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  #1  
Old 02-24-2015, 01:41 PM
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Restoring Proper Boost Pressure

Since I did the swap in my SL, the boost has been pretty much limited to 9psi. In researching this condition, I'm seeing that this is a pretty standard kind of thing on these old diesels. While I'm mostly happy with the performance, it would be nice to restore the boost levels to 12psi or so factory specs.

Since so many people are seeing the same reduced level of max boost, my working hypothesis is that the spring in the wastegate actuator weakens over time, probably analogous to the weakened spring in the fuel pressure regulator which is pretty much universal.

Seems like there are two ways to fix the issue. The first would be a direct approach involving adjusting/replacing the waste gate actuator. Adjusting the actuator is kind of a pain involving removing the cover and making iterative changes to hopefully get the adjustment right. Many posters have discussed the hassle and aggravation of getting the retaining spring in and out, to the point where funola actually fabricated retainers to hold the cover without the retainer.

Closely allied would be replacing the wastegate actuator. A reasonable choice except for the fact that there a lots of different ones and getting the adjustment right is the same as above.

Research shows that there is another quick, dirty and cheap solution that I've decided to pursue. This involves the use of a "boost controller". These devices are nothing more than an adjustable needle orifice designed to bleed a metered amount of air out of the pressure line to the wastegate actuator. The adjustment basically allows the turbo to put out 12psi while the actuator sees 9psi, causing the wastegate to open at the desired 12psi rather than the current 9psi. Since this is a "set point" kind of device rather than a proportional device, the turbo will provide designed boost through it's entire range, up to the max boost point.

I know that boost and fuel are directly related, with the ALDA designed to provide additional fuel as boost pressure comes on. So the obvious question is, is my lower boost potentially due to the ALDA not functioning properly. To test this, I removed the pressure line from the turbo actuator and plugged it. I then took it for a test drive. I got 13psi of boost no problem, all the while monitoring EGT to ensure no temp problems. The ALDA is unmolested.

I also monitor fuel pressure so the lower boost is not due to pump, filter or regulator issues.

The turbo appears to be in good condition with respect to bearing play and turbine visual inspection.

I ordered the boost controller yesterday so we'll see what happens. The other nice thing is that this is easily removable if it fails to function properly.

Here is the device I plan on using.



Again, this is not a performance mod, rather restoring to factory specs. I think there are adequate safeguards in place as I monitor EGT and boost continuously, the ALDA is stock and the overboost sensor/switchover are in place.

I'm open to thoughts and observations on this project.
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Restoring Proper Boost Pressure-image.jpg  
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  #2  
Old 02-24-2015, 02:09 PM
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I installed one awhile ago and it works great. I can't believe all the nonsense people suffer through to adjust the wastegate when $20 gets you whatever boost pressure you want (including stock, if you turn it all the way down).

-Rog
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  #3  
Old 02-25-2015, 12:32 AM
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i also have an MBC. it works, but it does not save us from the "iterative changes to hopefully get the adjustment right". it must be possible to get right, but mine is still off (set too high).
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  #4  
Old 02-25-2015, 01:08 AM
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i had a MBC but decided to properly adjust my wastegate one day to tidy things up a bit. i remember the MBC would sometimes allow the boost to spike pretty high? now it will hit 14psi on a hard kickdown. kinda a pain to get the "tang" popped out on the wastegate at first. clean with brake cleaner and take some pics with your phone or something so you can see where it is and which way to pry from. i slightly bent mine for easier removal. this is on a om617 with a garrett turbo btw...
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  #5  
Old 02-25-2015, 09:45 AM
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Weird. I've never had a problem with mine. This is the one I'm using, which is basically the same one you can make, but where I live I couldn't get the parts cheaper than just buying that one, and it's already made.

-Rog
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  #6  
Old 02-25-2015, 11:57 AM
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I built a simple electronic boost controller for the 87. It consists of a pressure switch which is fed boost from the manifold.
http://i.imgur.com/1v4fyB6.jpg
And a solenoid valve that was originally used to control EGR on my old 2.6.
http://i.imgur.com/DCqEANx.jpg

The idea is simple. Below 13psi the valve feeds vacuum from the vacuum pump to the wastegate actuator in order to keep the wastegate shut tight. Above 13psi it switches to sending boost pressure to the wastegate actuator. This prevents wastegate creep (look it up) for faster boost response and controls max boost. At WOT it can reach 13psi at 1800rpm instead of ~2400rpm stock. Once at that peak pressure the boost gauge fluctuates between 13 and 12 psi as the circuit quickly pulses on/off. Works beautifully and makes the car much more responsive at part throttle and low rpm. Theres a steep hill on my way to work that I can climb in 4th gear instead of 3rd prior to this modification.
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  #7  
Old 02-25-2015, 12:32 PM
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Quote:
Originally Posted by tjts1 View Post
I built a simple electronic boost controller for the 87.
Interesting solution. I thought about the possibility of building a microcontroller to do the job, but quickly discarded that as the first option. The hassle of dealing with hysteresis or PWM as part of the code, made me opt for the simpler mechanical no-moving-parts solution first.
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  #8  
Old 02-25-2015, 03:14 PM
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Neat stuff, looking forward to reading about how it does.

This post is mostly for reference so I can find this thread easily in the future, working on the assumption that at some point I'll have time to tinker with my diesel again.
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Old 02-26-2015, 09:59 AM
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Mine is a Vibrant. When I get the truck on the track I'll set it to about 1 ATM and forget it! But I have the advantage of operating pretty much at a steady state (WOR) so I have an unusual operating scenario.

Dan
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  #10  
Old 02-26-2015, 11:33 AM
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Quote:
Originally Posted by Dan Stokes View Post
Mine is a Vibrant.
That's a pretty nice unit. They all seem to operate on the same simple metered-bleed principle. I like the two piece design idea of the one I ordered, but the quality of the Vibrant is definitely superior.

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  #11  
Old 02-26-2015, 03:01 PM
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Quote:
Originally Posted by mach4 View Post
... is my lower boost potentially due to the ALDA not functioning properly. To test this, I removed the pressure line from the turbo actuator and plugged it. I then took it for a test drive. I got 13psi of boost no problem, all the while monitoring EGT to ensure no temp problems. The ALDA is unmolested. ...
On first read, this sounded like the ALDA was a factor. On more thought, it seems you proved the ALDA was not limiting boost until ~13 psig. To clarify for others, the ALDA limits fuel to avoid over-boost. The waste gate does also, but by bypassing exhaust around the turbo. By removing the turbo's "pressure line", mach4 disabled the bypass. The higher 13 psi limit was then due to the ALDA becoming active. Thus, the lower 9 psi limit must have been from the bypass opening early (weak spring).
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  #12  
Old 02-26-2015, 03:24 PM
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EDIT: found answer

Quote:
Originally Posted by BillGrissom View Post
On first read, this sounded like the ALDA was a factor. On more thought, it seems you proved the ALDA was not limiting boost until ~13 psig. To clarify for others, the ALDA limits fuel to avoid over-boost. The waste gate does also, but by bypassing exhaust around the turbo. By removing the turbo's "pressure line", mach4 disabled the bypass. The higher 13 psi limit was then due to the ALDA becoming active. Thus, the lower 9 psi limit must have been from the bypass opening early (weak spring).
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  #13  
Old 03-25-2015, 09:49 PM
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Well I got the boost controller installed today and sad to say, the results are not good. Well they are good in that I'm getting great performance and good boost - just no control. I do get boost up to about 15psi where it appears that the over-boost solenoid is kicking in causing the ALDA to cut fuel as it should. It makes no difference whether the adjustment screw is OFF or ON, the results are the same.

So what I surmise is going on is that the pressure relief valve in the Tee is set too high so the pressure never reaches the wastegate or the bleed valve. My plan is to cut the spring a bit to lower the pressure at which it allows pressure through. I'm not quite sure why there is the pressure relief valve there as the Vibrant one is just a needle valve...maybe better control by not bleeding all the time, only above a set point.

I could probably safely run with it the way it is. Using the just completed coast-to-coast trip as a baseline, there were only four climbs that had the potential to over-boost and I was monitoring EGT and boost for all of them as a matter of course any way.

More to come....
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  #14  
Old 03-26-2015, 04:39 PM
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Spent some time on the boost controller project today. First tried to find a spring that would allow the check valve to open at maybe 8-9 pounds but no luck. So I just removed the check valve allowing the system to function like the Vibrant with only the needle valve to provide bleed.

It works pretty well. I've currently got the controller set to provide a maximum boost pressure of 12.3 pounds. This is a bit under the 12.8 or so maximum for stock so I've got a bit of a cushion for now. I'll continue to monitor things for awhile and maybe open it up just a bit more provided EGTs don't get out of line or the pressure creep up. No smoke to speak of either.

So for the time being I'm happy with the much improved performance the additional boost provides.

Not sure I like the yellow silicone tubing, but anyway here's my installation -



By the way, the fittings on the Tee are way too small for the tubing, so I used a small length of silicone tubing as a shim. With the clamps it's quite secure.
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Restoring Proper Boost Pressure-boost6.jpg  
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  #15  
Old 04-17-2015, 07:30 AM
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All you really need are varying sized vacuum tee's. they are quite reliable unlike Chinese made controllers. The whole idea is that you are bleeding off a bit(or a lot) of the boost signal to the wastegate actuator
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