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Old May 12, 2015 | 10:09 PM
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spark knock
I have a 89 f150. When warm I believe it has some spark knock. I have tried seafoam and It didnt really help. 91 octane helped slightly. I have not checked the timing yet, but it doesn't idle high or anything like the timing is to high. Also it kind of surges at idle sometimes, and it used to die when first started until I switches to 91 octane. Any suggestions?
 
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Old May 12, 2015 | 11:00 PM
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I would check for codes.....Kind of sounds like a sensor
 
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Old May 13, 2015 | 07:57 AM
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I would verify base timing is correct (with SPOUT removed). That may be your issue.
 
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Old May 13, 2015 | 08:09 AM
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Code check and base timing are the way to go before spending money on parts or that expensive 91 octane fuel.
 
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Old May 13, 2015 | 09:08 AM
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Yeah I better check the timing, what else could cause spark knock besides carbon deposit or advanced timing?
 
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Old May 13, 2015 | 10:42 AM
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Wrong heat range spark plugs. Faulty sensor feedback signal triggering the PCM to add more timing/pull out enough.

FYI..on a modern EFI engine too much initial timing will not affect idle RPM, the computer adjusts for that..
 
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Old May 13, 2015 | 11:58 AM
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Originally Posted by rla2005
Wrong heat range spark plugs. Faulty sensor feedback signal triggering the PCM to add more timing/pull out enough.

FYI..on a modern EFI engine too much initial timing will not affect idle RPM, the computer adjusts for that..
But on our trucks it does right? When I did the timing on my 90 f250 the idle went up and down with the timing
 
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Old May 13, 2015 | 12:36 PM
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Incorrect base timing on EFI 460's doesn't seem to affect idle RPM, although it seems to affect idle quality a little.
 
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Old May 13, 2015 | 02:16 PM
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Originally Posted by BLK79
Incorrect base timing on EFI 460's doesn't seem to affect idle RPM, although it seems to affect idle quality a little.
Ok maybe thats what i was hearing. Your probably right
 
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