Boost issues??

[Jonota]

Trying to figure this beast out, for more enjoyment, and to have any bugs worked out before the wife has it for a month.

To wit, I have been monitoring what I can, which includes boost. I have posted previously about a percieved issue not making appropriate boost, but as it was in a somewhat un-related thread it didn't rate reply. I understand to expect ~15.6psig (as stated in numerous places, magazines, etc). When I first purchased the car, 10-11psig is the maximum I would ever see. This continued until a few days ago, had some heavy rains on the way home, and the boost gauge went crazy erratic.

Figuring I got some water on the admittedly poorly wired gauge connections (intend to fix tomorrow), I opened hood and traced around to find it. Ended up "jiggling" most everything, but nothing stood out as a problem. When I got back in the car, I discovered several changes:

#1) Idle, cruising vacuum. Previously 10in hg was about as low as the vacuum would get. I didn't think much of this, as a mini that I worked on showed this consistently, as have other 4 cyl that I have played with. Now however, it shows 20-25 in hg at idle, and slightly more on deceleration.

#2) Boost "shows" up. In 1st and 2nd, usually hit around 13psig, and 3rd/4th usually ALMOST make it 15psig. I briefly skimmed the Cobb articles on the boost control system, but would need to see it in action to truly understand. Does the computer calculate a torque product, and use it to limit boost?

Jon

 

[Blendercloud]

Many users report that they are not making as much boost as Mazda advertises. Here may be a couple of reasons why you're experiencing this. Any one or all of these three could be affecting you:
1. Your boost gauge can and may be wrong. I've had the best luck monitoring boost via a laptop computer. Gauges are often not as accurate as the manufacturers lead us to believe, particularly with regard to boost.
2. The atmosphere around you can affect how the gauge reads. Forzda is an excellent person to explain how atmosphere affects your boost gauge.
3. Your stock bypass valve may be coming off the seat/flange under higher boost values. It is plastic. Users often find that because of the material, it tends to bend/flex off the seat easily.

With regard to your #1) concern, do you feel a difference with the car? Can you describe that difference if there is one?

As for your second #2) concern, the boost table the ECU uses is dependant upon which gear you currently have engaged. First and second gears share a boost table. Third and fourth gears both have their own, separate tables. Fifth and sixth gears share a boost table together.

You will produce lower boost values in first and second than you would in other gears. This is important because it will keep you from ripping the PTO apart and also snapping axles. It also helps with traction in the MS3, though us MS6'ers don't have to worry so much. You should be producing about 14psig in third. In fourth you will be at 15psig or so, and in fifth and sixth you will be making full boost (15.6psig).

 

[Jonota]

Thanks for the reply Blender!

The boost gauge working correctly is exactly what I'm questioning. Either it was working correctly before when it was only showing 10 in hg at idle, and 10 psig at boost; or it is working correctly NOW at 20 in hg idle, and 13-15psig boost; OR it's STILL not working correctly....

There isn't a discernable difference in performance from before.... although I haven't driven it much since the change (have been driving the Subaru the past few days since it's full of gas).

I understand atmosphere's effects on gauges, and don't really think that's an issue. My current questioning of the vacuum shown on the gauge comes from my understanding: at decel, the vacuum shows almost 29in hg: almost perfect vacuum. Something I've never seen in a vehicle before.

Jon

 

[FORZDA 1]

Thanks for the reply Blender!

The boost gauge working correctly is exactly what I'm questioning. Either it was working correctly before when it was only showing 10 in hg at idle, and 10 psig at boost; or it is working correctly NOW at 20 in hg idle, and 13-15psig boost; OR it's STILL not working correctly....

There isn't a discernable difference in performance from before.... although I haven't driven it much since the change (have been driving the Subaru the past few days since it's full of gas).

I understand atmosphere's effects on gauges, and don't really think that's an issue. My current questioning of the vacuum shown on the gauge comes from my understanding: at decel, the vacuum shows almost 29in hg: almost perfect vacuum. Something I've never seen in a vehicle before.

Jon

Sounds like you have a faulty boost/vac gauge, except that the "new" values are closer to normal. I prefer the old-fashioned mechanical gauges for accuracy. Depending on your local elevation, your idle vac should be right around 20in +/- ~2in and max boost will run anywhere from 9 to 16 psi, depending on gear, load, throttle plate(not necessarily the same as pedal) position.

You are correct that the ECU targets torque, not a boost level for load. The boost has max values it is allowed to reach, but the value seen may be well below the max if the ECU targeted load is reached.

For reference, I'm ~100ft above sea level and my idle is ~21.5 in.

If you want full control over the ECU tuning, you can get the AP from Cobb.

 

[Blendercloud]

I say don't question a good thing! Haha.

I think if you check out the wiring on that gauge, you may find that it was previously malfunctioning or reading incorrectly. I say this considering you haven't really experienced a change in the way the car performs or feels.

 

[Jonota]

I'm certain that it's shoddy wiring.... the lone power wire for the sensor box runs to the underhood fuse center, and is jimmied under a fuse with an open ended wiring connector. I will be fixing that later today. I myself also prefer the mechanical gauges, but what I have is what I will go with for now. The "other" 2 gauges aren't even hooked up to their inputs..... not that I need them (a/f narrow and oil temp)

Forzda, it was your input I was waiting for, as you seem to have quite a bit of experience with the ECU. I will eventually be getting an AP, but for the time being I'm more interested in ensuring the car is all good to go for my wife to drive for a month without me being able to help or fix any issues. As the boost varied, I wanted to be sure what I was seeing was good. I think the gauge is fairly accurate at this point.

 

[SMOKEYS36SHOP]

jonota i have a prosport boost gauge. i just recently got the cobb ap and my boost gauge is about 1-2 pounds higher sometimes that what the cobb ap says it is. also i want to add that another reason on why you might not be holding boost so high is due to your stock bypass valve.i know for a fact , which i have said before, that my stock bpv hold 2-3 pounds less boost vs my aftermarket one. but some other people will swear that the stock one works for them...but in my case it didnt and have proved it many times to myself lol. maybe look into an aftermarket bpv would be in your best interest if you havent already gotten one!

 

[FORZDA 1]

I'm certain that it's shoddy wiring.... the lone power wire for the sensor box runs to the underhood fuse center, and is jimmied under a fuse with an open ended wiring connector. I will be fixing that later today. I myself also prefer the mechanical gauges, but what I have is what I will go with for now. The "other" 2 gauges aren't even hooked up to their inputs..... not that I need them (a/f narrow and oil temp)

Forzda, it was your input I was waiting for, as you seem to have quite a bit of experience with the ECU. I will eventually be getting an AP, but for the time being I'm more interested in ensuring the car is all good to go for my wife to drive for a month without me being able to help or fix any issues. As the boost varied, I wanted to be sure what I was seeing was good. I think the gauge is fairly accurate at this point.

Yeah, I think all is good for now, so don't sorry about it. Just tell your wife to not worry about the boost gauge if the car is running fine and has power. You can sort out the gauge wiring later.