Very hot fuel ballast resistor!

[Zebvance]

So today I was putting a newer style valve cover on my 1988 renix 4.0 mj to fix my blow by problem ( so far it has worked), while the truck was running I was checking for vac leaks and I touched the fuel ballast resistor and it burned the crap out of me! Is this thing suppose to be that hot?

 

The truck has been running very rich, which I have started this thread about and not many people have put in there input about.

 

 

Thread here: http://comancheclub.com/topic/44352-overwhelming-exhaust-smell-updated-10-7-14/

 

 

 

So is this a issue that might be connected with my mj running rich? Or is it no issue at all?

[onlyinajeep726]

It should not be getting hot.  Also, that shouldn't have anything to do with it running rich.  Bypass the resistor and permanently connect the two wires together.

[HOrnbrod]

Yes, it gets hot enough to burn the crap out of you. Check it with your ohmmeter - should read a little over an ohm.

 

As far as your other thread, I still think you have too much injector. Get a fuel pressure gauge at Autozone or somewhere and check pressure at the rail with vacuum and w/o vacuum to the regulator.

[Zebvance]

Yes, it gets hot enough to burn the crap out of you. Check it with your ohmmeter - should read a little over an ohm.

 

As far as your other thread, I still think you have too much injector. Get a fuel pressure gauge at Autozone or somewhere and check pressure at the rail with vacuum and w/o vacuum to the regulator.

Thanks I'll check the ohms tomorrow after work. Would I be feeling a loss of power because it's running rich?

 

Also, I have a pacesetter header, opened up the exhaust to 2.5 inches, have a high flow cat, and a magnaflow muffler.

Along with a snorkel, if you want to count that as a cold air intake.

And I'm buying a 60mm throttle body next week. Will it need more fuel with the bigger throttle body? If it's running rich now will it be at the level it needs to be with the bored throttle body?

 

I know I need the fuel pressure numbers to really know, which I will hopefully have for y'all this week, but these are "in theory questions"..

[gogmorgo]

Resistors do get hot... they reduce voltage by turning electricity into heat.

 

When you replaced your exhaust, what did you do with your o2 sensor? They're quite easily damaged is what I'm getting at. Also, I understand that they "breath" through the connector in some way, so if you wrapped the wires in some way, you could be interfering. But a vacuum leak or something is more likely than a bad O2 imo.

[Zebvance]

I put a brand new o2 sensor in it. I don't feel like it is a vacuum line issue, because it idles and runs for the most part pretty good.

[HOrnbrod]

Also, I understand that they "breath" through the connector in some way, so if you wrapped the wires in some way, you could be interfering.

 

This is true.

 

For an O2 sensor to operate, It has to have a supply of outside air(reference air) to compare to the exhaust stream. On older style sensors, this air was supplied via holes in the sensor housing. It was found that these holes would get plugged overtime so the engineers designed a sealed sensor that draws its reference air thru the wire strands inside the insulation. If you solder the connections, then the solder seals the path for the reference air and the sensor can't 'breathe'

 

I found this out the hard way. When I first put exhaust headers on, I needed to extend the wires about 6" as the exhaust bung was too far away for the stock O2 sensor harness to reach the connector. Since my O2 sensor was almost new, I soldered in extension wires using 50/50 rosin core, heat shrunk the solder joints and hooked everything back up. It ran fine but would intermittently switch from open loop to closed loop, then back while driving. I could see it on my A/F meter. I found the above quote somewhere looking for the cause, and the light bulb went on. The fix was to replace the MJ/XJ O2 sensor with one from a ZJ; the harness was long enough to make the distance w/o splicing. There are also manufactured O2 harness extensions you can buy for both 3-wire and 4-wire sensors if you can't find an O2 sensor harness long enough for your application.

[onlyinajeep726]

I must be the only one that doesn't get a hot ballast resistor, then... :dunno:

[Zebvance]

 

Also, I understand that they "breath" through the connector in some way, so if you wrapped the wires in some way, you could be interfering.

 

This is true.

 

For an O2 sensor to operate, It has to have a supply of outside air(reference air) to compare to the exhaust stream. On older style sensors, this air was supplied via holes in the sensor housing. It was found that these holes would get plugged overtime so the engineers designed a sealed sensor that draws its reference air thru the wire strands inside the insulation. If you solder the connections, then the solder seals the path for the reference air and the sensor can't 'breathe'

 

I found this out the hard way. When I first put exhaust headers on, I needed to extend the wires about 6" as the exhaust bung was too far away for the stock O2 sensor harness to reach the connector. Since my O2 sensor was almost new, I soldered in extension wires using 50/50 rosin core, heat shrunk the solder joints and hooked everything back up. It ran fine but would intermittently switch from open loop to closed loop, then back while driving. I could see it on my A/F meter. I found the above quote somewhere looking for the cause, and the light bulb went on. The fix was to replace the MJ/XJ O2 sensor with one from a ZJ; the harness was long enough to make the distance w/o splicing. There are also manufactured O2 harness extensions you can buy for both 3-wire and 4-wire sensors if you can't find an O2 sensor harness long enough for your application.

 

 

I did this exact thing when installing my pacesetter header. Hopefully this is the problem then.

 

[big66440]

My ballast used to get very hot also, but i bypassed it and don t worry about it anymore.

[Zebvance]

I'm not going to bypass it. It was put there by a electrical engineer with more knowledge than me for a reason. I am going to trust that it is there for a good reason and to serve a purpose in making the correct ohm load go to the fuel system.

[HOrnbrod]

The 1.3 ohm fuel pump ballast resistor is a high power wire-wound resistor placed in series with the fuel pump 12V supply and acts as a current limiting device for the pump. This makes the fuel pump run at a lower RPM, run quieter, and prolongs it's life as it doesn't have to work as hard after the engine starts. It's supposed to get hot, that's why it's mounted in a porcelain heat sink. 

[mvusse]

And in 1987 they didn't even have a ballast resistor. My stock pump without a resistor lasted more than 20 years.

 

I think it was added more to keep customers from complaining about the pump being too loud than to prolong its life.

[HOrnbrod]

Probably true, but maybe if they had installed ballast resistors in 1987 the pump would have lasted 25 years? We'll never know..........

[cruiser54]

And in 1987 they didn't even have a ballast resistor. My stock pump without a resistor lasted more than 20 years.

 

I think it was added more to keep customers from complaining about the pump being too loud than to prolong its life.

EXACTLY true. If prolonging it's life happened, that was a bonus. 

[big66440]

And in 1987 they didn't even have a ballast resistor. My stock pump without a resistor lasted more than 20 years.

 

I think it was added more to keep customers from complaining about the pump being too loud than to prolong its lifevery

Very true it is louder now than before but I know I'm not driving a luxury car by any means besides I can only hear it when I'm idling once I get moving the noise from the $&!^* vent windows and tail gate chattering drown it out, as far as making it last longer I guess it depends on who you ask my take on it is it's D/C current so the pump will only take what it needs, if it where A/C I could see the pump getting burned out much quicker with the increase of "juice" when you bypass the resistor.

[HOrnbrod]

After the engine starts and the fuel pump relay switches in the ballast resistor to limit the fuel pump supply voltage, the pump runs constantly until you turn the ignition off. Because the ballast resistor is a current limiter and lowers the supply voltage to the pump, it runs slower and quieter. This prolongs the life of the pump. The fuel pump doesn't "take what it needs"; it runs at a fixed RPM depending on it's available supply voltage. And I have no clue what you are referring to with AC motors.

 

And yes, they started using the resistor initially because of excessive pump noise complaints, but an added benefit is that the motor doesn't have to work as hard thus extending it's life. Jeeps are not the only vehicles that incorporate a ballast resistor in the fuel pump supply circuit. But you do what you want to mate.

[Zebvance]

Only had time to put a meter to the resistor today. Was 1.5 ohms. I jumpered it and started the truck and it was defiantly louder. Also I really think the rich exhaust smell was stronger when it was jumpered. I could have been already light headed from the exhaust smell to begin with but it really did seem more potent.

[Zebvance]

Didn't get a chance to check the fuel pressure due to a overwhelming day at work and the lack if motivation to do anything when I got home. Fresh out of school and two months of being a engineer have really tested my brain a lot more than I thought it would. My brain feels like mashed potatoes.

[mvusse]

The fuel pressure at the rail should have nothing to do with the pump. As long as the pump can supply more volume than the engine needs at a higher pressure than the fuel regulator is set at, the fuel regulator controls the pressure and bleeds the excess off through the return line back to the tank.

 

I run a 4.0 fuel pump in my 2.5 because I had it sitting on the shelf and didn't see a point in buying the correct one since the 4.0 one works fine. No difference in how the 2.5 runs.

On my trail truck I run a circle track fuel cell to which I added a return line. Since the cell is meant for a carbureted vehicle it has no provisions for a pump. I run a universal external pump rated ed at 70psi with enough flow to feed a small V8. Fuel pressure at the rail is right where it should be and just like the 2.5 with the 4.0 pump, the truck doesn't run any differently.

[Rockfrog]

[cruiser54]

It's just a resistor placed there to reduce interior noise (due to customer complaints) it was eventually dropped from the line.

Had nothing to do with pump longevity, and undervolt in a DC motor doesn't make it last longer or work easier. Those mashed potatoes are over thinking it a little.

I would start looking elsewhere for a suspected rich running condition.

This^^^^^^

[big66440]

After the engine starts and the fuel pump relay switches in the ballast resistor to limit the fuel pump supply voltage, the pump runs constantly until you turn the ignition off. Because the ballast resistor is a current limiter and lowers the supply voltage to the pump, it runs slower and quieter. This prolongs the life of the pump. The fuel pump doesn't "take what it needs"; it runs at a fixed RPM depending on it's available supply voltage. And I have no clue what you are referring to with AC motors.

 

And yes, they started using the resistor initially because of excessive pump noise complaints, but an added benefit is that the motor doesn't have to work as hard thus extending it's life. Jeeps are not the only vehicles that incorporate a ballast resistor in the fuel pump supply circuit. But you do what you want to mat

From what I understand about electrical A/C current will force itself through a load like plugging a 115V accessory to a 220V outlet will fry the accessory , since the fuel pump runs on D/C current it will only take the volts and amps that "it needs" to run even though there is 12+ volts and quite a few amps from the source, now that I think about it you are right by running the fuel pump with the resistor it will slow the pump down which in theory should last longer due to less stress.

[onlyinajeep726]

From what I understand about electrical A/C current will force itself through a load like plugging a 115V accessory to a 220V outlet will fry the accessory , since the fuel pump runs on D/C current it will only take the volts and amps that "it needs" to run even though there is 12+ volts and quite a few amps from the source, now that I think about it you are right by running the fuel pump with the resistor it will slow the pump down which in theory should last longer due to less stress.

 

Your understanding of how current and voltage works is lacking.  In terms of DC, increasing the voltage will cause a basic motor to spin faster.  Ohm's law states: V = I*R, where  V: Voltage, I: Current, & R: Resistance (measured in Ohms).

 

Say the fuel pump motor has 3 ohms of resistance (I just made up a random number for this example).

 

Assuming no ballast resistor is used in series with the fuel pump, the total resistance is the 3 ohms I made up before.  Lets also assume the pump pulls 4 amps of current.

 

V = 4*3.  V = 12 volts DC.  Easy enough.

 

Now, add that ballast resistor in series like AMC did.  We now have 4.1 ohms of total resistance (3 from the pump, 1.1 from the ballast resistor).

 

The pump is still only supplied the 12 volts DC so the current must go down because the resistance went up.  12 = I*4.1.  Divide 12 by 4.1 and you get I = 2.92682 amps.

 

The point I'm trying to illustrate is that by adding resistance in series with a motor (in this case the ballast resistor) with the same voltage supply, you will lower the current that is supplied to said motor.  This, in turn, will cause the motor to spin slower.  Current is what drives a motor.

[big66440]

I completely understand the resistance (from the resistor) will slow the fuel pump down, I really don't mean to sound like a smart @$$ but I stated that at the end of my last post, thanks for taking the time for posting the example tho i haven't gone into the ohms law equations in a loooooong time.