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What causes the rotor and dist.cap to corrode?

Den nakne viking

NAXJA Forum User
Location
Norway
I am trying to diagnose rough idle. I found that one of the factors was corroded rotor and dist.cap connections. So I replaced rotor, dist. cap, wires and sparkplugs for about 3 weeks ago. It got a bit better...

...today I continued the search and found out that the same had happend with the rotor and touch points in the dist.cap. What could cause this?
Coil?
Battery?
Ground cables?


I am also thinking there is a leakage in the intake manifold or fuel injectors. and a bad IAC.

Powerful, runs smooth, clean exhaust. only rough idle.
New o2 sensors, new header, exhaust and tune up.

97' 4.0 xj
 
Condensation coming from the crankcase.Specially seeing where your from,thats why short trips are so hard on things.On long road trips the moisture will burn away due to the longer/higher sustained temps!
 
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Think about driving at about 60MPH/100KPH. The distributor in spinning at half of engine speed- engine about 2000RPM, dist. at about 1000RPM. With six contacts, you are having 6000 make/break cycles each minute. A mini electrical storm all in the space of a few cubic inches/cm. Once an electrical circuit is established, energy does not want to stop flowing. Now, even though the shot of electricity is just momentary, a spark jumps the gap, as the rotor is whizzing by a contact. It can't stop and wait for the field to dissipate, because just as fast , the rotor is off to the next contact, starting a discharge cycle all over again. Add into that some damp air and condensation, which is electrically conductive, and you have a real firestorm going on. Breaking electrical arcs is the hardest work a contact could do. Yeah, they're designed for it, but ultimately the energy wins.

Make sure the dist. cap is seated squarely, possibly wipe a bead of dialectric grease around the seam before seating the cap, and I'm not sure about the shaft seal, but maybe it's worn, allowing hot vapors to rise out of the crankcase, causing vapors to accumulate inside the cap. I've seen Chevys push oil up. a real mess.

Hope all of this sheds some light on your problem.
 
I had one episode. a distributor with a tiny amount of moisture (likely from a motor wash) that would settle in the bottom. After the motor would cool down it would re condensate and run down to the bottom again. Cold weather was a factor. Drove me nuts until I finally figured it out.
Another factor is most of the distributor caps have a vent, if they salt the roads, eventually the salt finds it's way into the distributor. Close the vent with a dab of silicon. On the early XJ distributors, a Ford cap would fit (without the vent and actually a little cheaper), not sure about a 97.
I've found buying quality rotors and caps is helpful. I#ve also noticed the rotors and caps tend to wear (corrode and pit) faster than my plugs do.
 
Forgive the details here but just trying to add a little more light and my 2 cents on the topic. My background is that I currently have three Cherokee 4.0L XJs, one of them is a 97 like yours and the others are 96 and 2000, I am not an expert but have had Cherokees continuously since 1985 and have done all service/repair work myself. Just for reference and firstly I wonder how bad the idle is on yours... mine all exhibit what some may consider a "rough idle" both warm and cold, I have always considered this minor fluctuation in idle speed (RPMs) normal. I purchased the 96 brand new and it has always had this characteristic. If you are new to these they may seem to idle a little rougher than other engines. Secondly did you gap the plugs according to the spec.? Thirdly, in reference to the contacts in the distributor cap, I also wonder if you have a problem there, this depends on how much corrosion you are seeing and if it is all around the metal contacts or only on the "faces" where the connection is made. The actual spark current is passed from the rotor to the distributor contact via an arc or plasma, not by direct contact. This arcing will cause the contacts to look "corroded or burnt" after a short while of normal use. RCP and oldman are correct about the overall corrosion (of this and many other parts as well) if the engines are not continuously run up to full temperature. Lastly if the idle is rougher than you previously had or think is unreasonable then further troubleshooting is warranted. Other forums I have read indicate that the some of the items you pointed out may be the cause: fuel pressure (check fuel pressure on fuel rail, should be around 45 PSI I believe - low pressure indicates a clogged fuel filter which is located inside the gas tank), dirty injectors/valves, vacuum leak, sticky idle motor, intermittent Crankshaft Position Sensor (or associated connections) or a cylinder which does not have enough compression thereby not firing completely (check engine compression). Dirty injectors on one of my other vehicles caused rough idle and poor performance, one bottle of injector cleaner in a full tank of gas worked miracles on this problem, does the gasoline you routinely use include cleaning additives such as the "Top Tier" gasses sold here? Good luck, have fun and let us know what you find.
 
Are you buying quality components?

Seriously, the cheaper caps and rotors will deteriorate faster.
 
wow... alot of good ideas and great reflections. Nice;) this helps me a lot.

I am running a premium cap. The one that I changed was also premium stuff.

I know that the corrosion deposited on the terminals is a direct result of High Voltage Arcing. And that corrosion in the long run is unavoidable. The theory about humidity is reasonable, since i live in the land of ice and snow (its been raining for 2 months). But something tells me there is an electric problem also. I am still thinking that my battery, battery(ground) cables or coil are making some of the trouble??

Tomorrow I am going back to the garage. Gone try another battery, test vacuum and spark plug gap, check engine ground and battery cables, distributor for humidity.

How exactly is the IAC sensor working?

I have cleaned the TB, IAC sensor and run injector cleaner fluid.

No cat, and new o2 sensors.

Descripion of Rough idle. runs at 700-800, suddenly fall and vibrate. the exhaust kinda builds up pressure and pumps bb b bb b bb b bb continuously.
 
the IAC is actually an actuator not a sensor - it is a linear stepper motor which drives a plunger in and out to control the amount of air that passes the throttle at idle.
 
the IAC is actually an actuator not a sensor - it is a linear stepper motor which drives a plunger in and out to control the amount of air that passes the throttle at idle.

We have a winner! :cheers:
 
Sounds like you're dropping a cylinder. Is the check engine light lit? if you have acccess to a scan tool I would plug in and see if there are any trouble codes. If there are any codes between P0301 to P0306 the last digit corresponds directly to the misfiring cylinder. A P0300 indicates a random (misfire moves from cylinder to cylinder) or multiple (more than one at the same time) missfire situation.
 
Listen to the distributor while the engine is running, can you hear a -tick.tick.tick- If you can then the rotor is hitting one of the cap terminals. This indicates that there is wear on the housing/shaft.
If so replacement of the dist is required.

Wayne
 
Could this also be caused by leakage between the engine and intake manifold? I noticed the rough idle after i replaced the exhaust manifold. (I had only had the jeep one week).

It is not throwing any check lights. Is it possible to check the codes without a scanner tool?
 
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Here's a list of the codes for older Cherokees

codes are:
11 Ignition
13 Manifold Absolute Pressure (MAP) Sensor Vacuum
14 Manifold Absolute Pressure (MAP) Sensor Electrical
15 Distance sensor or circuit
17 Engine running too cool
21 Oxygen sensor or circuit
22 Coolant temperature sensor or circuit
23 MAT sensor or circuit
24 Throttle Position Sensor (TPS) sensor or circuit
25 Automatic Idle Speed (AIS) circuit
27 Fuel injector control
31 EVAP solenoid or circuit
33 Air conditioning clutch relay
41 Alternator field
42 Automatic shutdown relay
44 Battery temperature sensor
46 Battery over voltage
47 Battery under voltage
51 Oxygen sensor – lean condition
52 Oxygen sensor – rich condition
53 Internal engine controller fault
54 Distributor sync pickup
55 End of Code output
62 Emissions Maintenance Reminder (EMR) mileage accumulator
63 Controller failure EEPROM write denied

 
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My 96 would occasionally run like crap. After a restart it would often be OK. I'd recently replaced the CPS and was thinking the new one may be questionable, when my automatic door unlock stopped working with the remote.
You may have the same setup I have on my export. The same module that controls the remote door unlock, also interrupts the ASD relay. Just something to think about if the common stuff doesn't turn out to be the problem. My ASD relay function got real iffy for awhile, sometimes it would work, sometimes not, sometimes it would kind of work and run like poo.
 
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