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Ballast Resistor Revisited

S

sflasal

NAXJA Forum User
Location
Broward County FL
After figuring out ( in a large part through NAJXJA you guys ROCK! ) that my starts but wont run issue is most likely a Ballast Resistor gone bad, I set out to buy a replacement. I've searched high and low locally NAPA,
Benet, AutoZone, Advanced Auto, even the Jeep Stealership, er Dealership's Parts Department and no one has one. No one can even tell me where to get one.

Since I cant find the part, I'm going to jumper around it. Problem with that is, I'm not 100% certain what my Ballast Resistor looks like :dunce:

Is this the ballast resistor
l_9107f428c7cb46cbba788a314c847c88.jpg
 
No, that's the MAP sensor.

The ballast resistor is, as mentioned, just behind the driver's side headlamp. It's an off-white ceramic dingus, about 1/2" square in cross-section and 3-1/2" to 4" long. It will have two wires connected using 1/4" spade terminals.

Note that the ballast can be safely eliminated - it was added as a "Voluntary Recall (NVH) in late 1987/early 1988, and was installed from the factory from mid-1988 to around 1995 or so. My 1987 never had one, my 1988 has had it removed - just get a short section of wire (I think the OEM there is 14AWG,) put a male 1/4" spade quick-connect lug on each end, and connect the two female lugs together using that jumper. Tape (or heat-shrink) to insulate, and problem solved. That's how I eliminated it on my 88 (I don't think I even bothered to take the failed resistor out - just bypassed it and called it good.)

You'll get a bit more pump noise doing this - that's why it was added, was NVH complaints - but it shouldn't cause anything more difficult than that. I eliminated mine something like five or six years ago.
 
BrokenXJ said:
MAP. Manifold ??? Pressure for the fuel injection
Click to expand...

"Manifold Absolute Pressure" - RENIX and Chrysler controls use pressure and temperature to compute the amount of air going into the cylinders for fuel metering, and trim that using the HEGO (Heated Exhaust Gas Oxygen sensor) in a feedback loop.

This differs from Ford, which uses a MAF (Mass AirFlow) sensor directly in the intake plumbing to read how much air is flowing through it.
 
Thanks 5-90 (once again!)

What really blows my mind, is that the part isn't even available at the dealership. I've gotten used to NAPA and the others telling me they cant get some esoteric part. This is the 1st time I've ever gone to a dealership's parts department only to be told, "Sorry don't have it, cant get it! Go to a junkyard"
 
sflasal said:
Thanks 5-90 (once again!)

What really blows my mind, is that the part isn't even available at the dealership. I've gotten used to NAPA and the others telling me they cant get some esoteric part. This is the 1st time I've ever gone to a dealership's parts department only to be told, "Sorry don't have it, cant get it! Go to a junkyard"
Click to expand...

If you take a look at the contacts on it (the small copper bits, duh...) you should see a number stamped into one up near the ceramic. This is the resistance value in ohms - and you can always just take that in and say "I need a ballast resistor with a value of X.x ohms." Their catalogues should list that as well.

Typical values for a ballast resistor are 5 ohms are less, with most of them being 2 ohms or less. The primary purpose of a ballast is a "current-limiting device," used to increase the resistance of a circuit slightly to reduce current. This is typically done to either reduce the noise of a DC motor, or to reduce heat in a static coil assembly (like an ignition coil, on older vehicles. With the key in START, the ballast was bypassed for a hotter spark. With the key in RUN, the ballast was back in circuit to keep coil heat down.)
 
Just went outside and looked and I've positively ID the part.
Is there any reason why I can't/shouldn't just clip off the spade connectors, strip down the wires a bit,put the 2 ends together with a but joint connector, and then heat shrink over the whole repair area?
 
sflasal said:
Just went outside and looked and I've positively ID the part.
Is there any reason why I can't/shouldn't just clip off the spade connectors, strip down the wires a bit,put the 2 ends together with a but joint connector, and then heat shrink over the whole repair area?
Click to expand...
thats exactly what I did with mine - mine would start up and run for a couple secs and die - see what happens is when you start the jeep the fuel pump gets full power then after like 3 seconds the power is redirected via a relay through the ballast resistor which cuts down the power to the fuel pump to make it quieter
 
sflasal said:
Just went outside and looked and I've positively ID the part.
Is there any reason why I can't/shouldn't just clip off the spade connectors, strip down the wires a bit,put the 2 ends together with a but joint connector, and then heat shrink over the whole repair area?
Click to expand...

None at all. It was "added" on my 88, so I just went the other way. Besides, I keep loads of wire and terminals around anyhow - I'm always doing something-or-other electrical...
 
Would this cause the vehical not to start after fuel pump replacement.

Had a loud fuel pump that gave insufficeint fuel pressure and would start when it wanted too. Replaced with new pump but will not start. I have power at relay but little to no power at the pump.

Would any one know the currect voltage suplied to the pump during start up.

Sorry for the Hijack
 
i went through this whole mess myself, couldnt find anything wrong in fuel system but it would run for a few seconds than die, replaced the resistor, still had the same problem so I just deleted it and never had the problem again. I dont like leaving mysterys unsolved but i will accept this one and my now noisier fuel pump with no complaints.
 
vwfoolwhy said:
Would this cause the vehical not to start after fuel pump replacement.

Had a loud fuel pump that gave insufficeint fuel pressure and would start when it wanted too. Replaced with new pump but will not start. I have power at relay but little to no power at the pump.

Would any one know the currect voltage suplied to the pump during start up.

Sorry for the Hijack
Click to expand...

during start up, i believe the pump gets full power(12V). once started the power curcuit goes through the ballast which reduces the power. the ballast is by passed during start up so i dont think its your problem.

i would swap the fuel pump relay with another one in the relay center. what pin are you measure the voltage from. the relay will have a 12v trigger and a 12 volt output, but i forget what the number is for the output side of the relay. i will look to see if i can find it.
 
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