So, brought the truck in for an inspection today, and on the 35 minute drive home, through the backwoods, with no cell reception, it started acting up!

I first noticed something was off, when I stepped on the gas to speed up coming out of a 30mph zone. I gave the peddle some good play, and got very little engine reaction in return. The truck continued to slow, and act "bogged down" when I'd step on the gas. Tried revving it in neutral, that worked sometimes. Then it didn't want to stay at a steady idle, and started bouncing between 700rpm and 200rpm (just shy of stalling). After a couple minutes of futzing with it, and feathering the throttle in neutral, everything returned to normal.

This whole routine played itself out a few more times on the way home. Each time it felt like the truck was choking and trying to die. I have to climb a massive hill to get to my house, and had to feather the throttle the whole time just to make it up.

Oh, and I forgot to mention the banging noises I'd get from the engine, while it was in gear and I'd be feathering it... not a backfire, or a misfire, more like a small...detonation.

Sound like a plenum problem to anyone else yet?

* Heavy spark knock under load (sounds like a can of marbles when you have your foot in it). ----- Check.
* Truck feels like it was castrated (loss of power). ----- Check
* Trouble getting up hills ----- Check

So I pulled it into the garage when I got home, popped the hood, took the airhat off (ok, really, the first thing I dead was pull up the End All Plenum Thread...), and popped a lighted borescope down past the throttle plates... To my surprise, the plate was clean and shiny... It's cleaner in there, than the outside of the engine!

I also did the magnet test, and it stuck. So either the plate is original, or the previous owner replaced it with another original plate... But, since buying the truck, I've found enough signs that point to the previous owner being the laziest SOB on EARTH, that I can safely bet on it being original. Changed the oil on day 1 after getting the truck home, and I think THAT may have been original, too!

So - plenum symptoms, but no obvious signs of failure. It's got good gas with a little seafoam in there, and it's not throwing any codes. And it runs fine, when it's not throwing a tantrum. It it cost me $300 to get a sticker on it today, so I'd loooove to be able to drive it, without needing a AAA membership. Especially since it's snowing again...

 

Possible cat failure. Fairly common on that year vehicles. My 2000 had those kind of symptoms, loss of power and farting and would not rev normal. Almost sounded like an out of gas condition. My son's 01 Dakota did some of the same when he had 1 of his 3 cats go bad. If it does end up being a cat be sure to change out your O2 sensors and only use NTK brand.

 

Well fark... I'd rather replace the plenum than the cat! (from a cost standpoint, anyway)

If that does turn out to be the issue, any suggestions for an affordable replacement? OEM, junkyard, tin can with steel wool in it, steal one off the neighbors truck...?

 

You can find high-flow direct fit cats for around 200 bucks or so, check rock auto, summit, jegs, etc.

Trouble is, since it is intermittent..... diagnosing is going to be fun. If it starts acting up reliably, remove the pre-cat O2 sensor, and take it for a drive. See if it is any better. If it is, the cat is bad.

 

Yeah, I had a feeling this one would be fun... Inconsistency for the win. And here I thought my next paycheck was going to go towards new tires

 

I would be starting with a comp test before anything else. This will give you an idea if you should spend money on this motor.

 

Comp test is definitely slated as a future project. All kinds of fun little tests I'd like to do, if I only had the equipment...

 

Just went out for an hour long drive in the snow, to watch the crazy people. All back road driving, <35mph, some in 4x4, most in 4x2. Ran as expected, until about 45 minutes in, when it started bogging down, and I had to feather the pedal to get anywhere (of course that happened in 4x4, on a snow covered trail in the woods between the beach and main road). As soon as I was on pavement again, I put it park and shut her off. Waited 10 seconds, started back up, and everything was fine for the rest of the ride home.

 

Pulled the O2 sensors this morning, both were slightly carbon fouled. The upstream more so than the downstream, as expected. Both looked fine otherwise.

Put the downstream sensor back in, then put the upstream sensor in a ziplock bag, taped the hell out of it, and zip stripped it high up under the truck.

Then went for a trip to Tractor Supply - 16 miles each way, 25 degrees out, snow storm last night, still snowing today. Without the sensor in, it sounds like I should be red lining it through a mud bog somewhere...

About 8 miles in, the rpms got a little unsteady, bouncing between 400 and 800. Gave it a little gas, got the rpm's up without any argument, then she was fine the rest of the trip there.

On the way back, the rpm's got a little unsteady again, at almost the same location (maybe the truck just doesn't like Wolfeboro??), and I didn't have any issue giving it some gas. Made it home, and boy is it loud in the garage.

It never felt bogged down, didn't get any "marbles in a can", and the gas mileage didn't suck any more than it usually does

Still sound like a plugged cat...?

 

Think I would be finding a muffler shop that could test it......