Sluggish/loses power going up a hill
 

Background:

98 Ram 1500 4x4 318. This summer when towing a uhaul across the country the try displayed the wild vents issue for the first time. This has now happened several times in the past six months (keeping in mind that there are no hills unless I leave town which is rare). While going out to dinner last night in a town 20 miles away I had to get up a fairly steep hill that was maybe 1/4 mile long. Very quickly after starting up the hill the engine starts to miss? or something, resulting in it chugging along at less than full power. On the back side of the hill (not as steep) it did the same thing but not nearly as bad (and I had a LOT of momentum to make sure I got up it). No lights were tossed up.

I took it into a shop today and was told they could not replicate the problem. They said they also vacuum tested it and found no problems.

So in my mind this leaves several possibilities but I am not sure where to go with it as I have no idea how to test this short of getting stranded on a rural road in Montana during the middle of winter.
* Bad/dying fuel pump (please god no). Pump is now at 1/3 tank now that I am back. I have run it down to the fuel light twice recently, which is more than this has happened in the past five years.
* Clogged cat (cat and I believe the upstream was replaced about two years ago)
* Plenum/head gasket really is blown but they missed it
* TPS (Entire throttle body was very, very thoroughly cleaned by removing it and the tps replaced about 9 months ago)
* To throw something wild out there, maybe it has something to do with having overheating the OD by not turning it off while towing? See https://dodgeforum.com/forum/2nd-gen-ram-tech/165745-ticking-from-left-side-while-towing-in-progress.html for background.

Suggestions?

I doubt it's a fuel pump problem. Does it ping and knock when it's missing? If so, I would first check plugs and plug wires. A 9 mo. old TPS shouldn't be giving you any problems but I'm sure there are exceptions. If you have a repair manual (Hains, Motors, Chiltons, etc.) it'll show you how to test your sensors. Does it act like this frequently or is this the first time? Could be you got some bad fuel some place.
I'm no expert but I've had problems like this and my first hunch is plugs and or plug wires.
If this doesn't help maybe someone with greater experience than mine will respond.

I would need a good definition of pinging/knocking first. It seemed underpowered and as if it were missing/misfiring/something, but I am not sure why the plugs would act up here.

Actually, I wanted to pull the plugs (last replaced 2 years or so ago) but the dealership replaced them the last night and they are far too tight for me to get off.

All the incidents are posted above.

My truck does the same thing, just that it isn't always when going up hills. At about 75ish on the highway the check engine light starts flashing and it feels like the truck is missing really bad. resulting in bad chugging and lose of mile an hour big time. Then all of a sudden the check engine light will stop flashing and the truck will be alright. The light stayed on once and it read "misfire cylnder 8" but then went right back off, checked plugs and all were fine.

has your plenum gasket/plate ever been replaced. the vac leak and lean condition associate with that makes them a little sluggish.

the wild vents can usually be fixed by replacing the check valves in the little vac lines. this has little or nothing to do with being sluggish.

i was going to say to replace TPS, but you already did that.

what size tires have you got. anything taller than stock begins to sap power quick on the 3.55 gears. my 275/75's really suck. taller tires need 4.10 gears to get back to the proper factory feeling of get up and go.

are you driving with Overdrive on. i ALWAYS turn o/d off whenever speed is less than 55-60. i have no power at all below about 2000 rpm. so that means i have no power when OD is engaged unless my speed is 60 or more. the combination of overdrive on, stock 3.55 gears, taller tires, and low rpm's are just more than the 318 can handle.

Get the cat pressure checked. The bigging down on minor inclined makes me believe it's the cat. I believe you said there were misfires, and the cat will cause a misfire on #6 and/or #8 when clogged.

It does have larger than normal tires (the largest you could select at the factory) but I do not see how this could in any conceivable way be the combination of the above. The truck has run perfectly fine for 10 years and has gone up the same hill before and been perfectly fine.

The shop vacuum tested it yesterday, would that not have detected the plenum leaking?

No, it won't detect the plenum leak. There is a certain way to test the plenum doing it with a vacuum check. http://dodgeram.info/tsb/2000/09-05-00.htm Of course the cat. is probably bad too,due to the bad plenum gasket.

Damn. Ok, will have the shop do that the next time I take it in. It is a tad too cold to try to look down into it.

Again though, is a plenum leak going to make it run *that* poorly?

I should clarify, we might have different definitions of minor. I live at the base of the Rockies. The hill in question is at absolute most 1/2 mile long and about the steepest grade you will normally see on a major road. I can go up the hills in town with no effect.