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The Parts Guy
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Discussion Starter #1
I just have three quick questions. I'm installing a RPM switch to control the IMRC's on my 4.6L DOHC. First, where should I get the tach feed signal? I was thinking of splicing into the wire that goes to the factory tach. Second, on a 94 Mark 8, do I need to open the circuit to the IMRC control valve to open the IMRC's or do I need to close the circuit to open them? Basically, does the IMRC control valve require power to keep the IMRC's closed, or does it require power to keep the IMRC's open? Finally, does anyone know the factory rpm at which the IMRC's open?

Thanks,
Rod
 

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The IMRC sol. valve is energized to port vacuum to the actuators. So vacuum holds them shut until the rpms reach 3000 plus or minus 100. When the said rpm is reached the sol. valve is grounded (deenergized) which allows the vacuum to be bled off and the IMRCs spring open. The fail mod for the setup is open. Just the opposite from a Cobra or 97/98 Mark where they fail shut.
 

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The Parts Guy
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Discussion Starter #3
Thanks Lonnie. So I need to open the circuit at 3000 rpms to open the IMRC's, right?

-Rod
 

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Yes, it needs to be energized (closed circuit) to port the vacuum and hold them closed. Then deenergized (open circuit) to release the vacuum and allow them to open.
 

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The Parts Guy
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Discussion Starter #5
Thanks Lonnie, I just hooked it up. Just need to find a wire to get a tach signal from, then the IMRC's are ready to go.

-Rod
 

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The Parts Guy
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Discussion Starter #6
Does anyone know of a problem with splicing into the tach feed signal wire (wire # 648, W/PK) behind the instrument cluster for a tach feed signal? My only concern is that it could possibly damage the EEC.

To those of you who have used a RPM switch to operate the IMRC's: Where did you get your tach feed signal from?

Thanks,
Rod
 

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Which one do you have? I normally run the white wire to any of the neg (-) trigger wires at the coil pack.
 

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The Parts Guy
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Discussion Starter #8
The switch I'm using is the Summit RPM switch. It's pretty much the same as the MSD version (as far as wiring goes), but it doesn't require RPM pills to adjust it.

Do you think everything would be ok if I spliced into the tach feed wire at the instrument cluster? I've already run all of the wire and soldered all of the connections except for this last one, because I'd like to be sure about this before I splice into that wire.

By the way, I'm using a 97 4.6L LX dash, EEC, and engine harness.

Thanks,
Rod
 

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It won't hurt the EEC I'm pretty sure. Some don't put out enough of a signal though so it may not work. Same with some coming off the coil pack. You'll just have to try it. If it doesn't you may need a tach driver. I ran into that with the Lincoln and one of the Tbirds. The Lincoln worked for a few days and then quit. So I had to install the tach driver. If you read the MSD instructions they say to try it without the drivers and if it doesn't work then install the drivers.
 

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The Parts Guy
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Discussion Starter #10
Thanks Lonnie, you've been a big help. I'm going to splice into the tach feed line, since I've already run the wire inside the car to the instrument cluster. If it doesn't work, I'll just hook up a tach driver.

Thanks again,
Rod
 

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Lonnie said:
Yes, it needs to be energized (closed circuit) to port the vacuum and hold them closed. Then de-energized (open circuit) to release the vacuum and allow them to open.
I'm confused and need a little clarification. Usually the only time a solenoid is activated is when it needs to change from it’s “steady” state to the alternate (least used) state. In other words, its "normal" state (open electrical circuit, no current flow though the coil) is the state that it’s in “most of the time”. Then when it needs to open or close (depending on the design of the solenoid, normally open or normally closed) something either provides voltage or ground (depending on how it's wired). That way there is only current flow during limited times and not all the time which saves heating the coil and also wear on the small springs internal to the solenoid.

So you’re saying that during normal cruising, while the IMRC’s are being held closed by vacuum (ported through the IMRC solenoid), the EEC is providing a ground and thus energizing the solenoid coil? Then at 3000, the EEC removes ground and the solenoid de-energizes and the IMRC’s “snap” open due to the flat springs on the IMRC runners.

Isn’t that backwards from the way most solenoids are wired?

Don’t get me wrong, I’m not questioning you. It just seems like that is backwards from the way most solenoids are wired. I haven’t researched the IMRC’s yet, but I just assumed that when de-energized, they would pass the vacuum to the IMRC’s and they would stay closed, then at 3K, the EEC would energize the circuit and close (or vent) the vacuum and the IMRC’s would close by the springs.

Any guesses why Ford would have current flow through the EEC when it’s not necessary? :2huh:

Oh wait, I’m trying to comprehend Ford engineers. My bad! :leftright
 

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Yes it works backwards like I stated above. It doesn't function at all like you stated.
 

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Thanks for the clarification! :thumbsup:

I didn't doubt you by any means since you have just a little experince with the DOHC. :bowdown:

I just wanted to make sure I understood it correctly. :rolleyes:

Sometimes I wonder about Ford engineers... :leftright
 

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Lonnie, I know I asked you before about this IMRC stuff, but I still have problems with my setup. I am using Cobra intake with IMRCs on my 95 Mark. I have a relay that is begin activated by the signal from the ECU. In the "rest state" (when the ground from the ECU is present = under 3k RPMS) the relay is engaged, and no power is being sent to the IMRC motor. When the ground signal is lost above the 3k mark, the relay "rests"" and sends 12v to the IMRC motor. With this setup I burned up two Johnson IMRC motors (they were wired directly, without the electronics). If I stay a lot above 3k, there is power at that little motor all the time, and it just doesn't hold up.

What does the Cobra controller box electronics do ? I was thinking of building a circuit so that once the IRMCs are open (that can be verified by the sensors inside the box), a 1ohm resistor would be run in series to reduce the load on the motor. I think the original electronics have a similar role. If I only knew what signals are sent to the controller box connector ??? there are 5 wires going to it ....

thanx in advance for any help ...
 

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What kind of amps are you running to the motor? 15 amps is what is supplied to the motor on the Cobra. I took out the electronics to my controler and ran the 12 vdc straight to the motor. It's been that way for 3 years now and I haven't burnt up anything. The electronics are part of the monitor system that sets off the check engine light. It just lets you know if one or the other IMRCs didn't open.

edit

I just looked at a drawing of the controller and it shows there are some other components in line with the power and it splits off to the a/c compressor coil. So I'm thinking that may be part of the a/c cutout instead of having a WOT a/c cutout. But other than that it shows nothing else. It doesn't mean that there isn't though.
 

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Well, I think I got it figured out. Apparently, when you send 12V to the controller via the electronics, first it sends full 12v 15A to the motor, but a split second later, I believe it minimizes the Amps, since the motor doesn't provide the full tension to the mechanism, just enough to hold them open. I am using the signal in/out and a LED inside the cabin to verify if they IMRCs in fact open up. Now if only there was a parameter in the EEC IV to move the opening point a bit, or have them open only at WOT, it would be perfect. :( :( :(
 

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The Parts Guy
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Discussion Starter #18
I know I'm bringing up an old post here, but here's what is going on:

Apparently the tach signal wire behind the instrument cluster didn't give enough of a signal for the rpm switch. So tonight I tried using one of the negative trigger wires at the coil pack, with the same results. I'm guessing it's time for a tach driver.

Which of these two tach drivers would you choose (if there is any benefit to either)?

MSD Tach Driver

Ford Racing Tach Driver

Thanks,
Rod
 

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Now if only there was a parameter in the EEC IV to move the opening point a bit, or have them open only at WOT, it would be perfect.
There is in the SCT software. Only problem is a lot of others have tried to set it at different rpms thinking they could out smart the Ford Engineers and ended up running slower or ill results. There's also fuel and timing tables that have to be changed to make it all work. Lots of trial and error.
 
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