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post #1 of 46 (permalink) Old 11-01-2012, 10:29 AM Thread Starter
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Tweaking sensors to tune modified engines

Curious first to ask if anyone has tweaked any of their sensors for mods they have done. Such as TPS, MAP, ACT, ECT.

I just wanted to share my benefits with my TPS sensor tweak. I bumped the initial voltage up to about .86-.87 volts. Stock is what? around .68? I have a max of 4.64v. Anything above that max voltage throws a CEL on my car and runs it in limp mode. I'm using a Ford tps on a 70mm tb. This is still with the Charger/Magnum intake and exhaust manifolds on my 2.7. With turning the idle voltage up, the ecm thinks the throttle is open more than it is. Man what a difference. It helped pick up my low end a lot. It also shifts at a higher rpm and shifts much more firm. And it bumped my mileage up a couple mpgs.

Seems I still have a lean condition at higher rpms. My engine falls on its face at 4,000 rpm. Usually, a 2.7 doesn't pick up till close to that. I've confirmed lean condition from pulling plugs after normal driving and after a short drive at higher rpm. I believe its from the larger throttle body and slightly better flowing manifold combination. Its just getting too much air and the stock ecm calibration just can't handle it correctly.

My solution is to tweak the MAP sensor. If I raise the voltage to it, it will richen up my fuel table slightly. A basic "MAP Enhancer" is being built. Jeep guys do this when they build stroker motors. http://jeep-xj.info/HowtoMAPsensor.htm

With what he explains about 80% throttle and below is all O2 controlled, is true for our cars from what I've noticed. My car does accelerate faster at half to 3/4 throttle than it does full. Its also noticeably faster before its warmed up(though I tend not to do this as it is hard on an engine).

Now if it does work out better, I may also make a switch to lower the coolant temp reading to the ECM so I can take advantage of it more when I want to play around.

Thoughts?
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post #2 of 46 (permalink) Old 11-01-2012, 08:08 PM
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...I have a max of 4.64v. Anything above that max voltage throws a CEL on my car and runs it in limp mode. I'm using a Ford tps on a 70mm tb...
Are you saying you need to drop the upper TPS voltage from what it is with the raised lower end? Would it help you to be able to raise the idle voltage without raising the WOT voltage? It would be easy to do using the Chrysler TPS that came with the throttle body you now have - in fact, you can get the two end points to whatever you want (with a linear curve in between). Let me know if you want to do that.

EDIT: I just came back after something occurred to me: I was under the impression that the PCM reads the idle point of the TPS at every start and also when it senses the max. WOT point, and re-calculates the end-point voltage readings for maximum accuracy of the trim profile. But I could be wrong. But if it does do that, then you shouldn't expect any significant effects of the TPS range being changed a little (because the PCM will recalibrate the curve to adjust for the changes). But maybe you've proven that there is no re-calibration by the PCM. Your response?


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Last edited by peva; 11-01-2012 at 08:58 PM.
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post #3 of 46 (permalink) Old 11-01-2012, 11:11 PM Thread Starter
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I initially had it set at .64 volts. The car shifted early and mushy. It often did the 1-2 rev. I had to step into the throttle more. Only thing I did was raise the idle voltage. I adjusted the throttle stop to keep max voltage within limit(throttle plate still opens nearly all the way). I think I need to find a way to adapt the factory tps to fit the ford throttle body. The ford tps reaches a higher max voltage.

I also reset the computer and the gain was still there with no settling out(no recal).

I am an amature in electronics.
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post #4 of 46 (permalink) Old 11-02-2012, 07:16 AM
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Ah. I thought you had a Ford TPS on a Chrysler TB.

If you are interested in *electrically* playing games with both ends of the TPS range (the one you have on there now or another one) - and without limiting the TB travel, I can tell you how to do it. Requires no modification to the TPS itself - it's done in the wiring.

Last edited by peva; 11-02-2012 at 07:20 AM.
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post #5 of 46 (permalink) Old 11-02-2012, 10:29 AM Thread Starter
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Please do.
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post #6 of 46 (permalink) Old 11-02-2012, 08:48 PM
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It would involve adding 2 variable resistors (potentiometers) - one in series with the ground wire, and one in series with the +5 volt wire going to the TPS. Stay with the TPS you have in there now if you want to.

But before you add the variable resistors, you would make some measurements. They would be:

1. With the TPS installed but the connector disconnected, measure the following on the TPS itself:
**a. Resistance from ground pin to +5V pin.
**b. With throttle at idle position, resistance from center (wiper) pin to ground pin.
**c. With throttle held to WOT position, resistance from center pin to ground pin.

2. With the TPS installed and the connector connected and the ignition on, measure the following on the wires going to the TPS:
**a. Voltage from ground wire to +5V wire.
**b. With throttle at idle position, voltage from ground wire to center wire.
**c. With throttle at WOT position, voltage from ground wire to center wire.

You would provide me with those numbers and the WOT voltage that causes the CEL/limp mode. Then we would agree on a value for the WOT voltage - one that would be just below that CEL/limp mode value - based on the 4.64 volts you mentioned in your OP, maybe go with 4.55 volts as a safe value - i.e., close to the max., but with some reasonable margin so the CEl/limp mode doesn't get tripped by small system variations (due to temperature, vibration, etc.).

From all of that information, I would develop the formulas to calculate the values of resistance to dial into the two variable resistors which would at the same time give any desired idle position voltage and the safe high WOT voltage.

IOW - you would end up with a table that would have 3 columns. First column would be a list of idle position voltages, starting with the unaltered idle position voltage that you measured before putting in the variable resistors, and then values increasing in, say, 0.05 volt increments up to, say, 1.2 volts. Then columns 2 and 3 would be the values of the ground wire variable resistor and the +5V wire variable resistor, respectively, to achieve the desired idle position voltage and the high safe (i.e., non-CEL) WOT voltage.

From there, it would be up to you to adjust the two resistors according to the table for different idle position voltages for experimenting. As you moved it further up, you would eventually hit an area of idle position voltage in which the performance/fuel mileage would start decreasing. Then you could dial it back down to the sweet spot.

Beyond that, you could either leave the variable resistors in for further experimenting, or you could replace them with optimum value fixed resistors.

If you're up for that, so am I. But I don't want to start it if we aren't going to agree take it to completion.


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post #7 of 46 (permalink) Old 11-02-2012, 08:59 PM
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I would be interested to see where this goes.
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post #8 of 46 (permalink) Old 11-02-2012, 09:59 PM
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I would be interested to see where this goes.
So am I, although I'm sure I will be drooling from confusion by the end. lol
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post #9 of 46 (permalink) Old 11-03-2012, 03:21 PM Thread Starter
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Peva, I'm all in. I've actually duplicated another circuit within the box I've made for adjusting the input voltage on the MAP sensor. I started to think about using that for the TPS and make my max return signal a safe level and then use resistors to bring the lower end where I want it. But since I don't need to adjust it once its done, I'd rather do it your way. I suppose I could use the extra modified 5v adjustment for the ACT sensor.

I want this thing running its strongest and best, but don't want to fork over the big cash to get the computer tuned. This way, I can dial it in fairly close and make future adjustments later if needed.

I have done this to some of my Ford trucks in the past, but I usually followed what others have done. I need to learn basic circuitry so I can quit bugging my oldest bro which has a masters degree in electrical engineering and an apprentice in electrical technician.

I will try to get those min and max values of the TPS tomorrow.
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post #10 of 46 (permalink) Old 11-03-2012, 06:15 PM
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I developed the formulas today - just need to test them with some mock numbers.

On the 1.b. and c. and 2.b. and c. measurements, it would be good to do each one 2 or 3 times so that you are satisfied that you are getting fraily repeatable readings on those (or average multiple readings on each one).

Last edited by peva; 11-03-2012 at 06:22 PM.
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post #11 of 46 (permalink) Old 11-03-2012, 06:30 PM
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Kay, as a serious question. Would something like this help me in my case with having a 3.5HO running off of a 2.7 pcm??
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post #12 of 46 (permalink) Old 11-04-2012, 05:42 PM
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OK - I've got my formulas fully developed and tested, and in a spread sheet ready to go.

Quote:
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Kay, as a serious question. Would something like this help me in my case with having a 3.5HO running off of a 2.7 pcm??
Might. Would probably have to try it to know.
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post #13 of 46 (permalink) Old 11-05-2012, 02:59 PM
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I will have to check it out once you guys have done it. Then it can be explained how to wire it in. I still have to re tackle and fix my autostick, my friend wound up splicing the upshift in to the cruise wire. I don't shift up, i turn the cruise light on..
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post #14 of 46 (permalink) Old 11-05-2012, 06:15 PM
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...I still have to re tackle and fix my autostick, my friend wound up splicing the upshift in to the cruise wire. I don't shift up, i turn the cruise light on..
You've got the beginnings of a Puttstick in reverse. LOL!
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post #15 of 46 (permalink) Old 11-08-2012, 06:10 PM
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Hello-o-o hell-o-o-o!
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