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Thread: Diesel Mechanic needs electronic help

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    Default Diesel Mechanic needs electronic help

    Hi fellas maybe you guys can help me I dont even know if it can be done here goes... I have 5 volts DC out of an ecm to a sensor and depending upon where the boost pressure of the engine is at, this sensor sends a signal back to the ECM anywhere from .25 volts all the way to the full 5 volts back to the ecm... Is there anything I can put in the return signal wire that would allow the sensor to send back the voltage normally but max out @ 4.75 volts instead of the full 5 volts... Another words anything that would limit DC voltage to 4.75 volts.. thanks for your time Richie

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    a simple voltage regulator and a resistor attached to it could make it fixed at 4.75v, but im not sure how to make it max out at 4.75v but still be able to fluctuate lower???

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    From what I can get out of this as
    1) you posted this in at a website without the expertise you want
    2) you only have 1 post (this one)
    3) you didn't give us any specifics on the engine or vehicle it came out of

    I can only guess that you are trying to overboost the damn thing and prevent ECU cutout without understanding the ramifications or EGT's that will result.
    I will not help you destroy your engine by doing something stupid, learn what you are doing before you modify it.

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    Quote Originally Posted by Cprossu View Post
    From what I can get out of this as
    1) you posted this in at a website without the expertise you want
    2) you only have 1 post (this one)
    3) you didn't give us any specifics on the engine or vehicle it came out of

    I can only guess that you are trying to overboost the damn thing and prevent ECU cutout without understanding the ramifications or EGT's that will result.
    I will not help you destroy your engine by doing something stupid, learn what you are doing before you modify it.
    With all do respect and I mean this respectfully you said you can only guess. Dont guess you'll hurt yourself. .. I posted this question here on this electronics site because I want electronics help... What I don't want is a lecture from you about the principles on how Turbo Diesel Engines work and the effects of pyro temps and boost pressure that I know inside and out Up and Down and side to side. I have been building them since you were wearing short pants and bibs. I am a Diesel Mechanic and have been for the past 30yrs I am not an electronics guru that's why I asked.. I am sure you are one of those guys and every forum has them that is the jack of all trades and know it all.. That being said if you can answer my question please do so .If you can answer and don't want to that's fine also.. Anything more then those 2 options answer the ? or don't please use the third option.... SHUT THE F___ UP....

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    You can install a resistor that can drop that 5V to 4.75V. Problem is, that resistor will drop all of your voltages leading up to 5V as well. Can't help figure out what value resistor because we'll need to know how much current.

    I may be wrong, but I don't think you're going to be able to maintain the same voltage as stock going up to 4.75V without going over 4.75V without implementing some sort of IC that's programmed to do so.

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    The simple solution, if the load is very light, is to simply use a zener diode (in series with a small-ish resistor) across the ECM <-> sensor connection to clamp the VECM to the zener's breakdown voltage. You'd need a zener with the characteristic VZ at 4.75V and a very tight tolerance (which could prove a bit expensive), but it's a no-brainer job, as long as the current is > say 5 mA. The Z-diode sinks current for all in-voltages above breakdown, so it's a dissipator, and as such is a bad idea for large current values, but I doubt that's the case here, as it would complicate the original circuit(s).

    The more complex solutions would be a buck-boost (huge overkill on all accounts) or a Low-dropout regulator (needs to be powered, and could be expensive). I can't quite go into details for these solutions, as that would take up way too much space (here) and (my) time. Just google both and see if you like any of those to better than a Zener solution.
    Careful what you wish for... You just might get it.

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    You mean < 5mA, right?

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    No, below a certain current value, the zener doesn't regulate voltage. Usually the required current is as low as 1 mA, but for tighter-regulating specimens, it can go anywhere from 3 to 10 mA. One only has to be careful with over-saturating the diode, so as not to cause too much heat dissipation (thus killing the silicon)... The standard P = U*I applies in this case, and since U ~= Vz, the only variable when the diode is clamping is the current.
    Careful what you wish for... You just might get it.

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    I am sure you are one of those guys and every forum has them that is the jack of all trades and know it all.. That being said if you can answer my question please do so .If you can answer and don't want to that's fine also.. Anything more then those 2 options answer the ? or don't please use the third option.... SHUT THE F___ UP....
    Well for one, you didn't post to an electronics forum. (As jack of all trades as you want us to be, most of the experts here focus on power supplies for PC's and all things PC related)
    To put it into perspective it would be like asking your dentist what the treatment would be for Strongyloides stercoralis just because he was a doctor. You may get incorrect advise.

    That being said if you can answer my question please do s
    That being said you failed gave me any of the information I said I might need to answer such a question.

    which is:
    3) you didn't give us any specifics on the engine or vehicle it came out of
    moving on...

    I have been building them since you were wearing short pants and bibs. I am a Diesel Mechanic and have been for the past 30yrs I am not an electronics guru that's why I asked..
    yeah, yeah, blah blah blah.

    .25-5V usually means you are dealing with a MAP sensor of sorts, these come in different flavorings, 1 bar, 2 bar, 3 bar, etc, and they all share one thing-They range from 0-5V on the signal.
    Dropping voltage on a given sensor means that you are telling the computer that the "boost psi" is less than it would be otherwise which results in less fuel being delivered by the electronic injectors. Now comes the sticky part: Without knowing what engine you are dealing with we don't have a f-ing clue what sensor is being used or what you are trying to modify. Now the other issue is do you want the sensor to read normally until it hits 4.75V and then not progress any further, as that would take more logic than just sticking in a resistor that would drop the voltage X amount.
    Last edited by Cprossu; 02-21-2011 at 04:12 PM.

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    Quote Originally Posted by McSteel View Post
    No, below a certain current value, the zener doesn't regulate voltage.
    Ah! Gotch. Cool. Thought it was a typo.

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