DASC Installed - Rough Idle, Low Boost
 

I just finished installing the DASC on my 97 M44 and I'm having a few issues. First, the idle is really rough. It bounces betweem 300 to 800 whenever I come to a stop.. after a few seconds it usually hangs around 500rpm. The engine light comes on, checked it, only code that it's giving me is the intake air temperature sensors doesn't seem to be working..

Took the car for a drive, it seems to be pulling hard but I'm not sure if its what it should be since I've never been in a DASC car before. My boost gauage doesn't seem to be going past 4psi.. no matter what.. hits it at about 2500rpm and just stays at 4psi.. could it be a faulty boost gauge or is that a stretch? Its hooked straight on one of the two nipples on the manifold.

Any help would be great. Could this be a vacuum leak that's causing low boost?

:(

It sure sounds like you have a leak some where around the manifold. Check all your hoses, the injectors, the gasket between the manifold and the head, the hose clamp on the bypass valve and the seal between the SC and the manifold.

thanks chris, I will go through everything again. For me to be loosing 4psi, should I rule out the little hoses, or could a leak that big come from anywhere?

how can I tell if the gasket between the head and the manifold or the SC and the manifold are leaking? would be a pain to have to take it off again.

there is a leak if it's stalling like that... maybe you can be able to hear it if you rev the car direcly from TB by hand in neutral...

If you didn't remember to add gasket sealant to the paper gasket that sits between the SC and the manifold, then that's the first place I'd look. You can spray starter fluid around the manifold and injectors at idle, if the RPMs go up, then you've defintitely got a leak.

UPDATE

Ok, had a big day. Removed the entire supercharger assembly, redid all the vacuum connections. I noticed there was a bit of a coolant line leaking so I fixed that. I took the SC assembly apart and re-sealed absolutely everything, added all the neccessary gasket sealant and really took my time making sure everything was on right and torqued right.

Adjusted the throttle cable as well. The car no longer has any idleling issues which is great! Took it for a spin, the boost gauge (which was tested now) still reads 4.1psi. The thing is though that the car pulls really strong. I've driven 2007+ 325 and 328 and I really feel I could keep up, so I'm thinking its running how its suppose to.

I forgot to mention earlier that I have a 8:1 compression ration because of a thick metal gasket when I redid my head. Could this be the reason for the lower boost? Since more air is needed to fill the cylinders.

If you lowered the compression you need to raise the boost to get the relative compression back to normal. You'll need to increase your drive speed by the percent you lowered the compression (Need to confirm mixture etc on a chassis dyno) Of course thats all dependent on the compressor curve of the blower. You can get the chart from magnesun. Each eaton blower has a sweet spot for how many lbs of boost it can put out in an efficient manner. The M62 should let you go way higher than 4 lbs. You may not have the "hit" your expecting off the line with the lowered compression but at mid range you can be way up because your at or above the level you had before the DASC. This can be good in a highly tweeked package because it tames the car on part throttle so you don't loop it from the boost hitting and breaking your tires loose.

This is where my lack of knowledge/understanding of force induction comes in. Those this mean that my lowered compression is effecting my PSI level? Since each cylinder requires more air, the blower can't create as much compression as the normal 10.5:1 setups (i think?)

VIDEOS
 

I thought I should post some videos of the accelaration, maybe that would give people a better idea of the current performance and if I'm par with a standard DASC setup.

I can't tell much from the videos, but is there any chance that your cams are out of time causing too much overlap? I can't imaging that just dropping the compression would lower the boost, but having too much overlap would blow your boost right through the cylinder.

I will look into it. Thanks for the input