mechanics of boost control ..

[mooserov]

I was on the highway today and paid attention to my boost gauge. at 75 mph I was running 10 to 12 inches of vacuum. as I said before, your rpm's are high enough to spool the turbo as soon as you hit the gas. In fact, a hill or bridge will put you slightly into the positive in cruise control at this speed, but only for a second or two. On flat ground, you are positively NOT in boost while cruising.
Thanks for the correction Matsuda, I was trying to explain stoich without getting too technical.

 

[matsuda]

I'm pretty sure I know which connector it is, visable straight down from the top, between the battery?ECU box and the engine. From what I've been able to read, 12 volts closes the valve.

Actually after kicking it around a bit I wonder if a better approach would be to trick the ECU into thinking it's in first or second gear, with a rocker switch ot actuate it in the frontside of the shifter knob, so you can flip it instantly.

I'll be looking into that approach as well ..

The valve is normally closed (with no power applied).
When the valve is closed, maximum pressure is applied to the wastegate actuator which results in minimum boost pressure.

BTW, you can't trick the ECU about 1st or 2nd gear.
The ECU determines gear selection based on vehicle speed vs. engine RPM.
The two switches on the transmission are for neutral and reverse.

 

[enganear]

The valve is normally closed (with no power applied).
When the valve is closed, maximum pressure is applied to the wastegate actuator which results in minimum boost pressure.

BTW, you can't trick the ECU about 1st or 2nd gear.
The ECU determines gear selection based on vehicle speed vs. engine RPM.
The two switches on the transmission are for neutral and reverse.

Thanks Matsuda, this is very interesting. It sounds like you could take control of the valve away from the ECU. If the ECU verifies continuity in this circuit, It could be fooled with a resistor.

No power to the valve - minimum boost in any gear.
Always power to the valve - full boost in EVERY gear.

Do I have your attention now? (drinks)
-enganear

 

[Breezy]

The valve is normally closed (with no power applied).
When the valve is closed, maximum pressure is applied to the wastegate actuator which results in minimum boost pressure.

BTW, you can't trick the ECU about 1st or 2nd gear.
The ECU determines gear selection based on vehicle speed vs. engine RPM.
The two switches on the transmission are for neutral and reverse.

Thanks for that Matsuda. What I guess I need is to wire a switch to the valve feeding it 12 volts whenever I want. I'll see how that works out. I'm envisioning a rocker switch recessed into the front of the shift knob that can drop the boost valve at cruise.

It's funny .. I've read a lot of stuff about ECU flashes, AcessPorts, Cobb, etc, and it seems the Mazda tune must be pretty damn good. Every once in a while someone pops up with a big dyno number but no product is ever available. And while some want to tune themselves .. well good luck on that .. I don't have endless amounts of dyno time, etc to shake out another 4 horsepower.

 

[ericrapp]

My attention has been here the whole time good sir ( eng ) and breezy I agree with reports being a bit inconsistent. And also thank you for the good luck wishes

 

[matsuda]

Thanks Matsuda, this is very interesting. It sounds like you could take control of the valve away from the ECU. If the ECU verifies continuity in this circuit, It could be fooled with a resistor.

No power to the valve - minimum boost in any gear.
Always power to the valve - full boost in EVERY gear.

Do I have your attention now? (drinks)
-enganear

Yes. You have my full attention!

The ECU uses PWM to control the valve opening, using the MAP sensor for feedback. If the valve were wide open, it would result in overboost (not enough pressure to the wastegate). The valve is typically open at around 50% at full boost (15.6 PSI).

If the valve is electrically disconnected, the ECU is aware of it but there isn't any adverse effect (and no CEL).

 

[matsuda]

Thanks for that Matsuda. What I guess I need is to wire a switch to the valve feeding it 12 volts whenever I want. I'll see how that works out. I'm envisioning a rocker switch recessed into the front of the shift knob that can drop the boost valve at cruise.

It's funny .. I've read a lot of stuff about ECU flashes, AcessPorts, Cobb, etc, and it seems the Mazda tune must be pretty damn good. Every once in a while someone pops up with a big dyno number but no product is ever available. And while some want to tune themselves .. well good luck on that .. I don't have endless amounts of dyno time, etc to shake out another 4 horsepower.

Just for fun, you might try pulling the connector and taking your car for a drive. Your car will be instantly transformed into the "MS3 lite".

 

[enganear]

Yes. You have my full attention!

The ECU uses PWM to control the valve opening, using the MAP sensor for feedback. If the valve were wide open, it would result in overboost (not enough pressure to the wastegate). The valve is typically open at around 50% at full boost (15.6 PSI).

If the valve is electrically disconnected, the ECU is aware of it but there isn't any adverse effect (and no CEL).

Thanks Matsuda-sensei, great information! I see applying 12V would be a bad idea, like no wastegate at all.

Those who wish to limit boost for reasons of mileage or valet parking could modify the circuit by:

1. Switch a resistor (or forward diode) into this circuit to limit boost for mileage concerns.
2. Mount a switch that opens the circuit for valet parking, etc.

It may even be possible to add a DC current level to the PWM signal to provide bias to the wastegate for higher boost levels from the same ECU output. I need to get the oscilloscope out and see what is really going on.
-enganear

 

[matsuda]

It may even be possible to add a DC current level to the PWM signal to provide bias to the wastegate for higher boost levels from the same ECU output. I need to get the oscilloscope out and see what is really going on.
-enganear

Well...

Keep in mind that the boost control is esentially a closed loop system with the MAF sensor as the input and the wastegate solenoid control valve as the output. If the ECU sees boost pressures that are higher than expected, it will compensate by lowering the duty cycle of the PWM signal.

 

[dkswim]

sub

 

[ericrapp]

Are we done? surely there must be more to discuss about or pretty close to it. Who is going to guinea pig it. Not me I don't have the self discipline to drive nicely.

 

[Breezy]

OK, I've done some testing, using instant mpg in the computer and cruising the same piece of road which had a consistent, very mild rise for a long time so the instant mpg reading would stabilize for maybe a quarter to a half mile. Keep in mind that these readings may not be your result because the road is not entirely flat and there is the possible issue of cruise control variations.
70 mph at 29.1 mpg
75 mph at 26.8 mpg
80 mph at 26.1 mpg
Those were consistent baselines. Then I disconnected the boost control module and was able to only test one speed, 80 mph, which presumably would make the biggest difference.
80 mph at 27.1 mpg

So the difference in cruise mode was only 1 mpg, exactly. The change was a bit disappointing to say the least. Is it worth it to gain 1 mpg at 80, and presumably less at lower speeds? Not really IMO. However looking at it another way, that's about 7 additional mph for the same cruise mileage. You can see there a pretty sudden drop in mileage between 70 and 75 mph.

I have left the unit disconnected for the time being to kind of feel out the difference. The car is still pretty quick, and the powerband seems a bit smoother. I'll be comparing an entire tank of gas which will give me a rough comparision to see if it affects around town driving much.

My driving habits are such that the average speed recorded in the computer is 30 mph. I believe that resets for every tank of gas but I'm not sure. In any case you can see that probably half my miles are "in town" stop and go. I do climb heavily into the throttle thru 2nd and thru 3rd maybe three or four times in a tank. The rest of the time I try to keep the revs at 3 grand or below for mileage reasons. We'll see what happens next ..

 

[Breezy]

It's been almost a week since I simply unplugged the boost control unit and so far that driveability has been quite good and the mileage appears to have increased quite a bit. I haven't used an entire tank yet, but I was checking this afternoon and I have a little over 3/8 tank left and have put 213 miles on the tank so far.

We'll have to see how it bares out but it's possible that the mileage could approach 27 mpg or so, which is about 4 mpg more than I have gotten so far. And on this tank I've had to run AC and been caught in a few traffic jams too. Considering those issues, it appears that the mileage has improved a substantial amount, and the car is still too fast for daily traffic.

Keep in mind this is a new car with only 1500 miles so it's still in break in, and mileage should increase a little as break in progresses.

 

[Breezy]

Well it was fill up time today and the verdict is in .. 24.86 mpg, which is a little more than 2 mpg better than the previous tank. I drove both of these tanks about the same, trying to be responsible with fuel but not sacrificing the speeds I drive at. Basically just short shifting (3k and under most of the time).

I did a few stints at aggressive driving in both tanks too. 3rd gear is just too much fun to ignore providing you can find a place to do it these days.

So there you have it .. I wouldn't race anyone with the boost control disconnected, but for day to day driving it increases the mileage nearly 10%. Oh and it's still very very fast to drive.

 

[Breezy]

It's been a while since I reported on this this, and yes, my boost control is still disconnected. Without changing my driving patterns I'm now getting right at 27 mpg. In general I'm shifting at 3500 to second and 3000 on other shifts, aside from opportunities to have a little fun. My highway cruise speed is around 74 to 78 mph. So I'm getting 325 miles to a tank now, refilling at about a 1/8th of a tank. I would have to say disconnecting the boost control is worth 10% or more in fuel savings. While I'm still using premium, I believe I could go with lesser octanes given that boost is restricted now to about 7-9 psi. BTW, last night I paid 4.02 for premium and it's not going to get any cheaper soon.

 

[ShadowSolution]

It's been a while since I reported on this this, and yes, my boost control is still disconnected. Without changing my driving patterns I'm now getting right at 27 mpg. In general I'm shifting at 3500 to second and 3000 on other shifts, aside from opportunities to have a little fun. My highway cruise speed is around 74 to 78 mph. So I'm getting 325 miles to a tank now, refilling at about a 1/8th of a tank. I would have to say disconnecting the boost control is worth 10% or more in fuel savings. While I'm still using premium, I believe I could go with lesser octanes given that boost is restricted now to about 7-9 psi. BTW, last night I paid 4.02 for premium and it's not going to get any cheaper soon.

HA!... dont complain dude i just filled up with shell premium at 4.53 a gallon!
The northwest brings about some of the highest prices in the united states unfortunately :/

 

[smakdown61]

Actually anything over 70 mph and you're in the boost. And just take a drive and set your computer to instant MPG. Very little throttle at 70 drops mileage substantially. That's what I'm looking to fix. I want to cruise at low boost to save mileage.

I'm surprised no one has pointed this out but that is completely wrong. Using my dashhawk, I can be rolling a 75mph in 6th gear on a flat surface at be at about 10 inches of vacuum (and thats using light throttle to maintain the speed). The trip computers instant mpg and average mpg is so far off its not even funny. I can get 30mpg on the highway by rolling at 65 mph.

 

[ericrapp]

yep,

 

[jeffreyeye]

(boom07) I'm still scratching my head in disbelief.

I just got back from a 2000 mile round trip haul from Austin to Moab for some canyoning. The trip up from Texas saw averages in line with the numbers posted here. The trip back, however, has me dumbfounded.

Running 70-75 on open highway with negligible net elevation change, on three different fill-ups, I tracked 38-42 MPG. What makes this all so weird, or even weirder, is that my home state octane is 97 and Utah/Arizona pushed 95 octane into my car.

Any takers on that one? Yeah. I filled the same way every time. A/C was on the whole way. I quadruple checked my math, and came up with consistent results. Now back in Texas, I'm again checking in at 30-32 MPG Hwy.

Maybe I should just move to Utah. It is tempting, for more reasons than this one.

 

[Aaron@JSC]

Actually anything over 70 mph and you're in the boost.

absolutely untrue. I cruise at 75-85 on the highway everyday and I sit there at 10-15in/hg in vacuum on my 60mm defi.

The on-board trip computer on the MS3 is not accurate at all, so anyone serious about this project should find a better way to measure actual mileage. My on board computer says I have 0 miles left to drive on my tank when, in reality, I have at least 5-10.

I will never understand the complaints about gas when you drive a turbocharged performance car.