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Fuel ballast resistor problem

ljobbins

NAXJA Forum User
NAXJA Member
Location
SD County
Renix!

So yesterday my car died on the freeway and I pulled to the shoulder. It started back up fine several times in a row but died instantly. It would not idle at all. Got it towed back to the house and then read on here about jumping the resistor to test it. I grabbed piece of wire and jumped it and it ran fine. I ordered a new resistor and had to drive the car all day today on the jumper wire. It ran fine all day. I just got the new resistor and put it in and it idled fine but the second I put a load on it, it died again. Threw the wire on agin to get to school and it ran fine again.

Ideas? The new resistor bad out of the box? Something on the same circuit causing resistance to the point of the new resistor causing too much resistance for the fuel pump to work correctly? How long can I run with it jumped before I cause damage to something else? I don't have a good wiring diagram. Is there anything in the circuit that should cause resistance? In other words, if I read wires for resistance should I expect anything in the same circuit before or after? Thanks!
 
The aftermarket ones are crap. Just bypass it. Later models do not have them anyhow.
 
On some models there is like five connectors between the resistor and the fuel pump. I've had one of those connectors partially melt down.

The easiest way to check is for a voltage drop between the pump side of the resistor and the fuel pump power in the rear.

You may also want to look at the pump ground.

You may also want to rent/borrow a gauge and check your fuel pressure.

Could be a faulty new resistor or what you postulated, you have more than one issue, multiple faults causing excess resistance.
 
Does anyone know what the voltage should be on the backside of the resistor or what ohms the resistor should be? I tried searching and couldn't find anything and don't have any numbers on my basic Haynes wire diagram.

My moms truck is having fuel problems so when I get a chance(probably Monday) I'll rent a fuel pressure gauge and check mine when I check hers. Hopefully I can find my resistance problem quickly. Thanks guys.
 
The fuel pump could be going out and will not run well enough with the resistor in series.
 
Does anyone know what the voltage should be on the backside of the resistor or what ohms the resistor should be? I tried searching and couldn't find anything and don't have any numbers on my basic Haynes wire diagram.

My moms truck is having fuel problems so when I get a chance(probably Monday) I'll rent a fuel pressure gauge and check mine when I check hers. Hopefully I can find my resistance problem quickly. Thanks guys.

You need to test the ground at the fuel pump versus the battery post negative, takes a very long test wire. Should be less than one ohm. Then test the voltage at the fuel pump, with the ballast resistor jumped/bypassed. It should read about 13-14 volts with the engine running at the fuel pump

Renix is notorious for bad/poor inadequate grounds.

The discharge hose on the pump inside the gas tank may be failing, and leaking and causing you to need peak voltage, power and flow output. Today's gas eats the old rubber up.
 
So I tested the wires from the backside of the ballast resistor.
All wires including ground from pump to battery are .3 or less ohms so they all test good.
Voltage to the pump is 13.5 on the pink(thicker wire) and 2.58 on the yellow or beige wire(thinner) with the ballast resistor jumped. I'm not sure which wire is the pump and which is the fuel level sender.
I also could not find what the correct resistance should be for the ballast resistor but mine is 3.1ohms.
Fuel pressure is 40 with the vacuum to the pressure regulator disconnected and 31 with it connected.
 
So I tested the wires from the backside of the ballast resistor.
All wires including ground from pump to battery are .3 or less ohms so they all test good.

Good

Voltage to the pump is 13.5 on the pink(thicker wire)

Good

and 2.58 on the yellow or beige wire(thinner) with the ballast resistor jumped.

Sounds Good

I'm not sure which wire is the pump THE 13.5 V wire should be

and which is the fuel level sender. THE 2.58 V wire should be the return signal from the 13.5 V input, I think.

I also could not find what the correct resistance should be for the ballast resistor but mine is 3.1ohms.

Sounds good to me.

Fuel pressure is 40 with the vacuum to the pressure regulator disconnected and 31 with it connected.

Both are dead on! Was that with the Ballast resistor bypassed??? If yes, what is if with it in the circuit?

Did the problem go away?
 
Test the fuel pressure with the ballast resistor connected, and then see how it idles in drive and what it does when you give it gas in park with the Vac line connected and pinched off.

If it runs fine and the pressures are 31 and 40, what was the old resistor resistance? If it was near 3 ohms, you may a different problem that is coming and going randomly and just happened to to do so when you were bypass the resistor?
 
The problem did not go away. The resistor was jumped for the pressure tests. I'll test the pressure in the morning with the resistor in series as it should be. I'm pretty sure I have the old resistor still so I will check that too. And I have a manual so instead of park with gas should I just be in neutral, or in 1st off the ground, or does it not apply to me? Thanks for the help.
 
Opinion, but you just need to test pressure idle engine cold, then again above 2500 RPM engine cold. Then again at idle engine at operating temp. then again at 2500-3000 RPM. Hold the higher RPM for maybe quarter-half a minute. If you have an issue it should show up doing this.

I've actually driven around with a fuel pressure gauge taped to my drivers side windshield wiper. :)

Two things going on with the pump, pressure and volume. Two things going on with the power to the pump voltage and amperage.

The voltage drop across the ballast resistor is IMO a better test than OHMs. The voltage drop changes some, depends on how hot (the demand) the resistor gets. Been awhile but the last time I tested one it was 1.1 ohms cold (I think). But like I said the OHM test can be iffy, the OHMs change as the ballast resistor heats up.
 
Test the fuel pressure with the ballast resistor connected, and then see how it idles in drive and what it does when you give it gas in park with the Vac line connected and pinched off.

If it runs fine and the pressures are 31 and 40, what was the old resistor resistance? If it was near 3 ohms, you may a different problem that is coming and going randomly and just happened to to do so when you were bypass the resistor?

At one time, when I first bought my third Renix I had a faulty ballast resistor, a marginal CPS, bad ground on my TPS, vacuum leaks and marginal O2 sensor. How they interacted is anybodies guess. I do know my symptoms kept changing.

Mine occasionally died at freeway speeds, turned out to be the ballast resistor.

Then it would buck at a round 2000-2500 RPM and wouldn't rev higher than 3500 RPM on the freeway. Turned out to be the O2 sensor.

Idle was crappy, all over the place, sometimes high sometimes low, turned out to be both vacuum leaks and TPS ground.

Iffy starts was the CPS.

Miss at idle was cables and low power to the ignition control module and corroded contacts on the coil.

Like Mike said you may have multiple faults.
 
The problem did not go away. The resistor was jumped for the pressure tests. I'll test the pressure in the morning with the resistor in series as it should be. I'm pretty sure I have the old resistor still so I will check that too. And I have a manual so instead of park with gas should I just be in neutral, or in 1st off the ground, or does it not apply to me? Thanks for the help.
------------------------------

Cruiser54's write-up is GOOD !! It helped me A LOT !!

I'm concerned about your 3.1-Ohms reading on the resistor. I just went through similar trouble with my ('89 / 242 cid / 5-speed manual). Autozone's part # 8214 (for '89 and '88) description says 0.8-Ohms.
Your last stated want-to-check fuel pressure with the engine running, is a good next step. The Resistor (circuit) is to reduce voltage to the Fuel Pump -after- the engine is running. But(!!), that circuit is activated by the Fuel Pump Relay (we can discuss that, later, if needed.)
I installed a 0.5-Ohm resistor, which dropped the voltage (voltage-test individually on the resistor terminals - to ground) approx 1.5-volts (engine running.)
- If yours is reading 3.1-Ohms, it may be reducing the voltage far below proper pump-speed to maintain 28-40 psi at the Fuel Rail test-point.
 
X-2

Also, most folks have just eliminated the Ballast resistor, bypassed. Cruiser said when He was at Service Rep the dealership Jeep (for years) Jeep had added the resistors to reduce customer complaints about fuel pump noise. It is reportedly there for no other known reason. No one has ever said they had any problem running with out them
 
Quite correct, Mike. It comes down to individual choice.

Based on my Forum reading, I had cut the wires (saved the pigtails) and through-connected the harness wires (eliminating the resistor.) But, I decided to put the resistor back in the circuit to (maybe) increase the fuel pump life. Will it make a difference? Who knows.

- When I reconnected the pigtails, I used bullet-terminals (one can use spades.) On one harness-lead, I put a male; on the other harness-lead, I put a female (and the opposites on the leads to the resistor.) Now,... if I need to bypass the resistor, I can disconnect those connections and plug the harness wires together.

Also, I found a comment (#9 on thread http://naxja.org/forum/showthread.php?t=1118963&highlight=starts+dies+renix) which specifies 1.1 Ohms.
 
im just going to throw my 2 cents in. if the resistor does drop the voltage down. it would in theory raise the current up and cause more heat. i still have my resistor in. i figure its there for a reason. i have had it bypassed and never noticed a difference.
 
So problem is still around but with a crazy school schedule lately I've been able to keep my daily driving down below 10 miles each day basically just living in textbooks and classrooms. I know something is funky but I'm not sure what yet. I'll swap resistors when I have a chance to see if a different one is 1 or less ohms. Fuel pressure seems fine at idle in all scenarios. Cold start, warm, revving for 30 plus seconds, blipping engine cold and warm. I've been testing resistors and so far everything is fine. Tps, iac, tb cleaned, injectors tested for power and change in proportion with engine speed, newer plugs and wires. I will check and replace if necessary the cap and rotor tomorrow. Both temp sensors good. O2 sensor is less than 4 months old with proper heater volts. Relays check good so far. All grounds good and refreshed. I'm close to just redoing all the wiring if I can't find something very soon. All vacuum hoses replaced with fresh flexible ones that I routed away from melting possibilities. Vacuum checks good too. Going to check compression maybe tomorrow to make sure I'm not missing something giant in the cylinder areas. Map sensor checks good.

Spring break is in a week and if necessary I will rip apart the electrical system to fix or replace all 29 year old wiring and connections. I would rather sit around and relax with no school work though so if anyone has any other suggestions to save me from going to such drastic measures please chime in.

Thanks for the help so far.
 
Clean al, the grounds. Remix XJ's are real finicky about grounds. When I say clean them I mean remove them and use sandpaper or a wire wheel and make sure all surfaces are clean and shiny. Check Cruiser54's Remix tips for locations of the grounds. Only took me an hour to do and made a big difference in running. Once done trouble shooting the fuel pump again. There is also no real down side to bypassing the fuel pump resister. Many of us run without them with no problems. The fuel pump is slightly louder is all.
 
Forget swapping in a different resistor, just bypass it and be done with it.

When the ballast resistor in my '92 literally crumbled into dust about 10 years back that's what I did, and I've never looked back. I didn't notice a noise level difference, you probably won't either - these are Jeeps after all, not Rolls Royces...
 
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