Been working on getting this 91 f150, 302 to run good, replaced motor, cap, rotor and wires, re gapped plugs to 54, running timing at 10 btdc and just replaced TFI module.....when driving along, the truck seems to have no pickup, when under load or accelerating the truck makes a popping sound like its backfiring....any ideas would be great..

 

Forgot to mention...i am getting no check engine lights or codes..im guessing if it were a bad valve or engine related i should get a code?

 

try fuel system....fuel filter,fuel pumps just to start....mine does that when I run out of gas or u just might have trash in the fuel system

 

how come you had to replace the TFI?

I had one go out, and even the new one was bad. Really bad when that goes out too. Feels like the engine is running against itself, and was hard to start, found out someone had dropped the box that the first new one came in.....those things are pretty touchy.

also, (im guessing you already know) but was the spout wire unplugged when you did the base timing?

also, since you replaced the motor, do you know if this one ran fine before you put it in? sorry for all the q's

 

This is a brand new crate short block 302....Originally the motor ran great....started getting hesitation, poor idle, lack of power when accelerating...replaced cap , wire and rotor and new plugs for second time since motor has been in....only 17,000 miles on it....replaced TFI after reading other posts on here and recommendations from others about similiar problems...when i set the timing i did unplug the spout...computer seems to take over. The truck just has a rough idle and makes a popping sound when accelerating....It always fires right up no matter how cold or how warm it gets after driving....i am at a loss here...maybe throttle body or throttle position sensor im thinking next.....then egr and so on.....i dont get a CEL and will run codes tomorrow....appreciate any ideas you guys have....

 

It could possibly be in the valve train as well. Even though it is a crate motor, they could have possibly put the wrong pushrods in. If they are too long, it would do exactly as you are describing.

 

Possible bad valve or motor wasnt properly broken In? Im taking a shot in the dark...Thanks for the input hawk!

 

Yeah, I know it sounds strange. A gentleman I know bought a crate motor. It was a rebuilt unit. They had milled the block and then put in the stock length pushrods. Whenever the engine first started, it had no problems until oil pressure came up. When the lifters stiffened because of the oil pressure, the valves were not closing completely, causing backfiring through the induction system, rough idling and poor performance. Its worth a look.

 

My Ford 302 does the same. I think it is from the timing being set to much in advance. If i use high octane gas it wont do it. You should try it.

 

I dont think its the throttle body or the throttle body sensor when my 302 had its going out it would surge when it was in park or in drive and stopped. If it has a cam in it then it will idle rough and loop up and down in idle. Mine does, we advanced the cam 4degrees and put roller rocker arm in it and you can hear it. I think Hawkman180 is right you should check the compression and make sure you dont have too much or too little lift. If you do there is always shorter push rods or shimms.

 

Found out mine was from The EGR vacuum Solenoid.....never thought about the exaust not having enough back preassure from when i went to 3 inch , took care of the rough idle....no more popping....runs like a ford should.....Thanks for all the help....

 

a bad 02 sensor will also exhibit similar symptoms.

 

I have the same issue. I have recently replaced the fuel filter and I have purchased an ignition Control Module. Has anyone seen this work or other recommendations?