Turbo back pressure question

FlyingLow

FlyingLow

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When I bought my truck the previous owner had the rear cats removed. In place of those cats the piping went from 2 1/2 to 2 inch then back to 2 1/2. (I think it was 2 inch.) It was definitely smaller. Anyway now that piping was recently taking out and replaced with all 2 1/2 inch piping. The problem I'm having is as soon as I give the truck some gas it almost instantly goes to 0 on the boost gauge. This causes the truck to bog down or hesitate. Then after a second or two the gauge shows more vacuum and the truck acts normal. So here is my theory and you guys tell me what you think. When I give the truck a little bit of gas it starts to try and build boost at the turbo. This causes the truck to fall on its face. I didn't have this issue before because the back pressure built just a little at the inlet of the smaller pipe. Now that pipe is gone so it tries to build the back pressure at the turbo. Remember this is a rear mounted turbo so it works a little different the a normal turbo. I have this problem at highway speeds also. So what do you guys think?

Smoke
 
take no offense smoke but I think you time would be better spent instead of beating yourself to death over this turbo system to take it to a reputable tuner and let him figure it out.

oh the that small a difference in piping isnt going to make any difference in boost.
 
If your program is dumping in a bunch of fuel at very low vacuum or slight boost, then thats the culprit. You do not want any restriction in your exhuast system with an STS setup.
Justin
 
Nowwhat said:
Smoke...I think you will find that your problem is in the software....
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I hope it is but I just don't know. Truck went from running good, just rich to the problems I stated above. The only changes were adding a VEC3, the piping, larger injectors and a little meth. Can you explain why you think it is the software?
 
its just the fuel map. on my custom tunes, I always have to spend a lot of time working on the "throttle pump" maps. these are to simulate the old throttle pumps from the carburetor days that supply fuel briefly during instant WOT conditions. When you stab the throttle, the vacuum (as you noted) drops to zero and a carb needs this vacuum in order to inhale gasoline. Fuel injected cars are computer controlled and on the normal fuel map you don't need a lot of fuel at 0 psi so you end up with a lean condition if you "stab" the throttle. but it's perfect if you gently hit the gas.

that's where the "throttle pump" (or equivalent dodge version) map comes into play. it's pretty easy to fix this hesitation.
 
there is a ton of variables here smoke
for one , are you running a boost controller? if not you need to.
next all the vaccum lines need to be in the proper place, one vaccum line in the wrong place can wreak havvoc in the way boost comes on.
exhaust will not give youtoo much a worry
what spring or wastegate are you using, you need to have the correct spring to work the wastegate.
bands and clamps on all the tubing, is it correct? tight? this can also cause big time problems.
then work on the tune, once these things are correct then the tune will go much easier.
but again it takes a turbo tuner to do it.
 
FlyingLow said:
When I bought my truck the previous owner had the rear cats removed. In place of those cats the piping went from 2 1/2 to 2 inch then back to 2 1/2. (I think it was 2 inch.) It was definitely smaller. Anyway now that piping was recently taking out and replaced with all 2 1/2 inch piping. The problem I'm having is as soon as I give the truck some gas it almost instantly goes to 0 on the boost gauge. This causes the truck to bog down or hesitate. Then after a second or two the gauge shows more vacuum and the truck acts normal.

Smoke
Click to expand...

Scott-

I had this problem when I had just completed the install. It went away as soon as I had all of the exhaust couplings welded. If your turbo sounds different in any way with the change in exhaust pipes, it shouldn't. Start there. It's the only variable you introduced since the problem surfaced.

I can't agree more with Stinker on rechecking stuff. I let my STS Vette sit for a few weeks since it came back running like shit after the clutch was replaced. WTF??? :dontknow:

I got after it today, and the first thing I found was that my carbon fiber air bridge had split open, then I found that exhaust was coming out of the wastegate at idle. The freaking "tech" had connected the boost line to the wrong port on the wastegate. It only takes a small mistake to make big problems.
 
Eric were the problems you were seeing there all the time? My biggest problem is right at idle. If I rev it up a little and then try to go there is no problem. I have been checking for leaks but have not found any.
 
AWDisuzu said:
. When you stab the throttle, the vacuum (as you noted) drops to zero
Click to expand...

Do you mean rises to zero. Staring in the negative numbers (about -15 vacuum) the gauge rises to 0 with just a little bit of gas. I'm not trying to be a smart-ass just trying to make sure we are talking the same.
 
FlyingLow said:
Eric were the problems you were seeing there all the time? My biggest problem is right at idle. If I rev it up a little and then try to go there is no problem. I have been checking for leaks but have not found any.
Click to expand...

My problem was under acceleration, and that's what I thought you meant by hitting the gas. All I can suggest is looking at anything that might have happened in the area the work was done in, but I'm sure you have already done that many times.
 
I rechecked the vacuum line this weekend and still no joy. I now have a better idea of what is going on. While parked if I give it a quick small throttle hit then I can hear the turbo sucking in air like crazy. I have never been able to hear that before. So the turbo sucks in the air, vacuum goes to zero, A/F gets lean and trucks almost stalls. Even with just a little bit of gas it does mostly the same thing minus the turbo air sound. Could this just be a tuning issue or is it likely something else?
 
FlyingLow said:
I rechecked the vacuum line this weekend and still no joy. I now have a better idea of what is going on. While parked if I give it a quick small throttle hit then I can hear the turbo sucking in air like crazy. I have never been able to hear that before. So the turbo sucks in the air, vacuum goes to zero, A/F gets lean and trucks almost stalls. Even with just a little bit of gas it does mostly the same thing minus the turbo air sound. Could this just be a tuning issue or is it likely something else?
Click to expand...

This may be something else you've checked, but are you certain that the vac line is connected to the correct ports on both of the wastegates? (While parked and idling, make sure there is no exhaust coming from the wastegate outlet pipes.)

It might not be a bad idea to give Rick Squires a shout if you haven't already.
 
Ram From Hell said:
This may be something else you've checked, but are you certain that the vac line is connected to the correct ports on both of the wastegates? (While parked and idling, make sure there is no exhaust coming from the wastegate outlet pipes.)

It might not be a bad idea to give Rick Squires a shout if you haven't already.
Click to expand...


I checked the connections. Nothing wrong.
 
I got a reply from STS today. Very quick considering I emailed them just 2 hours ago. They question the intake filter or something else being clogged. I'm going to take a look at a few things. I also have an appointment with Roe at the end of the month for a tune.
 
Pulled the air-filter off with no change. Pulled the tubing going to the throttle body with no change. Beat myself in the head with a hammer no change.
 
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