RideRed264

Hi guys, I've owned my cherokee for about maybe 3 years and it seems like I replace my cap and rotor way to often! I've probably burned through 8 or so..... Mostly of the BWD brand. Every one has excessive white buildup on the inside of the cap and usually the middle terminal is wore completely down and the plastic around it is melted. The last time I replaced the cap it had a giant hole where the center terminal USE to be. Should I head on over to the dealership to buy my next cap and rotor, or is there more to it than that?

Turbo X_J

I'll take distributor bushing for $200 Alex.

RideRed264

Last year the electronics went out in my old distributer, so I bought a brand new one. I still had this problem before I replaced it tho.

Firestorm500

Try a NAPA Echlin brand next time.

DFlintstone

Smartarse, Turbo. Plagiarism I say! (or did I steal that from you?) Anyway gasses from the crank case can make their way in there. A guy had his blow up like an m-80 a few years ago. Besides all the above, I might make sure my CCV valve and tube were clean, and that the front tube in the valve cover is free to vent.

DFlintstone

Wow, melted.

CCKen

Are you using a stock coil?

Are your plugs gapped at .035"?

Is there excessve vertical play in the shaft (up & down)?

What plug wires are you using?

freegdr

D- All of the above....For $500

RTorrez1

All of the above can cause the problem you are having.

kickice24

Plus cheap caps with aluminum inserts are terrible. make sure you buy a cap with brass inserts for best results.

RideRed264

I'm not really sure on the gap of the copper tops, and I don't remember if I gapped them or not. Shaft play is very minimum. Car quest 7mm suppression cable, with dielectric grease on the terminals. Stock coil

RideRed264

And the ccv valves are good

CCKen

I don't know what "copper top" spark plugs are but NGK ZFR5N spark plugs come highly recommended by many Cherokee 4.0 owners. The emsission label on your firewall will call for Champion RC12ECC plugs (factory installed) which are good but the NGK plugs should be used.

Spark plug gap is important, as described in the text I included below. Use a wire type gap checker not feeler gauges or one of those odd ball coin type gauges. Gap the plugs to .035" using the wire gauge. Do not trust the plug gaps of the plugs coming out of the box. I've found many that the gaps were too large.

The factory recommends replacing the plugs at 30,000 miles. This may be okay but I think the plugs and gaps should be checked at least every 10,000 miles (or less). The plug gap will increase while in use and may end up causing cap and rotor deterioration, so checking every 10,000 miles is not out of the question as far as preventive maintenance goes.

Those Car Quest cables may be okay but it has been found that Belden cables from NAPA, part number BEL 700444, have been proven to be superior.

As far as applying Dielectric grease to the cable terminals goes - don't do that. Just apply the Dielectric grease to the inner surface of the boots (at the plugs and cap, as well as the coil) using a Q-Tip. The Dielectric grease is intended to prevent moisture intrusion and make it easier to remove the boots from the plugs and cap. Dielectric grease is an insulator and will only add resistance to the ignition circuit if the contact between the cable terminal and the plug is marginal. The factory recommends replacing the cables every 60,000 miles, and good cables should last that long.

The cap and rotor should be a matched set (same manufacturer) to decrease the possibility that the gap between the rotor tip and the cap tower inserts are excessive. A mismatch of cap and rotor may increase the possibility of the gap being wrong.

Obviously, the rotor tip will errode and ash will build up on the tower inserts while in service, and should be checked every 10,000 miles when you check the plugs.

A matched set of cap and rotor would be Cap - Echlin ECH M030, and Rotor - Echlin ECH M031, both from NAPA.

Some data pertainingto spark plug gap:

Spark Plug Gap
Opening up the spark plug gap CAN increase the spark kernel (spark) size, thereby creating a more efficient burn. The problem lies in that any added gap creates more strain on the other ignition parts.

• Coils may not have enough stored energy to fire, or in the least case, not enough energy to cross the gap, creating a miss-fire.
• Plug wires will break down due to the added resistance as the spark tries to reach ground.
• Rotor and Cap, and the carbon bushing in the center of the distributor cap will show early failures.

All of this is because the greater the gap, the higher the voltage requirement to jump the gap. Do not forget the gap between the rotor arm to the distributor cap too. A high performance rotor is a bit longer, allowing less spark loss or chance of spark scatter in the cap as the spark attempts to jump the plug gap.
Proper Spark Plug Gapping:

• Proper gapping of the spark plug is necessary to get maximum spark energy as well as what is best for the longevity of the secondary ignition components (coil, cap, rotor, wires, plugs).
• When checking plug gaps, the correct way is to use ONLY wire gauges, though many of us are using the slider style gapping tools. These flat or feeler gauge style gauges do not accurately measure true width of spark plug gap.

Roler

Outstanding info on this,.once again, CCKen.

RideRed264

Wow, that was some good info CCKen! I'll defiantly be holding on to that info for the future! I received a new upgraded brass cap and rotor for free from the auto parts store, so I'll give this one a try for now. My plugs are champion RC12LYC's, and seem to be just below "like new" quality. Every one was gapped at .045, so I adjusted them to .035 using the method above. While the plugs were out, I also did a compression check just for the fun of it. "front to back": 166,181,179,173,175,175.