IAT Relocation and IMRC Delete Project

This page is to document my project to relocate the Intake Air Temperature sensor and to delete my IMRCs.

For those of you coming here to find the threaded IAT sensor part number, it is: F6SZ-12A697-A, thanks to Chingon on Modular Fords.  The full number on the parts box is: DY-754 F6SZ-12A697-A SENSOR, thanks to Toasty on SVTPerformance:

I was unhappy with the KB kit for my 96 Cobra because the IAT sensor was left in the stock location.  As a result, the tuning must be very conservative because the actual intake air temperature after compression heating is unknown.  And the fact that this kit has no room for a heat exchanger means no intercooler, which exacerbates the problem.  This led me to the decision to pull the supercharger off the car to relocate the IAT sensor into the intake manifold, after the supercharger.  I bought a Roush threaded IAT sensor from Frontier Ford.

I also thought about how the IMRC system works and came to the conclusion that I wanted to do an IMRC delete as a part of this project.  The rationale is as follows. (I am an electrical engineer, so my analysis is based on my understanding of transmission lines, which behave in a very similar way to intake runners and exhaust headers.)

When the intake valve opens, and the piston moves down, it creates a relative vacuum that starts a vacuum pulse going back up the intake port and runner.  The relative vacuum pulse is ended when the valve closes.  The time the valve is open determines the length of the vacuum pulse.  It takes a little time to travel up the runner till it hits the open plenum.  When it hits the open plenum, there is a major impedance change that acts like an open circuit in an electrical transmission line.  When the pulse hits the plenum, it causes the pulse to flip upside down and travels back down the runner as a pressure pulse.  If the length of the runner is correct for the valve timing, the pressure pulse hits the intake valve when it is open again, forcing extra air into the cylinder, and then the cycle starts all over again.  That is why long runner are good for the lower RPMs and shorter runners are good for higher RPMs.

If the vacuum pulse gets reflected as a pressure pulse, and it hits a closed valve, it is reflected without flipping the pulse upside down, in the same way a signal on an electrical transmission line reflects from a short circuit.  So when the pressure pulse hits the open plenum, it flips again and bounces back as a vacuum pulse.  If this reflected vacuum pulse hits when the intake valve is open, it will retard the flow of air into the cylinder, actually reducing the power the engine can make.

11/09/08:  For those who read my older page, I was mistaken about the way the 96-98 Cobra intake runners worked.  The way it really works is that there is one runner for each pair of intake ports.  At low RPMs, the IMRC system closes one of the ports on each cylinder, causing all of the air to enter the cylinder through only one valve, increasing the velocity of the gas, which promotes better AF mixing and more air being driven in to the cylinder.

So what happens when you install a Kenne Bell blower with an Open House manifold?  The runners are gone, resulting in the ports in the head as the only runner length to deal with, resulting in extremely short runners, so short that the effect is not in play.  As a result, you should not see a loss of low end torque by doing an IMRC delete after you have eliminated the runners in the intake manifold.  In fact, you should pick up extra torque at the lower end by doing an IMRC delete with a twin screw blower because the pressure goes up at low RPM with a twin screw, and you will get more air into the cylinder with both ports open.

This is the rationale for doing the IRMC delete at the same time as relocating the IAT sensor.  That and the fact that my IMRCs were sticking on a regular basis, causing a CEL every time was driving me crazy.

Since I run SCT's ProRacer Package with an Xcal2, I can do any necessary tuning, including the IMRC delete.  The MAF transfer function is dialed in pretty well in the current tune, but the timing is very conservative.  I am hoping to be able to safely get some more power out of the engine with more air from the IMRC delete and with more aggressive spark now that the PCM will know the actual Air Charge Temperature.

Now we will get on with the documentation of the project.


0. Disable the fuel pump and start the car to bleed the fuel pressure. (Thanks to George at Apex for this tip, which was way too late for this project.)

1. Disconnect the battery

2. Drain the coolant (I tried to open the burp bung, but managed to break my Craftsman socket adapter off in it.  Grrr.)

3. Remove the oil from the blower. (The syringe worked great, BTW)

4. Unhook and remove the IAT sensor from the air pipe.  I replaced the IAT sensor with the rubber plug that came with the Volant CAI.

5. Remove the 1/2" IAC line between the air pipe and the IAC valve.

6. Remove air pipe.

7. Remove the throttle return spring.

8. Disconnect the throttle and cruise control cables from the throttle body and remove the bracket from the supercharger.  Move the cables with the bracket out of the way.


9. Disconnect PCV valve hose.

10. Disconnect the vacuum line to the top of the EGR valve.

11. Disconnect the electrical connector to the EGR vacuum regulator solenoid.

12. Disconnect the electrical connector to the IAC valve.

13. Disconnect the 5/8" hose between the IAC adapter and the lower driver's side intake manifold.

14. Unhook the hoses to the EGR transducer.  (This step was later determined to be un-needed.)

15. Unhook the TPS electrical connector.

16. Remove the alternator top bracket.

17. Unhook the boost hose.

18. Remove the water tube.

19. Remove the serpentine belt.

20. Remove the alternator.

21. Remove the 9 Allen-head screws and nut holding the blower and upper manifold to the lower manifold.  (I snapped off the heads of 7 of the 9 screws, it seemed as if they were completely glued in.)  They are 1/4"-20x1" grade 8 stainless steel cap screws, according to Kenne Bell.

I can't for the life of me get the blower to come off the lower manifold.  It is like it is welded on.  I've had enough for the night.


I used a big pry bar under the base of the blower snout, and carefully broke the glue loose.  My son and I pulled the blower off the intake manifold and set it aside.

22. Unhook the electrical connector the the fuel pressure gauge (If yours is so equipped.)  Bleed the fuel pressure if you haven't done so before you started the project.  I had to loosen the fuel pressure gauge sender to see that the pressure had bled off since the car had been sitting for a few days.

23. Remove the fuel injector wiring harness standoffs from the intake manifold studs.

24. Remove fuel injector electrical connectors.

25. Unhook the vacuum/boost reference hose on top of the fuel pressure regulator.

27. Using a fuel line connector tool, disconnect the fuel supply line and the return line from the fuel rail.

28. Remove the fuel injectors.

29. Loosen, but don't remove, the two black inside manifold bolts.  Loosen the 9 bolts and one nut that hold down the intake manifold in the reverse order of the torque sequence shown in the KB installation manual.  Remove all 11 bolts and one nut.  Lift the intake manifold up and lay it on top of rags on the passenger side valve cover with the IMRC motor still connected.  Pop the IMRC cables off the IMRC linkages and fish the lines free.  Remove the intake manifold from the engine bay.  Remove the intake manifold gaskets, making a note of their orientation for reinstallation.  Remove the IMRCs.  Remove the IMRC gaskets, making a note of their orientation for reinstallation.  Remove the IMRC motor from the bottom of the intake manifold.

30. Wipe the IMRC mating surfaces around the intake ports on the heads clean with a rag.  Here is a trick you have probably never heard of.  Rather than using masking tape (which is weak) or duct tape (which leave a nasty gooey residue when removed), use gaffer tape to cover the intake ports on the heads.  The gaffer is the sound guy you see in the credits of movies.  Gaffers are the guys that handle the microphones and gaffer tape is the tape they use to tape their cables to the floor.  It looks almost identical to duct tape, but is comes off the cables easily without leaving goo, so the cables can be reused over and over.  Gaffer tape is a little expensive, but it works great.  I found some at my local Orchard Supply Hardware.

At this point we are ready to clean, clean, clean everything, and do the IMRC delete, and machine work to relocate the IAT sensor.


I looked at the IMRC motor and cables.  The IMRC motor looks like it is in good shape, but one of the cables (Passenger side) was pretty badly frayed very close to the valve end.  I suspect this was the cause of my sticky IMRC CELs.

31. I used a torch to heat up the lower manifold near each broken bolt.  While each one was hot, I used a vice-grip to get each broken bolt out, no problem.  I then cleaned the lower intake manifold.

32. Clean the mating surface of the upper manifold cover.  I used gaffer tape to cover the blower hole to keep it clean.

33. Clean the top side of the blower.

34. Remove the hex plug that is right behind the boost gauge fitting, and move the boost gauge fitting to the hole that the hex plug was in.  (finger tight)  This will make room for the machine shop to drill the IAT sensor hole offset but on top of the existing from hole.  Note: The IAT sensor I bought is the Roush Performance threaded ACT sensor for the F150.  The Ford part number is F6SZ-12A697-A, thanks to Chingon on Modular Fords.  The instructions say to torque the sensor to 18-26 foot-pounds.

35. Buy three 1/2" long 1/4", 28 thread pitch (fine thread) hex bolts.  These bolts will replace the bolts used to hold the IMRC motor.  Reuse the lock washers from the IMRC mounting bolts.  These bolts will seal the three holes in the bottom of the intake manifold.

36. Clean each of the fuel injectors.

37. Clean the fuel rail.  (There was tons of sticky red goo on mine.)


38. I cleaned the top of the engine, including the valve covers and the firewall since I had access to places that I can't normally get to.  Then I dismantled and cleaned the IMRC plates in preparation for the IMRC delete.  I documented the process here.

4/16/07: Dropped the blower off at the machine shop for drilling and tapping.  Dropped the IMRC plates off at the shop for TIG welding.  Hurry up and wait.

Edit 7/9/08: Toasty over at SVTPerformance.com did a good writeup on how he did the  drilling and tapping for the threaded IAT sensor:

You need to offset drill the existing boost port at the front left corner (looking from front) for the screw-in IAT sensor.

EDIT 1/10/14: My original web page showed the IAT sensor hole to be a 5/8" NPT hole, but I was in error. Apparently the hole is 3/8" NPT. Get the threaded IAT sensor before you drill to ensure you drill the correct sized hole and that you tap it with the correct pipe threads for your sensor.

I removed the baseplate from my KB, snipping the safety wire in the process and used a friends drill press to carefully and SLOWLY *offset* drill the new hole for the screw-in IAT.

The screw-in IAT referenced in the link above requires a 3/8" NPT *PIPE* tap to get the sensor to screw in correctly. A pipe tap is different from a normal bolt tap - I had to buy a special tap at about $25 to complete the job. Pipe taps cut the threads in a tapered fashion (narrow at bottom of hole, fat at top), so if you do this task yourself, don't run the tap too far past the bottom of the plate when tapping the hole - it will eliminate the 'taper' and lead to poor sealing.

Once the hole was carefully offset-drilled and tapped, I reinstalled the SC on the base plate, using some hi temp red silicone and torquing the capscrews to 21 ft-lbs, and then re-installing the safety wire (per KB's tech line). I bought 10' of safety wire from a local motorcycle shop (seemed to be the only people around that would sell me less than a 2lb spool). Safety wire is not normal mechanics tie wire - its a lot stronger and is made from stainless steel.

If you aren't comfortable drilling and tapping the hole yourself, take it to a machine shop and pay.

1/10/14 Edit: Others have placed the IAT sensor immediately below the blower outlet on the bottom of the Open House lower manifold. In my opinion you will get slightly more accurate readings there, but the tradeoff is that you will need to remove the blower and manifold if there is ever a problem with your IAT sensor. But they rarely fail so you decide where you want to put yours.

4/18/07: Got the welded IMRC plates back today, but no time to start grinding on them tonight.  Dang day job!  At least I got pictures posted on the IMRC delete documentation.

4/19/07: I got the rough grinding done on one of the plates and finished the fine work on the first port.  When I went to the second port on that plate, I noticed that I had broken through the hole on one side of the port.

4/20/07: I got the shop to re-weld the hole I had broken through on.  I also picked up the blower up from the machine shop with the IAT sensor hole nicely drilled and tapped.

4/21/07: I finished the passenger side IMRC plate.

4/23/07: I finished the driver's side IMRC plate.

4/24/07: If you have aluminum IMRC plates TIG welded, the plates will be warped.  You should have the plates milled flat again.

39. Put the 1/4"-28 (fine thread) 1/2" hex bolts into the IMRC motor mounting holes in the bottom of the KB manifold.  Use the red Anaerobic gasket sealer on the bolt threads.  Use lock washers.  Torque to 71-106 inch-lbs (6-9 ft-lbs).

40. Wipe off the cylinder heads, gaskets and IMRC plates.

41. Install the upper IMRC gaskets and IMRC plates on the upside down KB manifold using the two outside, middle bolts.  Tighten them finger tight.

42. Lay the lower IMRC gaskets on the heads.

43. Put the manifold and IMRC plates onto the heads as a unit.

44. Install the two black bolts inside the manifold, finger tight.  Tape up the intake ports to keep the crap out of the intakes.

45. Install the remaining 8 intake manifold bolts finger tight in the same places they came out originally.

46. Torque the 10 manifold bolts to 15-22 ft-lbs using the KB torque pattern:

47. Torque the 2 outside center bolts (that held the IMRC plates to the intake manifold) to 71-106 inch-lbs (6-9 ft-lbs).

48. Lube the injector O-rings with clean motor oil and install them and the fuel rails.  Torque the fuel rail bolts to 106 inch-lbs (9 ft-lbs).

49. Connect the injector electrical connectors.  Don't forget the little red gaskets that go inside of the injector connector.

50. reinstall the injector harness standoffs to the manifold studs.

51. Reconnect the fuel pressure gauge electrical connector.

That is enough for tonight.


52. Use clean motor oil to lube the fuel line O-rings and hook up the fuel supply and return lines to the fuel rail.

53. Hook the boost line to the fuel pressure regulator.


54. Spray brake cleaner around the edges of the bottom of the supercharger. Let it sit for at least a couple of minutes.

55. Put a bead of anaerobic gasket eliminator on the manifold sealing surface.

56. Put the supercharger on the manifold.  Put the nut on the stud, and the hex cap screws around the supercharger per the KB instructions.  Don't forget to install the IAC with its bracket as you install the left front hex cap screw.  Torque them to about 10 ft-lbs.  I used a chris-cross torque pattern.

57. Use Teflon tape on the threads of the boost hose fitting.  Install the boost hose fitting.  I actually did this after installing to IAT sensor.  If I had a deep 11mm socket, it would have been ok, but I don't, so it was a pain.

58. Install the threaded IAT sensor in the supercharger hole, and torque to 18-26 ft-lbs.


59. Reinstall the generator, without the top bracket.  Torque to 15-22 ft-lbs.

60. Reinstall the serpentine belt per KB instructions.

61. Oil the O-rings on the coolant cross-over tube and reinstall it.  (Make sure you don't pinch any of the wires under it, such as the fuel pressure gauge wire.  If you do, you will get to take it off and do it over again.)  Torque to 106 inch-lbs (9 ft-lbs).  Connect the two electrical connectors to the sensors.

62. Connect the boost hose.

63. Connect the TPS connector.

64. Connect the hoses and the electrical connector to the EGR transducer on the firewall.  This didn't really need to be disconnected for this project.

65. Connect the hose from the IAC to the lower fitting on the driver's side inlet.

66. Reinstall the EGR tube to the EGR valve and the top inlet fitting on the driver's side.

67. Reconnect the IAC electrical connector.

68. Reconnect the EGR vacuum regulator solenoid electrical and vacuum connectors.

69. Reconnect the PCV hose.

70. Reconnect the front and back vacuum lines on the passenger side of the inlet.

71. Reconnect the throttle and cruise control linkage.  Use gasket eliminator on the bolt threads.

72. Reinstall the throttle return spring.

73. Reinstall the CAI.

74. Reinstall the hose from the CAI to the IAC.

75. Reinstall the top alternator bracket if so equipped.

76. Extend the IAT wire to reach the new IAT sensor location.  Solder and shrink wrap the joints, and cover with cable protector and high quality electrical tape.  Use automotive quality wire.


77. Refill the coolant.

78. Reconnect the battery. (I charged mine for a while while I was putting the final things back together.)

79. Turn on the ignition, but don't start the engine to check the fuel pressure and for fuel leaks.  I had to do this 3 times to get the fuel pressure up.

80. Install the chip or flash the PCM with the tune that has the IMRC disabled.

81. Check again for fuel pressure and leaks.

82. Start the car.  Let it warm up.  Check coolant. levels. 

Mine ran like crap at first, missing like crazy and clattering too for the first 5 minutes.  I was worried that I had accidentally dropped something into the intake.  But finally, it went into closed loop and, after a bit, it stopped missing and smoothed out.  I drove it around a bit, and the coolant level dropped, and the temperature went up to the "A" in normal, but it was an 88 degree day.

I felt like the car was significantly slower than it was before I started this project, but it was very cool when I drove it last and pretty hot today.  I also suspect that the conservative tune I have was pulling a lot of timing because the air after the blower is a lot hotter than the hot ambient air.  I let the car cool down to the point where I could add coolant.  I put the stock IAT sensor in the stock location and plugged that sensor in so I could get more of an apples-to-apples comparison regarding the IMRC delete.  I went out an ripped on it some more, and it felt to me like I had picked up a bit in low end torque, although we won't really know till we get it on the dyno.  But it ran at least as well as it used to, and stayed relatively cool, even though the ambient temperature had only dropped to 83 degrees.  So it seems it was pulling a lot of timing with the IAT in the new location.  I also should be logging to see what is going on.

I have some dyno time for a new baseline on Thursday.  I will put the old IAT sensor back in the stock location for that so I can compare the effects of only the IMRC delete.  I will then move back to the new sensor and log it to see the difference in timing between the two locations.

After that, I will be getting busy working on more aggressive timing as soon as I can get some more dyno time.


It was a nice cool night with a consistent ambient temperature of about 60 degrees, so I went out to do a couple of data logs, one with the IAT sensor in the stock location and one with the IAT sensor after the blower.  I drove around a bit on the expressway and on the freeway.  I did a couple of 4th gear WOT runs up to about 100MPH on the freeway on ramps.

I carefully compared the logs in similar situations.  The IATs varied from 60-90 degrees in the inlet pipe (a Volant CAI) and from 170-200 degrees after the blower.  So the blower at 6# seems to heat up the air by a pretty consistent 110 degrees.

Here is the log of a WOT run with the IAT sensor in the stock location in the CAI.  This is the log of a WOT run with the IAT sensor after the blower.

If you look at the timing in both logs, you can see that the PCM is pulling 8-10 degrees of spark at the beginning of the run, reducing down to pulling a couple of degrees at the end.

Now the trick is to figure out how to tweak the spark_retard_for_act and spark_retard_for_act_multiplier tables to get the best safe power for any given IAT.


We got her on the dyno this morning, and learned that the power had dropped significantly since the 324hp we recorded last year.  I assume this is because we no longer have the extra spark advance from the IMRC tables.  We added a couple of degrees of timing, and got 330hp/321tq.  Here is the log of the dyno run, and here is the dyno sheet:

You can see the slightly lower torque at the low end of the run.  If you look at the log, you will see that the actual AF is about 3% richer than commanded at MAF counts below 670.  That will be the next tweak.


I have been fighting a problem where I was getting random misfire DTCs every time the engine warms up from cold.  Then I got the opportunity to work on my tune with Rick Erdman of Amazon Racing when he visited Apex Motorsports in Santa Clara today.  He helped me to figure out how to set up my base spark tables for the IMRC delete and how to set up the ACT spark adder table for the IAT sensor after the blower.  We were able to get to 341HP/357TQ with a pretty safe tune.  I still have to check to see if the MAF transfer function is dialed in like I like it, but I am finally happy with my setup.