gio64

iTrader: (1)

Hi, I might have asked this question before, but I did not get a good answer.

I have an AEM Tru Boost controller installed and I also have my old mechanical boost gauge sitting right beside it. They are both fed by the same line which has a "T" that splits the line in 2.

The boost reading is different between the mechanical and the AEM.
The Boost Gauge is hitting 10 very quickly and seems to sit there pretty much dead on, maybe leaning slightly past the 10 mark, but with the hand still on the mark.
The AEM is not hitting 9. I have to have some more time to get more accurate readings, however I had already checked this before and it had the same behaviour. They were about 1 psi off or so between each other.

The vacuum is as well (mechanical says 20 at idle AEM says 18), however, I believe somebody had said that they read vacuum on different units?

Point is, the boost reading is still off.

I just got the car back from changing the twins. I don't have a lot of time to drive now as there is salt on the roads here and I simply drove home, washed meticulously and parked in the garage.

Does anyone have any idea why this is happening?
Also, which gauge should I trust?

Thank you,
Giovanni

Reno_NVFD

iTrader: (2)

Is there a difference in vacuum line length? What happens if you switch the two vacuum lines?

jayscoobs

iTrader: (8)

I would test each gauge with a mityvac to see which one is actually off. And if it happens to be the AEM maybe the sensor is faulty.

XLR8

iTrader: (52)

I have found that even quality sensors can be off from each other. I have had a Defi gauge, Electronic boost controller, and ECU all read differently.

What Jayscoobs mentioned is a great way to bench test for accuracy.

Ultimately, the most important reading is what corresponds from your MAP. Which is why I would always adjust and monitor boost from what the ECU is seeing.

misterstyx69

iTrader: (142)

I got some quality stuff too monitoring my boost(defi) and controlling it.Greddy Spec2)
They do not read the same either,but I trust what the Haltech Ps1000 Ecu reads.

gio64

iTrader: (1)

Hi guys, and thank you for the suggestions.

A couple of answers/things I just remembered and I had forgotten to mention yesterday:

1) I had installed the boost gauge first and right after I bought the car (6/7 years ago). At the time, with original turbos and everything dead stock, the mechanical gauge (located in the exact same spot it is now and the pickup of the vacuum/pressure hose being the same) showed a perfect 10/8/10 pattern as per stock specs.

2) I did some slight mods (k&N, even cheaper bastard intake) and the car started to boost past 10, so for a short while, I used my right foot as a boost controller, then decided to buy an electronic one.

3) At the time of installation, the AEM came with a hard plastic and thin hose, so I ran that one in the place of the original rubber vacuum line I had installed. I went from rubber (at the UIM), to the plastic one around the firewall area, all the way to the back of the gauges, where I put a "T" in and got to the boost gauge with one and the AEM Tru boost with the other. The lines coming out of the T are pretty much the same, I did not measure them, but there should be no significant difference between them.

To recap, there is no reason for me not to trust the mechanical gauge reading, since it showed what it was supposed to, when the car was stock. Having said that, since I changed most of the line going to it, maybe that could affect its reading? I would doubt that, If anything, different lines would only make the gauge react more/less quickly than it did before, but it should still see the pressure/vacuum it did see before.

I do not have a mighty vac, I will see if the auto teacher at the school I teach at has one. Hopefully he does, so I can pressurize the line and look at what I'm getting.


XLR8, pardon my ignorance -I did not mention that I'm by no means an expert, I considered myself moderately able when it comes to cars and RX-7 in particular- but how do I get the MAP reading? The car is on a stock ECU.

Thank you again, I appreciate all of your input.
Giovanni

XLR8

iTrader: (52)

No worries bro.

There in lies the problem. With a stock ECU, there is no way to see the MAP sensors output without monitoring its voltage. This of course is not suggested as they dont like to share load.

Most all aftermarket ECU's allow this function. The Power FC is particularly handy as it can display all of the ECU based sensor outputs as well as most accessories on the Power Commander handheld. Just mount it in an easily viewable location.

I gave up on many of my gauges awhile ago. EGT's and wideband are all I use from aftermarket.

Depending on your long term power goals, the PFC is a great solution for monitoring and control.

gio64

iTrader: (1)

Thanks again,
I had the opportunity of either getting a Power FC (with base map already in) or PFS intercooler. I decided to go with the intercooler, because I thought I'd rather cool things down (I put a Koyo in as well) first, then start messing around with electronics to get more power. Matter of fact -like I said- I had installed the Tru Boost with the purpose of keeping the boost where it is supposed to be, as opposed to increasing it.

I appreciate the help, I will certainly look into a Power FC as one of the next purchases. I will have to figure out where I want the controller to be, I have to tell you, I don't like seeing it in the car... But that's just a detail.

Giovanni

sbnrx7

iTrader: (4)

Boost is measured in pounds per square inch (PSI), vacuum is measured in inches of mercury (in Hg). I think this is what you were asking.

Steve

gio64

iTrader: (1)

No, what I was referring to is that I believe the scale used to measure vacuum on one gauge is different from the scale used to measure vacuum in the other; I believe I had asked AEM at some point at least a year ago and they said something along that line.

On a different note, I used a mighty vac on the line.

Here's what I found:

If I apply vacuum, the gauges read identically. But after I turned the engine on and they did not. They are a slight bit off, but they are nonetheless. The AEM boost controller/gauges reads lower values of vacuum when the car is idling as opposed to what the mechanical boost gauge does.
When the mighty vac is applying vacuum and the reading is the same on both gauges, these also agree with the mighty vac gauge.

If I apply pressure with the mighty vac, they also read the same value. It is the first time I use it, so it seems to me that the gauge on the mighty vac does not work when I apply pressure, so I did not pit the gauges pressure against the mighty vac's pressure gauge.. I went out and drove a bit (I need to do the emission test, so my mechanic told me to drive it around a bit). As you can imagine, I can't stare at the gauges and drive while accelerating at the same time, so for what I can see, the mechanical gauge seems to be a bit quicker in reacting as opposed to the digital gauge in the Tru Boost. I believe (I need to triple check) that once the boost is approaching 10, the values become very similar. But as the mechanical gauge races up to 10, it seems to slightly get past it while the other one is still reading 9, 9.3, 9.7 or so; once the pressure is stabilized, then they are almost identical.
Giovanni

arghx

iTrader: (3)

If I buy two different brands of bathroom weight scales from the store, do you think they will read the same?

XLR8

iTrader: (52)

The boost controller will not lower boost, only raise it. The efficiency of your wastegates compared to the flow you are throwing at it will keep boost down. As you begin to increase the efficiency of the system by opening the exhaust, intake, and larger intercooler, boost will inherintly increase and the effectiveness of your stock wastegates will be overpowered. A boost controller "can" help stabilize spikes, but it is simply a bandaid for a wastegate that is being overpowered.

With a stock ECU you want a consistent 10psi. 12psi is asking for trouble.

There are other options with aftermarket ECU's, but few have the "out-of-the-box" capability of the PFC. They essentially would need tuned, where the PFC comes with a modified stock map.

Below is good FAQ to help you...
http://www.xsadclan.com/files/PFC/PowerFC_FAQ.pdf

Below is a good comparison of what a few maps are capable of...
http://www.xsadclan.com/files/PFC/PowerFC_FAQ.pdf

gio64

iTrader: (1)

I don't, but if I weigh 200 on one I don't expect to be 180 or 220 on the other either.

My issue is not to have the gauges show the same. My issue is to know which one I need to consider to setup the boost controller. I want the boost to stay at 10/8/10, but do I use the numbers showing on the mechanical, or do I use the numbers showing on the Tru Boost? Which is the reason why I am studying the problem.

The vacuum is showing the same on mighty vac, mech gauge and tru boost, in any case. It does vary however, like stated, when the vacuum is coming from the car operating as opposed to the mighty vac

gio64

iTrader: (1)

Thanks for the links, I'm going to read through. At this moment I do have to pass emissions and I spent a shitload of money to get the turbos and install them.

I also have a set of Enkeis in my garage waiting for rubber. Since the present tires are getting bold on the inside and I need an alignment/setup, those will be my next "necessary" things. After that I will definitely look at getting a Power FC.

I do not agree with you on one thing, however. The boost controller can put the boost at whatever PSI I want it to be (within the specific controller's range, of course). The Tru Boost starts with a setting that does not deliver more than about 4 PSI IIRC. It even has a setting that can be trimmed low so that if you leave the car to a valet parking, they won't be able to drive the wheels out of it, and it does this by setting the Boost to whatever lower than stock/standard you want it to be at.

My car has only simple mods:
I got a PFS intercooler/intake from another member, I have a DP and that is it, all else is dead stock (I have a Koyo rad and a few more "amenities", however, they are not performance mods). At the time I installed the Tru Boost the car only had a K&N and the DP, with the even cheaper bastard intake box mod. It was with this last one that the boost started to jump past 10. I have never -however- seen 12, I was just getting a bit over 10, so I went to get that and I installed it.

Thanks again, there is a wealth of info, material and knowledge that is available and that I love to be more informed on. My only problems are funds (I don't think anyone here feels he has enough money to do to this car what it needs/they want to do) and of course, a place where I can do the work. I have a garage, but I don't have a lift. It is also not heated, so here in Canada the time that goes from the end of November to at least mid March, you realistically cannot do anything in there. When I installed the Tru Boost I was working inside of the car with the doors closed (for the most part) and an electrical heater on in the car to keep myself from needing fingers amputations...

Can the Power FC be installed easily? I believe is almost a straight swap?
Thanks again, I appreciate all your input, this is a great community.

chaos7

iTrader: (2)

I think a lot of electronic gauges need to be calibrated to local base pressure, both defi's i have owned had to be calibrated after a full reset (both generally read a psi or two above zero before base calibration). Might be the same for others?

XLR8

iTrader: (52)

No problem. Glad to help where I can.

The Power FC install is quite easy. The FAQ I provided outlines its instillation.

As far as your situation and finances, I hear ya. You are thinking right by performing the reliability mods you have. Additionally, not hunting for power is a good thing. Keeping things relatively stock at slightly elevated power levels will help with overall longevity of the drive-train. These cars are absolute money pits, and getting the basic needs of the car sorted out initially will help you in the future.

Unheated in a Canadian winter? Get yourself a propane tourch heater and enjoy working in a t-shirt again . It's what I use, and it works very well.

The boost controller will only effectively lower boost as much as the wastegate allows. Despite what setting you set it to. If the internal wastegates were wide open, they would still only vent a given amount of exhaust gases at a given flow. How effective it does this, depends on the overall flow of the system as a whole, or the amount of exhaust gases you are introducing to the wastegates themselves. Your car is likely "stock enough" to allow you to lower boost as you mentioned, but as you "open" the system, the additional flow will overpower the wastegates. That maximum lowered level, will then rise.

This is why people get spikes, creep, and have issues controlling boost. This is also the reason people port the wastegates.

gio64

iTrader: (1)

I understand what you're saying, yes, once the wastegate is fully open, if the flow is still too high, I'll be trying to flow a fire hydrant through a funnel... Yes, at that point, I'd have no way to disperse that boost...

Like you said, I'm quite sure I'm not there yet and, yes, I am not trying to get a lot of power out of the car. A little more than stock is good, but I won't be racing people on the street and IF I track it occasionally, it'll only be after I have reinforced my piggy bank...

The car has been OK, barred the turbos issues (knock on wood...). The ones I installed are '99s, so that should also be a nice upgrade and should get rid of the smoke/oil burning problem.

Lol, I hear you with the torch heater... I would love to use the winter time to do stuff, but I always think about that damn garage and give up. I have thought about insulating it, but doing the roof would be a pretty high expense in itself, it is a double car garage. I'll consider the torch heater, sounds like a good idea. Normally the car does not go out of the driveway from November to March and that's a great time to do stuff, so I can drive it when it is possible.
Giovanni

gio64

iTrader: (1)

Thanks, that's an interesting piece of information. I would have to read through the manual for the AEM. As far as the mechanical gauge, I don't see how that could be done. After using the mighty vac, It looks like it is more of an issue of reaction time than actual reading. If you set the pressure, then go in the car, the gauges are pretty much identical. The difference is so small that it could just be the angle at which I look at the mechanical gauge needle.

I might try another mighty vac today, I'll see if I can check the reading on the mighty vac gauge for pressure as well, I wasn't able to do that.
Giovanni