AP Boost and Gauge Boost

[SallySpeed3]

Hey guys. Now that I have an AP, I'm monitoring things alot more. Even though I have a prosport boost gauge I decided to monitor boost as well with the AP on my way home today. AP states that I'm boosting 18.4 lbs but the gauge only goes to about 16. I don't think it's an actual boost/turbo leak cause I certainly don't feel a lack of power. I assume it's some sort of vacuum line leak but I've checked the line and it looks good to me. Any way to tell for sure?

 

[Darth Vader]

Gauges can indicate slow sometimes and...if they are electric, are prone to error from low resolution senders and small circuit malfunctions. The AP is also drawing its conclusion inferentially, via the ECU, from the MAP sensor outputs. Pick your poison, which do you think is more accurate? I like a dumb, manual, analog backup, like a mechanical boost gauge.

 

[AutoEuphoria]

Yeah, I would just say it's error in the gauge. The AP is displaying what the actual sensor is seeing, so I would tend to trust that over a gauge.

 

[SallySpeed3]

Thanks for the replies. I thought it was an error was well, but glad that others agree. Unfortunately, my gauge has turned into more eye candy now then anything. I at first got it for a real purpose, but now, oh well. At least it looks cool.

 

[AutoEuphoria]

Well, it can be used as an "idiot gauge" kind of thing. If it's not building at all, it's bad. If the vacuum is at 0 at idle, you have a leak somewhere. If it's going above where you want it to, you know you should back off.

They do look cool though LOL

 

[MSMS3]

So, an electronic sesnor of unknown tolerances, is sending a generated signal, converting one unit of measure (pressure) to another (electric) to the ECU which is making a computer calculation from that signal, then sending it to the AP's onboard computer that is making its own calculation and display of that electronic data, and we are to assume that the combined tolerances, resolutions and hardware/software handling of this data is always spot on accurate?

Has anyone ever set two electronic thermometers or barometers next to each other and noticed whether they read the same? Chances are quite good that they do not. They will be close but not identical.

Specifically, electronic sensors and devices are not inherently more accurate than mechanical devices where direct pressure measurements are being made.

I'm not saying that the AP reading is false. I'm not saying that the mechanical boost gauge is false. That they are different may well be a reflection of small inaccuracies, tolerances, resolution capabilities and calibration in both, one or the other. We don't know.

I agree with Darth. For me, I trust digital and electronic measurements for many things, but when it comes to measuring a purely mechanical phenomenon, pressure or vacuum, I think analog direct pressure measurement is to be preferred and to be trusted as the primary means of measurement. The advantage AP or DH has is in the ability to data log, which can show relative changes over time in a way that can be saved and studied in relationship to each other. But it does not mean that the numbers are more accurate in an absolute sense.

 

[Dano2010]

lets not forget that our MAP is only "fairly" accurate to around 21 PSI, not that this matters to many between 16-19PSI. Just another example of how everything is reletive and you can't expect two different monitoring devices to have the same reading. FYI, My Prosport typically measures about 1.5 PSI HIGHER than My AP. I think I read somewhere on here that a guy looked up our MAP sensor part number [bosch] and found a direct replacement MAP/Tmp sensor that goes to 3.5 bar. Better than tapping an AEM probe into your intake. Course you would have to re-cal your scale in ATR but maybe it would be more accurate???

 

[spoolin_05]

have you calibrated your MAF?

 

[SallySpeed3]

no i haven't. Just got ATR so I'm slowly getting informed on doing all of that stuff

 

[AutoEuphoria]

Let's just put it this way...a boost gauge measures boost through the vacuum lines. The DashHawk or AP are calculating boost based on actual input from sensors that is the same input the ECU is working from. So while neither may be 100% accurate, I'd say the numbers from the AP/DH are probably more relevant.

 

[SallySpeed3]

Thanks for all the replies guys. It still bothers me that my gauge isn't accurate, but oh well. It's better that than having more serious wrong with my turbo so no big deal

 

[MSMS3]

I think the gauge is accurate and have no reason to believe the direct pressure through the vacuum line to its diaphram is less accurate that the electronic conversion from pressure to electronic signal made by the MAP sensor.

 

[Dano2010]

Agreed not less accurate just different. If you want to be more scientific about it get three different inputs gauge/DH/AP and average the results. If you care (lol2)

Personally I go off the AP [or DH if thats what you are running] because they are getting their boost readings from the ECU which is making all the decissions on load targets and limit tables, period.

The AP/DH is for tuning and the boost guage is bling. IMHO

 

[MSMS3]

I guess I've been blinging since the eighties now on my fifth turbo car - three Saabs and a Volvo before this. All had . . mechanical boost guages reading direct vacuum/boost directly from a vacuum line connected to the diaphram inside the gauge. Wow, I didn't even know my stodgy Saabs and Volvos were so blingy!

And all those earlier NA cars, particularly my carbureted muscle cars were tuned with mechanical vacuum gauges. Wow! I think that was probably all we had back then in the dark ages of the late 60's and into the 70's. What a POS those mechanical vacuum gauges must have been. Must have been loosing a lot of performance by not having some kind of maybe accurate digital sensor to interpret the true vacuum by turning it into an electrical impulse that then tried to estimate what the vacuum was. I never thought I would be so wrong to actually read the vacuum by a device that acually measure pressure directly.

All humor aside, I can see that if someone is going to be tuning the ECU then it makes sense to tune with the boost input the tuning device is reading from the maybe accurate, maybe not accurate MAP sensor. At least it would be consistent with what the ECU was "seeing." That is a real benefit for changing mapping of the ECU's various targets that are being adjusted.

I'm not changing the ECU so I just want to know what the real, directly measured, boost and vacuum readings are, but that's just old fashioned/blingy me. Is old fashioned/blingy an oxymoron?

Anyway, lets measure boost by some means we feel comfortable with. The differences in method are far less important than modding blind and going zoom, zoom, boom.

 

[Dano2010]

Breaking news!!

First off, I will assume you were kidding and this is all fun, but let the drama begin!

You might want to take a deep breath…seriously! Did my other post about the Forge sound get you worked up?? I don’t see how… maybe it’s just your personality or your having a bad start to the year. Now you’re over here taking offence at me calling a boost gauge bling? Really?? Please keep in mind that I called it that under the context of Sally trying to decide which device to trust with regard to tuning with the AP. If your car is controlled by an ECU, I would think it prudent to rely upon the sensors it uses to make corrections, in this example.

No matter what you drove in the 70’s, we live in 2010 [although I do want that car that can actually fly as we were promised by Hollywood] and back then a mechanical gauge was all you had. I might even go as far as to say that it is more accurate and one would show the same vac/boost on every engine you connect it to. What’s important here, is that a tuning question was asked with regard to two different devices registering different numbers, and which one to trust. I answered with a bit of humor then you unjustifiably attacked my post.

Now back to our regularly scheduled thread…..

 

[MSMS3]

I believe we will just have to disagree on a few points and leave it at that. ECU tuning should be done with the boost levels shown by the tuning hardware and software connected to the OBDII port. I think we agreed on that.

For absolute accuracy where it is desired, I continue to hold my ground that in some 40 years of modding and racing in every decade you simply cannot beat a diaphragm type mechanical guage to measure pressure accurately.

Once tuning is done on AP, Standback, etc., I would still feel far more comfortable with a mechanical vacuum/boost gauge that was telling me that (1) I had a reliable -22 vacuum at idle (meaning no vacuum leaks) and (2) showing me absolute boost under pressure. If there were a variance between that gauge and my AP or DH and the mechanical guage was showing either a leak or showing boost creep, I'd be thankful for having that gauge. But that's just me.

I've said these things as objectively as I know how without engaging in any personalities while trying to inject a little humor into the debate. I don't claim to know more than anyone else, but I do try to base any opinions I state here on whatever accumulated experience I have obtained and whatever data I can get from objective sources.

Disagreement should not be construed as a reflection on someone's personality, or the type of day that person is supposedly having or being worked up. It's just that - honest disagreement. I hope I've made my point and that it was done with civility, even if others disagree. Sorry if I have offended anyone. I'll post no further on this thread as my points are not being received as constructive.

 

[Dano2010]

Well actually I believe we agree on both technical points. It was the over use of sarcasm in your responce that I took issue with.

I certainly encourage you to continue to assist this community with your technical knowledge.

 

[Darth Vader]

Here's the problem with the "what the ECU sees" argument: You can trick the ECU into seeing whatever you want with a Standback or similar, right? Well, from that you can see that there's no guarantee that what the ECU sees is actual reality, it's just what the sensor is indicating reality is. A gauge measuring actual manifold pressure is what you should tune to. That's what the ENGINE sees.

Faith in any electronic sensor's unfailing accuracy is unfounded. Most of the sensors on any road car are not optimised around a performance calibration. They are optimised for meeting emissions regulations and maintaining good driveability; goals that are not always compatible with high performance.

No offense intended, just a POV on the subject.

 

[Dano2010]

Good insight and I certainly agree with both you and MSMS3 from a philosophical standpoint covering the inaccuracies of modern engine management sensors. If it were a perfect world we would replace all of Mazdas sensors and maybe even ECU but practically speaking this isnt possible for the majority of MZR owners nor necessary.

If you are not tuning toward the bleeding edge I think the sensors we have available should do the trick. I think we have far exceeded the spirit of the OP,s thread and in fact this topic could be an entire thread unto itself but I would rather spend my time trying to better understand our ECU and assist the community as a whole where we can.

 

[SallySpeed3]

I think we have far exceeded the spirit of the OP,s threadQUOTE]

Haha, I was thinking the same thing although I do appreciate all the intelligible responses I've received. After reading one of the previous posts, I checked to see if my gauge reads a steady -22 at idle, and it does. So either I'm just not getting my eyes over to the gauge at the right time to see a proper reading, or somewhere along the way Im losing about 2 lbs of boost. Either way, I'll recheck and retighten all hoses and clamps and see what happens.