Tbi stuttering

[MrobsMan]

So I just built a new throttle body for my 350 tbi with the lips shaved off the top of the bores, injector pod spacer and throttle body spacer all oem new parts iac tps injectors and regulator. I set the idle and adjusted the tps and it’s still stuttering when you get on it from a stop light.. I’m sorta stuck the tps readings looked ok it feels like a dead spot in the tps to me.. any thoughts??

 

[Schurkey]

Connect a scan tool, find out if there's a TPS issue. Verify all the rest of the sensors, and computer outputs including EGR and electronic spark advance.

What is the fuel pressure? How old is the fuel filter?

How old are the usual "tune-up" items--cap, rotor, plug wires, spark plugs, PCV system check, initial ignition timing check, air-cleaner heated air door check, etc?

"I" would remove the pod spacer if I didn't have a big-block sized throttle bore. The whole point of the spacer is to get the fuel spray cone to match the throttle-blade size--bigger on the big-blocks, so they raised the injectors a little bit to make the cone bigger down by the throttle blades.

 

[thinger2]

Did you put throttle shaft bushings in the TBI when you rebuilt it?
Out of round holes in the case where the shafts come through makes it suck air and can cause an off idle stumble.
Essentially a vacuum leak that doesnt cause a problem untill the throttle blades move.
Pretty common problem too.

 

[MrobsMan]

Connect a scan tool, find out if there's a TPS issue. Verify all the rest of the sensors, and computer outputs including EGR and electronic spark advance.

What is the fuel pressure? How old is the fuel filter?

How old are the usual "tune-up" items--cap, rotor, plug wires, spark plugs, PCV system check, initial ignition timing check, air-cleaner heated air door check, etc?

"I" would remove the pod spacer if I didn't have a big-block sized throttle bore. The whole point of the spacer is to get the fuel spray cone to match the throttle-blade size--bigger on the big-blocks, so they raised the injectors a little bit to make the cone bigger down by the throttle blades.

Timming was set at 4 degrees advanced I just put a 14 psi regulator spring in and it runs a little better it was starving for fuel I think. I’m gonna pull a plug later when the engine is cool..

 

[MrobsMan]

Did you put throttle shaft bushings in the TBI when you rebuilt it?
Out of round holes in the case where the shafts come through makes it suck air and can cause an off idle stumble.
Essentially a vacuum leak that doesnt cause a problem untill the throttle blades move.
Pretty common problem too.

Did you put throttle shaft bushings in the TBI when you rebuilt it?
Out of round holes in the case where the shafts come through makes it suck air and can cause an off idle stumble.
Essentially a vacuum leak that doesnt cause a problem untill the throttle blades move.
Pretty common problem too.

didn’t know about that how do I do that?

 

[thinger2]

didn’t know about that how do I do that?

check them first. Grab the throttle linkage with it disconnected and try to move it up and down, side to side.
You should not have any play in it.
Open the throttle a bit further and do the same thing.
Then, with it running and hot at idle, spray a little carb cleaner or brake clean right at where the shaft come through the housing.
See if the rpm changes or you notice any difference when you spray it.
Open the throttle a bit and do the same thing.
You can buy tbi bushing kits online or you can try calling around to injector cleaning shops.
Some of the old school places still know how to do this.
A complete rebuild and bushings up here is 200 bucks.
If you decide to do it yourself the only tricky part is that the screws that hold the throttle plates onto the shaft are "staked" in place to keep them from backing out and getting sucked down the intake.
The only way to remove them is to very carefully grind down the end of the threads with a dremel and not nick the throttle shaft.
Do not even attempt to remove those screws untill you have ground the staked part off of the end.
The head will strip out and then you have to attempt to drill out those tiny little screws while holding the throttle plate from moving and sticking a drill down inside the throttle body.
The replacement screws that came with the last kit I bought had tapered ends and were long enough that i could dremel most of that taper off untill I had about a 16/th or so left.
So I put both screws in just barely tightened up to make sure the plate wasnt binding in the bore.
Once the alighnment was good, snug down one screw to hold it in place, pull the other screw and use red loktite on it.
Let that cure.
Pull the other screw and loctite it in place and let it cure.
Grind the remaining threads down to a flat, slightly protruding end.
Get a spring loaded center punch.
The harbor frieght ones are garbage.
The "general" brand is better.
Flip it over, support the throttle shaft with a chunk of broomstick with a rag wrapped around the end of it.
And very carefully with that spring punch on a light pressure find the exact center of that screw and put a little dent in it.
Do the same thing to the other screw.
Wind up the spring pressure a little more and ding it again.
Go back and forth untill you have mushroomed the end of that screw enough that it cant unscrew anymore.
Now you have new bushings and you have re staked the screws.
Some people will think that the red loctite makes it too hard to take it back apart again.
And some people think that re staking the screws is overkill.
I just dont want any hardware going down the intake and I didnt think that a stuck sideways throttle plate while going downhill towing a trailer would be a good thing.
I figure that if GM was worried enough to spend 27 cents per vehicle on safety I should probably be worried about it too

 

[RichLo]

check them first. Grab the throttle linkage with it disconnected and try to move it up and down, side to side.
You should not have any play in it.
Open the throttle a bit further and do the same thing.
Then, with it running and hot at idle, spray a little carb cleaner or brake clean right at where the shaft come through the housing.
See if the rpm changes or you notice any difference when you spray it.
Open the throttle a bit and do the same thing.
You can buy tbi bushing kits online or you can try calling around to injector cleaning shops.
Some of the old school places still know how to do this.
A complete rebuild and bushings up here is 200 bucks.
If you decide to do it yourself the only tricky part is that the screws that hold the throttle plates onto the shaft are "staked" in place to keep them from backing out and getting sucked down the intake.
The only way to remove them is to very carefully grind down the end of the threads with a dremel and not nick the throttle shaft.
Do not even attempt to remove those screws untill you have ground the staked part off of the end.
The head will strip out and then you have to attempt to drill out those tiny little screws while holding the throttle plate from moving and sticking a drill down inside the throttle body.
The replacement screws that came with the last kit I bought had tapered ends and were long enough that i could dremel most of that taper off untill I had about a 16/th or so left.
So I put both screws in just barely tightened up to make sure the plate wasnt binding in the bore.
Once the alighnment was good, snug down one screw to hold it in place, pull the other screw and use red loktite on it.
Let that cure.
Pull the other screw and loctite it in place and let it cure.
Grind the remaining threads down to a flat, slightly protruding end.
Get a spring loaded center punch.
The harbor frieght ones are garbage.
The "general" brand is better.
Flip it over, support the throttle shaft with a chunk of broomstick with a rag wrapped around the end of it.
And very carefully with that spring punch on a light pressure find the exact center of that screw and put a little dent in it.
Do the same thing to the other screw.
Wind up the spring pressure a little more and ding it again.
Go back and forth untill you have mushroomed the end of that screw enough that it cant unscrew anymore.
Now you have new bushings and you have re staked the screws.
Some people will think that the red loctite makes it too hard to take it back apart again.
And some people think that re staking the screws is overkill.
I just dont want any hardware going down the intake and I didnt think that a stuck sideways throttle plate while going downhill towing a trailer would be a good thing.
I figure that if GM was worried enough to spend 27 cents per vehicle on safety I should probably be worried about it too

I just read that whole thing expecting it to take a hard left turn somewhere like normal thinger2 posts but that is surprisingly on-track the whole time! I'm greatly disappointed, lol

 

[thinger2]

I

I just read that whole thing expecting it to take a hard left turn somewhere like normal thinger2 posts but that is surprisingly on-track the whole time! I'm greatly disappointed, lol

I fell off of the ladder and hit my head.
Suddenly, it all makes sense.

 

[MrobsMan]

I

I fell off of the ladder and hit my head.
Suddenly, it all makes sense.

I don’t see any excessive play in the throttle shaft. I believe my distributor is bad because the timming suddenly changed. And it really only stutters when it’s warmed up..

 

[thinger2]

I don’t see any excessive play in the throttle shaft. I believe my distributor is bad because the timming suddenly changed. And it really only stutters when it’s warmed up..

Is the distributor loose? Can you turn it my hand without loosening the hold down clamp when it is cold?
Try to turn it again when it is hot.
Is the hold down clamp bent or cracked or installed upside down?
The gasket on the distributor is actually a "friction washer" and they are avaiable in different thicknesses.
That is how you set distributer gear lash.
These days, gasket kits and aftermarket distributors come with a really cheap really thin paper dist. gasket.
like .020 thin and that gasket has zero friction material in it.
They are garbage.
The most common problem with stabbing a chevy dist is being off one tooth.
The sneaky little problem on a tbi is when you go through all of the effort to set it at 0 TDC and you check that over and over.
When they have what they assume are downstream performance problems they never go back to see if the dist is moving.
Remember, if the distributor is moving even a couple of degrees the ecm will try to control it. Slowly but surely as the distributor slips.
So the normal instinct because you know for a fact that the dist is at tdc is to get a timing light and look at the balancer marks and try to chase advance and wonder what the hell is going on.
Here is the tricky part about a poorly seated distributor.
If it is loose enough and that friction washer is not doing its job.
During acceleration and decelleration the distributor body can lift out if the bore and spin and then drop itself back into the same bore but just a little off.
If you hit it hard a different way,?
It might just drop back into the same spot that it was before.
You need to pay as much attention to lash on a distributor as you would on the diff.
And is very much the same process.
Paint the gear, bolt it in place, pull the fuel pump fuse, pull the injector pulse fuse.
Crank it
Pull it out and look at the pattern.
Any chunk that snaps off of the distributor gear or the cam gear is hardenned steel and it will break something.
Probably your wallet.
I know, this sounds like a lot of bullshit to go through and it kinda is.
But. This is not a new thing at all.
Even back in the 80s we knew that detroit made factory parts had to be adjusted and shimmed and made correct for your block.
Distributors have never been a bolt in part. That is why the used to sell "corrective friction gaskets"
Starters have never been a bolt in part.
That is why they sell starter shims.
Another left turn for those of you who asked for it.
If you have a starter that is weak but does not grind or screech?
Do not ever ever ever turn in that starter for the 10 buck core.
The starter gear to flywheel dimension is determined by the nose cone on the starter and how it bolts to the block.
If the old nose cone is not cracked, you can buy a new end bushing for it for 4 bucks.
The only thing you need is the 50 buck motor.
Buy the cheap 50 buck starter.
Put your factory nose on it.
Torque it back in place.
Done deal. I might be a dumbass but I havent shimmed a chevy starter in 30 years.
Its the nose cone.
If it works? that is like gold