2002 5.4 Knock Sensor Issue
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2002 5.4 Knock Sensor Issue
I have a 2002 F-250 with a 5.4 engine. I borrowed a buddies programmer the other day and used it on my truck to see if i had any codes and the knock sensor code popped up. My CEL never came on. I cleared the code with the programmer and went on with my day. i later noticed that my truck really doesn't come out of the hole like it used to. I started from a stop light headed up a slight grade today and it felt like i had a 8000 lb trailer behind me. The engine sounded powerful and tached up like normal but didn't seem to have any power. The engine was warm and i am running good gas.
Can the Knock sensor be to blame for this sluggishness? How do i test the knock sensor? Also, and most importantly, i am not required to test for emissions where i live, can i do away with the knock sensor all together? What will happen if i do away with it totally and reset the codes?
I would appreciate any help, ideas, and talk from past experiances with this. Thank you
Can the Knock sensor be to blame for this sluggishness? How do i test the knock sensor? Also, and most importantly, i am not required to test for emissions where i live, can i do away with the knock sensor all together? What will happen if i do away with it totally and reset the codes?
I would appreciate any help, ideas, and talk from past experiances with this. Thank you
Post Fiend
Joined: May 2006
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From: Central Florida
The knock sensor is worth keeping, it retards the timing to keep the engine from damaging itself. I don't know of a test for it, but if it's reading too much or the knock count is very high, I couldn't suspect it as being the trouble. I would expect the sensor to become less sensitive as it fails, allowing more detonation. You might a top end cleaning, either a motorvac or a can of seafoam first.
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Thanks,
I've used seafoam on this engine before and i am a complete believer in that stuff. Hoever, what is this motorvac thing? Is is a different cleaner like seafoam? I'll give it a try if you let me know what it is. thanks
I've used seafoam on this engine before and i am a complete believer in that stuff. Hoever, what is this motorvac thing? Is is a different cleaner like seafoam? I'll give it a try if you let me know what it is. thanks
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Thanks, I live north of Pittsburgh, i don't think anyone around here does that motorvac stuff in this area. I've never heard of it and i've been working on vehicles for years. I'll look into it a little more then probably end up doing the seafoam.
FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
What was the exact code you got for the knock sensor?
I believe, and someone will correct me if I'm wrong, that the PCM tries advancing the timing up to a point where it SHOULD knock and if it never senses the knock, it knows the knock sensor is bad.
It MIGHT go into a mode where the timing is very retarded because it knows that it'll never hear it ping if it does. Which might be why it's such a slug.
However, did it get sluggish AFTER you cleared the code? It might just need to relearn everything again, but it shouldn't be THAT noticable.
I believe, and someone will correct me if I'm wrong, that the PCM tries advancing the timing up to a point where it SHOULD knock and if it never senses the knock, it knows the knock sensor is bad.
It MIGHT go into a mode where the timing is very retarded because it knows that it'll never hear it ping if it does. Which might be why it's such a slug.
However, did it get sluggish AFTER you cleared the code? It might just need to relearn everything again, but it shouldn't be THAT noticable.
Post Fiend
Joined: May 2006
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From: Central Florida
I always believed that the timing was more or less set with a set advance table for load/rpm. You have a base timing, then the timing is brought up per the tables/formula. Then the knock sensor only tells the ECM to backoff when the knock count goes up. While watching my scan tool, the knock count is pretty high, but I don't think it's the computer always trying to advance the timing to detonation (I think it was the timing adjustments I had tuned in.)
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FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
Someone here has said there is a test the PCM goes through for the knock sensor. Johnny Langton, I think, or maybe one of the other PCM gurus. It advances the timing up to a certain limit, assuming it will hear the knock. When it doesn't it logs a code.
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Post Fiend
Joined: May 2006
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From: Central Florida
Perhaps as a start up routine? If the PCM is constantly testing the knock sensor, Ford would have to detune (deafen) it to a point so there is a margin for safety. Which with a good tune and fuel you could probably go to a more sensitive sensor for more power.
Postmaster
Joined: Oct 2006
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From: SE Texas
There's the boderline knock table for spark advance,and that's basically the spark table the engine runs on. There are modifiers to these spark values like ACT (air temp), ECT(coolant temp), time since running,etc,etc... Then there's the knock sensor input. The PCM uses another table that has a max spark advance value, and after the timers expire for this table to start advancing timing it, begins to advance spark advance based on a certain # of degrees/second up to the max allowed, unless it detects knock. If it does that, then the exact opposite happens-it will retard spark based on a certain number of degrees/second, and that's limited by the max spark retard allowed. Knock sensor control is fairly involved,but it's not too bad if you have all of the tables in front of you-makes alot more sense then.
JL
JL
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