rompn4x

My 97 F150 with the 4.6 has roughly 176,000 miles on it now. On my last fill-up I had to use 87 octane fuel (I normally run 89). On my way home on the freeway it sounded like someone was shaking a can full of rocks or marbles. I had to back off the throttle because the detonation was so bad. The fuel I used was Mobil, not a no-name brand gas. I usually run 2 bottles of Seafoam in the gas tank (holds 30 gallons) every 12k miles and the engine was Seafoamed through the brake booster line 30k ago. I just filled up the truck with 91 octane gas and threw in 2 bottles of Lucas products fuel cleaner today... Seemed to smooth out the rough idle but what else could cause such bad detonation? Do these trucks have knock sensors? I checked for vacuum leaks using carb spray and everything came out gravy. Also it has 30k on new 02 sensors

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atvrider93

lower octane gas

rompn4x

But these trucks are supposed to be able to run on 87 octane

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98blue54

higher octane gas has a slower burn rate for high compression motors... which are bmws and mercedes etc. realisticly we can run w/e we really want in our motors. ive run 91 and 87 and it makes no real difference. but we do have knock sensors... if you look just under the intake manifold on the right bank behind the alternator thats where mine is on my 5.4 which is basically identical to the 4.6 also check your timing, maybe something ot upset on the heads

rompn4x

The truck just threw a code P1131... Ill have to see what that is but also said something about a lean condition.

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Mustanger

All my Fords have pinged from brand new no matter what the manual says they can burn.... so when I tow I use premium...it helps but not 100%

I don't know the solution, I always vary the rpms to find the sweet spot going up grades with the trailer...WOT makes it worse. The manual says LIGHT spark knock is ok...what is classified LIGHT spark knock?

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Whitener0420

Did you ever find what was causing the P1131 code?? Just curious because my truck is showing same code. I have replaced all the O2 sensors exept one..the front passenger O2 sensor.

rompn4x

P1131- lack of HO2S switch- sensor indicates lean. From what everyone has said it is probably a MAF malfunction. The O2 sensor is indicating a lean mix, and with the engine pinging the 02 is telling the truth. I disconnected the MAF to throw the system into fail safe mode. I cleared the codes and the P1131 never came back

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TheJMC

Your 97 should have an Octane Adjust shorting bar. Pull the plug and it will retard timing. It is a black connector with a plug in the end of it. It has two wires; dark green and gray with red stripe. it is hanging off the main cluster of harnesses behind the battery just off the firewall. It might have a gray plug or a black one.

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Jean Marc Chartier
Warn XD900i E-fans, M5OD w/ Hurst short throw, Procharger @12psi, Troyer tuned.
Swap notes 4.6 to 5.4; http://www.f150online.com/forums/art...ml#post3570245