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Tweaking sensors to tune modified engines

7K views 45 replies 10 participants last post by  Dirdy 
#1 ·
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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#2 · (Edited)
...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?
 
#3 ·
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.
 
#4 · (Edited)
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.
 
#6 ·
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.
 
#9 ·
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.
 
#10 · (Edited)
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).
 
#13 ·
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..
 
#18 ·
Yeah sorry. Car has been parked. I had the one spring cup on my strut break. The result was me smashing into a curb head on. Broke the strut and ruined my 18s. I'm not real happy about it. I haven't been able to even check the car out to see if any other damage was done. So till I get time to fix it, this has to wait.
 
#21 ·
It was the spring seat on top, the plastic one. The bearing had been going since not long after I installed it. It broke earlier in the day. At night on the way back, I let my focus from the road go for a second to take a drink(of water) and hit the curb. The strut bearing being broke can make the car pull. I'm pissed I ruined my expensive 18" tire. I have a spare matching rim. And yeah, could have been a pole or something there.
 
#22 ·
So after reading through the jeep thread it looks like the MAP sensor is indeed the only thing that matters as far as the ECM is concerned at 80%+ throttle, which if you're going for making the car faster is what really counts.

What about the rest of the range though. The ECM reads O2 to decide fuel, so how does the TPS play into the equation in the ECM? I'm all for remapping the fuel curves, but I feel like there is a hole here in this method that we aren't talking about.
 
#26 · (Edited)
Yes, I did do some of this. With some issues arising still. Got the "MAP Enhancer" installed. Found out some weird stuff about it. I thought I had to richen up the fuel mixture. Turns out its not the case exactly.

I initially did raise the voltage from the stock 5.01v(about 5v exactly) to 5.5v. Great improvement power wise. Though I smelled fuel at idle. Then I went to town going up and down with voltage driving it around. At just shy of 6v, it was a rocket!!! I had to keep the steering wheel 90 degrees to counter act torque steer. It spun tires till 3rd gear! I was amazed. But it seemed to lag on the lower throttle and smelled awfully rich at idle. It was the first time I've ever had the car spinning both tires from a stop going straight.

Then I went the other way. And finally got settled to around 4.5v. Has great power till half throttle. Takes off with no effort and maintains speed like a dream. I have to keep letting off and tapping the pedal to maintain any speed up to 80mph. But now it falls even more short at higher to full throttle.

I tried putting the TPS down to near stock voltage and was around .65v. Had horrible shifts. The trans shifted way early and was slipping between gears. But it did smooth out power through the entire range more. I put it back to where I had it at .87v to correct shifting.


I'm a little lost at it all. I don't have a wide band O2 to really see whats going on. I'm listening for detonation and smelling for gas. But from what I gather, it seems like I need larger injectors to really get it tuned for what I've done. Seems like I'm flowing too much air through for the stock programming to compensate for. I'm not going to dish out $$$ for tuning a ECU in a car I'm only going to drive through till spring(have the new car and a 3.2 to put in it).

Anyone help on what the stock injectors are supposedly? I've found mixed results searching. How about higher flowing ones? Any other ideas what might be going on?

Could it be my fuel pressure regulator is bad and pressure is too high? Maybe causing it to run rich at idle and low? Its not leaking through the vacuum. But with out adapters to test the rail for pressure, I don't really have a way to test fuel pressure. I've seen bad ones that don't leak.
 
#27 ·
Okay, cant seem to edit my post right now.

There is no CEL codes for lean or rich. But I do have the infamous "IM DYING" code p0601. Maybe it wouldn't show anymore codes regardless. I'm swapping computers today anyways.
 
#28 ·
You've added a variable that would be beneficial - that is, the supply voltage, or Vref. It is likely that to get the optimum tuning that you are in the process of determining, to get the upper end TPS voltage, you would need a negative resistance added between the top of the potentiometer and Vref. Since we know there is no such thing as a negative resistor, your jacking up of Vref is the perfect solution. From there, the real value resistors could be determined.

Fortunately I anticipated that when I built the formulas - I made the Vref as one of the variables, so all that would be required would be to pick a Vref voltage that is determined to be high enough, and go from there. That would allow you to raise the idle voltage and the WOT voltage at the same time using the variable resistors at both ends at settings determined from the formulas.

For your experimenting, it would probably be easier to set a fixed voltage for Vref determined to be high enough for a range of possibilities, and put in adjustable resistors on both ends - then dial in the bottom and top end TPS voltages by setting the variable resistors according to the formulas. That way you can quickly experiment with different settings of the two ends simultaneously across all operating conditions - not just trying to optimize bottom, top, and middle in separate test runs. Just a suggestion.
 
#30 ·
Now the way I have it currently is raised voltage at idle. The top end(full throttle) is cut down by not letting the throttle open all the way. With it the way it is now, I'm lean on the top end still. With what your saying to be done, I can't make the top voltage any higher for the WOT. I understand what your saying, about getting the low voltage where it needs to be and then the high voltage, but it seems like I already hit a wall with that. I'm lean with a maxed out TPS signal on a throttle body that isn't open all the way yet. Its cut down to about 85-90% now. I think the throttle body is too large. I do have a smaller 60 or 65mm to try out.

If I can't get this done here soon and have it set correctly, I may just put the stock 2.7 intake back on and just tweak the MAP sensor alone. I love the extra low end kick, but the hit in mileage just isn't worth it to me. I was only getting 21-22mpg with the way I ran it for a long time. With just turning the MAP's vref down alone, I'm back to about 26mpg. And thats with winter fuel. Before I tore into the engine I could get 30+.

If it was easy to take the MAP's vref and have it lower on the low throttle and higher on the high throttle, I would do that. I'm just not that knowledgeable to design something like that myself.

If I can do the above, I will fix the TPS voltage how you say. But I need to fix the fuel issue first. Know how to build a variable 5v circuit ran off the TPS signal?
 
#33 ·
When I wrote my previous post, I missed where you said you were altering the MAP voltage - I was thinking TPS the whole time.

...Know how to build a variable 5v circuit ran off the TPS signal?
You'll have to explain what you want it to do - meaning what you want the output to be for a given input. But should be able to do pretty much anything you want.
 
#31 ·
21-22 MPG and you could spin tires? I get 15-16 MPG on a good day with my 3.5 and I can't even get a chirp unless the road is slick and i'm accelerating into a turn! Fantastic progress so far though. While most of this is over my head, I enjoy reading through all of it.
 
#32 ·
Not to go to far off topic here, but my 3.5 was averaging 10.3L per 100kms or 22.8 mpg (according to http://www.convert-me.com/en/convert/fuel/) and she can chirp into second gear when I stay on her. So there may be more at war with you there..

So on a 3.5, if one was to replicate this, with the rich at idle would smaller injectors help at all or is that a pipe dream??
 
#34 · (Edited)
@ gardidien if you can't even get a chirp with your SXT there has to be something wrong. I have good tires on mine and I have to watch how I hit the accelerator when I take off, or I end up doing burnouts all of the time.
If I try to do a burnout, it will seriously smoke both of the tires too. That's something I try to avoid doing though, because it gets expensive in many different ways. :baller::auto_04:
 
#36 ·
well, I've got too much other things that need done. For the sake of it running like it should and mileage, I'm putting the stock intake back on. I'm still going to use the map enhancer as I suspect the more free flowing exhaust manifolds will need it to have a little adjustment. I'm swapping the stock configuration back on with another harness and computer. My harness is chopped up for this intake and my ECU is nearly dead. Good thing I bought an identical '99 for just the body. And its good I didn't sell my K&N intake yet. I just don't think I'll have time to deal with this much more.

Hey, I'll get to see the difference this intake made again. Maybe its not all I thought it was. I did replace a lot more at the same time. The new lifters and exhaust may have made all the gains I felt.
 
#38 ·
It sucks. Apparently it added more than I thought. I have no low end power compared. Upper rpm power seems to have smoothed out. I really wish I hadn't switched it back. I used all the same sensors from intake to intake. I think I'll work on the charger intake a little and put it back on. I need to clean up the front of it as it still made contact with the hood.

I will try a couple more tweaks with the stock intake but overall, I'm disappointed with the switch back.
 
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