TBI Off Idle Transition Problem

[440sixpack]

Ever since I bought my K10 the TBI 350 has jumped when you go from idle . it runs great but when you go to take off no matter how hard you try not to it jumps and sometimes even chirps the tires.

It has a new cable and I replaced the TPS and nothing changed. it does seem like it pushes awful hard and maybe it's just that when you overcome the throttle spring it goes too far , but there's no way to adjust it .

Any ideas ? is there any other spring I can get for the throttle that's not so stiff ? it's like having a stall converter.

 

[Vbb199]

Is it a stock tbi 350? If so, i find it hard it has enough power to bark tires unless the axles are geared stupid low like 5.38 lol
You dont by chance have it in low range and dont realize it? What kinda trans are we working with? When is it chirping tires? Off the line, or when it shifts?

 

[440sixpack]

Stock 350 out of a '92 in my '77 K10. 4.11 gears. it will chirp the tires on smooth pavement if you don't really ease into it . if you really ease into it then it just jumps. once you get rolling everything works perfect.

700r4 transmission. I don't think the transmission has anything to do with it because the engine doesn't rev up before you launch it just jumps when the RPM jumps.

It's plenty drivable as is it's just irritating .

 

[Vbb199]

So it does bark tires from a stop, not when it shifts from 1st-2nd?

Is the tv cable set correctly? The tighter it is, the higher the line pressure, and the more violent it'll get.

 

[Vbb199]

I wonder if something is binding in the driveline and causing it to jump?
It doesnt have an excessive lift or broken leaf springs or anything does it?

Just throwing ideas out. I personally cant fathom a stock tbi 350 having enough grunt for all that, but ive been wrong before, ive owned several of them, and they leave alot to be desired in terms of power output. They drive and operate just fine for a daily driver. My "hotrodded" tbi 350, with 4.10s, and a 700r4 in my suburban can break a tire loose, but most of that was done away with when i installed a locker.

 

[440sixpack]

No everything is in great shape. the entire drive train is like new .

When I say chirp I don't mean a burn out, it just slips a tire. it shifts great through all the gears the best way to describe it would be a mild neutral start. the engine jumps from about 700 RPM to 1200 when you press the throttle hard enough to take off. it really feels as if there was a way to lighten the throttle spring pressure it would fix it. when it goes it goes too much. I tried to put a spring on to counter a bit of the throttle spring pressure to see if it helps but then it doesn't return to idle properly.

I'm not sure what the tv line is or what it looks like but I can research it.

 

[Vbb199]

No everything is in great shape. the entire drive train is like new .

When I say chirp I don't mean a burn out, it just slips a tire. it shifts great through all the gears the best way to describe it would be a mild neutral start. the engine jumps from about 700 RPM to 1200 when you press the throttle hard enough to take off. it really feels as if there was a way to lighten the throttle spring pressure it would fix it. when it goes it goes too much. I tried to put a spring on to counter a bit of the throttle spring pressure to see if it helps but then it doesn't return to idle properly.

I'm not sure what the tv line is or what it looks like but I can research it.

Tv cable runs from the passenger side of the transmission to the linkage of the throttle body.

 

[Bextreme04]

It sounds like maybe you either have a binding throttle cable or something wrong with the torque converter that is not letting it slip right. On a 350, it should have a 1500-2000 stall at least. Maybe something wrong with the lockup that is causing the torque converter clutch to lock when it shouldn't?

 

[Vbb199]

Too loose, slides into gears, burns up the transmission quickly, and the inverse; too tight it slams gears, it has boosted pressure, a similar effect as "tow haul" on a modern computer trans.

But after seeing you saying 700-1200 suddenly, that DOES seem throttle cable related, but doesnt explain the jumping/tire chirp, that seems converter related.

 

[gmbellew]

does it jump on park or neutral, or only in gear? same question about park or neutral, but if you manually move the throttle under the hood instead of using the skinny pedal?

 

[SirRobyn0]

@440sixpack So will it do it out of gear as well. So like if it's idling and you give it just a touch of gas to try to raise it to maybe 1,200rpm does it jump way up higher than that?

If that's the case I'd look at the following.

Binding throttle cable.
Binding throttle shaft or throttle plates.
Dirty throttle body and / idle air control valve.
TPS sensor that has a dead spot in it.
Idle air control valve that is worn out and causes excessive air to pass by it when you step on it a bit.

 

[Itali83]

Your throttle plates are binding in dirty throttle bores. Or your throttle shaft has enough wear that the throttle blades can **** just enough to bind in the bore. I know exactly the jump off idle you’re talking about.

start out by just taking fine scotch brite and some carb cleaner spray. Wire open the throttle and spray some in the throttle bore and scrub the bore with scotch brite. Report back.

Ben.

 

[Ellie Niner]

A number of the early TBI vehicles I've driven have a fairly aggressive throttle tip-in. Sometimes, if you can modulate the throttle with a velvet slipper, you can actually get the engine to stumble a little between on and off idle instead of lurch. But it's never a particularly smooth transition.

I've been able to get the tires to "eep" on my 305/700R4 with 3.08 gears fairly easily with sudden power applications from a very (too) low idle, so I wouldn't be surprised if 4.11's produce this with a TBI 350 when there's a sudden switch from rotary flow to vortex flow in the torque converter.

 

[440sixpack]

I'll check all these suggestions out thank you.

the 700r4 doesn't have a lock up converter does it ? the shifts are pretty firm but I assumed when it was recently rebuilt they may have done that.

 

[SirRobyn0]

I'll check all these suggestions out thank you.

the 700r4 doesn't have a lock up converter does it ? the shifts are pretty firm but I assumed when it was recently rebuilt they may have done that.

None of us can tell you if there were any modifications made to your tranny during rebuild, but from the factory, 700R4's all had a lock up converter and locked in 4th. Many of them also locked in 3rd. lock up converter provided that it is functioning properly will not effect shift feel, and if it's staying locked up to much there would be other symptoms.