4.0 hits a wall

[Treecutter]

I’ve been working on getting this 4.0 running right. It runs strong until about 4500 and then seems like it hits a wall. You can back out of it so it shifts and it will pull hard until 4500 again. It does surge some after 4500 like it is starving for fuel. I can hook my scan gauge to it and watch ign timing and it will pull all the timing out. Back to like 9° at wot &4500 rpm.

Things I’ve done, plugs, wires, intake gasket, injectors. Before injectors I was getting a miss code and 0171 lean code. Since injectors I’m getting 017,0174 and 0420.

Timing chains we’re supposed to have been done before I bought the car. Just normal driving and you would never know anything was wrong with it.

 

[Pentalab]

Several years ago, my 2010 GT started to gag, but only when I tried to get into boost. The fuel pressure would drop to 5 psi ( down from 40 psi). Turns out the problem was the 'sock filter' that goes on the bottom of the fuel pump. It was completely clogged. Did you also check the fuel filter ? It could also be the fuel pump.

 

[Tman]

Yeah I was thinking fuel filter also.
Or possibly obstruction in catalytic converter.


Sent from my iPhone using Tapatalk

 

[Treecutter]

Several years ago, my 2010 GT started to gag, but only when I tried to get into boost. The fuel pressure would drop to 5 psi ( down from 40 psi). Turns out the problem was the 'sock filter' that goes on the bottom of the fuel pump. It was completely clogged. Did you also check the fuel filter ? It could also be the fuel pump.

I tried to get my scan gauge to read fuel pressure but so far have been able too. I also can’t find anywhere to connect my gauge to check it. I did change the one under the car. The fuel pump duty cycle seems to stay down like it’s not struggling to keep up but would like to be able to see the pressure.