Experiencing some preignition on a 1997 F150 Lariat supercab 4x4, 4.6 auto.

What are the first things to check out?

 

Clean the MAF sensor.

 

I used a tb spray cleaner on it. Still getting a little ping under load, just not as often.

 

I would run some Chevron Gas or Techron cleaner, may take a lot of it. cured mine.

 

Yeah, I've run some B12 through. I may try cleaning the maf again as well as using another additive.

 

Ford has 2 TSB's out of detonation . I think one is at light throttle and the other at or near WOT . I have had both performed on my 4.6 to no availe. The only success I've has is mixing B-12 " steel can " and some Lucas UCL but that was for only a short period .

I would sure like to hear of the fix ........................... because man, I mean this think spark knocks bad at WOT , so bad it's going to kill the ring lands so I stay off the gas .

 

Great forum! Lots of good stuff. I also have a 4.6 in a 98 expy that pings like an SOB. I tried a lot of stuff Spark plugs, (that was fun) cleaning MAf, trying to reduce carbon by high RPM's etc. Tomorrow th thing is going in to get the Knock sensor changed. This is not fun either... Will let you know what goes on...

 

Seems like a thorough cleaning of the maf and b-12 did the trick. I am going to try some 87 octane when this 93 runs out.

 

Eh, its back. Time to go back to 93 till I figure this out. I may just get a steeda adjuster. Technology sucks. I hate not being able to tinker with/ do simple tuneups/ make decent torque/ cheaply modify/ actually work on this thing. Man, I really like my 95. :rant off:

 

Yeah! Knock sensor helped a lot! Still not sure if it's quite right yet but it's definitely better. seems that there's not a lot of power til 3k or so and who wants to listen to that all the time? Any body have any ideas? thanks.

 

I may do the same. Where is the knock sensor located?

 

Knock sensor is under the intake manifold!!! Took my mech. 5 hrs! do not do lightly. The upside is that the intake gaskets tend to leak and could twist a rod so this is a two benefit repair. Hope this helps...

 

Not really lol! But thanks for the info.

 

Here's what is most likely causing your problem:

New engines have an EGR sensor and valve which recirculates exhaust gases back through your air intake to lower emissions. What do you think happens after exhaust gasses have been running through your intake for awhile? The intake gets all clogged up and the buildup causes restriction in airflow and an increase in heat. The increase in heat is what causes the preignition.

To solve the problem you either have to take the whole intake system and manifold off and clean by hand with chemicals (the best way), or pour carbon cleaner through your engine while it runs and let it cycle through. I've never personally done this but in all of my reading on different message boards this is the leading cause of pinging (spark knock or whatever you want to call it) I hope this helps!

 

Thanks! When the Mech took all the intakes off to get to the knock sensor he said all that was in good shape. I dont have hardly any trouble with preignition now(a little at WOT, but I think that's normal) now the trouble seems to be power that is not smooth. I'm going along and start to ask for more power it feels sluggish and if you leave the throttle at the same position all of a sudden the power will come. Any ideas... BillsBig Ford