4.6L knock under load
Thread Starter
|
New User
Joined: May 2003
Posts: 17
Likes: 0
4.6L knock under load
I have searched the posts and am looking for any other ideas. I have a '98 F150, 4.6, auto, 3.55's, 120k miles, and pull a 4,000 # combined weight boat and trailer. We purchased the truck at the end of last summer and used it only once to pull the boat. When it got above 60 mph or going up hill it pinged like crazy. I changed out the original plugs and have checked and cleaned the MAF sensor. Since last summer, we have driven the truck 15k miles and no ping (just truck, no load). Pulled the boat this weekend and it pinged like crazy above 60 mph or going up hill. The check engine light has never come on. Should i change the plug wires or would a code scanner (vs reader) help, or coils or??? It is definitly knock (predetonation) vs some other engine sound.
Sorry for the long post. Any help would sure be appreciated. Thanks.
Sorry for the long post. Any help would sure be appreciated. Thanks.
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
4.6L knock under load
Hi Fordmannn and welcome to FTE 
Did it ping before you replaced the spark plugs?
Have you tried different brands of gas? Sometimes that's all it takes.
Have you had your fuel pressure checked? Low fuel pressure can cause a ping but will usually cause a lean condition which would turn on the MIL (malfunction indicator light or Check Engine light).
Does the engine run at a normal temperature?
If those arent it, your engine could be carboned up. If someone there has a Motorvac or Wynn's injector/engine cleaner you might want to try having that done.
Then I think I would have it scanned for codes in case anything shows up, even though the MIL hasnt come on. Sometimes a code will show up with the engine running but it wont be in memory.
A Ford dealer can go for a roadtest with their WDS scanner hooked up and monitor the MAF, O2s etc while driving. Sometimes that will help pick up something too.
Let us know how it goes.
Did it ping before you replaced the spark plugs?
Have you tried different brands of gas? Sometimes that's all it takes.
Have you had your fuel pressure checked? Low fuel pressure can cause a ping but will usually cause a lean condition which would turn on the MIL (malfunction indicator light or Check Engine light).
Does the engine run at a normal temperature?
If those arent it, your engine could be carboned up. If someone there has a Motorvac or Wynn's injector/engine cleaner you might want to try having that done.
Then I think I would have it scanned for codes in case anything shows up, even though the MIL hasnt come on. Sometimes a code will show up with the engine running but it wont be in memory.
A Ford dealer can go for a roadtest with their WDS scanner hooked up and monitor the MAF, O2s etc while driving. Sometimes that will help pick up something too.
Let us know how it goes.
Thread Starter
|
New User
Joined: May 2003
Posts: 17
Likes: 0
4.6L knock under load
Thanks for the suggestions! It did ping with new and old plugs. I thought about the carbon thing too but when i pulled out the original plugs they looked great other than really wide gap - although i guess it would be hard to tell from the plugs. Temperature seems to be ok. I think the fuel pressure is a good thing to check next. It does have 125k on the original pump. Has anyone ever replaced one? I assume it is in the tank and dropping the tank down is the only difficult part.
