View Full Version : Help with vaccuum and boost issues?

07-18-2015, 09:47 PM
Need some help here guys. I have a late model ported m90 with one of those 7% sc pulleys and a 10% jackshaft pulley, mp tensioner springs and a 38.5? Inch long belt and I'm only seeing around 10? Psi of boost? Any ideas? Buddy of mine sees somewhere around 17psi on a stock late model blower with the exact same mods. Seems like it has power but it's hard to tell if there's an issue? Now when I installed the mp springs one of the pegs on the back of the tensioner broke, but it still has the other and the big bolt so I didn't think there was an issue? I'll include pictures of everything.

Another issue is the routing of my vacuum lines, I routed them one way and here is how it sits after my dad messed with it. I know it's wrong but I'm not sure where to put everything?

The car idles alittle around 1k-1.5k rpm and maybe alittle more then half way between 10 and 20 inhg vacuum.

I haven't had a chance to smoke it other then a cigarette into a vaccuum line(just messing around seeing if we could find anything) and I could see the tb leaked, haven't had a chance to bring it up to the shop and smoke it since it's not on the road atm. Other then those issues the car starts ring up and runs good. Let me know what you think guys need some help here! If you need a complete list of mods I will include them but it's a pretty straight forward bolt on car with a tune. 6379963800638016380263803

07-18-2015, 10:16 PM
Are you reading off the stock gauge for boost.Our gauges are notoriously off. A good exhaust would cause your intake manifold pressure aka boost to drop. Thats a good thing. Try to get the EVTM (electronic vaccum trouble shooting manual) for your year of SC of ebay or maybe someone has a goto pdf that the can upload. I know a wiring schematic ....huge pdf was uploaded but i think it is in a members only section

07-19-2015, 08:45 AM
I'm reading off the stock gauge but I have either a sunpro? Or an auto meter boost gauge I'm gunna wire in and see if there's a difference. It also has a 2.5 inch true dual exhaust with stock manifolds and downpipes and cats.

07-19-2015, 10:47 AM

you have a loose hose somewhere...the vac sounds low, idle really high...in post seven of the thread i linked it has a pic of the tee that you have bypassed.

07-19-2015, 04:50 PM
So I hooked up my autometer boost gauge and it was around 18-19 at idle! Which is good. I also figured out where the vacuum lines are suppose to run behind the plenums but I have yet to change the routing. So I took it around the block, stupid me I ran up the block real quick and I ran out of gas-_- filled it up quick and went around again, 1st to 2nd and I hear "boom" car died and I see the intercooler tube popped off for my front mount. Filled it up with some more gas and tightened down my tubes again. Crank crank crank nothing... I don't even hear the fuel pump priming so I towed it home and parked it.. I guess I'll mess with it another day

07-19-2015, 06:45 PM
Hope that autometer boost gauge is also a vacume gauge. If not no wonder the tube connection blew off.

07-19-2015, 09:06 PM
Yeah it's a vacuum gauge as well, it was 18-19 inhg vacuum at idle. But that pump is a brand new 225lph walbro from scp! I've only driven the car around the block a hand full of times and I run of of gas once today and it burns the pump up? All the fuses are fine so that's not the issue. I'll do a fuel pressure test and go over all the wiring and lines before I pull the pump out but it's just ridiculous because the pump is brand new! I wonder if the intercooler tube hasn't been tight the whole time and that's why I wasn't seeing as much boost? That thing was pretty wrenched down though so I'm not sure. I really need to smoke the motor so I can figure this stuff out. It's very frustrating haha any insight from anyone would help. Im also going to pull that tensioner off with the broken peg and see if it's causing something but I doubt it.

07-20-2015, 07:30 AM
was the boom your balancer knocking out the intercooler tube and thats why its only cranking now?

07-20-2015, 02:12 PM
No the balancer is fine I can hear the fuel pump isn't priming when I put the key in the on position

07-20-2015, 02:15 PM
I can hear the fuel pump isn't priming when I put the key in the on position

What about when you jumper at the VIP port?

Did you check the multi-wire connector down on the right side of the steering column to see if it's coming apart?