Well, everyone who has heard about my boost problem of missing 2-3 PSI at high RPM's knows what's up, so I'm not going to re-cap a whole lot.

In general, ever since I got my V1 SC with 3.25" Pulley installed, I haven't been able to produce more than 5-6 PSI at redline, and my Dyno Numbers (without MEVI) are a paultry 231hp.

The previous owner had a stick and a CatBack system, and got 9PSI and 290hp at the wheel.

So I was expecting to get at least 8 PSI with my Auto and at least 250 at the wheel without the MEVI. This is what others have gotten with the same setup.

I've been to many mechanics, spent much time with friends troubleshooting the installation, looking at the belt system, air intake, vacuum system, exhaust, etc, etc. No luck.

The one thing some people had suggested is that I get a new boost gauge, because the one I got with the SC seemed to be moving strange and may have not been reading correctly.

So I just got today an AutoMeter Lunar Series boost/vacuum gauge. I installed it, and the boost reading reads the same...no more than 6PSI at any time. Noone I know only gets 6PSI with a 3.25" pulley.

When I reinstalled it I replaced everything, fittings, hose, and even re-tapped the lighting. (It's Indiglo, and very cool looking, by the way)

The INTERESTING part is that I am only reading 14Hg of vacuum. Nissan spec is 17-22, and I was getting no less than 17 on the previous gauge. This tells me maybe there was something wrong with the previous gauge, but still doesn't fix my problem.

I appear to have a vacuum leak of at least 3Hg. Seeing as most SC'ed Maxes pull 22-24Hg, It may be considerably larger.

But many mechanics have looked at it, and none could find a leak. Including the time my friends and I have spent troubleshooting the vacuum and Intake system alone, about 40 hours have been spent re-tapping and re-installing the vacuum system. I've tried 4 different spots for the gauge now, and re-zip tied everything twice. Same readings each time.

Anyone have any suggestions on what would cause vacuum pressure to drop besides a leak? Compression? Bad Coil?

I've also been checking the ECU every week. I've gotten left bank lean twice now, and adjusted the Cartech FMU accordingly. It's been 2 weeks, and I'm getting "0505" - All Systems Operational.

Thanks!
IanS

 

grrrr


vacuum leaks are bad...

 

Wow, that's strange. If that's the case, then it must be the SC itself.

 

I don't really think it's a vacuum leak. If it was a leak, you would easily be able to hear 3 PSI leaking at boost.

One more person is going to look at it today, and if he can't find anything, then I'm sending the SC to Vortech as soon as I can get the time to remove it.

The person who sold it to me blew their engine shortly before selling it, and didn't think it was important data, so he never told me.

He blew it on the Dyno at full RPMs. That means the SC went from spinning at 15,000 or so RPM to 0 instantly.

I've been hoping it was something else, because of the costs involved with fixing it (my seller has offered to pay for 1/2, IF something is wrong). But from my and the seller's conversations with Vortech, the symptoms of a blown SC just aren't there. (No oil in the piping, no rythmic grinding noises, etc)

So I've been trying to find other things that could be causing it.

IanS

 

Make sure the S/C belt isn't slipping. I have a 3.33 pulley and I was getting 9.5-10psi. I replaced the pulleys and tightend the crap out of the belt and I noe get 11 psi @ 6500rpm with a 3.33 pulley.

 

I don't know if you checked it, but is it your VI leaking? Try taking the T off of the FPR/Vacuum tank and connect only the FPR. Maybe your T, tank, or MAP switch are leaking vacuum.
-hype

 

Czar and I spent the day looking at it today...

We changed where the boost gauge was checking from, re-tightened everything, and put sealer on the boost gauge ends.

I'm now hitting 8PSI! Because I have no CatBack, this is about what I expect. I should be at 9PSI with the CatBack, wouldn't you think?

But the problem with the vacuum is still there. currently my gauge only reads 15 vacuum. We tried Czar's gauge on it, and it read the same.

We covered the SC up with a pillow and spent about an hour listening and checking for any leaks anywhere. (With the MEVI disconnected at the T going into the manifold, and a vacuum gauge on that T)

So my vacuum is still off, but the car feels WAY faster. I don't know how or why it's got more power, but both Czar and I agree it definately does.

Anyway, still need to figure the vacuum thing out, but the extra 2 PSI is certainly nice to have!

This tells me most likely the SC itself is fine. I'm going to try tighteneing the belt a little later this week and see what happens (I tightened it before really tight with no improvement on the gauge, but I think the gauge was reading wrong at that point....I then put it back to 90 degree deflection).

IanS