I have a 1994 Mazda Navajo. Yes I know this is a Ford forum but seeing how the Mazda forum does not acknowledge the Navajo's existence and the fact that the Navajo is a re-badged Explorer, I figured I would give it a shot. I have somewhere around 175k on it, it is a 5 speed 4x4 with a 4.0 V6. At idle and under light acceleration there is no problem. When there is a decent load you can hear a definitive rattling from the engine, I am fairly confident it is spark knock/detonation. I have recently replaced the spark plugs with Motorcraft platinum's, spark plug wires, enging oil, tranny fluid, rear diff fluid, radiator fan, and an exhaust gasket (post cat) as preventative maintenance. I was wondering if the plugs I am using are causing the problem or if I did something else wrong of if there is a common problem with the ignition system. Any insight is greatly appreciated. Thank you in advance.

 

I'm not positive ,but if your vehicle has a knock sensor , it is supposed to control that problem. Did you consider using one tankfull of premiun fuel to help clean out any built up deposits in the cylinders? It's worth a try and only costs a little extra to clean the junk out. hanky

 

That would make sense, however, this is not something that has happened gradually. It happened very rapidly, so that kind of eliminates any carbon buildup on the pistons or valve train. I also ran some BG top engine cleaner through about a year ago and I put BG44K in the gas once or twice a year. I don't think it is a mechanical problem, I am suspecting electrical. Having said that I have been wrong many times before and I'm sure I will be again.

 

If we take this one at a time,
Did you have this problem before changing the plugs? Your answer could determine your next course of action.
Lets look at what causes the engine to ping/rattle ,preignition.
Ign timing, running hot, deposits in the cylinders, knock sensor not working and I can recall heated intake air being too hot caused preignition,quality of fuel and there are probably some more causes.
We can't always depend on something in a can to correct/prevent some problems. A tankful of premiun fuel should eliminate some of those causes .I certainly would consider`trying that first. hanky

 

again I appreciate the help. Im not entirely sure if it is the plugs or not. I replaced all that fun stuff, drove it 600 miles and loaned it to my dad. When I left it there was no problem, the next time I drove it, there it is. I have also noticed it does not do it when it is cold. All the gauges are reading normal. When he had it he was doing a decent amount of towing a trailer with it, not sure if that makes a difference or not, but...

 

Just to cover all the bases, did Dad buy some poor quality fuel when using the vehicle? If that's all it is, you may be unecessarily concerned . Ask and you may get an answer to your concern. If that is the case , adding some good quality fuel should eventually clear up the problem. It's certainly worth a try. hanky

 

I put some premium octane fuel in yesterday, it helps the detonation considerably. However it is still there, it is less prevalent obviously due to the higher octane rating. I crawled under the hood this morning and discovered a vacuum leak. Judging from its location I may have broken it when I was replacing the spark plugs. Hopefully that will take care of the problem once and for all.

 

Good job , glad you found the problem. hanky

 

Well unfortunately that wasn't it. The detonation is much less since I plugged my vacuum leak but under heavy throttle it is still there. I think I can hear something that sounds like a vacuum leak from around the power steering pump. After looking for a few minutes I cant locate and vacuum hoses in the area. Am I overlooking one?

 

First; sometimes power steering pumps make a noise that sounds like a vacuum leak,

second; I would like to think you have been under the hood enough times to know if you heard that sound before.

If it is safe to do so, spray some carb choke cleaner around that area where you suspect a leak, if the RPM changes something is going on there just don't get too close to the regular air intake.

Until you can definately find something mechanical I still suspect the fuel.
hanky