Beating a dead horse. O2 sensor issues.

[Keekleberrys]

3 efans? Does it not have a mechanical fan?

 

[Jimhd7500]

I removed the mechanical fan for a more powerful electric. Just to hit on the electrical issues again, I was blinded looking for what I know should be there and not looking for what should not be. And the short to ground was not there until the vehicle was powered through the PCM and the ASD, so it was a tricky one for sure, but with the help I never gave up.

 

[Keekleberrys]

Why would you remove the mechanical fan?!

It takes a hell of an electric fan to match the CFM of the mechanical , I am sure there are some more powerful electric ones out there but I am stickler for OEM when it comes to underhood components. How did you wire them up? The electric fan isn't commanded on by the PCM until 223*F. So unless you have wired a switch up or they are constantly on, it is gonna operated at a higher temp. Which could be trouble if the cooling system is already questionable.

The mechanical fan is fully engaged before that, and has a cooling effect even when not fully engaged.

 

[Jimhd7500]

I have a thermostatic switch that can be set, and it comes on at 160. They have some pretty high tech systems to control it, some will turn on when the A/C is and you can also shut it off if needed, like in a deep water crossing, it is all enclosed so its water proof. I have one of those on my Chevy. There are a number of electrical fans that move more air then the mechanical, and by removing it you get rid of the parasitic drag, freeing up HP and a small improvement in MPG.

 

[8Mud]

Oh and just to put this out there, corrosion and high resistence in a circuit normally will cause lower amperage in a circuit and will NOT cause a fuse to blow.

Sounds good but, the facts are the fuses burn through, watts (heat) not amps is what melts them. Instead of say a twenty amp fuse it would be more accurate to call it a 260 watt fuse. Copper heat sinks, the heat travels the entire length of a wire or a bus and radiates some, but the heat can be accumulative and may build over a period of seconds or even minutes before it reaches the threshold needed to melt the fuse. The amperage you are drawing, plus the stored heat, can cause a meltdown on a fuse for a circuit drawing less than max fused amperage. Amperes X Volts equals watts, watts can be either heat or horsepower. The fuse is little more than the weak link and hopefully has the lowest melting point in the system. The heat stored in the wire and what the circuit draw together, are accumulative.

Though you are correct on one point, the 5.5 +/- amp draw of the two O2 sensor heaters together and the heat stored or generated in the wiring or the bus, make burning through a twenty amp (260 watt) fuse unlikely. Though I have seen a whole lot of melted wire and connectors over the years, copper melts at around 2000 F. My guess is the fuse melts at a much lower temperature than that.

 

[Bryan C.]

Sounds good but, the facts are the fuses burn through, watts (heat) not amps is what melts them. Instead of say a twenty amp fuse it would be more accurate to call it a 260 watt fuse. Copper heat sinks, the heat travels the entire length of a wire or a bus and radiates some, but the heat can be accumulative and may build over a period of seconds or even minutes before it reaches the threshold needed to melt the fuse. The amperage you are drawing, plus the stored heat, can cause a meltdown on a fuse for a circuit drawing less than max fused amperage. Amperes X Volts equals watts, watts can be either heat or horsepower. The fuse is little more than the weak link and hopefully has the lowest melting point in the system. The heat stored in the wire and what the circuit draw together, are accumulative.

Though you are correct on one point, the 5.5 +/- amp draw of the two O2 sensor heaters together and the heat stored or generated in the wiring or the bus, make burning through a twenty amp (260 watt) fuse unlikely. Though I have seen a whole lot of melted wire and connectors over the years, copper melts at around 2000 F. My guess is the fuse melts at a much lower temperature than that.

I see where you are coming from, however I have yet to see such a thing occur in an automotive environment. Yes, I have seen many melted connectors and wires but never a blown fuse because of them unless they touch ground. I have seen fuses melt the plastic that holds them together before the fuse will actually blow. So, I'm not saying you are wrong, but that is more of a theoretical situation rather than a real world situation.

EDIT: Also, according to ohms law, high resistence in a circuit lowers both the voltage and the amperage, thus drawing fewer watts.

 

[Jimhd7500]

They have always taught us in aviation that the purpose of the fuse was to save the wire. So with ohms law you decide the wire size needed for a circut and then use the correct amperage fuse for the wire needed, if that makes sense written like that.

 

[8Mud]

I see where you are coming from, however I have yet to see such a thing occur in an automotive environment. Yes, I have seen many melted connectors and wires but never a blown fuse because of them unless they touch ground. I have seen fuses melt the plastic that holds them together before the fuse will actually blow. So, I'm not saying you are wrong, but that is more of a theoretical situation rather than a real world situation.

EDIT: Also, according to ohms law, high resistence in a circuit lowers both the voltage and the amperage, thus drawing fewer watts.

The flaw in your thinking is when you say draws watts, watts (especially in a heater circuit) is heat and it is accumulative. The wire radiates, if the temperature rises faster than it can radiate (or sink) the heat away, the heat continues to build.

It depends on how close the heat source is to the fuse and how much heat is radiated and leeched down the wire. If the wire absorbs enough heat it can get hot enough to burn through a fuse or trip a circuit breaker. In my experience the heat source needs to be within a couple of feet in an automotive system, household systems it can be a lot farther away.

I've seen it numerous times, a classic example is the dash illumination circuit for renix and most HO's. The rheostat (in the headlight switch), in effect a heater or resistor, has a partial melt down, the rheostat is powered by the Tail light fuse, then the power goes back down to the fuse block from the rheostat, through another 7 amp fuse (I think) then back up to the dash lights. The heat generated by that rheostat will blow the 7 amp fuse even though it is after the heat source. It may or may not blow the 15 amp tail light fuse.

Numerous times I've seen fuses burn through because the fuse holder was loose, the heat generated would eventually cause the fuse to fail. Even in your house, a loose connection between the fuse and say a light fixture can trip the fuse, the heat eventually finds it's way back the to fuse or circuit breaker, hopefully before the loose connection starts a fire.

Pretty common failure, really it does happen. If the heat builds faster than the wire can radiate or leech it away, the fuse will fail, it is accumulative, the heat builds, it can take seconds or even an hour.

I started out on auto electric sometime in the early sixties and moved on to bigger stuff. I learned on M-48, through M-60 and then on to M-1 main battle tanks, enough wire in one of those for a fleet of XJ's.

 

[Bryan C.]

The flaw in your thinking is when you say draws watts, watts (especially in a heater circuit) is heat and it is accumulative. The wire radiates, if the temperature rises faster than it can radiate (or sink) the heat away, the heat continues to build.

It depends on how close the heat source is to the fuse and how much heat is radiated and leeched down the wire. If the wire absorbs enough heat it can get hot enough to burn through a fuse or trip a circuit breaker. In my experience the heat source needs to be within a couple of feet in an automotive system, household systems it can be a lot farther away.

I've seen it numerous times, a classic example is the dash illumination circuit for renix and most HO's. The rheostat (in the headlight switch), in effect a heater or resistor, has a partial melt down, the rheostat is powered by the Tail light fuse, then the power goes back down to the fuse block from the rheostat, through another 7 amp fuse (I think) then back up to the dash lights. The heat generated by that rheostat will blow the 7 amp fuse even though it is after the heat source. It may or may not blow the 15 amp tail light fuse.

Numerous times I've seen fuses burn through because the fuse holder was loose, the heat generated would eventually cause the fuse to fail. Even in your house, a loose connection between the fuse and say a light fixture can trip the fuse, the heat eventually finds it's way back the to fuse or circuit breaker, hopefully before the loose connection starts a fire.

Pretty common failure, really it does happen. If the heat builds faster than the wire can radiate or leech it away, the fuse will fail, it is accumulative, the heat builds, it can take seconds or even an hour.

I started out on auto electric sometime in the early sixties and moved on to bigger stuff. I learned on M-48, through M-60 and then on to M-1 main battle tanks, enough wire in one of those for a fleet of XJ's.

I think you missed the point by trying to prove how smart you are.

 

[offroadordnance]

Jumping the fuse with a fused loop of wire and using an amp clamp might give you a better idea of when, where, why its happening. Use the amp clamp on each circuit load after to pinpoint any short or faulty component drawing excessive amperage. I'd use a DSO with an inductive amp probe if available, to get an even better picture of the problem.

 

[Jimhd7500]

We had a nice scope when I was working 727's in MN., and it would tell you how far down the wire the problem was. That was very helpful working a large system like an aircraft.

 

[offroadordnance]

I see where you are coming from, however I have yet to see such a thing occur in an automotive environment. Yes, I have seen many melted connectors and wires but never a blown fuse because of them unless they touch ground. I have seen fuses melt the plastic that holds them together before the fuse will actually blow. So, I'm not saying you are wrong, but that is more of a theoretical situation rather than a real world situation.

EDIT: Also, according to ohms law, high resistence in a circuit lowers both the voltage and the amperage, thus drawing fewer watts.

Better check that again, high resistance = high voltage.

 

[Bryan C.]

Better check that again, high resistance = high voltage.

I know what the equation says, but how are you going to get more than 14 volts from an automotive charging system? Amperage goes down as resistence goes up with the voltage being unchanged.

 

[8Mud]

Better check that again, high resistance = high voltage.

Resistance, in a simple circuit, changes the current from electricity to heat. You can change the form of energy but like the main man said, conservation of energy means it is never lost.

On a practical level, I can take a penlight battery with a volt and a half and maybe a 1000 milliamps and heat a piece of aluminum foil placed between the the two poles to over 600 degrees (likely a lot higher). Fuse material melts at a round 1000 degrees or a little more ( I round off for easy figuring).

When figuring how to fuse a circuit you start out at 75 F (closer to 73 F. actually) and subtract 10% or raise the fuse rating 10% for every hundred degrees in the wire or in the environment (that is what the engineers say who design the fuses). The environment means wherever the heat is coming from, the O2 heaters, the resistance in the wire, the engine compartment, radiated heat from the exhaust, wherever, even a faulty connection generating heat.

The heat has to go someplace, some radiates, some is leached/absorbed down the wire, whatever is generating the heat is still generating. The heat builds if it is generated faster than the wire can absorb it and radiate it.

The fuse gets to a little over a thousand degrees (closer to 800 F. in my experience) and it melts through.

I'm not trying to prove how smart I am, I'm not an engineer, except sometimes on a practical level. I'm just saying if you find no ground fault, or low ohm fault in a circuit after multiple tests, it is possible for heat to be the cause (or a factor) of repeated fuse failure. Not common. but it does happen. The reason the manufacturers supply you with a table to size fuses, with a heat component included, so you can size the fuse to the amp load and the heat.

Jeep had a TSB out, a recall, for fires started by loose connections in the PDC.

 

[8Mud]

I know what the equation says, but how are you going to get more than 14 volts from an automotive charging system? Amperage goes down as resistence goes up with the voltage being unchanged.

In a simple circuit, amperage goes down with resistance, but the amperage also changes state and becomes heat and is not electricity anymore.

 

[8Mud]

I know what the equation says, but how are you going to get more than 14 volts from an automotive charging system? Amperage goes down as resistence goes up with the voltage being unchanged.

In a simple circuit, amperage goes down with resistance, but the amperage also changes state and becomes heat and is not electricity anymore.

Edit: I re read that and we are talking past each other, sorry, I have a lot of distractions here at the moment.

 

[offroadordnance]

I know what the equation says, but how are you going to get more than 14 volts from an automotive charging system? Amperage goes down as resistence goes up with the voltage being unchanged.

You won't get more that 14 volts. A good electrical connection should have 0- .1 volts across it. A bad connection might be .1-.5 volts or more. An open circuit obviously can have no more tha source voltage. It's called a voltage drop test. When there's more or unintentional resistance in a circuit, the voltage across the component or connection increases. You made it sound like volt drop decreases across a bad connection.

 

[Bryan C.]

You won't get more that 14 volts. A good electrical connection should have 0- .1 volts across it. A bad connection might be .1-.5 volts or more. An open circuit obviously can have no more tha source voltage. It's called a voltage drop test. When there's more or unintentional resistance in a circuit, the voltage across the component or connection increases. You made it sound like volt drop decreases across a bad connection.

That isn't what I said. The whole point was somebody made a post that somehow high resistence in a circuit would cause a fuse to blow. 8mud is talking about heat causing the fuse to blow which is a valid point but I feel it has little practical application in an automotive environment. That isn't to say he is wrong or that it can't or will never happen.

Your point of high resistence means there will need to be more voltage to carry the same amount of amperage is correct in the sense of ohms law. Again, my point is that when there is a fixed voltage in a circuit your point doesn't work out quite the same in a real world automotive environment. I never said that voltage will increase in a bad circuit, we are simply talking about amperage draw in the given circuit in relation to the higher than normal resistence. The ohms law equation indicates that the 3 values(volts, amps, and resistence) are all related. When voltage is fixed, and resistence is fixed, then the amperage of the circuit becomes the variable.

So lets get this straight.

12 volts with 2 ohms resistence means the circuit will draw 6 amps.

Since the voltage in an autombile is fixed at around 12 volts that value in the equation will not change. So let's try the same equation with higher resistence.

12 volts with 4 ohms resistence means the circuit will draw only 3 amps.

So ohms law dictates that high resistence means lower amperage when voltage is fixed. The real world also says that if the resistence is high enough the voltage will drop as well. That is why one of the best tests for high resistence in a given circuit is not by placing an ohm meter lead on each end but to perform a voltage drop test while the circuit is loaded.

 

[offroadordnance]

You need to think of the circuit as a voltage divider when there is unintentional resistance introduced in series of the circuit. For example and easy math

10v volts across a 100 watt bulb draws 10 amps. The bulb resistance is 1 ohm and wattage across a good connection is 0 volts. The wattage across the connection is 0 since 0 volts x 10 amps=0watts.

If the connection were bad, say .111 ohms there would be 1 volt across the connection and only 9 volts across the bulb. The amp draw would be 9 amps calculated, 10 volts/1.11ohms=9 amps. Since the connection has 1 volt and 9 amps the wattage at the connection is 9 watts and the connector heats up. Since the bulb has 9v and 9 A it is 81 watts and dim.

 

[Bryan C.]

You need to think of the circuit as a voltage divider when there is unintentional resistance introduced in series of the circuit. For example and easy math

10v volts across a 100 watt bulb draws 10 amps. The bulb resistance is 1 ohm and wattage across a good connection is 0 volts. The wattage across the connection is 0 since 0 volts x 10 amps=0watts.

If the connection were bad, say .111 ohms there would be 1 volt across the connection and only 9 volts across the bulb. The amp draw would be 9 amps calculated, 10 volts/1.11ohms=9 amps. Since the connection has 1 volt and 9 amps the wattage at the connection is 9 watts and the connector heats up. Since the bulb has 9v and 9 A it is 81 watts and dim.

So what you are saying is that you agree with me, good.