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MA
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NeVeRmiNdQ Offline
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Post: #1
MA
I have a map sensor adjuster giving out 1.25v instead of 4.95v and the "Check Engine Light" came on. Before it came on I was getting really good gas mileage. Now that it is on will it just ignore the reading that it is getting from the map sensor which is really the map adjuster's 1.25v output, and just give fuel as it pleases?
02-22-2008 05:18 PM
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mike Offline
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Post: #2
RE: MA
Presumably so.

Is your adjuster of the type found in this article? If so, that article may help you. Look down a ways for the "MAP" section.

What you want to do is get your adjuster adjusting the signal the correct amount. Then it will do you some good. If it's adjusted so far that the computer discounts it's information, you could achieve the same result by disconnecting it. The point is neither is a workable solution.

This article may also help.

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02-22-2008 05:55 PM
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NeVeRmiNdQ Offline
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Post: #3
RE: MA
I have the MAp at 1.25v instead of the 4.95 it is normally at, the check engine light came on, but I have a switch to put it back to normal. When I have the switch on 1.25 I floor it and it only goes to 35OO rpm to accerate, and when I flick the switch to put it back to the normal 4.95v I floor it and it goes to 65OO rpm's as normal, does this mean even though the light is on it is still taking the reading, and another question....is 1.25v really ideal, I'm fine with how it drives but I don't know if that is good fuel wise. Can you give me some advice, the article wasn't clear on this part.
02-23-2008 07:13 PM
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mike Offline
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Post: #4
RE: MA
I've never messed with MAP adjustment. But others on this forum have, and hopefully one of them will see this and chime in.

But, if it were me, I would build an adjuster that let me adjust the signal less. You're currently changing the signal too much. It sounds like you have a fixed signal that gives the ECU 1.25 volts, no matter what the MAP is outputting. Or, if it is a varying signal that parallels the MAP in some way, it's just too much of a change.

I would use the circuit diagram in the link above, or see qsiguy's diagram (look about half way down the page), and make one like that. Then you can adjust the signal to, for instance, reduce the MAP signal by .5 volts. If that improves performance (mpg), then you might want to then set it to reduce the signal by .75 volts, or 1.0 volts. The point is that you can then adjust the signal by some smaller increment that then gets you an improvement in mileage, without freaking out the computer (computers don't like to be freaked out).

Almost assuredly if you get a CEL by over adjusting a sensor, the sensor's data will be ignored to the detriment of fuel mileage.

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02-23-2008 07:42 PM
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qsiguy Offline
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Post: #5
RE: MA
I'd like to see a diagram of what you've actually done and to which circuit. Have you modified the signal going to the MAP or the output of it? Have you used a voltage regulator or just a pot or resistor? From my understanding, what you've done by itself will only limit the amount of fuel that the ECU will order the injectors to inject. Since the MAP will max out at a lower voltage the ECU believes there is no additional load and won't send any additional fuel. Sounds good but unfortunately it won't go above 3500 RPM. I believe it does recognize the sensor but it knows something isn't right. As Mike said, you will do much better with a voltage regulator or pot so you can find tune the voltage to a point the ECU will still accept. Now if you only want to reduce the voltage going to a sensor it can normally be done with just a pot. The circuit I posted at the link Mike posted above allows you to go above or below the standard VREF (voltage reference).

When you offset the various sensors in the vehicle you are altering the "lean limits" the ECU will accept as good. The O2 is typically the first that you need to modify. Then you would get into the MAP/MAF, IAT (intake air temp), and coolant temperature sensors. By tweaking all these sensors you convice the ECU that all is well and it can safely lean out the fuel. You may also find that as you offset more sensors the ones you've already offset may accept greater offsets because many of them just need to be within a particular range from the other sensors. There are, of course, maximum limits but you aren't likely to hit them unless you offset every monitored sensor. For example, if the abient temperature is 40* outside the ECU will know this from the IAT. If you offset the IAT to tell the ECU it's really 100* ambient it will allow less fuel to be injected because the air will be less dense at 100* than it is at 40*. You should be able to offset the MAF more after you do this.

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(This post was last modified: 02-24-2008 03:39 PM by qsiguy.)
02-24-2008 03:19 PM
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NeVeRmiNdQ Offline
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Post: #6
RE: MA
qsiugy the last paragraph was very interesting and gave me some good advice, I started with the O2 sensor and then went HHO gas, and now I am doing the MAp sensor drive a 2OO3 Ford Ranger 2.3L 4 cylinders. Ford does their map sensor differently. Instead of the output changing voltage, it stays constant, but the frequency at which the voltage is sent, changes. So basically what I did will do nothing, it will lower the voltage output but I don't think that will make a difference. What I had did wrong was change the VREF directly from the ECU from 5v to the 1.25 and you shouldn't do that because that 5v VREF goes to ALL the onboard sensors, like the TpS, MAF, and MAp. Thats why it wouldn't go above 35OO rpm. So I'm not sure whether I have to put a 1O to 25 ohm resistor on the MAp's GROUND, or the OUTpUT. I appreciate the advice.
02-26-2008 06:39 PM
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qsiguy Offline
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Post: #7
RE: MA
I'll be honest and admit I haven't done it myself but understand it to be the GROUND wire on the MAP you would put the resistor on, NOT the OUTPUT.

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02-27-2008 09:05 PM
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mike Offline
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Post: #8
RE: MA
Have you read something about the frequency modulated types? I don't see how a resistor to ground will alter the frequency. I haven't seen anything on modifying the signal of the Delco frequency type MAP sensors, but would love to see an article if you know of one where this was done in a simple fashion.

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02-27-2008 09:24 PM
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tanahiro Offline
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Post: #9
RE: MA
what is a vref and how can i find this in my camry 2002?
02-28-2008 07:25 PM
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NeVeRmiNdQ Offline
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Post: #10
RE: MA
Vref stands for Voltage Reference, which is the amount of voltage going into a unit. For this case the VREF is 5v bc the sensor uses 5v. Oh and Mike, here is a link that will explain the frequency based sensors that are most commonly used on Ford vehicles...it's the fourth paragraph from the bottom.

http://fueleconomytips.com/2008/02/15/tu...ge-part-2/

I finished putting a resistor on the maf and map sensor on the ground wire yesterday and noticed it made a big difference. The maf couldn't handle 33 ohms so I took it down to 22 ohms, on the other hand the map took 33 ohms and possibly could go further bc I have tried past that, which really surprised me it went that high.
(This post was last modified: 02-28-2008 07:33 PM by NeVeRmiNdQ.)
02-28-2008 07:31 PM
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