Ballast Resistor Problem?

[rock jock]

My Jeep only starts when I jump the ballist resister.What are the causes? What should I look for? Need to get my Jeep running by Monday for work.


Rock Jock 88 Cherokee 4.0:eyes:

 

[ehall]

Re: Ballist Resister Problem?

What do you mean "jump"? You can bypass the thing, all it does is lower voltage for less noise. Just connect the two wires directly together.

It's not used during the start circuit so dunno why touching it would make it start

 

[rock jock]

Re: Ballist Resister Problem?

I dont know why theres no power to the leads going to the ballist resister? Resister itself has been tested and is good just no power going to it. Jeep only starts when I run a wire from power source to resister leads what does the resiser control? Is it for the fuel? What could be the possible causes for no power to the leads? Ignition switch is fine any help would be appreciated.

Rock Jock

 

[lucky9]

Re: Ballist Resister Problem?

Ignition relay, and wiring can cause this. Relay is usually under the hood. Not sure on an '88.

 

[ehall]

Re: Ballist Resister Problem?

I dont know why theres no power to the leads going to the ballist resister? Resister itself has been tested and is good just no power going to it. Jeep only starts when I run a wire from power source to resister leads what does the resiser control? Is it for the fuel?

Okay this makes sense. There are two circuits for the fuel pump. When you first turn the key there is a direct circuit that primes the pump at full voltage, pressurizing the fuel system. Once the engine starts the car switches over to the low-power circuit with the ballast resistor, which maintains pressure at lower voltage and less noise. So the ballast resistor isn't supposed to have voltage during startup. By routing battery power directly to it, you are forcing the pump to run. If the car won't start without doing this, then your ignition circuit is probably bad.

I don't know about the RENIX circuit stuff so I can't help you beyond that.

 

[djgrayxj]

Re: Ballist Resister Problem?

Note from DJ

B Latch Relay on a Renix
Automatic Shutdown Relay ASD (or B Latch on a Renix)] it can give problems with fuel delivery and spark.

The ballast resistor (eliminated in 94) is a white ceramic piece mounted to the driver's side fender well. It reduces the power from the fuel pump relay to make the pump run quieter. It can be a problem if it is burned out causing an open circuit. It can be bypassed without any issues other than possibly a noisy pump.

There are multiple paths of power to the fuel pump. When you turn the key to ON, power to the pump is 12 volts through the ASD (or B Latch on a Renix) relay bypassing the ballast resistor, and this lasts for about 3 seconds and then the PCM/ECU cuts the ground to the relay if it hasn't sensed a crank sensor signal. Next, when you turn the key to START, the fuel pump gets 12 volts from the starter relay, bypassing the ballast resistor. Third, when the engine is running, from idle to just short of WOT [Wide Open Throttle], the fuel pump gets power from the fuel pump relay, through the ballast resistor where the power is reduced to approx. 6 volts. And last, when the engine is at WOT, the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Relay Locations:
If you stand next to the passenger-side front fender and look down you will see 3 or [4 if you have AC] plastic cube shaped devices lined up in a row, these are the relays discussed above.

There placement is in this order from front to firewall in the order below order.

Fender
02 – Fuel Pump – B+ – AC
Engine

In front of these relays is a larger metal relay with a lot of wires connected to it, this is the starter relay.

If I was trying to correct your problem as I understand it I would mark the fuel pump relay with some tape. Then remove it and plug it back in several times, this will clean up the contact points some. Now try and start the Jeep.

If starts and runes then you only had dirty contacts if not swap this relay with one of the other relays, preferable with the AC relay if you have one second choice would be the 02 relay and try starting the Jeep again.

I hope this info helps post back what happens.

 

[Ecomike]

Re: Ballist Resister Problem?

Note from DJ

B Latch Relay on a Renix
Automatic Shutdown Relay ASD (or B Latch on a Renix)] it can give problems with fuel delivery and spark.

The ballast resistor (eliminated in 94) is a white ceramic piece mounted to the driver's side fender well. It reduces the power from the fuel pump relay to make the pump run quieter. It can be a problem if it is burned out causing an open circuit. It can be bypassed without any issues other than possibly a noisy pump.

There are multiple paths of power to the fuel pump. When you turn the key to ON, power to the pump is 12 volts through the ASD (or B Latch on a Renix) relay bypassing the ballast resistor, and this lasts for about 3 seconds and then the PCM/ECU cuts the ground to the relay if it hasn't sensed a crank sensor signal. Next, when you turn the key to START, the fuel pump gets 12 volts from the starter relay, bypassing the ballast resistor. Third, when the engine is running, from idle to just short of WOT [Wide Open Throttle], the fuel pump gets power from the fuel pump relay, through the ballast resistor where the power is reduced to approx. 6 volts. And last, when the engine is at WOT, the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Relay Locations:
If you stand next to the passenger-side front fender and look down you will see 3 or [4 if you have AC] plastic cube shaped devices lined up in a row, these are the relays discussed above.

There placement is in this order from front to firewall in the order below order.

Fender
02 – Fuel Pump – B+ – AC
Engine

In front of these relays is a larger metal relay with a lot of wires connected to it, this is the starter relay.

If I was trying to correct your problem as I understand it I would mark the fuel pump relay with some tape. Then remove it and plug it back in several times, this will clean up the contact points some. Now try and start the Jeep.

If starts and runes then you only had dirty contacts if not swap this relay with one of the other relays, preferable with the AC relay if you have one second choice would be the 02 relay and try starting the Jeep again.

I hope this info helps post back what happens.

Lots of very good info there, but I disagree on a few points:

When you turn the key to ON, power to the pump is 12 volts through the ASD (or B Latch on a Renix) relay bypassing the ballast resistor, and this lasts for about 3 seconds and then the PCM/ECU cuts the ground to the relay if it hasn't sensed a crank sensor signal.

Near as I can tell, the ECU closes the fuel pump relay for several seconds in run position just before cranking, and then powers it off, not the B+ latch. BUT, if the B+ latch does not work at initial power up, I am not sure if that causes ECU problems? I do know the B+ latch relay stays on after the engine is turned off, to allow the ECU to reset the IAC valve on the throttle body, for proper air flow during the next restart.

I do see a hot 12 volt route through the O2 sensor heater relay, that seems to power the fuel pump in position one, and the power the O2 sensor heater in position 2, which seems very odd, to say the least? The fuel pump relay coil seems leads seem to run to the Ignition control module, the oxygen sensor, and the fuel pump, a common yellow wire, then the other end of the fuel pump coil leads to the ECU, probably for the ground, but the more I look at this drawing, the stranger it looks!

Next, when you turn the key to START, the fuel pump gets 12 volts from the starter relay, bypassing the ballast resistor. Third, when the engine is running, from idle to just short of WOT [Wide Open Throttle], the fuel pump gets power from the fuel pump relay, through the ballast resistor where the power is reduced to approx. 6 volts. And last, when the engine is at WOT, the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Problem I am having, is the drawings I am looking at, only show the relays, and the ECU, and do not show the actual wiring to the fuel pump itself. I am looking at the Haynes drawing. Perhaps the FSM drawings are better?

I am curious, where did you find this claim:

And last, when the engine is at WOT, the fuel pump gets 12 volts from the oxygen heater relay, bypassing the ballast resistor.

Does O2 heater get turned off at WOT in the process? It looks to me, that if that is correct, then the ECU may be using the O2 sensor heater relay to power the fuel pump in the initial seconds of powering up to start?

FWIW, I have started and run a Renix for months, with the O2 sensor's heater power relay PULLED!!!! I did this because the O2 sensor heater wire had shorted to ground, due to a close encounter with the Ex-Manifold.