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Old 08-29-2013, 05:15 PM
JEFFFAFA JEFFFAFA is offline
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Spark Knock in my Harley F150

Hey Guys. I normally hang out in the 67-72 truck section but I'm having trouble with my 2003 Harley F150. It has Diablo programer,s/c power pulleys,12# boost,throttle body,C&L air duct,and Cold air intake. These have all been in it for years. Nothing changed except maybe the gas here in Phoenix Arizona. It does seem to be better with Chevron.
Driving home from work it is normal at first. After maybe about 10 miles it starts spark knocking under load up a grade. The farther I drive it, it spark knocks easier. By the time I get home 30 miles from work it will spark knock even on a level city road if I lug it in overdrive and accelerate like passing a car. The funny thing is that if I stop and get gas it reverts back to normal on the drive home. No codes in PCM. I had a tech here at the Ford dealer I work for read my PCM. It says everything normal and the knock sensors are working. Any Ideas?
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Old 09-26-2013, 09:09 PM
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sounds like you maxed out the MAF and burnt at least one plug...


so start with the plugs gapped for the additional boost, and if the issue persists, then swap out the COPS



and time for a MAf upgrade and a TUNE
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Old 02-20-2014, 05:20 PM
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Just swap out the COPs?? Don't even test them?? That's one expensive swap to do without confirming they are faulty. Besides, bad coils won't give spark knock. Spark knock (Detonation) happens when the compressed air/fuel mixture in the cylinder ignites from heat BEFORE the spark plug fires. Therefore it couldn't be a COP. It can destroy a normal motor quickly let alone a S/C motor. You most likely are having a lean condition, or too low octane fuel. Check for gaskets leaks all around the S/C and intake. Pretty much anything after the MAF sensor including vacuum hoses. I've read about the S/C'ed 5.4s having a vacuum line leak at an elbow behind everything out of sight.
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Old 02-20-2014, 05:20 PM
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Oops old thread. My bad.
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Old 02-28-2014, 06:17 PM
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Oops old thread. My bad.
Actualy I'm glad you did. I never did figure out what the problem is/was. I had the plugs changed which helped but was still there. Now that it is cooler temperture around here it is a lot better. A couple times recently at a stop light it started to stumble like the gas tank was empty. Putting it in neutral and reving it a littlle cleared it. I figured I need a new programmer. A vacuum leak as you suggested is possible I suppose. What is your O now?
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Old 06-26-2014, 07:01 PM
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Well gentleman now the air temp is back up so is my detonation. The problem may be I had the engine's thermostat changed a bit before this problem started. I had the aftermarket 160 taken out while the cooling system was flushed and a factory one installed. I figured either way the engine would reach the same running temp. What is your opinions? What brand stat and from whom do you guys buy yours?
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Old 06-29-2014, 10:59 PM
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is your intercooler pump working??
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Old 07-01-2014, 11:44 AM
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is your intercooler pump working??
I had thought about that at one time and then forgot. Thanks for chiming in and reminding me. Will check it out.
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Old 07-01-2014, 11:44 AM
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