ok heres the deal .... i just installed a new long block 5.0 in my 91 f-250. old one went bad . put in a new fuel presure regulator, tps, full tune up, oil pressure switch, replaced some broken plastic vacuum lines, cleaned carbon from a fairly new egr valve and sensor, map sensor, all new o-rings on injectors, i mean i did a real good job on the swap.(dont mean to pat myself on the back sorry )

my problem is that when im driving on the highway up a hill i get a wicked spark knock. timing is adjusted to 10 degrees btdc with spout plug REMOVED. old motor had same problem with the knock but it also had NO power either so i hollowed out the rear converter and could not get to the front converter (2 converters from y-pipe) seemed to give me back some power before the old motor went but still had the knock to it . i just went and spent $300.00 on a new y-pipe and converter and have not installed it yet (need a torch to heat up exhaust manifold bolts)

is there anything else that i should be checking first before i just keep throwing money at this thing? a neighbor of mine who is a fairly good mechanic said i should try retarding the timing a couple of degrees and try that first before i go putting the new exhaust on . opinions on this would really help from some senior members . also i am getting no codes what so ever. fuel system is up 100 % new fdm's in tanks and lines are clear and not kinked either.IM STUMPED ON THIS ONE

 

pinging or knocking is usually a sign of pre-detination (timing). you could try changing the timing a little but as ive found out the computer likes to change the timing too. you can also try gas with a higher octane rating.

 

already tried the higher octane gas and it didnt help. tried octane booster as well , no luck. i dont want to destroy a brand new motor because of some little detail i have missed , there is only 188 miles on the motor and they are all easy miles.im still in the break in stage of milage on this motor and these few miles are the critical ones . dont wanna see a brand new motor going up in smoke.

 

well tonight i tried to adjust the timing again . both times with the spout plug REMOVED. i adjusted 2 degrees back (8 btdc) and drove it still the same knock . i adjusted it 2 degrees ahead (12 btdc) and drove it again with the same knock. both times it had a loss of power and ran rough.setting at 10 btdc it ran good and no power loss but still have the knock. looks like im putting the new y-pipe and converter on asap. unless someone can steer me in a different direction with this problem. damn truck is all gonna be brand new when im done gonna have to re register it as a 1991/2005.lol

 

This is just an idea, but I had a bad pinging in my 93 F-150. I fixed my by rerunning my #8 plug wire. Check out this thread.

https://www.ford-trucks.com/forums/s...3&page=1&pp=20

 

Something is fishy. The difference between 8 BTDC and 12 BTDC should not be enough to cause "a loss of power and ran rough". A couple of degrees of timing should be a fairly subtle change -- a little more knock sensitive at 12 BTDC, a little less at 8 BTDC, but the engine should idle and run about the same. Are you confident you understand where the "zero" is on the timing pointer, and by how much you are changing the timing? Is the harmonic damper mounted correctly? Is the cam timing right? Personally, I find the timing pointer fairly unobvious as to where exactly "zero" is, and had to locate TDC by feeling the piston position through the spark plug hole to have any confidence in it.

As you advance the timing, the idle will tend to speed up. The computer will close down the IAC to compensate. Similarly, as you retard the timing the idle will slow down and the computer will advance the IAC. So if the IAC is acting up you MIGHT get an interaction effect that could cause rough running.

If you had a bad vacuum leak, or one of the fuel injectors is partially clogged, one cylinder out of 8 may be running lean. This could cause rough running and knock sensitivity. Take a close look at all 8 plugs and see if one of them is different from the others.

Another avenue to consider is re-routing the PCV to the center of the plenum, rather than to the back like the stock truck. The blowby due to the not-yet-seated rings might be diluting the charge to the rearmost cylinders.

As rkersh409 suggests, crossfire between plug wires is another thing to check out.

 

This absolutely worked for me! I tried lots of other things (seafoam, tuneup, hi-octane gas, new injectors......) - many of which were needed & I'm sure helped - but until I re-routed my #8 wire around the exhaust manifold my 1992 F-150 would ping every chance it got. Since the re-reoute - NO PINGING! UNBELIEVABLE!

Thanks for the suggestion!

 

would a partially plugged cat cause ping?

 

well after i put on the new exhaust manifolds (broke all the bolts in the old ones ) new y pipe , converter and a new o2 sensor the ping and knock went away . so it was one of them