Gap bridging on spark plugs

[JViking]

I have a '92 Cherokee, 4.0L engine. Not long after i purchased the car I replaced the rotor and dist cap.

After some months, the engine started to become non-responsive after driving for about 20 minutes. Now it takes less and less time before it sort of becomes "dead".

I checked the spark plugs when I replaced the rotor/dist. cap, and they looked fine. When the problems started to occurr, I also replaced the spark plug wires.

I still had this problem, so today I replaced all the spark plugs. We'll on 2 of the plugs, there was deposits closing the gap between the electrodes (is this what they call "Gap Bridging"?) Ah, so I found the problem I figured.

Well, after about 15 minutes driving, the same problem occurred, and I guess (though haven't looked) that there's deposits on the plugs again.

What might be causing this, and how do I fix it?

One of the cooling hoses sprung a leak once, before this started to happen. The engine did get quite hot, but the meter was not in the red as far as I can recall, before I was able to stop and fix it. Could this cause a problem like this?

[Saudade]

Were they "hard" deposits? You might have a lot of carbon build up in the combustion chamber (top of piston, around the valves, etc.). This could be flaking off and closing the gap.

Have you checked your compression?

[JViking]

Originally Posted by Saudade

Were they "hard" deposits? You might have a lot of carbon build up in the combustion chamber (top of piston, around the valves, etc.). This could be flaking off and closing the gap.

Have you checked your compression?

Unfortunately I don't have the tools nor experience to check the compression. As for being "hard" deposits, I was able to just blow the deposits off the plug. They were silver in color.

[theFREAKnasty82]

what color was it? If it's white, it could mean that it's the incorrect heat range for that particular spark plug, thus allowing it to get too hot.

[JViking]

Originally Posted by theFREAKnasty82

what color was it? If it's white, it could mean that it's the incorrect heat range for that particular spark plug, thus allowing it to get too hot.

It was white/silver in color. But if it's the wrong heat range, why did it suddenly start to happen? I checked the plugs about 2 months ago, and they were fine then.

The replacement plugs are the ones specified in the Haynes manual.

Could it be possibly be stuck valves? Strange though that it happens on 2 cylinders.

[theFREAKnasty82]

if you have the right plugs, then the alternative cause for the white deposits is an over advanced ignition timing, lean mixture, vacuum leak in your intake manifold, sticking valves, or a weak cooling system. If you have issues in any one of those areas, will cause the problem you are describing. Check also to see if your check engine light is on and see if a code for the EGR comes up, a faulty EGR can cause similar issues.

[JViking]

Originally Posted by theFREAKnasty82

if you have the right plugs, then the alternative cause for the white deposits is an over advanced ignition timing, lean mixture, vacuum leak in your intake manifold, sticking valves, or a weak cooling system. If you have issues in any one of those areas, will cause the problem you are describing. Check also to see if your check engine light is on and see if a code for the EGR comes up, a faulty EGR can cause similar issues.

Thanks, I was thinking in the lines of the plugs being a symptom, not the cause of the problem.

No Check Engine Light.

I'll be taking the car to a repair shop, hopefully they'll find out what is wrong, without emptying my wallet... :-)

Thanks for your help!

[vamc]

Use 91 oct or better and see if that helps.

[JViking]

Originally Posted by vamc

Use 91 oct or better and see if that helps.

Well, living in norway I can only get 95 and 98 octane. There's only one gas company that sells 92 octane, so it's impossible get anything below that.

[vamc]

Sorry, then try to use 98 oct. I wish we had that oct. over here. The highest oct. over here you can get at any goven station is between 93-94 oct. I been to germany where they had 112 oct. right off the auto bohn(sp) I thought that it was neat seeinh this b/c you dont see that here.What is the highest you can get over there at any given station?

[JViking]

Originally Posted by vamc

Sorry, then try to use 98 oct. I wish we had that oct. over here. The highest oct. over here you can get at any goven station is between 93-94 oct. I been to germany where they had 112 oct. right off the auto bohn(sp) I thought that it was neat seeinh this b/c you dont see that here.What is the highest you can get over there at any given station?

The highest octane we can get here in Norway is 98, and that is availableat all gas stations. They all have 95 and 98.

I'll give it a shot, doesn't hurt trying a higher octane.

The car is going in tomorrow to get fixed, hopefully they'll find out what is wrong, I'll let you know what they find out.

[vamc]

Thanks, take it easy.

[JViking]

Got the car back yesterday from the repair shop, and they couldn't find anything wrong with the engine. They did however find out that the transmission needed an adjustment and they felt that the problem was related to this. They meant that the car would not drive in the optimal gear at all times.

Unfortunately, they were wrong. I still have the same problem, in addition to the fact that now the transmission shifts a lot harder, sort of jerks when it shifts into overdrive.

Could the problem be related to bad mixture? It only starts to appear after the engine gets real warm, after about 10-15 minutes when the RPMS are at about 2000.

Or could the repair guys be right, that it could be related to the transmission?

Btw, no help in using 98 octane either :-)

Thanks for all your help and suggestions!