Tired 350 TBI, suggestions to wake it up a bit?

[4WDKC]

I just put a new exhaust on and it runs better and new O2 sensors, just put the factory 15”s on and I’m not sure about the gears

any little leak will do it, it doesnt have to be a massive leak, also the studs for the manifolds are known to break on the 4x4 trucks. Factory 15s wheels or the stock size tires from the door jam sticker? Check the glove box for a stick with alot of 3 digit codes, get all the ones that start with G and we can figure out what the truck came with.

 

[Darth Plasma]

any little leak will do it, it doesnt have to be a massive leak, also the studs for the manifolds are known to break on the 4x4 trucks. Factory 15s wheels or the stock size tires from the door jam sticker? Check the glove box for a stick with alot of 3 digit codes, get all the ones that start with G and we can figure out what the truck came with.

I just got 15” rims, I think the tires are the stock size. The headers are perfectly intact and don’t leak as far as I know

 

[Galane]

A hissing sound can be back pressure escaping because the catalytic converter is just about plugged. Lots of exhaust back pressure will make it run real poorly.

Proper fix is a new cat, but on the older vehicles that don't have sensors downstream of the cat you can get by with knocking the ceramic core out, if there's no emissions testing where you are.

Something to check is remove the distributor cap and see if the rotor can be wiggled sideways. I've no idea how the 1991 350 I rebuilt for my 82 was able to run because it had at least 1/8" slop in the distributor shaft. Only cure for that is a new distributor. I couldn't find rebuild kits or anywhere that rebuilds the distributors. I found a super deal on a new billet aluminum small cap HEI, complete with cap, rotor, and module on eBay.

With that many miles it's bound to need a rebuild. Chevy small blocks are notorious for the lifters getting stuck so they can't rotate, which soon leads to major wear on the cam. Had a 78 1 ton Chevy van with extra heavy springs. Both heads were cracked because the nuts that owned it before never bothered to fix the heater leak. It seemed to run decent but while the intake and heads were off I decided to pull one of the lifters and it was concave on its bottom. So the whole engine had to come out. New cam and lifters, ridge ream and hone, new crank bearings and piston rings, new timing set and fuel pump. Only cam available off the shelf was a slightly hopped up 327 profile. That van would ruuuuun.

 

[Darth Plasma]

A hissing sound can be back pressure escaping because the catalytic converter is just about plugged. Lots of exhaust back pressure will make it run real poorly.

Proper fix is a new cat, but on the older vehicles that don't have sensors downstream of the cat you can get by with knocking the ceramic core out, if there's no emissions testing where you are.

Something to check is remove the distributor cap and see if the rotor can be wiggled sideways. I've no idea how the 1991 350 I rebuilt for my 82 was able to run because it had at least 1/8" slop in the distributor shaft. Only cure for that is a new distributor. I couldn't find rebuild kits or anywhere that rebuilds the distributors. I found a super deal on a new billet aluminum small cap HEI, complete with cap, rotor, and module on eBay.

With that many miles it's bound to need a rebuild. Chevy small blocks are notorious for the lifters getting stuck so they can't rotate, which soon leads to major wear on the cam. Had a 78 1 ton Chevy van with extra heavy springs. Both heads were cracked because the nuts that owned it before never bothered to fix the heater leak. It seemed to run decent but while the intake and heads were off I decided to pull one of the lifters and it was concave on its bottom. So the whole engine had to come out. New cam and lifters, ridge ream and hone, new crank bearings and piston rings, new timing set and fuel pump. Only cam available off the shelf was a slightly hopped up 327 profile. That van would ruuuuun.

I replaced the entire exhaust system from the end of the headers back and it does run better than before, is it ok that I have the cat and the muffler welded to each other? I’ll check for slop in the distributor. Yeah once I get off to college I’m probably gonna pull it and rebuild it or LS swap it

 

[Darth Plasma]

I am bringing this thread back from the dead for a little bit, over the past couple months I’ve been doing a lot of work to the TBI, these are the new parts: O2 sensor, EGR valve, EGR solenoid, IAC, both coolant temp sensors, thermostat, new thermostatic fan controller for my electric fan (still constantly runs at 210 which I don’t like, never overheats) air filter, fuel filter, fuel tank and pump (replaced over the winter), completely new exhaust, spark plugs, wires, cap, rotor, coil, 3 new transmission detent cables, couple cans of seafoam. Truck definitely runs better, no OBVIOUS vacuum leaks. It has a hissy/rapping sound under load like a slight exhaust leak, it’s definitely not an engine knock. But the truck still wants to bog down a little bit before downshifting on hills, still consumes excess fuel, and still wants to stall when coming to a stop. When in park idling, it idles great and revs great with no backfires or stutters, but if I hold the throttle and let it go suddenly it’ll try to stall and won’t start, and when I turn the wheel all the way and do the same thing it’ll stall. I’m running out of ideas, what could be left?

 

[78C10BigTen]

Does that throttle body have a throttle position sensor??

 

[Darth Plasma]

Does that throttle body have a throttle position sensor??

Yes it does

 

[78C10BigTen]

Have you tried that? Every tbi that ive had that did that it was the tps

 

[Darth Plasma]

Have you tried that? Every tbi that ive had that did that it was the tps

That’ll be the next thing I order

 

[Darth Plasma]

So I found 3 snipped wires coming from a plug in the driver’s side of the 700R4 transmission, purple, yellow and green wires. I was searching for electrical connectors on rock auto and it seems to match the connector to a torque converter clutch solenoid, does this sound accurate? If so I have no clue where these wires go or where they are hooked up to, and could this be a reason for the delayed shifts and stalling when stopping?

 

[78C10BigTen]

So I found 3 snipped wires coming from a plug in the driver’s side of the 700R4 transmission, purple, yellow and green wires. I was searching for electrical connectors on rock auto and it seems to match the connector to a torque converter clutch solenoid, does this sound accurate? If so I have no clue where these wires go or where they are hooked up to, and could this be a reason for the delayed shifts and stalling when stopping?

I would best guess yes probly... im not sure where they go, i have a th350

 

[4WDKC]

So I found 3 snipped wires coming from a plug in the driver’s side of the 700R4 transmission, purple, yellow and green wires. I was searching for electrical connectors on rock auto and it seems to match the connector to a torque converter clutch solenoid, does this sound accurate? If so I have no clue where these wires go or where they are hooked up to, and could this be a reason for the delayed shifts and stalling when stopping?

No those wires are only for lock up, the 700r4 is hydraulic transmission and uses springs, servos and fluid pressure to determine when to shift not electrical components. THe tv cable for that trans is critical.

 

[Darth Plasma]

No those wires are only for lock up, the 700r4 is hydraulic transmission and uses springs, servos and fluid pressure to determine when to shift not electrical components. THe tv cable for that trans is critical.

Where do those wires run? I’d like to hook it back up

 

[4WDKC]

Where do those wires run? I’d like to hook it back up

Depends if the truck came with the trans or not.

 

[Darth Plasma]

Depends if the truck came with the trans or not.

Now that I think about it, it didn’t, the engine/trans are out of a 1990 suburban. Was there any changes from 1987 to like 1991 for the TBI engines or 700R4’s? I’m starting to question whether having the original computer for the original TBI is messing up the engine in it now