High RPM (3500-3900) boost issue... not reaching target??

Ok...

So I built a high RPM tune (2006 LBZ). It fuels all the way to 4k (went through EVERY table that has anything to do with high rpm stuff). After doing my custom lift pump setup rail pressure holds up top now as well. But Boost is dropping off??

My tune is nothing crazy, but it makes around 25-26psi max in the 2500-3000 rpm area... and then starts dropping off... I am seeing maybe 22 at best at 3900. I played with turbo vane positioning to see what I could do there.... when opening the vanes up some (19-20 in the high rpms) I only saw 19-20 psi at 3900. When I closed them down a little tighter (around 40) I see 22psi at 3900...?

I raised my high rpm boost target tables up to around 26-27psi and that had no effect.

I used the timing calculator and targeted about a 45/55 split.

Truck seems to smoke worse up top too, especially with the vanes opened up (which makes sense) Was really hoping to see 24-25psi up top... seems like I have enough fuel, I'd like to make better use of it up there and also make a little bit more power (running this tune to keep out of 5th gear).. I aimed my tune at making more top end power and not a ton more torque (again trying to go a little easier on the trans)

Just looking for some pointers / advice?! THANKS!!!

(I am close to 7000ft elevation as well...)

Hey General,

One thing to remember is that the desired boost table values are not what the gauge will read, you have to subtract out barometric pressure. For example if the desired boost table value is 30psi and barometric pressure is 14, your actual boost is 16psi on your gauge.

Also, make sure your max allowed boost is high enough (table b2226), and your vane position max tables as well (b2222-b2224)

Also, check your intake air temp multiplers and your altitude multipliers aren't a limiting factor as well, hope this helps!

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Originally Posted by LBZoom

Hey General,

One thing to remember is that the desired boost table values are not what the gauge will read, you have to subtract out barometric pressure. For example if the desired boost table value is 30psi and barometric pressure is 14, your actual boost is 16psi on your gauge.

Also, make sure your max allowed boost is high enough (table b2226), and your vane position max tables as well (b2222-b2224)

Also, check your intake air temp multiplers and your altitude multipliers aren't a limiting factor as well, hope this helps!

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good explanation :good:

Why thank you! lol

Also, another point worth mentioning General, is that the desired boost table will overcome the vane tables to achieve the desired boost pressure as far as I know. So if you need to experiment just adjust the desired boost table and don't worry about setting your vane position yet, it'll save you some steps for now. Just be sure to disable the MIL's associated with the boost system because if the vanes position doesn't match correctly it will throw a check engine light. You can go back and "dial" in your vanes to achieve faster spoolup at a later time.

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Originally Posted by LBZoom

Why thank you! lol

Also, another point worth mentioning General, is that the desired boost table will overcome the vane tables to achieve the desired boost pressure as far as I know. So if you need to experiment just adjust the desired boost table and don't worry about setting your vane position yet, it'll save you some steps for now. Just be sure to disable the MIL's associated with the boost system because if the vanes position doesn't match correctly it will throw a check engine light. You can go back and "dial" in your vanes to achieve faster spoolup at a later time.

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setting LOW mm3 values in B2231 and B2232 will eliminate the need to turn off those DTC's. setting the values low with force the ECM to reference the boost tables and adjust the vanes to match whatever you have requested boost wise. Setting the values higher than stock (or whatever the mm3 per rpm you operate at) will force the ECM to reference the vane tables and whatever boost is made is whatever boost is made.

Thanks for the input. I had already adjusted all my boost tables to what I was looking for. But the truck won't meet the boost in the upper rpms??

I had it set as high as 27psi (after comp. for atmospheric pressure) and it still only reaches 21 maybe 22 up top.

Adjusting vane position did allow me to get a little or more depending on what I requested.... which is strange, I did not realize the truck will override the vane posi table! It's acting like it's not reading from the boost tables actually. I would think I wouldn't need THAT much vane posi. on the top end to make the boost. I am running about 25% more pulsewidth up top btw. I'm sure being at 7000ft just makes it that much harder for the turbo to reach those boost levels but that still seems low.

I have been over and over all tables related and I don't see anything.. I'd post the map but I'm an HP guy :( (long story) .... I do appreciated the advice though.

It's a little frustrating, I'm all about the high rpm power... (mainly because I'm trying to keep the torque numbers from getting to high on a stock trans).. but the truck does seem to make pretty good power even with the boost low.

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etting LOW mm3 values in B2231 and B2232 will eliminate the need to turn off those DTC's.

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What's the name of these tables since I don't have EFI live? I haven't thrown any codes so it must not be too out of whack but just curious to take a look etc.

Thanks!!!!!

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Originally Posted by GeneralTJI

What's the name of these tables since I don't have EFI live? I haven't thrown any codes so it must not be too out of whack but just curious to take a look etc.

Thanks!!!!!

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anything over 1800RPM you shouldn't have to worry about it as the tables in stock form are already set to 1 and 2 mm3 which is low.

Oh.. the boost control enable / disable tables... gotcha, yea I left those as they were.

How much vane % is in theory ok to run in the high rpms?? (with my 25% added pulsewidth) .. I was running up around 40 on my max vane posi tables from 3600 on... figured going to high would be counter productive? (choking out the motor and running really high drive pressure etc.)

Are you using the edge for your only boost gauge? That ain't going to work neither is running your truck up to 4000RPM. There is no reason to go over 3600 with the stock turbo. you shouldn't need your vanes at much if any over 20% at high RPMs.

Keeping the truck out of 5th gear on a stock trans is a pretty good reason to rev the truck up close to 4k.

I am using the Edge to monitor boost.... the truck targets about 26 and up to around 32000 rpms it seems to hold pretty right on (Edge reads 26) I suppose it wouldn't hurt to install a manual gauge at some point!?

I agree I shouldn't need high vane position, but for some reason the truck won't build that kind of boost without closing them down. Maybe thats because I'm not running super high pulsewidth levels? I just don't have the fire to drive the turbo with the vanes opened up??