Advanced Member

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    Keep in mind that a resistance check with a standard VOM will only tell you part of the story. A coil with decent windings will show good resistances but a failure in the insulation that breaks down at 1kV or so will not be detected by this test.

    At the very least swap coils left and right and see if the problem follows the coil or stays on those cylinders.
  7. ppartain

    ppartain Member

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    MY LATEST UPDATE : I swapped coil packs and made no difference. I just removed the tower brace so I could get my hands on the IMRC linkage. Now I cranked the car and it was sounding/running like it was on 6 cylinders. I assumed IMRC problems but I opened them up by hand and I heard maybe a little more air flow but no change in running. Now im guessing the issue is something else. I may have a IMRC problem but its not whats causing the 303/305 misfire codes and the not running on all cylinders sound. The car has MSD digital ignition box. Could the box be an issue? I would think it would cause problems on all cylinders. Thoughts? Getting frustrated lol.
  8. wmburns

    wmburns SN Certified Technician

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    Consider using a "noid" style test light to confirm a firing pulse on the coil primary. While you are at it, also confirm the firing pulse to the fuel injector.

    Inspect the electrical connector on the primary coil side. Look for bent/pushed pins.
  9. ppartain

    ppartain Member

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    took it to the dealership today and they hooked it up and found the IMRC controller to be bad. said it would cause misfires. now to delete or not?
  10. Clayton302

    Clayton302 Member

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    I mod everything so I may not be the best to answer but I say delete them. The car will not loss much or even noticeable low end. We did it on my bothers car years ago and it ran better without. It's a restriction above 3000 or so RPM even if its working right. Although on a stock car the restriction is small.

    Now with all that being said if it were me in your shoes and I could fix it without pulling all the manifold off and stuff I would fix the IMRCs and leave them on. Also you might want to check with a tuner to see if any adjustments are needed to air to fuel or with possible codes from the IMRCs being removed.
    http://www.lethalperformance.com/96-98-svt-cobra/induction/imrc-delete-plates

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