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Ecu Wattage Output For Temperature Sending Unit?

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This one will stump all but the most seasoned mechanics.

I need to know the output wattage from the ECU to the coolant temperature sending unit so I can jump the wires with a resister (I'm installing a 2 ohm resister to limit idle speed for cold start but I need to know if my 2 watt, 2 ohm resister is good enough).

Best of luck with this one!

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This one will stump all but the most seasoned mechanics.

I need to know the output wattage from the ECU to the coolant temperature sending unit so I can jump the wires with a resister (I'm installing a 2 ohm resister to limit idle speed for cold start but I need to know if my 2 watt, 2 ohm resister is good enough).

Best of luck with this one!

What will the ECU "see" in ohms after the engine is at normal operating temperature - coming from the CTSU?

Great question. The answer is as follows:

On my 1996 LS400, the temp sending unit has the following resistance given the following temperatures (the brain sees these numbers)

4 ohms resistance at 43 degrees

3.8 at 47

2.75 at 61

1.83 at 81

1.37 at 98

1.05 at 110

.88 at 120

.57 at 145

.45 at 160

.30 at 195

My issue is that I need to know how much power the brain sends to this temp sending unit because if I put a 2 ohm, 1/2 watt resister inline and the signal is stronger than a 1/2 watt, the resister will just blow.

I'm just looking to right size my resister.

By the way, the whole idea is to trick the car into thinking it is warmer than it is so that the idle will drop from 1500 to 1600 down to a more reasonable 1100 or so during cold start.

I've heard the cause for the excessive high idle is anything from a dirty/bad idle air control valve to motor mounts but no one can tell me for sure. My IAC works just fine other than cold start so how can it's failure indication be too much air?

I can see no reason why a motor mount would cause a high idle either so I'm down to what I think I know and that's the temp sending unit.

Anyway, maybe I'm whacked but I think the resister idea is worth the time to try and there's no downside (can't do any harm).

Thanks all and if you can come up with another explanation, reason, I'm all ears.

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Your quest has nothing to do with the experience of any mechanic. You'll need the factory data showing the resistance of the sending unit according to temperature, and confirm that your sending unit is within those specs.

The sending unit is of course an input device, whereas the IAC valve is an output device. At least you're on the right track, but engine temperature dictates far more than idle speed as far as the ECU is concerned. Fuel-air ratio and ignition timing are also partially determined by that input.

And yes, you're probably whacked trying this....

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Your quest has nothing to do with the experience of any mechanic. You'll need the factory data showing the resistance of the sending unit according to temperature, and confirm that your sending unit is within those specs.

The sending unit is of course an input device, whereas the IAC valve is an output device. At least you're on the right track, but engine temperature dictates far more than idle speed as far as the ECU is concerned. Fuel-air ratio and ignition timing are also partially determined by that input.

And yes, you're probably whacked trying this....

Both my old and the new temp sending unit I bought read the same resistance per temp so we know the temp sending unit is good.

I'll slice in a 2 ohm, 2 watt resister this morning and let everyone know if it worked. If not, I'm out a dollar for the resister ...and a little pride.

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This one will stump all but the most seasoned mechanics.

I need to know the output wattage from the ECU to the coolant temperature sending unit so I can jump the wires with a resister (I'm installing a 2 ohm resister to limit idle speed for cold start but I need to know if my 2 watt, 2 ohm resister is good enough).

Best of luck with this one!

g:

The ECU applies a (bias) voltage to the Sensor and as a result, current will flow in that series loop, dependent upon the resistance of the sensor/sending unit, which is dependent upon temperature. You appear to have correctly "mapped" the resistance vs temperature characteristics of the sensor. Now, if you put another resistance (no matter how high of a resistor value it is) in parallel with the sensor, the total loop resistance that the ECU "sees", goes down. As a result of that, the loop current will go up. The magical question is "how much current (or load) increase can that circuit on the ECU tolerate before it GOES UP IN SMOKE ?"

The ECU does not put out any "wattage" whatsoever. It provides a bias voltage to the sensor (as I said above) and current flows. Yes, the level of wattage is a result of volts/amps/resistance values. There is a fixed "terminating resistance" value and associated total wattage capacity for the sensor input to the ECU that cannot be exceeded, or "POOF". Are you prepared for that possibility?

Additionally, if you put another resistor in parallel (or series, for that matter) with the sensor, you destroy the design linearity of the circuit and how it responds to changes in temperature. It is understood that is what you wish to accomplish (properly of course), but all that is going to happen is that the "response curve" will still be objectionable, just in a different way. That's assuming the ECU input doesn't go up in smoke.

Using your numbers above, if the supply voltage to the sensor is 12 Vdc (logical assumption anyway), then you would need a 72 watt resistor. 12 volts divided by 2 Ohms is 6 Amps. 6 amps times 12 volts equals 72 watts. That's one great big monstrosity of a resistor. More than likely, it is a lower bias voltage, or it is a current loop, an altogether different animal that I won't even begin to try and describe.

Your question is actually a bit flattering, but nevertheless, unrealistic. There really isn't going to be anyone out here/there that is going to know this information, no matter how good of a mechanic they are. When these (or similar) types of problems come up, most of the time the problem is "black boxed". Meaning that the offending component is identified as quickly as possible, removed and replaced with a new/rebuilt working part.

I guess my point in all of this is that unless you can get your hands on the schematic for that particular ECU input, you'll never know enough about it to keep from burning it up. These circuits are designed, tested and built by people with thick glasses, vinyl pocket protectors, white, ink stained shirts who pull wings off flies for their only hobby in life. The one thing they have going for them is they know exactly what they are doing. I think your problem lies elsewhere and that you will be much farther ahead by trying to find it and resolve it at the source.

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This one will stump all but the most seasoned mechanics.

I need to know the output wattage from the ECU to the coolant temperature sending unit so I can jump the wires with a resister (I'm installing a 2 ohm resister to limit idle speed for cold start but I need to know if my 2 watt, 2 ohm resister is good enough).

Best of luck with this one!

g:

The ECU applies a (bias) voltage to the Sensor and as a result, current will flow in that series loop, dependent upon the resistance of the sensor/sending unit, which is dependent upon temperature. You appear to have correctly "mapped" the resistance vs temperature characteristics of the sensor. Now, if you put another resistance (no matter how high of a resistor value it is) in parallel with the sensor, the total loop resistance that the ECU "sees", goes down. As a result of that, the loop current will go up. The magical question is "how much current (or load) increase can that circuit on the ECU tolerate before it GOES UP IN SMOKE ?"

The ECU does not put out any "wattage" whatsoever. It provides a bias voltage to the sensor (as I said above) and current flows. Yes, the level of wattage is a result of volts/amps/resistance values. There is a fixed "terminating resistance" value and associated total wattage capacity for the sensor input to the ECU that cannot be exceeded, or "POOF". Are you prepared for that possibility?

Additionally, if you put another resistor in parallel (or series, for that matter) with the sensor, you destroy the design linearity of the circuit and how it responds to changes in temperature. It is understood that is what you wish to accomplish (properly of course), but all that is going to happen is that the "response curve" will still be objectionable, just in a different way. That's assuming the ECU input doesn't go up in smoke.

Using your numbers above, if the supply voltage to the sensor is 12 Vdc (logical assumption anyway), then you would need a 72 watt resistor. 12 volts divided by 2 Ohms is 6 Amps. 6 amps times 12 volts equals 72 watts. That's one great big monstrosity of a resistor. More than likely, it is a lower bias voltage, or it is a current loop, an altogether different animal that I won't even begin to try and describe.

Your question is actually a bit flattering, but nevertheless, unrealistic. There really isn't going to be anyone out here/there that is going to know this information, no matter how good of a mechanic they are. When these (or similar) types of problems come up, most of the time the problem is "black boxed". Meaning that the offending component is identified as quickly as possible, removed and replaced with a new/rebuilt working part.

I guess my point in all of this is that unless you can get your hands on the schematic for that particular ECU input, you'll never know enough about it to keep from burning it up. These circuits are designed, tested and built by people with thick glasses, vinyl pocket protectors, white, ink stained shirts who pull wings off flies for their only hobby in life. The one thing they have going for them is they know exactly what they are doing. I think your problem lies elsewhere and that you will be much farther ahead by trying to find it and resolve it at the source.

Well, that's what I was to say, but you beat me to it! :rolleyes:

Just kidding..... :D

I agree with everything he said. B)

Hi Randy;

In and amongst all my jaw flapping, I forgot to mention that as far as I know, 1500 RPM cold idle is completely normal. I've got a '95 and that's exactly what it does. Lucky for you, I'm out of breath now.........

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Wow...all that high-tech talk makes a tingle run up my leg! :wub:

threadcutter = uber

Well, if I ever have any questions about electrons..... I'll know where to start!!

Heck, all this time I thought he was "plumber". :ph34r:

Of course, I have learned my lesson about avitars..... you just can't tell! :blushing:

Threadcutter Rocks!! :cheers:

Outstanding replys everyone - especially the one that discussed pulling wings off of flys : ) In talking me back from the ledge of foolishness, you have accomplished two things:

1) you talked me out of melting a perfectly good ecu

2) you shamed me into measuring the input voltage for the sending unit - it was 5 volts

Thanks again and I guess I'll just live with what seems to me to be a high cold idle

Now I'm back to not having any problems with my car so I have nothing to do all weekend. Maybe I'll go hang out with my wife or something... yawn.

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Wow...all that high-tech talk makes a tingle run up my leg! :wub:

threadcutter = uber

Well, if I ever have any questions about electrons..... I'll know where to start!!

Heck, all this time I thought he was "plumber". :ph34r:

Of course, I have learned my lesson about avitars..... you just can't tell! :blushing:

Threadcutter Rocks!! :cheers:

Outstanding replys everyone - especially the one that discussed pulling wings off of flys : ) In talking me back from the ledge of foolishness, you have accomplished two things:

1) you talked me out of melting a perfectly good ecu

2) you shamed me into measuring the input voltage for the sending unit - it was 5 volts

Thanks again and I guess I'll just live with what seems to me to be a high cold idle

Now I'm back to not having any problems with my car so I have nothing to do all weekend. Maybe I'll go hang out with my wife or something... yawn.

g:

Now I'm back to not having any problems with my car so I have nothing to do all weekend. Maybe I'll go hang out with my wife or something... yawn.

If it is of any consolation, I'm in exactly the same boat................

Look at it this way.......If any damage did occur (not necessarily a given), you'd have the anxiety of a dead ECU AND you'd still end up hanging out with the wife or something.............

However, you could start thinking about a re-design for the location of the starter. If you could make a kit to re-locate it to where it should be, you'd make millions!

Best Regards,

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Hey man...no shame at all.

I was impressed that someone would venture that far down that path. Scared me just reading what you were thinking of doing. :D

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Hey man...no shame at all.

I was impressed that someone would venture that far down that path. Scared me just reading what you were thinking of doing. :D

2X......... :cheers:

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Haven't had much time lately for contributing to forums, but still scan them occaisionally. Interesting topic this one so I had to jump in. Gt, you're idea is a valid one. Reduced to basic principles, as the coolant temperature increases, the resistance of the sensor decreases, providing a varying output voltage to the engine's computer. To lower the idle in an open loop fuel trim you could add a resisitor in parallel to lower the resistance. You'd have to use a value that gives you the idle you want. Put in the wrong value and you could wind up stalling the engine. Don't forget, the ecu doesn't know what it's putting out when in an open loop, it's operating on a programmed fuel trim. You'd also have to make it switchable/disabled (in series) once the fuel map goes into a closed loop. Otherwise you're likely to run rich with the sensor sending a lower temp signal because the resistor's enabled. Could also result in a rich misfire, stalling, rough idle, hesitation, overheated cats, etc. That's the simple version.

If you're idle doesn't settle at ~650 when warmed up or takes an overly long time to get there, instead of trying to re-engineer the EFI setup, why don't you try checking the obvious? Like a sticking butterfly / a pinched air hose / worn out isc / dirty iacv / malfunctioning ecu / coolant level / coolant sensor connections / sticking stat / radiator hose or dashpot clamps position interfering with TB closing properly, etc. I would avoid stressing the drivetrain by shifting into gear at high idle, just wait for the idle to come down. One other thing you can do is install a block heater and plug it into a timer so it's not on all night long. It will preheat the coolant and reduce your warm up time.

:cheers:

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Haven't had much time lately for contributing to forums, but still scan them occaisionally. Interesting topic this one so I had to jump in. Gt, you're idea is a valid one. Reduced to basic principles, as the coolant temperature increases, the resistance of the sensor decreases, providing a varying output voltage to the engine's computer. To lower the idle in an open loop fuel trim you could add a resisitor in parallel to lower the resistance. You'd have to use a value that gives you the idle you want. Put in the wrong value and you could wind up stalling the engine. Don't forget, the ecu doesn't know what it's putting out when in an open loop, it's operating on a programmed fuel trim. You'd also have to make it switchable/disabled (in series) once the fuel map goes into a closed loop. Otherwise you're likely to run rich with the sensor sending a lower temp signal with the resistor enabled. Could also result in a rich misfire, stalling, rough idle, hesitation, overheated cats, etc. That's the simple version.

If you're idle doesn't settle at ~650 when warmed up or takes an overly long time to get there, instead of trying to re-engineer the EFI setup, why don't you try checking the obvious? Like a sticking butterfly / a pinched air hose / worn out isc / dirty iacv / malfunctioning ecu / coolant level / coolant sensor connections / sticking stat / radiator hose or dashpot clamps position interfering with TB closing properly, etc. I would avoid stressing the drivetrain by shifting into gear at high idle, and just wait for the idle to come down. One other thing you can do is install a block heater and plug it into a timer so it's not on all night long. It will preheat the coolant and reduce your warm up time.

:cheers:

Gawd!! ... I love it when he talks "dirty" like that!!! :lol:

I think I may have a solution. It was so simple, I can't believe I didn't think about it earlier...

I'll just go buy a 2009 G8 GXP 6 speed in obnoxious blue, order the LS3 to LS9 turbo/intercooler kit and install a stonger clutch. That package should not only idle about right, it'll have about 650 hp too!

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I think I may have a solution. It was so simple, I can't believe I didn't think about it earlier...

I'll just go buy a 2009 G8 GXP 6 speed in obnoxious blue, order the LS3 to LS9 turbo/intercooler kit and install a stonger clutch. That package should not only idle about right, it'll have about 650 hp too!

Bingo!!! As IS400 likes to say, "easy peasy lemon squeasy"! Funny how that "650" number keeps coming up. :whistles: The obnoxious blue is a nice touch. :blink:

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These circuits are designed, tested and built by people with thick glasses, vinyl pocket protectors, white, ink stained shirts who pull wings off flies for their only hobby in life.

Hey, watch it TC, you are getting personal now. Only I quit pulling fly wings long ago(still burn an occasional ant though). ;)

The bottom line on this thread is that of course the proposed "solution" (parallel resistor) is, at best, a concoction.

BTW, the ECU probably has a constant current output circuit of a few milliamps so the resistor would not get hot.

The original sensor gets to 300 milliohms@195 F, right? Essentially a short. No engineer worth his salt would design an input circuit

that would blow when shorted.

The temp sensor is an NTC type device (Negative Temperature Coefficient...as temp goes up, resistance goes down and vice versa).

IF you were going to attempt such a thing, gtolds, you would want to counter it with a PTC device(Positive Temperature Coefficient...resistance goes up with temp).

That way the PTC would essential remove itself from the circuit as the engine heated up. Of course you would have to attach the PTC device to the engine block. Again..uh, jury rig.

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These circuits are designed, tested and built by people with thick glasses, vinyl pocket protectors, white, ink stained shirts who pull wings off flies for their only hobby in life.

Hey, watch it TC, you are getting personal now. Only I quit pulling fly wings long ago(still burn an occasional ant though). ;)

The bottom line on this thread is that of course the proposed "solution" (parallel resistor) is, at best, a concoction.

BTW, the ECU probably has a constant current output circuit of a few milliamps so the resistor would not get hot.

The original sensor gets to 300 milliohms@195 F, right? Essentially a short. No engineer worth his salt would design an input circuit

that would blow when shorted.

The temp sensor is an NTC type device (Negative Temperature Coefficient...as temp goes up, resistance goes down and vice versa).

IF you were going to attempt such a thing, gtolds, you would want to counter it with a PTC device(Positive Temperature Coefficient...resistance goes up with temp).

That way the PTC would essential remove itself from the circuit as the engine heated up. Of course you would have to attach the PTC device to the engine block. Again..uh, jury rig.

landar;

Hey, watch it TC, you are getting personal now. Only I quit pulling fly wings long ago(still burn an occasional ant though). ;)

Agreed......I'm into High voltage garden bug zappers, teriyaki skewers to push 'em between the grids (more smoke & flames that way) & Cuervo.......Nuthin' finer on a Saturday night.

The bottom line on this thread is that of course the proposed "solution" (parallel resistor) is, at best, a concoction.

Agreed.

BTW, the ECU probably has a constant current output circuit of a few milliamps so the resistor would not get hot.

Agreed. My concern isn't the resistor.

The original sensor gets to 300 milliohms@195 F, right? Essentially a short. No engineer worth his salt would design an input circuit

that would blow when shorted.

Hah!, That's Rich!................I can't tell you the number of failed circuits I've seen in the field (Power Elex's, VFD's, ASD's, Vector Drives, Servos, Gas turbines, Wind turbines, Diesel Electric locomotives, etc) where you'd say "No engineer worth his Salt"...........But Nooohhhh!.........

IF you were going to attempt such a thing, gtolds, you would want to counter it with a PTC device(Positive Temperature Coefficient...resistance goes up with temp).

That way the PTC would essential remove itself from the circuit as the engine heated up. Of course you would have to attach the PTC device to the engine block. Again..uh, jury rig.

My opinion; Not possible. There will be a lookup table that the ECU references for loop current. The hardware (sensor curve) matches the S/W program & the lookup table (probably in some form of ROM). If you could start with a completely clean sheet of paper, yeah maybe. Personally, I don't think it's worth the bother.

Some people wish for a world without hunger or wars. I'm more plebeian. Give me a world where Lexus relocates the starter to where it should be, fixes the EGR pipe fiasco and gets rid of the POS P/S rack solenoid screen/filter. Now that's something to pray for!

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.. plebeian...

Thanks Threadcutter.... I just learned another "dirty" word!!! :lol:

Randy;

hobbies?........any?.......

just kiddin'..... :cheers:

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My opinion; Not possible. There will be a lookup table that the ECU references for loop current. The hardware (sensor curve) matches the S/W program & the lookup table (probably in some form of ROM). If you could start with a completely clean sheet of paper, yeah maybe. Personally, I don't think it's worth the bother.

Some people wish for a world without hunger or wars. I'm more plebeian. Give me a world where Lexus relocates the starter to where it should be, fixes the EGR pipe fiasco and gets rid of the POS P/S rack solenoid screen/filter. Now that's something to pray for!

Threadcutter, you rascal! By using the term "plebeian" you deny plebeian status, don't you know?

Yes, I am well acquainted with LUT's to linearize inputs. The PTC thing was a compromise to the original parallel resistor (which would

really just be a fixed offset bias). The PTC would at least become less of a factor as its temperature increased. Nonetheless, agreed...a kludge and not worth pursuing.

The starter is what it is. I used to grouse about the under-engine plastic cover but every time that I remove it and see how impeccably clean that engine is, I bless the

boys who had the audacity to place it there.

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