87 FWD Turbo Riv

[TTypeRiv]

Hey guys,
I finally got my FWD Turbo Riviera project running pretty smooth now. Just a couple questions if anyone can help:

1. I know most people out there know about RWD cars, but mine is FWD, but maybe someone can help. When I first installed the turbo and got it running, I put check valves in all the vacuum lines. This was fine except for the tranny. It would shift up okay, but it wouldn't downshift. It would slip and almost seem like it was getting caught inbetween gears. So I disconnected the vacuum modulator, and it shifts fine, just like it should. Can I just leave the vacuum modulator unhooked and plug that vacuum line? Or will this hurt my tranny?

2. While my car seems to run okay, I think it could run better. First off, it seems to cut out a little at anything over 3500 RPMs. I think this may be the computer trying to retard the timing, and it not being able to since I don't have a turbo computer. I am using the stock 87 Riviera computer. I tried hooking up an 85 GN computer, but that didn't work. I also tried putting an 85 GN chip in my 87 Riv computer, but still didn't work. So I didn't know if somone out there could burn a chip for me that would work in my 87 Riv computer, but still work with the turbo?

Thanks guys for any help you can give.

 

[b4black]

1. You might be trapping vacuum between the check valve and modulator. Try putting a tiny pinhole in the line to bleed the vacuum.

2. Even though it's not a "turbo computer", I bet it still uses ESC (knock sensor), which is what makes a turbo computer a turbo computer. You're probably knocking and reatrding timing. I'd get a scan tool or knock guage.

 

[TTypeRiv]

b4black,

1. I figured that is what was happening, that I was trapping vacuum and it wasn't letting the tranny shift. That is why I wondered if I can just let the vacuum line unooked? B/c if I put a pinhole the line, I am losing vacuum all the time.

2. yes, my car does have a knock sensor. But the last time I checked Turbolink didn't work on my car. And I am waiting to hear back from Caspers to see if their knock guage will work with my car, or what I have to do.

Thanks,
Derek

 

[b4black]

1. The leak would be tiny, but I understand the concern. Another option is a in-line T and on the new leg, put the check valve. This leaves the modulator wide-open to vacuum, but when boost comes on, it blows out the check valve. (Kinda like a tiny BOV for your vacuum line)

2. I suspect the Casper's gauge will work. Instead of Turbolink or a scanmaster, you can try a scantool not dedicated to the SFI motor. Someting like a OTC Monitor 2000 (search ebay). I'd get both - the scan tool is great for diagnosing other sensor as well.

 

[TTypeRiv]

Okay, I will look into both of those. Thanks a lot.

 

[turbofish38]

You might want to see how GM does it on the 91 and newer supercharged 3800. Some versions use a check valve in the vacuum line for the modulator. I'm not familiar with the ESC part of either 87 Riv and 91 SC so I'm not much help there. I'm thinking in your particular case turbo and SC would be close enough to crossbreed some ideas/solutions.

 

[TTypeRiv]

I know on 89-91 Pontiac Grand Prix Turbos they used a check valve in the line to the modulator, and then a "T" fitting at the modulator with one end of the T going to the tranny, and the other just out into the air. I figure the air side of the T is a contorlled leak to make the tranny shift right under boost. But still my worry is that this will also leak engnie vacuum under normal driving, which might cause problems on my car. That is why I wondered if I can just drive my car with the modulator unhooked.