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post #1 of 2 (permalink) Old 10-27-05, 02:15 PM Thread Starter
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lean condition spark knock/detonation

I have a 1997 F-150 4.6L (VIN engine code 6) with 159100 miles on it. For quite some time I have had to run higher octane fuel to keep from getting a spark knock at medium to high acceleration. I was sure it had something to do with carbon build up, but I have done all I can with out spending A LOT of money to clean it out. I managed to go through some TSB's and found one that fit my problem (Article N. 98-23-10). Before I go into all the data I have to help diagnose this problem let me explain the symptoms in more detail. If I run 87 octane fuel I get spark knock at medium to high acceleration, the knock is even worse the colder the ambient temperature. In fact when it is cold outside it seems to happen even at light acceleration. Today I hooked up a scan tool and pulled some sensor readings, hopefully this will help any of you that have more knowledge than myself. KOER self test indicated codes P1127 HO2S Downstream not tested, and P1116 ECT sensor out of range. I think the ECT sensor was just a one time thing because I found no other indication that it was not working properly.

At Idle:

LFTRIM 1 - -2
LFTRIM 2 - -3

MAF (gm/s) - 4.51
MAF (V) - 0.78

Spark Advance - 17 degrees

Baro (kPa) - 95
Baro (Hz) - 153
(live in Houston)

ECT (V) - 0.66
ECT (F) - 196

3000 RPM:
MAF (gm/s) - 21.10

Spark Advance - 30 degrees

Baro - SAME

2000 RPM:
LFTRIM 1 - +7
LFTRIM 2 - +3
SFTRIM 1 - -4
SFTRIM 2 - +8

The TSB that I pulled was for MAF contamination, and from what I can gather it is working properly, but unfortunately I cannot do a road test with the scan tool, so I cannot test with the engine under a load.

I have heard many other Fords with the same problem, my Fathers 1996 Thunderbird 4.6L does the same thing, and I heard a Ranger knocking on the freeway today. Any information will help a lot, thankyou in advance.
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post #2 of 2 (permalink) Old 01-13-06, 09:51 AM
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Re: lean condition spark knock/detonation

My brand new 2005 Mustang GT spark knocks on the recommended 87 octane. What good are knock sensors if they allow the car to knock loudly and embarrassingly for a half second or so every time you upshift or accellerate at highway speeds before they get around to telling the computer to roll back the timing or whatever it is that goes on? I would just assume rip those worthless things out and just use an appropriate level of octane for the engine which nearly has 10.1 compression. Why does Ford even attempt to run this high performance 4.6 engine on lawnmower grade gasoline anyway? Who do they think they are fooling?
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