7psi or overboost.

[tonateen]

When I go to set my g valve to 12# it either goes from 7# or complete overboost no inbetween. Sometimes when it's at 7# it will spike to 12# and hold until I shift to the next gear then it will go back down to 7#. Any ideas? Could it be a bad boost controller?

[tryingbe]

Year, make, model, engine option, transmission option, modification, stage 0 done, engine bay picture...?

[tonateen]

Year, make, model, engine option, transmission option, modification, stage 0 done, engine bay picture...?

1988 daytona Shelby, 2.2 turbo, 5 speed, stock.

[iTurbo]

Does the grainger valve have a proper bleed hole? If it gets plugged up or is not the right size, it can cause problems.

[tonateen]

Does the grainger valve have a proper bleed hole? If it gets plugged up or is not the right size, it can cause problems.

Here is the boost controller I'm running

[dwh4784]

So it seems like you are either getting minimum boost (7psi) or too high. Is the spring too stiff? There should be plenty of adjustment from when it barely catches the threads (low boost) until you have tightened it quite a bit. Also make sure you have the ball in the bottom (straight fitting) and have intake pressure to that side also. The 90 degree fitting should go to the wastegate.

Strangely enough I have an identical looking grainger someone made, and have a similar problem. I get instant full boost cutout as low as 12psi even with an MP comp which is supposed to give you more "overboost" time before it shuts down. I've been chasing this problem forever, I have a wideband and plenty of fuel so I think I'm just going to try a zener diode. No matter what I do it overboosts continuously unless I either take the ball out of the grainger or get it set around 10psi.

[tonateen]

So it seems like you are either getting minimum boost (7psi) or too high. Is the spring too stiff? There should be plenty of adjustment from when it barely catches the threads (low boost) until you have tightened it quite a bit. Also make sure you have the ball in the bottom (straight fitting) and have intake pressure to that side also. The 90 degree fitting should go to the wastegate.

Strangely enough I have an identical looking grainger someone made, and have a similar problem. I get instant full boost cutout as low as 12psi even with an MP comp which is supposed to give you more "overboost" time before it shuts down. I've been chasing this problem forever, I have a wideband and plenty of fuel so I think I'm just going to try a zener diode. No matter what I do it overboosts continuously unless I either take the ball out of the grainger or get it set around 10psi.

I have the straight side going to the nipple coming off the turbo then the 90 degree hooked up to the wastegate. I'll try what you said and see what it does.

[dwh4784]

It should work like you have it but I don't think it's recommended to use the nipple on the turbo to control the wastegate. Better to have a line that sees actual manifold pressure.

[iTurbo]

Looks good. It's different than the grainger valves I've seen and made myself but should work. The bleed hole should be about .020" if I recall. Just enough to bleed off the small amount of air that returns through the valve as the wastegate shuts. If the hole weren't there, it would make the wastegate hold open because of the way the ball/spring valve works.

+1 on 'referencing' the boost controller to actual manifold vac/pressure source. Don't share that source with anything else like a boost gauge or the MAP sensor or fuel pressure regulator either. Give it it's own dedicated source. You might want to take your g-valve apart and clean it with Brakleeen just to eliminate it as a possible problem. I've never seen a g-valve made like that, but it *should* work.. You gotta be careful assembling the g-valve so that the spring seats correctly.