a few vacuum gauge questions

msm15 · Post by **msm15** » 19 Nov 2008, 18:19

I just got my gauge and I have a couple of questions I was hoping someone could help me with.

98 s70 GLT

1. where is the best place to tap into the vacuum ? can I go straight into the tree near the throttle body ? is there a way to go into the manifold directly, or are there other places I should know about ?

2. PSI's - from what I read up at Idle it should be around 20 psi of vacuum and when boosting it should go up to 5-7 psi for my model, are these figures correct.

3. turbo vs. non turbo : if I do indeed have a leak in my lines will my performance be the same as a stock non turbo engine or once I have a leak and my car is set to run with the turbo - things then get messed up and the performance is even worse then a stock non turbo engine ?

thanks for the help

msm15 · Post by **msm15** » 19 Nov 2008, 18:33

one more question, where can I get the tube through the fire wall for the gauge ?

Post by **holler1** » 19 Nov 2008, 20:50

I installed one on my 98 V70 about 2 months ago.
1. I hooked up to the vac tree- seemed to work fine
2. Mine shows -20 (vacuum) at idle, goes to -23 or -24 when I let off throttle after revving. Boost is about 5-7 max (light pressure turbo).
3. I don't know. I replaced the PCV system and fixed vac leaks before installing vac gauge.

Firewall- On my car there is a set of small rubber tubes coming out of the firewall below the fuse boxes where small hoses, wires will go through. I should have taken pictures but didn't.

msm15 · Post by **msm15** » 19 Nov 2008, 22:20

thanks that was exactly what I needed to know, I wanted to set it up first before I fix other stuff to see if I have a leak.

I just tested it and I got 20 psi at idle but it took 2 minutes to get there, I havent driven it yet to see what it goes up to

Post by **holler1** » 20 Nov 2008, 05:49

Mine doesn't have a 2 minute delay; goes to -20 pretty quickly on startup. The turbo won't boost without a load on the engine, so you can't check boost by revving the engine. I didn't realize that before installing the gauge.

I agree it seems to be a good tool to help with vac leaks. I still haven't hidden the tube, but I did get a mount to put the gauge up beside the windshield. MIJ gave me the website to buy the mount.

msm15 · Post by **msm15** » 20 Nov 2008, 12:35

so then this gives me some insight into my cold start sluggish performance I started the car this morning and it took a few minutes for the vacuum to reach 18/20. I started it again later n the day when it wasnt as cold and it went straight to 20 ?
what does that mean - it does reach the correct vaccum but it takes time - so is that a leak ?

also I went for a drive to see how it boosts and it hits 3.5 psi quickly but I have to hold down the pedal for it to go higher, after a couple of seconds of holding it down it went up to 5.5 but that was the max it hit.

when it is rated at 5-7 psi for the light pressure turbos does that mean it hits 5 right away and if you hold down he pedal it will reach 7 ? or are those just approximate numbers for the turbo as a whole ?

at a traffic light it will go down to 18, cruising on the highway when I let off the gas it will go down to 20/21, and if I let off the gas after boosting it will go down to 24

Post by **MadeInJapan** » 20 Nov 2008, 15:21

Sounds pretty tight to me...although there is a concern that there might be some leaking when cold which "seal" up when things warm up....but I'm not sure. I really haven't paid much attention to mine recently during cold start conditions. I'll check and post back. 24 of vacuum is a lot more than I get (max 21 for me) but I idle at around 17, so???

msm15 · Post by **msm15** » 20 Nov 2008, 16:36

ok that sounds good to me but what about the fact that its only going up to 5.5 - is that normal ?

Post by **MadeInJapan** » 20 Nov 2008, 17:11

I think a GLT should push 7or 8...mine was at 10 (T5) before upgrade and now it's at 15, spikes up to 17.

msm15 · Post by **msm15** » 20 Nov 2008, 18:34

yeah thats what I thought