2003 B3000 3.0 V6

On any acceleration beyond minimal, the truck starts to bog down. Going up a hill, it will get sluggish down to 20 mph or even less. But even on flat ground, it barely responds to heavy acceleration. It drives fine on flat ground under light acceleration, and does great downhill. Also, it seems to get worse the longer I drive it, and it does a little better if I park and kill the engine for a few minutes.

I had a bad spark plug cable (broken terminal inside the boot) but I think that was unrelated. It's replaced with no change. Last night I noticed a leak in the front left (driver) exhaust pipe. I'll be replacing that today.

I guess my question is, if the new exhaust pipe doesn't fix it, what am I looking at next? I'm guessing testing for a vacuum leak.

I don't think my catalytic converter is plugged. The output from the muffler seems normal.
I don't think it's anything related to compression or ignition. It idles fine and revs great in Park.

Any other ideas I should be considering? Thanks for any input.

 

Before, or after the O2 sensor?
Are you getting spark on all 6 plugs?

Not a good test, especially as you said it only happens when the engine is under load.

Also not a good test, there is no load on the engine.

You're going to have to expand on the 'bog down' comment; does it misfire, does it make that flat sound as if misfiring, but smoothly?

 

The TPS(throttle position sensor) on upper intake tells computer what driver wants to do
Does same job as accelerator pump did on a carb engine

When driver presses down on the gas pedal air flow increases instantly and there will be a delay from "Jets" or MAF sensor reading this quick increase in air flow.
Accelerator pump squirted extra gas into engine to get instant throttle response until "Jets" could catch up to increased fuel demand.
TPS does same thing for computer/fuel injection, it tells it to add more fuel instantly
Also to change spark timing for richer mix(carb engines used vacuum advance)

So sluggish throttle response could be TPS not working as it should
Easy to test with volt meter and sewing needle
Use sewing pin to pierce wire to test voltage
Key on, engine off
Upper wire on TPS will have 5 volts, test it first

Center wire should have under 1volt when throttle is closed, .69-.99 is spec
While testing center wire, manually open throttle and watch voltage, should instantly go up as throttle opens, at wide open it should be 4.5volts or higher
Move throttle around and make sure voltage response is instant.



MAF(mass air flow) sensor, these get dirty, so can't read air flow correctly, usually you will get Lean Codes when this happens
But easy enough to clean MAF sensor, Google "cleaning MAF sensor", this should be done every 5 years, like changing fuel filter, if you drive in dusty areas alot then once a year for MAF cleaning, and change air filter
Dirty air filter can slow quick changes to air flow, so can cause bogging

 

Yup, very easy to clean the MAF, this stuff is under $10 from Autozone.

 

Thanks to everyone for their replies. I've got the issue identified now, and will get it fully resolved soon. It ended up being a clogged cat, which I suspect got gradually worse through the week, as my symptoms worsened.

To answer a few of the questions. Hopefully this will help someone out in the future.
Yes, I did have spark on all six cylinders.
I went ahead and replaced the plugs. I had a broken spark plug wire (loose at the boot, unrelated to larger issue) so I got new wires and checked the plugs (installed by me 18 months ago). All three on the driver side had their terminal points burned off, I assume from excessive heat from the upper CAT on that side. I also had two small holes form in the weld joints of that upper CAT.
Fuel pressure was fine
RonD, thanks for the info on the TPS. I checked it out through all this and it was bad. Obviously I had other larger issues, but it still needed to be replaced.
I also installed new air filter and cleaned MAF sensor.
The problems originally started with my description of the bogged down behavior in this post. To describe that further, when going uphill, it would feel like I was pulled a very heavy load. There would be no skips, no misses. Just the speed would reduce as if I was hauling something too heavy for my truck.
As the problem got worse a day or two later, I couldn't even get it above 25 mph, only about 10 mph on any type of decent incline, and I even stalled out on one steeper hill. It didn't die, but wouldn't go any further.

Also, through all of this, I never got a CEL related to the CATs. I would get random misfire codes, likely side-effects of the poor performance. I also got other codes related to the TPS, but they went away once I replaced it. But never a code related to the CAT or exhaust. I read on another post that someone with a clogged CAT never got related codes. So that's just something to watch out for.

I hope this describes the situation pretty well, and can help someone. I didn't want to believe it was the CATs. Getting to that O2 sensor was hard. Another easy test to do would be to test the vacuum at the intake manifold. If it's lower than normal (I think 12-15 psi on my truck is normal), that would point to a possibility of a clogged CAT.

 

Thanks for coming back and closing the story.

Sounds like the misfire codes were caused by the bad HT lead connection.

The spark plug terminals burnt off on the drivers side is because of the wasted spark system and the plug not being a double platinum - not a massive problem, they need replacing more often, but i'm curious how many miles you did since replacing them.

O2 sensors just check the difference between the outside air and the amount of Co2 in the stream after the cats, they're pretty basic - a clogged cat won't cause a condition they care about.

 

I drive a lot. I've done just over 50,000 miles since I installed those plugs.

 

So that makes sense, thanks for that.

Unless you spend the money on actual double plat plugs, the wasted spark system will eat the non platinum terminal, otherwise spend the regular money on regular plugs and change at the older "regular" interval, about 30k i think?

 

I wonder if the faulty TPS caused the cats to fail ???
An overly rich running engine would have plugged up the converters, but then there should have been a code for that given from the oxygen sensor(s).
Too lean as well will burn them out.

 

Cats don't care about any of that, i'd doubt it.

Cats break up and/or get foreign bodies in them, then break up etc etc - it's Ford, they're cheap cats, and there seem to be freakin' 5 of them!!

 

5 ????
My 99 has two with one down stream oxygen censor in the middle of them.
The 2 cats are sold as a unit.

Something had to have caused them to fail _ or plug up rather.
A lean condition can melt the ceramic matrix itself.

 

My '02 seems to have 3 pre-cats and two main cats, two up steam sensors and i think one down stream.

:(

 

YUP, you're right, Ford must have had to add more converters in 2002 (and who knows when they started) to meet more stringent emission control standards.

The 3 pre-cats on mine are totally not there, just simple exhaust pipe.

And of course the op's 2003 shows the same at RockAuto...

EDIT:
I just looked up for 99 Ranger and Mazda, RockAuto both show the downpipes with at least 2 cats.
I'm betting the Canadian models don't have those converters _ different emission control standards I guess.

 

Hmm, that's a good possibility, it's all about the cold start emissions, they wanted them down/out and pre-cats were the way.

I'm seriously tempted to remove them at some point, they won't affect the downstream stuff so long as the main cats are still there.