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Wolfys11
Well-Known Member
Im not fully sure but as far as i know, imrc doesnt change runner length but instead causes turbulance in the air to reduce flow and promote better air fuel mixing for more effevient low rpm burn
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MyStang
Well-Known Member
- Thread starter
- #3
You are right about not changing runner length.
I have been searching the web/forum for information on what happens when the system is active at startup. I have checked my vacuum solenoid, manually activated the vacuum canisters to close the IMRC valves, so I know they hold vacuum. I don't think they are getting a signal to close from the ECU. I guess my question should have been. Does the ECU tell the IMRC valves to close at startup?
Cobra Jet
Well-Known Member
The IMRC system has been in play since the introduction of the 1993 Lincoln MKVIII that came with the 4.6 4v DOHC modular V8 engine (from which the Coyote eventually evolved from as years progressed). A derivative of that DOHC evolved and was then used in the introduction of the 1996 SVT Cobra, where the engine was obviously tweaked and modified with SVT specific parts.
The IMRC system has been problematic since 93 with runners/butterflies gumming up, control motors failing, and/or as we seen with the S550’s - the IMRC runner rods breaking.
To get to the meat of your question:
IMRC's are plates that are sandwiched between the intake and heads. Again it’s been essentially the same design since 93, but obviously with technological advances and modifications over the years from Ford. The original system is comprised of butterflies that are found between the secondary intake valve ports, actuator motors and rods (design and parts used across the engine platforms again depend on vehicle platform, model years, and specific factory tuning for those specific vehicles). Those butterflies close when the vehicle is under 3250rpms (this was the baseline originally, it *may* be different for the S550’s such as a higher RPM baseline); the butterflies will then open once the RPM’s are above 3.250.
The design concept and why they were added to the DOHC (and carried forward into the Coyote variations) was to aid in and produce more low end power/torque.. So think of it this way in simplistic terms using the DOHC 96+ Cobras as an example, essentially the engine is a “2v” engine when under 3250 and once the RPM exceeded 3250, the PCM opened the IMRC butterfly flaps up, adjusted timing curves, and now the engine was a fully breathing 4v engine.
A really, really, really basic analogy:
2 barrel carb vs 4 barrel carb
The main problems with the IMRC system I had already outlined above. Usually when the PCM notices the IMRC system isn’t working it should throw off timing and should send a DTC to let you know there’s a malfunction. Sometimes the DTC pops or is present, other times it won’t blip for sporadic fluttering of the IMRC plates BUT should throw a solid when the system completely fails due to one of the reasons previously mentioned.
On a street driven untuned engine, deleting IMRCs has no gain and essentially you lose low end power/torque. On a Forced Induction setup (turbo or supercharger), deletion of the IMRCs and an obviously needed tune negates any issues on the low power/torque aspect.
If anyone is having issues with the IMRCs, there are a two great DIY “fix it” threads in here where (2) different members came up with (2) different repairs that do work.
Repair method #1:
https://www.mustang6g.com/forums/threads/possibly-broken-imrc-shaft.183221/#post-3689879
Repair method #2:
https://www.mustang6g.com/forums/threads/gen-2-coyote-repair-and-maintenance-plans.211760/
Deleting IMRCs has been around since the 4.6 DOHC era, that is nothing new. There is plenty of historical dyno runs from various Mustang platforms where the IMRCs were or were not present that can be used as reference. But essentially, if you’re going to delete the IMRCs on a street driven stock or slightly modified N/A application, the car needs a tune to really benefit from the deletion.
The IMRC system has been problematic since 93 with runners/butterflies gumming up, control motors failing, and/or as we seen with the S550’s - the IMRC runner rods breaking.
To get to the meat of your question:
IMRC's are plates that are sandwiched between the intake and heads. Again it’s been essentially the same design since 93, but obviously with technological advances and modifications over the years from Ford. The original system is comprised of butterflies that are found between the secondary intake valve ports, actuator motors and rods (design and parts used across the engine platforms again depend on vehicle platform, model years, and specific factory tuning for those specific vehicles). Those butterflies close when the vehicle is under 3250rpms (this was the baseline originally, it *may* be different for the S550’s such as a higher RPM baseline); the butterflies will then open once the RPM’s are above 3.250.
The design concept and why they were added to the DOHC (and carried forward into the Coyote variations) was to aid in and produce more low end power/torque.. So think of it this way in simplistic terms using the DOHC 96+ Cobras as an example, essentially the engine is a “2v” engine when under 3250 and once the RPM exceeded 3250, the PCM opened the IMRC butterfly flaps up, adjusted timing curves, and now the engine was a fully breathing 4v engine.
A really, really, really basic analogy:
2 barrel carb vs 4 barrel carb
The main problems with the IMRC system I had already outlined above. Usually when the PCM notices the IMRC system isn’t working it should throw off timing and should send a DTC to let you know there’s a malfunction. Sometimes the DTC pops or is present, other times it won’t blip for sporadic fluttering of the IMRC plates BUT should throw a solid when the system completely fails due to one of the reasons previously mentioned.
On a street driven untuned engine, deleting IMRCs has no gain and essentially you lose low end power/torque. On a Forced Induction setup (turbo or supercharger), deletion of the IMRCs and an obviously needed tune negates any issues on the low power/torque aspect.
If anyone is having issues with the IMRCs, there are a two great DIY “fix it” threads in here where (2) different members came up with (2) different repairs that do work.
Repair method #1:
https://www.mustang6g.com/forums/threads/possibly-broken-imrc-shaft.183221/#post-3689879
Repair method #2:
https://www.mustang6g.com/forums/threads/gen-2-coyote-repair-and-maintenance-plans.211760/
Deleting IMRCs has been around since the 4.6 DOHC era, that is nothing new. There is plenty of historical dyno runs from various Mustang platforms where the IMRCs were or were not present that can be used as reference. But essentially, if you’re going to delete the IMRCs on a street driven stock or slightly modified N/A application, the car needs a tune to really benefit from the deletion.
Last edited:
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MyStang
Well-Known Member
- Thread starter
- #5
Cobra Jet,
Thank you for the information. It's greatly appreciated. I'm professionally tuned by Wengerd My IMRC is not locked out. I'm using the VMP Mustang GT IMRC Swap Harnesses for the 2018 Intake Manifold. I tested the vacuum solenoid and it's working as expected. There is no movement at the vacuum canisters whatsoever at start up. I'm getting rough idle/ stalling at startup. No codes or check engine light. The car performs great other than start up. If the ECU tells the IMRC valves to close at startup, that would explain rough idle/ stalling, because they're not receiving the signal to close.
Thank you for the information. It's greatly appreciated. I'm professionally tuned by Wengerd My IMRC is not locked out. I'm using the VMP Mustang GT IMRC Swap Harnesses for the 2018 Intake Manifold. I tested the vacuum solenoid and it's working as expected. There is no movement at the vacuum canisters whatsoever at start up. I'm getting rough idle/ stalling at startup. No codes or check engine light. The car performs great other than start up. If the ECU tells the IMRC valves to close at startup, that would explain rough idle/ stalling, because they're not receiving the signal to close.
