2000 4x4 3.0L Will Not Run More Than 3700 RPM

[jmayle]

I have a 2000 4x4 AT 3.0 L V-6 that will not turn more than 3700 RPMs, with the peddle to the floor 4000 RPMs is its max and is running very rough. I have changed everything I could think of. Plugs, wires, coil, EGR valve, EGR sensor, and camshaft position sensor. I have 67 PSI fuel pressure. There are 3 cats, 2 at the exhaust manifold and 1 after the Y pipe. I was able to remove the single cat and it ran the same. any help would be greatly appreciated.

 

[rusty ol ranger]

Does it do it under load, in neutral or both?

 

[Curious Hound]

Fuel filter? Stretched throttle cable?

It would be wise to have codes read.

 

[RonD]

Get a vacuum gauge, $10, or borrow one
Hook it up to intake manifold
Raise RPMs up to 2,500 or so and hold steady, watch the vacuum
If its slowly dropping you have a partially clogged exhaust
If its slowly going up you have an air intake restriction

Fuel pressure is a bit high, but not the issue, 55-65psi is expected, so 60psi average

"and is running very rough"
Does this mean only above 3,000rpms it is running rough
OR
Its running rough at any RPM, just noticed more at higher RPMs under load

The computer has an RPM Limiter set at 3,000rpm when transmission is in Neutral or Park on an automatic
On drivers side of transmission is the DTR sensor/switch, it tells the computer what Gear the transmission is in
Try shifting into 2nd and see if you can accelerate and maintain RPMs at 4,000 without "running rough"
If so then DTR may need adjusting or replacement, i.e. its telling computer you are in Neutral when shifted into D, so REV Limiter is "on"

 

[Cliff_m]

Is CEL on? Get the codes pulled. Check live data for fuel trims. What were the symptoms leaking up to the drivability issues? MAF and baro sensor will cause drivability issues like you describe.

 

[jmayle]

Does it do it under load, in neutral or both?

Both

 

[jmayle]

Fuel filter? Stretched throttle cable?

It would be wise to have codes read.

It does not show any codes

 

[jmayle]

Get a vacuum gauge, $10, or borrow one
Hook it up to intake manifold
Raise RPMs up to 2,500 or so and hold steady, watch the vacuum
If its slowly dropping you have a partially clogged exhaust
If its slowly going up you have an air intake restriction

Fuel pressure is a bit high, but not the issue, 55-65psi is expected, so 60psi average

"and is running very rough"
Does this mean only above 3,000rpms it is running rough
OR
Its running rough at any RPM, just noticed more at higher RPMs under load

The computer has an RPM Limiter set at 3,000rpm when transmission is in Neutral or Park on an automatic
On drivers side of transmission is the DTR sensor/switch, it tells the computer what Gear the transmission is in
Try shifting into 2nd and see if you can accelerate and maintain RPMs at 4,000 without "running rough"
If so then DTR may need adjusting or replacement, i.e. its telling computer you are in Neutral when shifted into D, so REV Limiter is "on"

thanks, I am on it

 

[jmayle]

Is CEL on? Get the codes pulled. Check live data for fuel trims. What were the symptoms leaking up to the drivability issues? MAF and baro sensor will cause drivability issues like you describe.

No it is not

 

[Cliff_m]

Need to figure out if it's lean or rich. Scan tool will tell you more about diagnostics than any amount of parts or guessing.