Are TBI 350’s just this sluggish?

[Dover]

My 90 C1500 RCLB 5.7 TBI with almost 300k on the clock was that way when I first brought it back from Washington. After a new EGR valve and intake manifold gasket along with a TBI rebuild she’s a beast off the line and at low to mid range revs but kinda gutless on the top end. I second the others on fuel delivery and coil, and vacuum lines but would also recommend checking the EGR. The passages in the intake on mine were completely plugged with carbon when I pulled it. One of the thing I personally love about the TBI engine is it’s simple enough to work on with just enough computer to add some reliability and diagnostics.


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[LVJJJ]

Brad, there is probably absolutely nothing wrong with your engine. These mid '90's 350's are crap. I bought my '94 GMC k1500 about 3 years ago, a one owner, always garaged, always maintained 130,000 mile creme puff to tow our 5,000 lb travel trailer. Wouldn't even go 65 mph running solo. Did discover while the owner changed all the fluids regularly (got the CarFax) he never changed plugs, cap, wires or rotor. But that didn't help much. After avoiding some mountain passes and driving in 2nd all day against a headwind in Nevada (6 mpg) I got ticked off and started making some changes. The best thing was to get rid of the very restrictive air intake box that reduced the intake from 4" to 3". Got rid of the choke aparatus and replaced it all with a 4" dryer duct going directly from the fender to the air cleaner. Helped a lot. Have since added a second air intake coming from the other side. Added an adjustable timing control from MSD, helped some. A little better but still a dog. Next best thing was intalling dual exhaust and getting rid of the cats. That was a big improvement, but still underpowered, had trouble going over 40 mph up mountain passes, lots of them here in the west.

Going up these passes in 2nd gear at about 3700 rpm began cracking exhaust manifolds. So far have cracked 4. So after putting up with no power I bought and installed a 383 stroker from S&J Engines in Spokane and that solved the problem Those things have so much torque I can pull in 4th most cases but I don't too much as it might ruin the weak 4L60e tranny. Put a bigger cooler on it for that purpose.

Guess what?, just got back from Eastern Washington and 100 degree heat with another cracked manifold. Had enough of that, headers will be here tomorrow. The only replacement exhaust manifolds you can get these days are Chinese or Vietnamese, pure crap.

So, as I said, probably not that much wrong with your engine, it is just a underpowered boat anchor. The 383 was only $2300 with roller cam and help to install it. Had to have the chip re-programed by Old EFi on this forum.

 

[LVJJJ]

Oh, and since you have 3.42 gears your's will be really slow, I've got 3.73 's which gives me a little more grunt.

 

[DerekTheGreat]

I don't think they're crap at all. Especially compared to how commerce hauled things up until the 70's. It wasn't uncommon to see straight sixes hauling crap around in medium duty trucks. They got it done. In the past two months I've towed quite a bit with my '89. Two trips were in excess of 5,000 lbs. I wouldn't want to do it every day (1/2 ton brakes, wow..) but it got the job done for me and it felt confident around town. Last thing I towed was a '79 G10. ~4,200 lbs I guess. It struggled a tad on some hills but down shifting to direct fixed that. For everything this truck does for me, I have no complaints. Couldn't replace it with twice the truck if I paid twice what I've got into it.

 

[noabarron3]

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

That AC fluctuation is normal for these trucks. It is the compressor clutch working hard is all.

 

[noabarron3]

Oh, and since you have 3.42 gears your's will be really slow, I've got 3.73 's which gives me a little more grunt.

The fact that you have 3.42 gearing is surprising the k1500s with the 5.7 all had 3.73 to my knowledge... the 3.42 came stock with the 4.3...

 

[noabarron3]

OP, what is the history with the truck? Sounds like you just bought it? Is the engine original? I've come to realize you can't trust much trucks of this vintage that have had multiple owners. Sure someone once upon a time didn't replace the 350 for a 305? Not sure how you could tell though.

Just throwing ideas out there...

More likely someone swapped out the 4.3 v6 for the 5.7 but never regeared from the 3.42s

 

[bamabound]

The fact that you have 3.42 gearing is surprising the k1500s with the 5.7 all had 3.73 to my knowledge... the 3.42 came stock with the 4.3...

I've seen lots of original 350 and 305s with 3.42s. Seems almost 50/50 between 3.42 or 3.73 regardless of engine. I'm only speaking of 4wd 1/2 ton and have never seen any other gear for them, though I've heard others say 4.10s were available. Only 4.10 ive seen is in 3/4 or 1 ton.

 

[Outlaw910]

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!

I have a '92. Last year it started out doing the same thing as yours. Two weeks later the fuel pump went out. I also changed the fuel filter and injectors. It has been running great every since.

 

[Old Ugly]

The reason 5.7 TBI motors will last forever with minimal maintainence is that they don't make enough power to destroy themselves.