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Setup is:


Megasquirt 2 pcb 3.57





I found out I had the wrong settings, so changed those to the recommended 19.5hz and 20ms dwell. The plumbing is as shown on the link as well for the two port waste gate.


According to what I am reading the wiring is indifferent? So it should function to correlate to increased duty cycle value = increased boost. Or is this something that has to be checked and the inversion applied via the output polarity? 


The problem is trying to set my duty table I'm finding all sorts of examples that contradict each other.


The game plan is to set the over boost limit quite low at 15lbs to make sure even if I set it incorrectly I don't over boost.


My current table looks something like this:


I found some guides online suggesting either starting off at 100% and dialing down the areas that causes over boost limit to engage, and another that said to start off at 0 and add 5% until you hit your limit. Kind of my hybrid attempt at the moment.


Any thoughts? Or am I heading straight into failure?




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That was another question. Fuel cut vs spark cut vs both.


From what I gathered, fuel cut seems to be the way to go, fuel shuts off the fuel immediately, so even if there is some residual fuel it won't even ignite as the mixture is too lean. Where as spark cut would allow excess fuel into the turbo manifold and could cause damage to the turbine wheel if it ignites in there.


Found a decent guide I think I'm going to follow. 


1. Basically find your base line by disabling boost control. 

2. Set all values to 100% and enable overboost protection at slightly under desired boost. 

3. Find a long stretch of road ideally slightly uphill for maximum load

4a. If boost cut engages note the RPM it engages, set points 200 rpm on either side and adjust so the boost cut does not engage. Repeat through out the range.

4b. If boost cut does not engage, wipe out the table and set all values to 0%, try again and note the RPM boost cut engages and set poitns 200 rpm on either side and adjust so boost cut does not engage. Repeat through out the range.

5. Increase boost cut by a slight amount to account for maximum load conditions.

Edited by seattlejester
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Very thoughtful guide!


I went the easy way out and took my car to ForceFed Performance in Abbotsford BC. They did my dyno tuning and overboost protection programming.  They are the JZ/Rotary specialist for the NW in my opinion... I was very pleased with the numbers they produced with original Coil packs, injectors and turbo...

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  • 6 months later...

Well interesting problem has come up.


I fixed some things and now I am overboosting again.


Following the guide I turned down the boost duty slowly, only I am finding that megasquirt is not switching the duty cycle.


I monitored the boost duty cycle as a gauge, I even lowered the throttle to 30%. At 4k rpm hitting at 50% throttle I should squarely be in the lower boost duty portion of the table, but it is keeping the boost duty % at 100%. It doesn't seem to want to shift at all. Any thoughts? It definitely is keeping the waste gate closed, but now it seems it is keeping it forceful closed without reducing pressure at my target value.

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  • 1 month later...

Well some updates regarding the issue.


Tested the solenoid and I could hear it clicking via test mode on the pulse setting, I am not hearing it click on with the on button.


I changed the table, setting the value to 35% everywhere to see if I could get the duty cycle to shift. 


Heard the boost solenoid while the car was running, duty cycle at 35%, everything good. Took the car out and it made about 7-10lbs under load with partial throttle. Picked up a friend shot some footage, got back turned the car back on and couldn't even start getting into it as it hit 20+lbs at 4k rpm under partial load.


So the boost control was working periodically? Before allotting the oddness to writing problems with using a mac I went back and ran a simple test of repeated on/off cycles



It seems sometimes the solenoid just doesn't trigger? I can hear a high pitched whine when it isn't audibly clicking. Is this just a bad solenoid? I've used these in other applications, but usually when a solenoid dies, it just ceases to function. Am I just catching it on the tail end of going out? 

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  • 4 months later...

Old thread here, but I thought I'd mention a trick that might extend the life of the solenoid. I suggest that you add or change the throttle axis to include a low TPS position at which the duty cycle is 0. That way, the solenoid won't always be needlessly energized while cruising, or even while cranking to start. The solenoid doesn't like being constantly energized. I think the max recommended duty cycle is 95%.

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I think the boost table has a start point that you set in the 100+ kPa range so at times when you are off boost or idling the solenoid does not actuate.


The solenoid never had a chance in this situation as I did not plug a bottom wastegate port. 


I did take it apart and grease it, but after this I was not sure if I wanted to deal with it sticking as such, so I switched to a manual spring and ball type. I'm pretty happy with it for the time being.

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Haa Haa . Just had a big argument on Guild Of EFI Tuners on why a simple MBC can sometimes be the easiest solution to Boost control on a DD. Big arguments that B&S MBC is archaic, didn't have Boost taper, Boost per gear, Traction management etc. Millennials couldn't grasp the fact that not everything has to be electronic. 


OP was fighting a Boost curve that wouldn't stay linear with his MS2 Boost management ( MS3 Boost management is much more sophisticated than MS2 ) I suggested a simple B&S MBC as that would be more than sufficient for HIS needs. Man you should have heard the whining and bitching from the Internet coaches.  :banghead:

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I can see if you put time into it you can get some cool results like have a turbo act like a super charger with gradual build of power, or boost by gear and such.


Alternatively you could run a MBC and not mash the pedal to the floor everywhere you go. 


Interesting thing when I talked about it with, some people were still thinking the bleed type valves and were saying I should switch. Kind of shocks people when I tell them I went from an EBC to a MBC. Granted as stated my EBC never had a chance to work.


I'm getting pretty close to bugging you. I want to do the trans swap and the power steering and maybe figure out a baffle or make a surge tank. Make sure all my ducks are in a row and all that.

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