Are TBI 350’s just this sluggish?

[BradHSo]

Hello,

Probably a silly question, but I find it hard to believe my truck is this underpowered.

I recently purchased a 93 K1500 auto 5.7 3.42, 115k miles (Stock sized tires).
So far I’ve replaced the TPS, CTS, MAP, new distributor cap wires and plugs. I will be doing the IAC later today (chasing down a slight stumble off idle).

So too my dilemma, I purchased this truck to tow a small aluminum boat (1200lbs including the trailer) I live in Charlotte and it’s not too hilly here. While taking it out for the first time on the freeway last week, I was doing about 70Mph and came upon a slight hill, by the time I topped the hill in 3rd gear and about 55mph, that was with the pedal to the floor. This truck is just gutless below 3000rpm. I’ve checked for codes, there were none. It makes no power below 3000rpm, absolutely none.

Am I experiencing an actual issue or is it with the 3.42 gearing it’s just this underpowered? I know it’s not going to be anything like a modern V8, I knew that when I bought it.

Thanks for any help!

 

[SUBURBAN5]

Does it feel like its missing?

 

[BradHSo]

It has a hesitation off idle, which is why I want to replace the IAC and clean the orifice. Hell, it could be a slight miss and I’m mis-interrupting it.

I just remembered when I was servicing the AC it wouldn’t hold at 1200 rpm, seemed to surge a little up and down

 

[SUBURBAN5]

Check your fuel pump or tbi injectors

 

[BradHSo]

Check your fuel pump or tbi injectors

The spray pattern looks good (nice cone shape, good atomization) I’ll buy a pressure tester and report back later. Thanks for the help!

 

[alpinecrick]

Lol, now you know why the 5.7 and 7.4 Vortecs were such home run for GM.....
The extra 50+ hp makes a big diff in the GMT400’s. I know, I have/had both.

The TBI motor does it’s best at just off idle to maybe 3500 rpm, then the swirl port heads plumb run out of breath. Remember, there’s “only” 200 hp moving a 3 ton truck.....

Although the hesitation suggests the motor may be not running at it’s full potential.

 

[BradHSo]

Lol, now you know why the 5.7 and 7.4 Vortecs were such home run for GM.....
The extra 50+ hp makes a big diff in the GMT400’s. I know, I have/had both.

The TBI motor does it’s best at just off idle to maybe 3500 rpm, then the swirl port heads plumb run out of breath. Remember, there’s “only” 200 hp moving a 3 ton truck.....

Although the hesitation suggests the motor may be not running at it’s full potential.

Yea I knew it wouldn’t be like the vortecs but didn’t expect it to be this much of a difference lol. The whole reason that I started this question over the lack of power is as a kid my mother drove a 95 suburban and I remember it lighting the tires up a few times. It just feels like such a difference.

You mentioned that the TBI’s run out breath after 3500rpm, but off idle through 3000rpm is where my dead spot. So something has to be up.

I’ll check the fuel pressure later after work, and report back.

Thanks again!

 

[PlayingWithTBI]

Check your timing too. It s/b set @ 0* with the EST (Black/Tan) wire disconnected. If everything else checks out, you can advance it a little, maybe up to 4* advanced and see if that helps. Yes, as @alpinecrick said the 350 should be good off the line up to ~3500 to 4000. When my 88 RCSB was stock I could spin the right tire off the line but, overall, it was a dog, ha ha.

 

[stutaeng]

Definitely sounds like something is not right. I personally have never owned a TBI, but my Dad has an '89 Sierra RCSB, my BIL has a '91 C1500 ECSB and brother just bought a '90 RCSB. All have the 5.7 TBI. I know they are not Supercar fast, but pretty peppy.

They all state that the torque at low RPM is what makes the tires spin on take off. Your statement that yours makes no power below 3,000 RPM is the hint that something is not right. We have some TBI gurus here, maybe they can help you.

 

[someotherguy]

Timing as mentioned, fuel pressure, CTS in good condition, all grounds good in the engine bay.. gotta cover the basics.

Also if your tires are oversized that 3.42 isn't helping, but it shouldn't be an outright dog unless you're way taller than original size.

Richard