Feeling Bucking Highway Speeds or Accel
 

I'm back once more! Yay!

New problem with my 98 Blazer, well, not new but I'm finally posting here cause after more than a month of off an on research here, I can't find anything that exactly fits my problems.

Now, some days my Blazer will run fine. It always idles perfectly, it sounds lovely, purrs like a kitten when sitting. However, some days it'll randomly hesitate when accellerating, specially sometimes around the switch from 1st gear to second. Then, at highway speeds, you can physically feel the whole car bucking as it feels like it's misfiring.

I've checked codes multiple times to see if anything was pending, but it comes up with nothing I'm not already aware of (ABS Open Circuit and Fuel Level Indicator Failure or something like that; My fuel gauge stopped working a couple years ago). There's no flashing SES light, no codes other than those above, and I don't know where to start with a diagnosis. I wish it'd throw me something just so I can know where to start.

Any ideas? I can't really afford anything right now, I'm extremely broke, so I don't know how much I can do on my own.

I guess I should mention this started soon after my episode in December where the cap and rotor went bang on me, and Midas replaced them for me cause at the time I had no idea what the problem was. I don't know what they replaced them with, and I know Blazers are very critical of non ACDelco parts cause they're the most speshulest of snowflake vehicles, so that is one possibility I'm thinking. But I don't know, I feel like if it were the cap and rotor I'd be seeing issues in more than just certain spots, and a lot more consistantly than I am.

First check...fuel pressure with what your saying. No fuel gauge also can be fuel pump which leads back to checking pressure. Look at the start here list..has pretty detailed write how to check it. Report results after you do that one.

The non working fuel gauge is most likely a bad sending unit. Which on your 98 I believe was all an integrated assembly with the pump.

Fuel pressure is a known issue with these trucks, so it's always a good first step to diagnosing drive ability issues to check that. Any chain parts store will rent you a pressure tester for free (you put down a deposit, which is refunded 100% when you return the tester) so it doesn't even cost anything, and at the very least will rule out fuel issues

I've had the same symptoms on my truck (hesitation under moderate throttle), and it was related to a bad rotor. Mine did not set any codes either. If the misfire is under a certain threshold it will not set a code.

All right awesome, I'll see if I can't rent a fuel pressure tester this weekend and go from there. The fuel sender has been bad for years, and the fuel pump is extremely loud, but all of that has been like that since before or right after I got the truck in 2016, so it's not been high on my list of things to fix.

Thanks for the replies!

So update on this:

I have not yet done a fuel pressure test, and I think I've diagnosed my issue without needing to just now.

I found that it really only acts bad on extremely humid days, and especially bad in the rain. I should have noticed this sooner, but the past 3 weeks have really solidified that, due to the random Dallas, TX weather of hot, dry, wet, hot, dry wet. Now, back in December I had Midas replace the cap and rotor as it would no longer run. Based on the fact that it runs bad in high humidity, I think it either this new cap and rotor combo, or my cables leaking electricity, or even both.

Any opinions on my diagnosis?

Sounds like an issue with the cap & rotor to me. Do a quick search for "misfire" and "rain" and you'll find a few different threads here about similar situations to yours.

Pretty much exactly what I did when I figured out there was a correlation between the rain and the misfiring. It does seem pretty conclusive that whatever that shop gave me for a cap and rotor, it's junk.

My shop has strict instructions to only use AC Delco parts whenever possible. It's usually more expensive but totally worth it.