[Crumpler]

After chasing low boost issues on the supercharger project, I decided to put a boroscope up to the throttle plate.
It does not open all the way to perpendicular.
In this video you can see it does not travel to the aluminum arm on the body housing.
This travel is while cable disconnected and me pulling open by hand.
The plate closes correctly so I think that rules out misaligned right?
So any adjustment possible on the spring side to open further?
My only thoughts would be the tps is binding?

[worf]

My only thoughts would be the tps is binding?

TPS has no “stop” for WOT travel.

I don’t think the throttle plate opens to perpendicular on any 928 throttle body.

[Crumpler]

This is why I’m confused.
My spare unit does.
I’m using a potentiometer TPS from the VEMS install, so I think it just rotates freely without a “stop” position.
I did have to make a spacer but that should have been bomb proof.

[Crumpler]

This issue would fit with the issues I have had since day one. If real.

[worf]

So… always helpful to remind folks when you are asking about failure modes for parts that the parts in question aren’t’ stock’ e.g. TPS.

Dumb question: you adjusted the bowden cables for pedal and linkage to ensure that mashing the pedal to the floor opens the plate as far as it will open?

As far as how far it opens, I confess that I’ve never measured it with a protractor. Thing is, once it gets past 80-ish ° it’s not going to matter that much.

[Crumpler]

I did mash it and quanitate, also pulling with cable unattached got me same results.
I don’t know, but will probably tear it down again and look.
Evidence so far:
This is a pic looking at plate with boroscope at the current wot position:


If you mimic the angle in the photo on the spare unit you get this:


It would explain why twice as much SC gets me same boost, and why I had to use such a small pulley on the first unit to achieve five pounds.

If air flow is choked there?

I did a boost test today after another anemic wot run. This video shows pressure into one blower pipe and capped on the other blower pipe, manifold and pipes all charged and holding. So I can vouch no real leaks.
I feel like I can say no belt slip, because both would have to slip at same time.

[worf]

If that, below, is WOT, then… you’ve got a condition.

6

[Crumpler]

Another tear down, because I have to know ;)

There was some tilt in the whole assembly due to one of those double threaded bushings to anchor TB had backed out while torquing from above on install I guess. That may or may not have contributed.

So the TPS.
It does not spin freely.
It’s got a stop roughly 90 degrees.
With tps off, there’s full movement on the plate again.

[Crumpler]

Reposition and different holes to drill gets me full range.

[Crumpler]

Nope.
No difference.
I’m still missing something.

[ladybug83]

Has the throttle body ever been apart before (maybe a previous owner)? I ask because when I re-assembled mine after cleaning, it was discovered that I installed the plate upside down and it was causing the same kind of hang up. To me, it all looked symmetrical, like it shouldn't matter, but there was in fact a slight variation in the plate that wouldn't allow it to open fully when installed upside down. Since you have it out, may be easy to flip the plate and see if it changes anything.

[Crumpler]

Has the throttle body ever been apart before (maybe a previous owner)? I ask because when I re-assembled mine after cleaning, it was discovered that I installed the plate upside down and it was causing the same kind of hang up. To me, it all looked symmetrical, like it shouldn't matter, but there was in fact a slight variation in the plate that wouldn't allow it to open fully when installed upside down. Since you have it out, may be easy to flip the plate and see if it changes anything.

Thank you for following.
I did go double check after reading, but appears correct.
My last post was misleading anyway, the Throttle now opens correctly but the boost didn’t improve.

I’m reevaluating my twin super charger existence;)
Two units making less then one, etc.

I saw seven pounds on the gauge and 3 pounds on the map data on one of the pulls. So I have some work to do here.