Wierd power loss under acceleration.
 

When I am accelerating and shifting through the gears I have a serious power/torque loss between 2500 and 3200 RPM's. It isnt enough to stall the engine... it stays at the same RPM, but it is enough to almost jerk you into the steering wheel.

I have the feeling it is a catalytic converter as there is a distict popping sound on hard deceleration. However, I am still at a loss as this only happens at those RPM's

Specs:

97 F150
4.2 5 Speed
4wd
3.08 gears.


Any help is much appreciated.

Josh

Sounds like the split port induction is maybe not working and you are staying in the low RPM mode.

Sounds like fuel starvation under heavy load.

IMO, you should replace your fuel filter. It's cheap and very easy to do (less than 10 minutes with the right line removal tool, including clean up time).

FWIW, I've driven vehicles before with a clogged fuel filter before where the loss in high rpm power was less noticeable than the power loss under heavy load at lower rpm.

i hooked it up to the OBDII scanner and it says lean condition of O2 sensors. sensors are fairly new.

I did change my fuel filter... and broke the fuel lines in the process... so $247 dollars + plenum gasket $30 + valve cover gasket (not necessary but i had access to it with the plenum off) $30 + fuel filter $10= $313 fuel filter change... and still no cure.


So off it goes to the shop tommorow for a professional diagnostic because I dont want to spend any more money without knowing what the hell i am replacing and that it will actually cure the problem.

josh

Both banks lean is a vacuum leak, probably the PCV elbow at the back of the intake manifold.

well it has been at the shop for a couple of days now...


And still no diagnosis. my mechanic hoked it up to the computer... still threw the lean codes.


Then he unbolted the exhaust to check if the CAT was plugged. still NO power. couldn't spin the tires in gravel.
Following that he check fuel pressure. he told me that factory specifications on fuel pressure is between 30 and 65 psi. It ran a constant 30 psi.


me thinks it will be fuel pump or fuel pressure regulator. BUTTT..... idk what the hell it will be.

Check your spark plugs. My wife's had not been changed since the truck was built. Couple that with vacuum leaks next to the firewall and it would bog down on acceleration and I thought it was the catalytic converter as well. I pulled the plugs and checked the gap. It was supposed to be around .050". The plugs had deteriorated to a .090 and .100" gap. Hope this helps.

I ficksed it!!!:thumbsup:

the DUmbass who had the truck before me did not tighten the hamonic balancer bolt... and the key way on the HB was wallowed out.


beings that the timing chain is attached to the HB it would idle fine but when under acceleration it would retard the timing... and therefore no pawah.


thatnks for all the help.

Good job finding that one!

Always hard to find something that should never happen. I guess that's why used trucks sell for less than new ones, lol.