I have the 2.7" pulley installed on my car. I just bought and put a new stage 2 belt and also a new oversized Intense tensionerpulley and a new tensioner shock (old one broke)for the car. The belt is incredibly tight and was damn near impossible to even get on so I really don't think i'm getting belt slippage.

Here's the situation... The car gets right up to about 18-19psi very quick like it should. However at about 5000-5500rpms the boost starts to fall off steadily. The redline is at 7k rpms and by the time I shift the boost is down to about 9psi or less. This only happens above 5500 or so rpms though. Also if I happen to let off the throttle a little bit, but get back onto it the boost jumps right back up to the full 18-19psi. Any ideas? Thanks ahead everyone.

 

check all the lines that come from and go to the boost bypass valve. if one has come off you could be bleeding boost. that would explain why it would drop off steadily. but be there instantly if you let off and get back on it. since it would not have had time to bleed off boost that fast.

 

I looked at the boost bypass earlier today and didn't see anything out of the ordinary, but this was my suspicion as well. Does anyone know how much a new boost bypass will run me?

 

This is actually pretty normal. Once our cars hit between 5500-6000 rpms, the boost automatically bleeds itself in order to prevent overboosting. Look at the mods in my signature, if I go past 6000 rpm it drops from 16.5 lbs of boost to about 12 psi in an instant.

 

mine doesn't drop like that .The first thing I would do is unplug the boost line from the bpv and plug it. then go for a rip. maybe the bpv solonoid is some how letting the boost through.

 

Do you have a way to data log or have any gauges to monitor the engine? I know the PCM protects the engine if it is not running safely. See if you are getting a lot of KR. That could be the problem.

The bypass actuator from GM only comes with the complete supercharger. ~$3,000 IIRC.

 

boost should not be bleeding off this much, it's dropping down to under 10psi and the top end just feels really doggish. Which line needs to be unhooked and plugged on the bypass?

i have hptuners and it is not showing any kr at all... you can't buy a new bypass if it goes bad? wtf?

 

bump for morning

 

PM mephisr24 he had the same issue, I think he fixed it.

 

with my 3.0" pulley, boost climbs to 15.5psi and never lets off, all the way to redline, no boost bypass mod either. i'd definitely check things out on your setup.

 

I hold boost all the way to redline. Go back and fix your car with HPTuners....

 

I don't think it's a tuning isssue, but I"ll have him send me the file he flashed to his car and check it out.


here that 607... e-mail me a read off your car... I"ll see if you missed something

 

If you lose boost before redline, it is probably caused by Knock. Knock will pull your boost if it is really bad. Since it is probably not Belt slip, this is my diagnosis. You might be looking at 10+*'s of knock.

 

The car has Zero Knock Retard, i've logged it numerous times now and still don't get any.

Doc - how do i fix the car with HPTuners ??? There is no KR... is there something that will hold the boost back or cause it to bleed off in the PCM?

06blackg85ss - Once I get home tonight I'll grab a read file from the car and email it to you. I'll also try the bypass mod just to see if it holds boost to the redline.

This car is pissing me off lol

 

So you have no KR? If you did not configure HP Tuners scanners properly, you will never see KR because the scanner does not mate up to the Cobalt. You need a config file to properly do it. There are a lot of people out there imporperly scanning their cars with the VCM Scanner.

Other than that, yes it is possible to electronically limit boost in HPTuners, highly unlikely that you have yours limited to 50%

 

When you're logging make sure it says 0.0 beside Knock Retard, if there's no number there then you're not logging it even if it says you are. You need to add it to the table.

 

the config file is correct - 06blackg85ss sent me his and I am using that. I did see some knock with the old Intense tune and when I first started tuning. I will get a blip here and there at times but i meant no KR as nothing serious or constant.

Also isn't boost only able to be limited in first and second gear? I'm using 3rd to pull my logs.

 

yes I did send him the proper config file to log KR correctly with a tune, so I dunno he is running a modied version of the same tune I am running in my car and I hold @19.5 psi all the way to redline. Hopefully it is just something small he over looked when reflashing his car.
I"ll be home a bit late tonight (gotta visit the grandma in the hospital) but I should be home @8pm or so.

 

Okay, I just wanted to make sure, because otherwise scanning the car is useless.

If you limit boost in Second gear, it will limit it in 2nd-5th.

 

when you record with HP Tuners, and you look at knock, is there a number on the left side of the graph? Because if that number isn't there, your not recording for knock.

I don't know why but it seems like everyone I know minus a few people with HP Tuners keep saying they're not getting any knock at all, and then I look at some of their files, and they aren't recording for it. If it isn't set up to record knock properly then no number will show up on the left, and you won't get any line on the graph.

doh, seems like I took too long to type

 

Trust me he has the correct config file for it. I sent him mine, and I def record knock.. stupid heat soak

 

this is incorrect...you can have something on the left side of the graph and it not be logged. It needs to be added to the PID. The two column table that is white with black letters. Knock needs to be added if I remember correctly....maybe thats boost..I can't remember now

 

It's been awhile since I've really used the software, damn MI winter, but I thought I remember it being that if you've got it setup correctly, next to where it says KR*, it should say something like 0.0 but if you don't have it set up, that wouldn't be there?

 

Thanks for all the info guys. I will randomly get a .3 or .7 knock here or there, nothing major. The tune is conservative right now as Paul wanted to just get me up and running and then we could tweak from there. I'm going to try doing the bypass mod tonight for a couple pulls and see if this changes things. I am 99% positive that the boost in first and second are both 100% in HPTuners but i'll do a full read just to make sure. I really think this has to do with the bypass valve, which sucks because I saw that thing is like $160 bucks

 

I am trying to remember how to open and close it....
Something you do will result in opening and closing it as a by product.....