Lacks Power

[Argos587]

2001, 4.0 lacks power on acceleration.
Feels like no spark advance. On highway, kicks down a gear, but has little additional power. Speed and rpm will increase, but much slower than normal. Otherwise runs great. Any advice?

 

[Pete Deering]

2001, 4.0 lacks power on acceleration.
Feels like no spark advance. On highway, kicks down a gear, but has little additional power. Speed and rpm will increase, but much slower than normal. Otherwise runs great. Any advice?

What engine and how many miles?

Clogged exhaust maybe!

 

[Mbrooks420]

Only the SOHC in 2001. Do you have a check engine light?

 

[Argos587]

What engine and how many miles?

Clogged exhaust maybe!

4.0 SOHC, 290,000 miles (doubt it's original engine) new to me at 200k miles.

 

[Argos587]

What engine and how many miles?

Clogged exhaust maybe!

4.0 SOHC, 292,000 miles.
Puchased with 200,000 miles already on it. Not sure if it's original motor.

 

[Argos587]

Only the SOHC in 2001. Do you have a check engine light?

No check engine light or codes.

 

[Turdle]

Does check engine light even work with key on?

 

[Argos587]

Does check engine light even work with key on?

Yes it does.

 

[Argos587]

2001, 4.0 lacks power on acceleration.
Feels like no spark advance. On highway, kicks down a gear, but has little additional power. Speed and rpm will increase, but much slower than normal. Otherwise runs great. Any advice?

Update. While driving today, was able to get RPM to increase as expected when needed. Will keep watching this and see what happens. Will check manifold vacuum as well for exhaust clog issue.

 

[Argos587]

Finally had time to spend on this issue. Replaced upper CATS, no change. Road tested with gap between upper & lower CATS, no change. Road tested with gap between lower CAT and muffler, no change. Feels similar to no timing/spark advance (for those who remember distributors from the 60s & 70s), any suggestions to verify timing advance & function? Transmission will downshift, but lacks power.

 

[Pete Deering]

Yo

Finally had time to spend on this issue. Replaced upper CATS, no change. Road tested with gap between upper & lower CATS, no change. Road tested with gap between lower CAT and muffler, no change. Feels similar to no timing/spark advance (for those who remember distributors from the 60s & 70s), any suggestions to verify timing advance & function? Transmission will downshift, but lacks power.

You should be able to scan live data on a OBD2 reader

 

[410Fortune]

Sounds like weak fuel pump/ pressure to me

Rail pressure should be like 64 psi
They will still run with like 45 psi but you will run out of power quickly and the fuel is dripping out the injectors not spraying.
Simple fuel pressure test or watch fuel trims on live data

We see these sohc engines go well over 200k miles when cared for just fyi and the factory fuel pump can last about that long too

 

[Argos587]

Sounds like weak fuel pump/ pressure to me

Rail pressure should be like 64 psi
They will still run with like 45 psi but you will run out of power quickly and the fuel is dripping out the injectors not spraying.
Simple fuel pressure test or watch fuel trims on live data

We see these sohc engines go well over 200k miles when cared for just fyi and the factory fuel pump can last about that long too

May try the fuel pump. It looses pressure in the rail overnight, so may be time anyway for that.

 

[Josh P]

When was the fuel filter changed?

 

[410Fortune]

Some of my My fuel pumps lose pressure in seconds, if the check valve wears out or is Mia (little rubber sock on older models)
The pressure in the rail w system primed (startup) and while running is what matters

 

[Argos587]

When was the fuel filter changed?

Fuel Filter was changed a month ago. No Change

 

[Argos587]

Was able to watch sensors while driving. Noticed the timing is acting in reverse. At idle or low speeds timing is between 18 deg to 25 deg, however with a heavy load or full throttle timing advance drops to 8 deg or less (hit 4 deg once). Have replaced the CAM sensor (this fixed my delayed straying issue). No change in timing reading. Any ideas? Believe the timing is to advance with RPM increase.

 

[C420sailor]

How do the fuel trims look?

I’d be checking fuel pressure, trims, etc before I start going down rabbit holes of backwards timing.

If you’ve got double digit trims, something is up with fuel supply or vacuum leaks.

How old are the plugs and wires?

Any indication that the engine has jumped time?!?

 

[Argos587]

How do the fuel trims look?

I’d be checking fuel pressure, trims, etc before I start going down rabbit holes of backwards timing.

If you’ve got double digit trims, something is up with fuel supply or vacuum leaks.

How old are the plugs and wires?

Any indication that the engine has jumped time?!?

Haven't found any vacuum leaks. Plugs about 1 1/2 years old, but only driven about 1/2 that time. Wires are 5-7 yrs old and same with coils. Haven't checked mechanical timing as timing chains were replaced about 1 1/2 years ago. Will check fuel pressures soon. Just seems odd that the ignition timing advance would go way down when it should go up. Of course, PCM could be seeing something else not right and adjusting for that as well.

 

[C420sailor]

No cam chain noise?

If it’s pulling timing under load, the knock sensor may be hearing something. Maybe lean ping?

No codes or pending codes?