First off, I'm a long, long time lurker and reader and I wanted to say thank you to everyone for all of the problems that I have researched and fixed on my own-saved me LOTS of time and money. However, I am totally stumped.

I have a regular run of the mill 2000 Blazer LS, 2DR 2WD, 325k miles, and outside of a rear brake job, 2 fuel pumps, water pump and radiator, has never given me any real problems. On acceleration, especially 1st and 2nd gears, it stumbles HORRIBLY until I really goose it. I can let off and it will shift to second fine, and then from third on it runs good, but acts like it's starving for fuel and cuts out in the first 2 gears. Especially around 2k rpm. When I'm on the highway, it will surge and buck in overdrive and normally drops down to 4th gear unless I'm lucky and it stays in overdrive. When it drops to 4th, I normally have to accelerate and let off gently, if I keep it around a cruising RPM it surges enough to be annoying. Here's where it gets good, though...

When I'm towing a trailer, one that's loaded down with firewood and beyond heavy, it runs perfect. HARDLY cuts out, doesn't surge, runs like it did the day I bought it. Seems like the more of a load it's under the better it runs. Starts fine, idles fine, revs fine in park/neutral, but every day driving is terrible. Wanted to ask everyone's opinion on here before I started tossing parts at it with this many miles on it. What I've done in the past few years:

-New coil wire/distributor cap/rotor button/plugs/wires
-Another cap and rotor button a short while later
-Fuel filter changed yearly
-New water pump and radiator


SES light has been on for years and I think the cat melted down a few years ago, was an incredibly bad rattle that I couldn't afford to have repaired and one day the rattling just stopped, but that was YEARS ago, long before these issues ever started. The closest reputable shop I can take it to charges 75 for a diagnoses and shortly after the cap and rotor button were replaced I noticed it doing this on the way back home, and the guy offered to take a look at it again. It got better for a while and I didn't worry about it, then it suddenly got worse. Don't think it's anything he did as they're a very, very reputable shop, but I should have taken him up on his offer.

So, in closing...anyone know what it could possibly be? Doesn't backfire or anything, just runs rough on acceleration in 1st, 2nd and smooth after 3rd until OD; no issues when towing trailer. I wanna make it to 400k with this thing lol

Thanks everyone.

 

I would start by getting those codes read and let us know what they are.

If your cat was rattling years ago, it likely has disintegrated and is either partially clogging the muffler or has blown completely out the tailpipe. They rarely blow completely out the tailpipe.

What brand of ignition components are you using? The aftermarket caps & rotors do not seem to be very consistent quality and can often cause more problems than they solve when used. AC Delco & Delphi both have good reputations for quality when it comes to the cap & rotor on these motors.

 

UPDATE!!

Sorry I've been dormant..the holidays took over and I didn't get a chance to have anything read or really mess with the car. But, I wanted to update the thread with some bad news. The Blazer is in it's final resting place. Ran straight to 260 on temp hand on way to work the other day, I pulled over and let it cool off, took thermostat out of it on side of road, slowly poured water in radiator while it was running so as to not crack it nor the block, and was able to make it to work. The following days, it used water like it was going out of style, and Friday, it stalled on side of road. After limping it to a shop of a friend of my Dad's, a quick look over, glance at the dip stick, and removal of the crank case pressure vent hose revealed a crank case 100 percent full of water. In hind sight, it ran hot about a year and a half ago and the motor ran a little worse, stumbled a little more every month leading up to this, so I am guessing that the first instance back then kinda put the whole incident in motion, and then last week finished it. At 325k miles it was bound to happen eventually. I never meant to let it run hot, as I've been having coolant issues and trying to keep a watch on it, usually it would run up 3/4 of the dial then immediately drop back down to normal operating temp. Flushed coolant out several times only to find mud buildup each time. I never knew that one could become so attached to their vehicle this way but I hate to see it go. I've read so many threads on this forum that has helped me in so many ways with my car, so I want to thank all of you contributors for the knowledge and expertise. Too many small things wrong with it to fix it, and I need something a little more dependable to get back and forth to work. I'm actively looking for another Blazer, though.