Loss of some power at lower RPM's ?

[Phil Trovato]

At about 18,500 miles my 2004 Sporttrac began to show some weakness in its powerband around the 1700 - 1900 RPM range. How the problem manifests itself is that while driving in that RPM range, mostly at in-town or highway traffic speeds, whenever the RPMs enter that range there is a slight dump in power and I feel the truck lag before it accelerates. There is also a slight vibration that can be both heard and felt through the gas pedal while this is happening. Once out of that RPM range, the trucks seems to run fine. It may be a coincidence but all this started about the same time I received an oil change and new air filter service from Jiffy Lube.



I took it to the dealership in Wayne NJ and they said their test drive didn't indicate a problem but that the computer showed about an 8 lb. drop in fuel pressure at that engine speed. They suggested a new fuel filter and an injector cleaning service might do the trick. Well, I am $247 lighter and the proble still exists. I called and suggested that I take the tech out on the test drive to duplicate the conditions during which the power loss happens, so we will see how that goes.



I am not a mechanic, but to me it feels like some type of loss of compression. I have seen strings on this site that refer to vacuum elbo problems. Could that be the cause? Or could it be as simple as an exhaust leak?



Any help or advice that you all may have would be very appreciated.



Thanks in advance

 

[EddieS'04]

Not sure if the elbow would be bad this soon...if so cel should come on...I would change the fuel filter myself and put a can of fuel injector cleaner in the fuel tank...maybe the air filter they used is too restrictive...check and see if lube people left a hose loose when changing the air filter...

 

[Todd Z]

Try driving the truck with the overdrive off and see if it does it. It just may be the torque converter locking up early.....



As for Jiffy lube. Double check the intake tube and air filter and housing, They are notorious for using the wrong filters or putting it back together wrong..

Todd Z

 

[Andy G]

Fuel pump?



Computer/Spark Issue?



I have seen a bad ground conection coming off of ignition modules do some funny stuff........

 

[Michael Cacioppo]

If it were fuel starvation, the problem would get worse with speed (load) not happen within a specific rpm range and then get better. The mechanics first guess, in my opinion, was wrong and didn't really make sense to be.



One possibility could be the Throttle Position Sensor (TPS). The position of the gas pedal would be repeatable for a given rpm range while under load.This is basically a resistor and can have a bad spot on its variable resiter. That would be one guess that I would persue.

 

[Yardsale]

I have a '01 (Job 1) 4WD that has done this, almost exactly as described, for as long as I can remember.



The fuel system is a sealed, circulating system and it seems to me that if there is a fuel pressure drop, it should be treated where the fuel pressure is developed, or where the fuel may flow where (or when) it is not supposed to. A clogged fuel filter, I would think, would exhibit whatever behavior it would all the time. If there is a faulty injector, it would probably be one that is not closing completely, however, I think that the fuel pump should be able to handle this - and, could a fuel injector fail in this manner in only this RPM range?



rantOn;

Oh yes, my friend, you are $247.00 lighter and I'd put on my heaviest steel-toed work boots and remind the service department of a thing, or two. This was not a routine maintenance service that you would have paid to have done whether or not there was a problem. This was the dealer suggesting that this might solve the problem and a costly, failed experiment.

rantOff;



Hi Todd,

I don't think it's the converter. It just doesn't feel "transmissiony" (if this makes sense). The sound is a typical low RPM kind of rumble (maybe in the exhaust), but the vibration is very engine(y). It's so quick, that there isn't time to get a good feel. I too, am stumped.

 

[FlipTrac_511]

How sad is it when we have to worry about service employees botching a task as simple as changing the oil and replacing a drop-in air filter? I know, I know, quality work seems to be a rare thing. In some ways I hope the problem is a simple thing as a loose hose or cracked elbow, but at the same time it would be sad for the problem to be the result of such poor workmanship.



Sorry I don't have an answer, Phil, but I hope things get worked out.

 

[Yardsale]

FYI - I was able to reproduce the vibration and noise with the overdrive off. This took a while as it's tough to get and keep the RPMs below 2000 with the overdrive off with little control of what gear is engaged.)