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Discussion Starter #1
I am considering buying the VDST tool from Technoresearch to help me do tuneups, but I am also considering a powercommander for my ST4s and my 749. Does anyone know if the VDST is of any use if you have a power commander installed?
 

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They really are different animals. The only thing they have in common is the VDSTS software can adjust the fuel trim on your stock ECU. The PCIII can adjust your fuel mixture very precisely at any rpm and throttle opening. The VDSTS software will still work with the Powercommander but you probably would do it in the Powercommander and use the VDSTS for the other functions it can do. Such as resetting your TPS, depending on model of ST4S and for sure on the 749, reset the maintenance reminder light, diagnose any error codes the ECU might throw and perform checks of most other functions performed by your ECU. If you like to tinker get the VDSTS but don't think it's a substitute for the Powercommander UNLESS all you need is a minor fuel adjustment at low speeds and small throttle openings.

Hope this helps.
 

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Thanks! You confirmed what I suspected, but not having seen either one in operation I wasn't sure. I do have very lumpy low speed fueling on the ST4s and it has been that way since I bought it. I got it used with remus pipes and I think the stock ECU. I suspect it is running lean at low throttle settings. I will get the VDST first and see how much I can sort out that way. Pretty much think I will need the power commander too to make it sweet.
 

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I'm not real familiar with the different generations of 4's so make sure it will work with the ECU in your year model.
 

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I do have very lumpy low speed fueling on the ST4s and it has been that way since I bought it. I got it used with remus pipes and I think the stock ECU. I suspect it is running lean at low throttle settings. I will get the VDST first and see how much I can sort out that way. Pretty much think I will need the power commander too to make it sweet.
If your airbox is stock you will not need a Power Commander to achieve excellent fueling. The stock ST4s ECU works well with aftermarket pipes. It's just a matter of tuning it properly.
 

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Discussion Starter #7
Thanks for the input and links! I have a stock airbox, although I read here people having good success with a cutout version. I use the ST4s for touring and reliability is very important to me. If I can tune it using the VDST to a reasonable state that will work for me. The good thing about rough fueling is it has helped me be very smooth with my throttle hand!

My 749 is a track only machine, so it will likely get the power commander and be my "learning experience".
 

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The VDST software is only a tool to assist in tuning. Duckman's note was spot on. To do proper complete tune-ups it helps to also have a balancing tool to check air flow on each throttle body and a gas tester to check the CO mixture. Of course the belts and valves should be adjusted and shimmed properly too.
Bill W.
 

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Thanks Bill. I have done the valves and belts a few times now and that is working fine after I learned to stand on my head with a flashlight in my mouth, a screwdriver in one hand to press on the closing rocker while gently trying a feeler gauge with the other hand to check the clearance on the horizontal exhaust valves...

I have a balancer for the throttle bodies and now with the VDST should be able to adjust the throttles properly. I don't have a CO analyzer and plan to leave that for my next purchase. I am thinking the CO analyzer is the lowest priority tuning tool of the three?
 

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Thanks Bill. I have done the valves and belts a few times now and that is working fine after I learned to stand on my head with a flashlight in my mouth, a screwdriver in one hand to press on the closing rocker while gently trying a feeler gauge with the other hand to check the clearance on the horizontal exhaust valves...

I have a balancer for the throttle bodies and now with the VDST should be able to adjust the throttles properly. I don't have a CO analyzer and plan to leave that for my next purchase. I am thinking the CO analyzer is the lowest priority tuning tool of the three?
Your description of doing the horizontal exhaust valves is spot on. That's pretty much how I felt after the first time or two. Doesn't seem to get any better.

I would say the CO analyzer is the one to leave for last but it's the only way to check for lean versus rich running conditions. Everything I've read says that getting the belts, valves, and balance correct may be the most important items.
Bill W.
 

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I am thinking the CO analyzer is the lowest priority tuning tool of the three?
While the fuel trim is an important adjustment, I have found it is not necessary to have a CO meter to set it. I do it by smell, ear and throttle response.

However, this assumes everything else is properly adjusted. The Throttle Position Sensor (TPS) is the most over-looked adjustment but it has the biggest effect on how your engine runs.
 

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I have found it is not necessary to have a CO meter to set it. I do it by smell
Quite a gift but I respectfully disagree. Especially when attempting to determine proper fueling between cylinders which, as you indicated, is affected by a number of factors. IMO... a CO meter is a very useful addition to the tool box and helps to remove a good deal of guess work.
 

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While the fuel trim is an important adjustment, I have found it is not necessary to have a CO meter to set it. I do it by smell, ear and throttle response. ...

What are you listening for with throttle response? When I'd dial in jetting on my carbed bikes, I'd listen to the revs after a blip: if they hung up, too lean, if they bogged down, too rich. Does EFI with a pressurised fuel rail and electronically controlled injector durations react the same to fuel mixture changes, or are you listening for something different?

I can identify with dialing in fuel mixture using the senses, and can also see the value of having it checked with a snifffer just to be sure.
 

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What are you listening for with throttle response? When I'd dial in jetting on my carbed bikes, I'd listen to the revs after a blip: if they hung up, too lean, if they bogged down, too rich. Does EFI with a pressurised fuel rail and electronically controlled injector durations react the same to fuel mixture changes, or are you listening for something different?
It's similar but different because the fuel trimmer has a little more effect than the idle adjustment screw on a carb (the effect extends further up the rpm/throttle range). I will adjust it too lean (until the idle speed drops) then adjust it too rich (again until the idle speed drops) and then set it 1/3 of the way from the lean setting to the rich setting. Then I will test ride it for off-idle throttle response. I make sure the exhaust smells right and periodically check the plugs for appearance. Any final adjustments are very minor compared to the range mentioned above over which the idle speed begins to change. I always stick to the leanest settings that do not cause any issues or concerns.

Because the fine-tuning of the fuel trimmer is the very last adjustment of any tune-up and because I can easily tweak it at any time I can treat the fine-tuning as a work in progress. This works well as long as the engine is otherwise properly tuned and has no faults (like a bad sensor, poor cam timing or valve clearances, etc.). If the cylinders are not balanced in breathing (whether the imbalance is caused by bad throttle synch or other causes) then an overly rich trim setting can mask the roughness so this is something that one needs to remain aware of.

Even if I had an exhaust gas analyzer I would still check the settings on either side of whatever target percentage I chose. That is because the affordable analyzers are not that precise and because no target fuel trim setting is necessarily the best overall setting.
 
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