Question : Low Vacuum Idle - Transmission Modulator

[Schmieder]

4t60e auto trans, 1996 Grand Prix SE Turbo 8psi

The idle vacuum is max 9-10 inHg due to cam timing. This, I believe, has caused hard shifts. The shifts are too hard, it slams into 2nd and I need to correct this issue fast. There is a turbo installed as well and I feel the turbo is reducing vacuum at lower throttle then a NA engine.

Will an adjustable vacuum modulator help correct the problem? I have a universal modulator with the two red strips, just haven't installed yet.

Should I install a vacuum reservoir as well?

Any advise is greatly appreciated. Thanks guys!

*notes: Check valve installed to prevent boost to modulator. Stock steel lines used. Transmission has low mileage and is in great condition, so far. Fluid is clean, filter replaced. Trans cooler installed and typical op temps are 160-190*F. The chack valve is rated well beyond the vacuum and boost and flows well so there is no restrictions there. No vacuum leaks found, I really scanned very well as I know vac leaks can be really hard to pin point sometimes.

[86FieroSEv6]

This is what electric vacuum pumps and accumulators are for. They also make belt drive vacuum pumps. Hook up all your vacuum stuff to it . . . . . it helps the tuning a bit as well.

[Schmieder]

As I was putting in the adj vac mod., I found a split in the vac line ahead of the steel. For some reason the split didn't register when I put a vac gauge on the trans vac line. But it was leaking easily.

So I swapped it for a new one. I removed the restrictor and now the trans is slipping some but shifts, when they do shift are soft.

So now, I plan to use a spare vac bleed valve to get the right vacuum to the modulator. Then tune the adj modulator.


But I like your advice for electric vac pumps. I will look into that, thanks.