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Old 02-20-2013, 07:07 AM
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VGT duty cycle question

I've been looking around and haven't found really what i'm looking for, so I thought I'd ask and see if anyone has any input.

I recently put on my MTW hybrid, but was told by my mechanic that my VGT duty cycle needs to be adjusted. He said that that the vanes are opening too early and not allowing me to flow air correctly early on, which is causing my low boost/high egts when accelerating. I was told by the tuner that my duty cycle in my current tune is 25% above stock, but I'm not exactly sure what that means.

I set my CTS to monitor VGT duty cycle and it seems that while I'm idling at about 600 rpms, its at 15% then goes up to 70% when idling at about 1100 rpms. When starting to drive the VGT drops to about 50% and I don't really get more than about 11 PSI of boost unless I'm really giving it some juice and accelerate hard. But then when I'm just keeping speed on flat ground the duty cycle is at about 20-25% and hovers at 1-2 PSI of boost.

The current tuner says they can raise the duty cycle to 30% above stock, but again, I'm not sure exactly what that means and if it will solve my issue.

Any ideas?
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Old 02-20-2013, 07:17 AM
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Should have asked me, the higher the % raise the tuner puts in the vanes would start the duty cycle close more. So at lower rpms the vanes will still closed more, then stry to open as rpm get higher, so you don't overboost. Either your truck is running with a lot of air flow, and needs vanes closed more, or the tune is not reacting, the VGT actuator may not be working right. Also might have a sensor not giving the right information for the ebp to know what is going on. Hope that helps.
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Old 02-20-2013, 07:22 AM
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If my truck is running lots of air, wouldn't that increase the boost PSI and keep EGTs down more? Is there a way to test if the VGT actuator isn't working right?
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Old 02-20-2013, 10:41 AM
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Stock or some very basic tunes never move the VGT more than 40-65%. The 25% above normal that your tuner applied is designed to give you faster response. It sounds like your tune isn't set right or you have a MAP error, other sensor error, boost leak or exhaust leak. Since you didn't give a lot of parameters it is hard to know what your tune is set up for. Who's tune is it?

You are running a hybrid on stock injectors. I would expect the tune to set the VGT to about 40-50% at 60mph and your boost would be around 3-7psi with the back pressure about 25psi (abs) (0 rel). As you move your pedal position the vanes would be moved accordingly. For instance, if you took your foot off the pedal, you should see 0 boost, 15 (0 rel) BP, and the vanes move toward 20% or less. As you move to WOT, the vanes would be at least 70% or greater with boost building to 25psi or more with 45+ BP.If I knew your PW, RPM and ICP, we could estimate your EGT for comparison. However, your EGT should be around 550-600 at 60mph. Your PW would be about 1.4, and ICP about 1200psi. At WOT your temps should not be more than 1200ish for your set-up (PW 2.6 or less), unless your are going to peg your speedo.
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Old 02-20-2013, 10:58 AM
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Currently I'm running the Looney. I also have the xtreme street from Tony and am having the same issues, but worse. (I'm waiting on an updated tune from him)

Your post gave me better information from what I had attempted to look up...from what I had seen before I believe the information must have been explained backwards. I don't remember where it was from, but it stated that when idle the duty cycle was supposed to be near 85%, as the turbo has the vanes 85% shut. This is apparently where I was getting confused.

When driving down a flat road keeping a steady 55, my boost is usually 1-2psi and my EGTs are between 7-800. When hammering it, I've seen boost up to 24 psi with EGTs well over 1400. My mechanic took it out after I brought it back thinking I had a boost leak, and told me that he got up to 32 psi of boost but also almost 1500 EGTs. However, he said once he started making good boost, the EGTs dropped down to around 1100, which is why he said that the vanes are opening too early and not allowing it to flow air correctly and build up the needed boost down low.
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Old 02-20-2013, 03:06 PM
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Quote:
Originally Posted by TruckNorris View Post
Idle the duty cycle was supposed to be near 85%, as the turbo has the vanes 85% shut. This is apparently where I was getting confused.
Yes, both the Looney and Extreme will give 80+ at idle, at a stop. All of the high perf tunes do that.

Quote:
When driving down a flat road keeping a steady 55, my boost is usually 1-2psi and my EGTs are between 7-800.
This is defining the problem, Unless your going uphill or pulling a trailer, the EGT is 200* high and your boost is a little low. Now with these tunes your boost would normally be about 6-10psi and the vanes around 55-60%. Again, ready for you to put the hammer down. Light to moderate acceleration should put your boost about 14-20psi with the vanes close to where they started. Before I tell you to clean your EBP fittings and tube, what year is your truck? Some have an inferred BP strategy. Today, the MadMan put out a post on items to check, follow it. You could also flash back to stock to see if your EGTs are still higher than normal at cruise. You would also find the vanes about 55%ish at cruise.[/QUOTE]

Quote:
When hammering it, I've seen boost up to 24 psi with EGTs well over 1400. My mechanic took it out after I brought it back thinking I had a boost leak, and told me that he got up to 32 psi of boost but also almost 1500 EGTs. However, he said once he started making good boost, the EGTs dropped down to around 1100, which is why he said that the vanes are opening too early and not allowing it to flow air correctly and build up the needed boost down low.
It sure seems to be slow to build boost, but once it does it is happy. The problem is the air needs to be in sooner. The problem is what would cause the vanes to open early, if that is actually happening, and what is the cause for the lack of air at the start of the boost process? There could be a small leak, but that wouldn't open the vanes. I might have though a clogged air filter for the slow boost, but that again, shouldn't open the vanes early. Perhaps your MAF needs cleaning or replacing. But I'm guessing on that. When did the problem start?

Last edited by twoicebergs; 02-20-2013 at 05:04 PM.
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Old 02-20-2013, 04:20 PM
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I'm running Tony's race tune in my truck right now. At idle my vgt % is at 85%. Cruising at 65mph...vgt % is at 55-56% with about 11-12psi of boost. I need tony to adjust the vgt % to lower the boost to around 6-8psi when cruising 65-70mph. When accelerating....if the truck is in OD lockup and at 45-50mph and i roll into the throttle....turbo will surge/cough pretty bad. I have to get off the throttle for the truck to downshift then get back into it so that the surging will stop.
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Old 02-21-2013, 05:28 AM
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[QUOTE=twoicebergs;4122170]Yes, both the Looney and Extreme will give 80+ at idle, at a stop. All of the high perf tunes do that.


This must be my problem. When I idle at 600 RPMs, or take my foot off the pedal while driving, my duty cycle drops to 15.

The only time I see near 80 is when I'm idling my truck for a few minutes after starting and the RPMs raise to about 1100. But then when I start to drive, it drops to about 45-50 while driving, and then I take my foot off and it drops back down to 15.

However, this morning I just pulled a P0470 code...something to do with the EBP. And my truck is an 04.5

Edit: apparently I don't know how to work the quotes...

Last edited by TruckNorris; 02-21-2013 at 05:31 AM.
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Old 02-21-2013, 06:04 AM
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Quote:
take my foot off the pedal while driving, my duty cycle drops to 15.
This part is normal. The stopped at idle with 15% is abnormal.

There have been at least 3 recent posts where the EBP tube was corroded with either having a leak or being plugged near or at the manifold. This could explain your problem. The tube joins the left exhaust manifold at #2. The early ones rise fairly straight to the valve cover. The 05-07 have a sweeping bend to the middle of the valve cover where the sensor is.
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Old 02-21-2013, 06:22 AM
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Thanks, I'll have to try to check it out to see what is going on with it. Hopefully that's all that I need to do. I'm excited to get this turbo working properly after what I've read from everyone else with one.
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