Slight vibration at idle, weak acceleration, no error codes...

[Nuke'em]

Hello my fellow Explorer enthusiasts! I had a tough time searching through the forum to find someone experiencing similar symptoms as mine.

I have a 2003 XLS V6 Flex engine purchased used from private seller. I've had it for a few months now and I've noticed the engine doesn't quite perform like I think it should.

It has a noticeable vibration at idle/stop, poor acceleration and there are no engine error codes/CEL is off. I verified the light works upon light check with key on but engine off position with the ignition. I changed spark plugs, check plug wires (resistance and voltage drops), changed fuel filter, replaced knock sensor (just in case), put in a heavy dose of Berryman's B12 in tank for injectors, verified no vacuum leaks (good), replaced air filter, cleaned MAF sensor (twice), checked throttle body (seems good/clean), replaced PCV (just in case). That's all I can think of so far.

I plan on taking out the IAC valve next to clean and inspect.

But besides that does anybody else know of something I should check that isn't monitored by the ECM that could be the issue?

Thanks,
Mike

 

[IPcamper]

You have checked all of the stuff, I would have checked myself. Do you have access to a good scan tool? if so monitor the engine for a while and see if the 02 sensors are good.

Is the engine running hot? I have had a Catalytic converter ( on a minivan ) fail and cause partial blockage of the exhaust act like that.

Question do you know if the previous owner had the timing chains done? You could also do a compression check and see if the compression is low in any of the cylinders.

hope you get it figured out.

 

[Nuke'em]

You have checked all of the stuff, I would have checked myself. Do you have access to a good scan tool? if so monitor the engine for a while and see if the 02 sensors are good.

Is the engine running hot? I have had a Catalytic converter ( on a minivan ) fail and cause partial blockage of the exhaust act like that.

Question do you know if the previous owner had the timing chains done? You could also do a compression check and see if the compression is low in any of the cylinders.

hope you get it figured out.

I didn't put a very good scan tool on it. Just a basic OBDII to see if there happened to be an error code. I'll see if I can get my hands on a decent one and monitor the sensors.

As far as what the previous owner had done; I have no idea. That's why I replaced the plugs and other things. I didn't want to assume they had done some of the basics.

My question regarding the O2 sensors and the compressions: aren't these both monitored by the PCM? Wouldn't they have sent a DTC if there was something off?

- Mike

 

[IPcamper]

Well, the PCM ( any computer ) only knows what the sensors ( input ) tell it. If the data coming is poor quality, the computer adjustment of the running condition may be wrong.

If the compression is low, then the engine won't develop the proper power output, the computer will try to optimize the fuel air ratio, but it still won't develop full power.

If the timing chains had be replaced, and were not adjusted correctly, that might explain the rough idle and low power.

you mentioned this is flex fuel engine, these have a fuel sensor that measures the ethanol content of the fuel and pcm adjust the fuel air ratio accordingly, I wonder if this is faulty, if it might cause some problems.

 

[Nuke'em]

Well, the PCM ( any computer ) only knows what the sensors ( input ) tell it. If the data coming is poor quality, the computer adjustment of the running condition may be wrong.

If the compression is low, then the engine won't develop the proper power output, the computer will try to optimize the fuel air ratio, but it still won't develop full power.

If the timing chains had be replaced, and were not adjusted correctly, that might explain the rough idle and low power.

you mentioned this is flex fuel engine, these have a fuel sensor that measures the ethanol content of the fuel and pcm adjust the fuel air ratio accordingly, I wonder if this is faulty, if it might cause some problems.

With your previous theory about the O2 sensors; would the sensors of concern be JUST the upstream sensors, downstream sensors, or all?

And regarding the timing chain; if the timing is off would that just require an adjustment? Or am I most likely looking at having to replace the belt, bolts, sprockets, etc?

I also noticed last night that the drive belt tensioner was bobbing ever so slightly. Should that be anything of concern?

 

[Nuke'em]

Hey all...it ended up being a clogged rear cat converter the entire time (my original theory from the beginning). The driver side cat had completely melted and the remains were clogging up the rear cat. Replaced them both, along with the O2 sensors, and now she's running like a champ.

Hopefully this helps anybody else who comes across this problem.


-Mike