I have a 98 expedition w/4.6 w/80 thousand miles. Have had for 5 yrs, great truck but one problem, it knocks and pings once it warms up. Ford says some knocking is exceptable. Maybe to them but not for me. I replaced the plugs 7,000 miles ago and they were fouled bad. Problem went away, now it is back. I do not want to just keep changing plugs, i want to get to the problem. I have thought about replacing the timing chain but not sure. Anyone with similar problem or any words of wisdom?

 

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Timing chain should not be the problem or the cause or solution for the pinging. Sounds like you have carbon build up (rich mixture) on start-up and then too lean when up to temp ....... might try different gas (higher octane) for a while and hotter plugs next time .....

 

Clean the MAF, worked for me.

 

Thanks 99 Navi Guy, will try different gas. Is there any additives I can buy that will help get rid of carbon build up. Ford dealer put a chemical in that made it smoke like crazy for a mile or two. Said it was for build up, but problem, not as bad, but still present.
And Great White, what is this MAF you refer to? Mechanically capable, I am just vocabulary handicapped.

 

I cleaned my MAF sensor and I believe that cured my pinging problem. I'm not dead sure of this, and testing is still in progress. The CURE is apparent, so far. Let's see if it withstands the test of time.
The Mass Air Flow sensor in my '98 Ford E150 van, with 5.4 L V8, lies in the fresh-air path to the throttle body, AFTER the air cleaner. It is a very, very delicate sensor with exposed filaments. Many folks advocate routine cleaning. After 75K miles, this is the first time I've cleaned it. This must be done with a spray that leaves no residue, not with a carburetor cleaner. I used an aerosol, CRC brand "QD Electronic Cleaner," which I bought at AutoZone for about $5. Search the web, and in this forum, for more instructions specific to your vehicle. Be very careful. Mine was cleaned very easily. I needed no tools at all.
My reasoning, for the big improvement in pinging and engine performance, is that the MAF informs the PCM (power control module; i.e., the car's computer) of the amount of air flowing into the throttle body. If this report is wrong, the PCM can follow with all sorts of erroneous instructions, not the least of which is to operate the engine too lean. Leanness can cause pinging, and can also burn your valves. So don't accept anyone's advice that pinging is OK. Did the car ping when it was new? Of course not. So fix the ping.

 

Tuck98,
Did you ever fix your pinging problem?
We just completed a stiff freeway drive, with no pinging. On previous occasions, the van pinged badly on this same drive. The difference: I cleaned my MAF. So I am quite convinced my MAF was causing my engine to run lean.
Leanness can cause pinging, because it causes the combustion chamber to run hotter. You have said that your engine pings "after it warms up." Well, that indicates a thermal correlation. Interestingly, I noticed the same thing. My van would be less inclined to ping at night, than during the day. Nights are noticeably cooler here than daytimes.
You might have to REPLACE your MAF sensor. I realize you said you cleaned it. Maybe you didn't clean it properly.
Please let us know how this works out, or if you've already solved your problem.
John

 

Thanks JohnPeter for the reply. I have not yet tried to clean the mass air flow sensor. I did try 93 octane gas and that is working for now, but can't afford to continue on that road for too long. Will definitely try to clean the MAF real soon. I am glad you said where to look for it because i did not have the first clue. Will let you know how it goes.
tuck 98

 

I encourage you to search for advice on how to clean your MAF sensor, before you take any actions. Dan the Oilman has published on that, and others have concurred with him. Search under Google. Never touch the delicate MAF sensor components. Only use the spray recommended...it leaves no residue. And, bear in mind, you might need to replace your MAF anyway; I've read of that happening.
You might provide a more elaborate description of your problem, so others might help you more. How LONG has your engine been pinging? Did it ping when it was new? Has the pinging increased gradually? When you say "fouled plugs," do you mean carbon, oil, or what?
Is there any reason to suspect that your air-intake passageway is subject to oil fumes? This would aggravate your MAF sensor.
OTOH, if you've got carbon caking in your combustion chambers, then you've got a different problem. That increases your compression ratio, necessitating higher octane fuel, to avoid pinging.
You said "80K miles" so I am not suspecting major engine damage or wear. Of course, if your engine has been inhaling grit, then all bets are off. Have you allowed your oil level to drop dangerously low? Has your engine's lubrication been lacking? If so, you should perform a compression check on all 8 cylinders, to see about ring damage, which could cause fouled plugs. But that doesn't wash with the pinging problem. Bad ring or valves DECREASE compression, they don't increase it.
OTOH, if your plugs are caked with carbon, that implies RICH mixture, which not only would cake the piston tops, but would cut the efficacy of oil, allowing cylinder wall damage to boot. Plugs speak volumes.