6My girlfriend has a 97 f150 4.6 auto short wheel regular cab. 140K Cold air intake, throttle body, flowmaster, and I think a chip/dunno where to look for it at but the last owner i think mentioned it.

It has some sort of rattle on the highway or when its under load above 2K rpms. I have been thinking it was the lifters. Then trying to narrow down other possibilities I tried high octane fuel. The rattling went almost all away! Except higher rpms wide open on the highway(dont worry we dont drive it that way)



I was wondering what would cause it to lean out? Any ideas? No engine light or codes. Thanks.

 

Sounds like a exhaust leak.

 

It's not an exhaust leak if it goes away with high octane fuel.

I'd strip all those intake mods off, put it back to stock, and figure out exactly what was done to the PCM and return that to stock too. You are running lean and/or with too much timing advance.

 

With the mods mentioned and the reference to the last owner having the issue, I would say the chip has the ignition timing too far advanced for truck use.
Only way to see this is with a scanner looking at the live timing data when the noise is heard..
Or remove the chip for trial testing.
Good luck.

 

i have the same problem. only mod ive done is the Gotts, an duel exhaust. its not full so i thing an exhaust leak is possible

 

I might try removing the chip for a test run, where would it be, and is it a plug n play type made for these?

Im thinking its just a couple injectors reaching the max load, or maybe a weak pump, or dirty filter, I just dont know.

Am going to need to test the fuel pressure at the rails I suppose.

Its happy on 93 octane for now. Maybe I should leave it be.

 

A. The chip would be near the computer because that's where it has to change the data.
B. A couple injectors don't reach max load. They are all pulsewidth modulated as electric solenoids to meter fuel as directed by the computer.
If any are dirty or plugged, it would result in a loss of power in those cylinders.
c. Testing fuel pressue is fine, then you know what you have.
D. Higher octane is the telling 'tail'. If higher octane reduces or eliminates the rattle or ping it tells you the ignition timing is too far advanced for 'regular' fuel.
.
The difference between the two octanes is the the speed of 'combustion' of the fuel grade. The higher octane fuel 'by it'self' does not make more power.
The reason the higher octane reduced the rattle is it burns 'slower' vs the ignition point of timing from the chip.
The lower octance burns faster and is ignited too early in the fireing stroke.
When this happens the pressure in the cylinder rises 'too fast' 'too early' near piston top dead center where it can't push on the piston downward due to the piston /rod vertical alignment at that point in crank rotation.
This action 'rings' the pistons, the rods, the cylinder walls, the heads, and the crank and could cause a head gasket loss from the high peak cylinder pressures.
This is what you finally hear as rattle or ping dampened by the coolant, crank case oil and other items attached to the block..
I hope this explains the issue I think you have from the feedback you gave.
Good luck..

 

Ignition timing too far advanced = chip-related. It's probably a high octane tune.

Now - is it a "chip" or was the PCM retuned with a programmer?

 

Generally you can reprogram only via the port under the steering wheel the ECM port. If they reprogrammed and there is nothing attached to the port it probably needs a reflash t get it back to stock.. if there is a programmer attached to the port I can only think remove it and un hook the battery and let it reboot..