IMRC delete without re tune come in

[venom1997]

guys im going to do the imrc delete and was wondering what happens with out retuning it? I will probably retune in the future but for now im going to run it with out a retune. Btw i had a complete tune done last year so im not on fords stock tune at all. Im tuned for 12 psi boost, 23* timing and low-mid 11 a/f. Will anything change by deleting them? I will be removing contol box(actuator and anything else involved in the delete) also the fuse from under the dash.

Thanks

 

[95PGTTech]

you'll throw a check engine light, for one. on your particular combination, moving that much air, I'd get a retune. without the butterflies there you may be going a touch lean up top.

 

[venom1997]

you'll throw a check engine light, for one. on your particular combination, moving that much air, I'd get a retune. without the butterflies there you may be going a touch lean up top.

cool i will look on that i have a wide band so i will keep an eye out.

 

[venom1997]

wow i just came from out side and with a flashlight i checked (from the front of the engine at the imrc shaft/bearing) and reved the motor to 4000 rpm and held and even higher and didnt see it move. So then i pulled the fuse from under the dash IMRC fuse(so that it disables the imrc) I did the same thing and it still didnt move. I wonder if they have been stuck all this time:shrug:

 

[mwolson]

you'll throw a check engine light, for one. on your particular combination, moving that much air, I'd get a retune. without the butterflies there you may be going a touch lean up top.

You will not go lean unless your MAF transfer function is off in your tune. The PCM reads the MAF voltage and adds fuel to get it to the commanded AF ratio for your WOT run. You will not go lean with the extra air down low either, due to the same MAF transfer function, assuming it is correct in your tune. It is good that you have a wideband with which to watch it.

Spark advance is a different issue. I'll write up an explanation about how IMRCs work, as far as I know at this point.

 

[95PGTTech]

You will not go lean unless your MAF transfer function is off in your tune. The PCM reads the MAF voltage and adds fuel to get it to the commanded AF ratio for your WOT run. You will not go lean with the extra air down low either, due to the same MAF transfer function, assuming it is correct in your tune. It is good that you have a wideband with which to watch it.

maf transfer function is irrelevant if he maxes out the meter. that's why I was concerned up top and not down low. he'll also want to introduce a lot more spark advance in the lower rpms to give the tune some snap and take away some of that grunt loss that IMRC deletes experience.

 

[mwolson]

True. I am assuming he is not close enough to the top of his MAF for that to happen with the small amount of additional air coming from getting the IMRC rods out of the way. But you make a point.

Venom 1997, how close to the top are you on your MAF counts? Can you log it with your Diablosport?

I also agree with the added spark down low.

 

[venom1997]

True. I am assuming he is not close enough to the top of his MAF for that to happen with the small amount of additional air coming from getting the IMRC rods out of the way. But you make a point.

Venom 1997, how close to the top are you on your MAF counts? Can you log it with your Diablosport?

I also agree with the added spark down low.

Im not even close to maxing out my maf(pro-m) also will i have to add spark down low? im at 23* timing which is more than most run, I hope i will be fine with out a retune:shrug: Also when i had my car tuned on my dyno graph there is no jump in the curve at 3200 rpms im thinking my tuner might of used 03-04 spark tables:shrug: When i do this i will see how see reacts to the delete.

 

[95PGTTech]

True. I am assuming he is not close enough to the top of his MAF for that to happen with the small amount of additional air coming from getting the IMRC rods out of the way. But you make a point.

I would also hope not.

 

[mwolson]

IMRCs are powered by 12 volts and ground. There is a PCM output that drives to IMRC control input. That is how the PCM commands the IMRCs to open or close. When the PCM drives the signal high, the IMRCs close. When the PCM drives the signal low (ground), the IMRCs open.

The PCM needs to know if the IMRCs are both open or closed when they are supposed to be open or closed. There is an IMRC sensor input to the PCM that can read voltage. That input has a resistor on it that is hooked to 5 volt power to pull the input up to close to 5 volts when nothing is connected to the input. There are two switches and two resistors in parallel inside the IMRC controller. One side of each resistor is connected to the PCM IMRC sensor input. The other side of each resistor is connected to a switch that goes to ground on the other side of the switch. Each switch is mechanically connected to the controller end of each IMRC cable, so that it closes when the IMRC opens.

If both IMRC cables are in the "IMRC open" position, then both resistors are switched in parallel to ground, pulling the IMRC sensor PCM input down to less than 1.6 volts. This is how the PCM knows that both IMRCs actually opened. If only one opens, only one resistor will be trying to pull the IMRC sensor input down, and that is not enough to get it below 1.6 volts. This is how the PCM knows if one or more IMRC is stuck closed. If the PCM detects they are stuck, it sets a DTC.

If both IMRC cables are in the "IMRC closed" postion, then both resistors should be out of the circuit since the switches should be open. This lets the IMRC sensor PCM input go up to over 3 volts. This is how the PCM knows that the IMRCs are actually closed. If one or both are stuck open, the resistor(s) will not allow the IMRC sensor PCM input to go over 3 volts. This is how the PCM knows if one or both IMRCs are stuck open when they should be closed. If the PCM detects they are stuck, it sets a DTC.

If you remove the IMRC controller, the IMRC sensor PCM input will always see a voltage of greater than 3 volts, so it will think the IMRCs are closed, regardless of what it commands.

I do not yet know the actual values of those resistors because I sold my IMRC controller long ago and have not been able to measure one yet.

Assuming the IMRCs are working properly, the stock tune in the PCM (from my 97 LLX4 tune) opens the IMRCs above 3250 RPM and closes them below that RPM. When the IMRCs are open, the PCM adds spark using 3 tables: Spark_Adder_to_Borderline_for_IMRCs, Spark_Adder_to_Max_Allowed_Table_for_IMRCs and Spark_Adder_to_MBT_Table_for_IMRCs.

The Spark_Adder_to_Borderline_for_IMRCs table adds from 0 to 8 degrees of spark advance to the borderline knock table when the IMRCs are open, depending on Load and RPM. The Spark_Adder_to_Max_Allowed_Table_for_IMRCs and Spark_Adder_to_MBT_Table_for_IMRCs tables add from 7 to 15.75 degrees of spark advance to the Max_Allowed_Spark table and the MBT_Spark table, depending on Load and RPM. So you can see that when the IMRCs open, the PCM can add a lot of spark advance and hence a lot of power.

When you delete IMRCs using SCT, then those IMRC spark adder tables are deleted. As a result, you tuner needs to compensate by adding the IMRC spark advance for the IMRCs being open back into the Borderline Knock, Max Allowed and MBT spark tables.

Some tuners just add the values from the IMRC adder tables back into the main tables, but I don't care for that approach for a KB blower equipped car. I prefer to make my spark tables look like the spark tables from 03/04 Cobras, since we have similar boost onset characteristics, and there is no long a jump in air when the IMRCs open, so why should we have a jump in spark under those conditions.

I digress. I do not know if you lose the IMRC spark adder tables if you delete the IMRCs in the tune using other tuners such as Diablosport. I do know you can delete the IMRCs without losing the spark adder tables if you are using TwEECer.

The other thing I do not know is if the PCM does not add in the IMRC spark adders if the PCM thinks that the IMRCs are stuck closed. If that happens, you will lose power by deleting the IMRCs and not deleting them in the tune or doing something with springs or a circuit to fool the PCM into thinking the IMRCs are still there. You will also get the CEL.

 

[tt54l32v]

even if the maf transfer function is right will it make up for 20-25 horse. which is what i guess he might gain. if not more if they are dirty and he cleans the secondary valves if they are dirty. my car ran ok pre tune after deleting them, but you have to assume its lean before the switch over. how much worse will his be with a pd blower that is close to full boost or so by that rpm.
me personally i would not chance it with 12 pounds of non intercooled meth supported boost.
i have a couple of questions :how much can a mass air make up for changes in airflow
and is it just a rumor that the pcm does not look at the mass air in wot

 

[mwolson]

Since the MAF senses more air and the PCM adds more fuel up top, you will get more HP out of it, assuming the timing doesn't get retarded for any reason.

A MAF is simply a meter that puts out a higher voltage the more air goes through it. It can actually go higher than 5 volts, but the limit of the voltages that the PCM can read is 5 volts, so that is why MAF's peg. When you get a bigger MAF, you are getting a MAF that puts out 5 volts at a much higher amount of air going through it. A MAF scaler such as a MAFia just scales down the voltage that the PCM sees for any given amount of air going through the MAF sensor.

During WOT runs, the PCM normally watches the output of the MAF sensor, and, from that, calculates a value called the "Load" which is a value for volumetric efficiency of the engine at that point in time. Using that value for Load and the current RPM, the PCM looks up what the commanded AF is for that point in engine operation, and then calculates how long to turn the injectors on to hit that AF ratio. This is the table the tuner adjusts when he decides what WOT AF he wants you to have. This process works very well as the engine spins up to redline.

But as you have heard, the PCM does not always look at the MAF signal during a WOT run. The MAF does a very good job of measuring how much air is going through the MAF sensor at any given point in time, but it is not as fast as we'd like it to be. As a result, it does take a few miliseconds to respond to fast changes in throttle. When you make a fast change to the throttle position, such as when you floor it, that is called "tip-in". It takes a little bit of time for the MAF sensor to detect that a lot more air is coming in, so the engine can go lean. As a result, the PCM is programmed to notice when the driver has made a sudden stab at the throttle, and it uses a table called "Load_With_Failed_MAF" to calculate the Load during tip-in conditions, until the MAF can catch up and carry on through the rest of the WOT run. The Load_With_Failed_MAF table gives a Load value depending on throttle position and RPM. So the only time the PCM does not look at the MAF sensor during a WOT run is when you first stab the thottle.

Hope this helps clear things up a bit.

 

[PSUCOBRA96]

As of right now I am running the deletes and a shortrunner without a tune, the car seems to be running fine, not perfect at idel as I feel a slight vibration but it holds the rpm steady. I will be getting a tune very soon, and btw honestly even wihtout hte IMRC's I really havent noticed a huge drop in power under 3500, car drives smooter and Ihave stock 3.27's for now.

 

[bestbuy654]

i ran a short runner and imrc delete with out a tune for a couple weeks and every time i would pull my car out of the garage on a cold start up it would start to bog out. other then that it ran fine but not ideal

 

[95PGTTech]

As of right now I am running the deletes and a shortrunner without a tune, the car seems to be running fine, not perfect at idel as I feel a slight vibration but it holds the rpm steady. I will be getting a tune very soon, and btw honestly even wihtout hte IMRC's I really havent noticed a huge drop in power under 3500, car drives smooter and Ihave stock 3.27's for now.

because you did a shortrunner (I'm assuming 1.5 - 2 inches) and IMRC deletes, we were referencing a delete only car. my 1.5" na svt shortrunner picked me up almost 20rwhp peak and 25rwhp under the curve on my VP103 tune.

 

[PSUCOBRA96]

how much timing did you add in the tune, similar to the 03-04 cobras?

 

[95PGTTech]

I didn't tune it, rick at amazon did. since I had purchased the pro racer package from him (after the tuner and lifetime tunes), he agreed to send me unlocked files so I could see what changes he was making and learn, obviously with me promising not to share them around.

keep in mind I'm referencing my VP103 tune. which is going to be slightly leaner and a few more degrees of timing than my 93 octane tune.

 

[mwolson]

Here is my Borderline knock table. It is similar to the curves you will see with the 03/04 tune.

If you paste this into Excel and graph it, you will see that I am running it pretty retarded from 2000 to 2500 RPM for the Load lines above 0.25. You will also see that I am particularly retarded (ha!) from 750 to 2500 RPM on the 1.1 Load line. This is all a cheap and dirty way around a nasty tip-in problem I was having. I still need to fix that. In the mean time, I am getting crappy gas mileage because I cruise right around 2K RPM. So if anyone wants to use this table, you should probably bump that range up a bit to put it betweeen the lines above and below it. At least as a starting point.

Borderline Knock Table											
Load/RPM	500	750	1000	1500	2000	2500	3000	3500	4000	5000	6500
1.999	-5	-5	-2	4	5	6	6	7	8	9	10
1.699	-5	-4	1	7	8	9	9	10	11	12	13
1.399	-2	-1	4	10	11	12	12	13	14	15	16
1.0999	1	2	3	9	11	12	16	17	17	18	19
0.799	4	5	6	12	13	14.5	18.5	19.5	20.5	20.5	19
0.5	12	12	13	20	23	25	30	32	33	33	32
0.35	17	19	25	30	33	34	39	40	41	41	42
0.25	27	30	34	38	40	43	43	44	44	45	45
0.15	40	43	45	46	48	49	50	50	50	50	50

 

[venom1997]

As of right now I am running the deletes and a shortrunner without a tune, the car seems to be running fine, not perfect at idel as I feel a slight vibration but it holds the rpm steady. I will be getting a tune very soon, and btw honestly even wihtout hte IMRC's I really havent noticed a huge drop in power under 3500, car drives smooter and Ihave stock 3.27's for now.

i should be fine then(the kb is basically a very short runner) also did you pull out the actuator and fuse from under the dash? or when doing the delete is it necessary to remove the fuse?