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Discussion Starter #1
So I recently picked up the car and it's already giving me grief. Sometimes when I get on it it feels amazing, boosts hard and burries the stock gauge (10/2.55). But then the next time I get on it down the road I might only see 3-5 lbs, and that's it (feels solid, just not making boost). It's tuned for 100 octane, and I heard that if it senses it's not getting that it will go into a sort of limp mode. Figuring the dealership put a tank of 91 in it I reset the computer after running a couple tanks of 100 through it and it's still doing the same thing.

On another note, sometimes when it is making good boost it feels like it hits a brick wall, and the boost either stabilizes, or drops significantly. I figure I'm probably getting some belt slip to account for some of it, but it just doesn't seem like that would be the major problem here. Anybody have any ideas for me to try and get this taken care of? Thanks in advance!
 

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I'm Your Pusher
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Belt slip and IAT2 issue pulling timing if motor is hot. That pulley combo is high. Needs supporting mods like hx, meth, and a hood (cough plug plug) lol
 

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Discussion Starter #5
I do have a fluidyne hx on it, but no meth. Also running on 100 octane. Most of the times I drive it is late at night, temps in the upper 80's to low 90's, so not too terribly hot. I am planning on grabbing a new belt for it, and also need to look at the tensioner to see what it has on it...Just need to find out which belt I need for it. Is there a way to adjust for the iat's in the tune, or would that not be smart?

Maxx, is that why everybody is doing the bypass mod on these things? Is there a way to test it to see if it's working correctly?

Syclone!
 

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get it on a dyno and check boost vs iat vs timing vs power output and you'll find your problem.
 

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Garth & LEP are tuning your V, right?
 

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Discussion Starter #8
Garth & LEP are tuning your V, right?
Yeah, it's just a matter of me getting it down there for him to look at. The problem is that the dealership had it and probably didn't run 100 in it the whole time like they should have, so trying to check and see if it was something that they may have screwed up somehow. I'm most likely going to go back to the stock upper and back her down to run on 91, just to make the car a little more usable.
 

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Yikes, I don't think I've seen anyone spinning the blower this fast with that combo. Most folks find that the 2.55 fits with the 9.1 or 8.6 well, but heat and belt slip start soon after that. Not to mention longevity of the setup...good idea to go back to a stock upper.

You can adjust how much timing is pulled based on IATs. But my tuner actually started pulling small amounts of timing earlier based on what he has seen with this LSA and SC setup. I'm pretty sure he would not put on a 2.55 with the 10" I have now on the lower pulley (stock upper).
 

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TOO much pulley, even for 100 octane without serious IAT2 cooling; cam and headers, IMHO. Even if you are going to keep just the 10" lower, you might want to consider the green belt for your blower. Agree with Red Baron also
 

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Discussion Starter #11
TOO much pulley, even for 100 octane without serious IAT2 cooling; cam and headers, IMHO. Even if you are going to keep just the 10" lower, you might want to consider the green belt for your blower. Agree with Red Baron also
I probably should have put up a mod list, so you guys don't think there was just a bunch of boost thrown at it with nothing else. It is a fully forged short block, zr1 cam and wcch stage 2 heads. Ported blower, fluidyne hx, 160 t-stat, AR Headers to hollow cats into stock mufflers. So the motor was built to handle a lot...
 

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Even so, most will say this combo is past the blower's efficiency range. I wont jump to judgement so let us know what you find out.
 

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Maxx, is that why everybody is doing the bypass mod on these things? Is there a way to test it to see if it's working correctly?
I'm having reservations about your problem being caused by the PCM limiting boost due to temperature or other issues mentioned by other posters. I could see it bleeding boost to control power output, but you're losing copious amounts (10-12 psi). And it seems to be somewhat inconsistent. I think you need to confirm proper opertion of the bypass valve first. You don't need to perform the bypass mod - that should have been taken care of in your tune with the boost-limiting parameter.

I see two possible conditions that could cause your problem:

1) The bypass valve is not consistenly closing all the way.
2) The boost control solenoid is leaking boost to the bypass valve actuator.

Take a look at the following images:

Hose (3) is the vacuum source for the actuator (8). It connects to the lower nipple on the SC (1).
Hose (2) is the boost source for the actuator. It connects to the upper SC nipple and the right nipple on the solenoid (5), marked with an X in the second image.
Hose (4) is the solenoid output. It connects to the left nipple, marked with an O.



During idle and normal cruising, vacuum is applied to the actuator and the bypass valve is pulled open (it's a normally-closed, spring-loaded valve). When a load is presented to the engine, vacuum drops and the valve closes. When the valve is closed, boost builds. With the stock tune, if boost exceeds 12 psi, the solenoid opens and allows pressure to the opposite side of the actuator diaphram, which in turn opens the bypass valve to bleed boost.

If the valve doesn't close completely, it will bleed boost. If the solenoid is leaking, it will pressurize the actuator, which will also bleed boost. Here's what I would do to test:

1) Pull the hose (3) off the upper SC nipple and cap the nipple. Manually push the actuator rod away from the diaphram to ensure the bypass valve is closed. Then a few WOT blasts. If the problem is gone, the bypass valve was sticking. Lube the shaft to fix. You may have to pull the SC lid to do this.

2) Pull the hose (2) off the upper nipple and cap the nipple. More WOT blasts. If this fixes it, replace the solenoid or leave the upper nipple capped if you don't care about the PCM bleeding boost for high temps, etc.

HTH, mm
 

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Keep us updated. Im curious about the fix. Might as well check the set screw on the bypass valve also. It wouldn't cause inconsistent boost but while you messing around in that area its an easy check.
 

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still saying belt slip and timing pulled... swings way top drastic for bleed off since stock still holds 9-12
 

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Discussion Starter #18
Okay, so after a nice conversation with Garth down at LEP it was brought to my attention that I have given the wrong information about my car (that's what I get for not paying attention I guess). My pulley combo is a 9.1/2.55, not a 10" lower. Going to order a new belt and get it on asap and take it from there.

Sorry for being ignorant!
 

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Okay, so after a nice conversation with Garth down at LEP it was brought to my attention that I have given the wrong information about my car (that's what I get for not paying attention I guess). My pulley combo is a 9.1/2.55, not a 10" lower. Going to order a new belt and get it on asap and take it from there.

Sorry for being ignorant!
That a MUCH better combo :) That happens to be the lower size / combo I would go with.

Do yourself a BIG favor, get a green belt, they are much stickier so slippage is virtually eliminated

Steve
 

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Okay, so after a nice conversation with Garth down at LEP it was brought to my attention that I have given the wrong information about my car (that's what I get for not paying attention I guess). My pulley combo is a 9.1/2.55, not a 10" lower. Going to order a new belt and get it on asap and take it from there.

Sorry for being ignorant!
Not ignorant, just didn't know. Call NAPA and get a Gatorback. If it is still giving you boost issues, bring it on down!


PS: Go buy some ET street's!
 
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