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Old 06-03-04, 07:49 PM   #1
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Question What the heck does a boost sensor do?

Just wanted to know exactly what a boost sensor does. I have a little black box labeled mazda boost sensor, I couldn't find the nipple it taps into, so for right now it isn't hooked up to anything. Perhaps this is part of the reason my car is running so $hitty lately. Is it a limitation device of stock boost or something? Thanks, people.
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Old 06-03-04, 08:15 PM   #2
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ummmmm i bet your car is running like total dick eh?????????????????????????

is it unpluged??????????????? if so your car isn't reading boost so it goes in a "im going to run like ****" mode....

i had forgot to plug it back in once and it smoked like mad!!!! please plug that back in!
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Old 06-03-04, 08:18 PM   #3
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Maybe you should get off the pot and learn more about how your car works.

What do you think a boost SENSOR does?
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Old 06-03-04, 08:25 PM   #4
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is this a joke?
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Old 06-03-04, 08:28 PM   #5
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I know I'm lamo don't have to remind me. Actually That's were I learn best in the office of course.

On a serious note however, there are different types of boost sensors I imagine. So I was just trying to get a better idea of what exactly this one did. I know some turbo timers have boost sensors to keep the car running for the cool down periods of turbos. And others for not overrevving the turbos. And some I imagine for correct fuel mixture????? I'm still learning everyday seriously... So what exactly does the one above the im on the firewall do? Thats why I was asking.
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Old 06-03-04, 08:31 PM   #6
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Quote:
Originally posted by moehler
is this a joke?
No this is not a joke? Just because someone owns a car doesn't mean they know every single aspect of the engine. I have owned turbo cars but never really messed around with them very much. But know that I'm trying to put this car back together I have no choice. I don't claim to be an expert, thats why I'm asking you guys...
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Old 06-03-04, 08:34 PM   #7
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I checked on the diagram and it says it plugs into the back of the IM. The diagram calls it a pressure sensor, but it has a fuel filter attached to it?
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Old 06-03-04, 08:35 PM   #8
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Quote:
Originally posted by lopedl
I know some turbo timers have boost sensors to keep the car running for the cool down periods of turbos.
Nope.

Quote:
And others for not overrevving the turbos.
Nope, not really.

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And some I imagine for correct fuel mixture?????
Bingo.

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So what exactly does the one above the im on the firewall do?
You just answered your own question.
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Old 06-03-04, 08:37 PM   #9
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Quote:
Originally posted by lopedl
I checked on the diagram and it says it plugs into the back of the IM. The diagram calls it a pressure sensor, but it has a fuel filter attached to it?
Not every filter is a fuel filter...

And you say you've owned several cars?
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Old 06-03-04, 08:52 PM   #10
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The FD uses boost pressure to determine the air/fuel mixture. Guess what? That's what's disconnected on your car.

Reconnect the vacuum line from the UIM to the underside of the sensor (yes, it should have a filter in it). You'll then have to reset the ecu if you still have the stock ecu. Reset the ecu by disconnecting the neg batt cable and pressing on the brakes for 30 seconds or so.
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Old 06-03-04, 10:08 PM   #11
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Quote:
Originally posted by jimlab
Not every filter is a fuel filter...

And you say you've owned several cars?
Yes i know I'm not a tard, I know that not every filter is gas filter :duh:, but in the diagram it specifically says, fuel filter. That's why I was puzzled. Click the image to open in full size.. Come on, Jim Lab I know your an old school and have a lot of experience when it comes to these cars, but you can't tell me you were born: an auto technician and knew everything about, rotaries, turbos, and ls1 conversions, soon as you popped out into this world. I know I'm coming off as a total newbie, which I am, but I'm baby stepping my way to knowing about this car. Anyhow thanks all for your help.
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Old 06-03-04, 10:21 PM   #12
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Quote:
Originally posted by rynberg
The FD uses boost pressure to determine the air/fuel mixture. Guess what? That's what's disconnected on your car.

Reconnect the vacuum line from the UIM to the underside of the sensor (yes, it should have a filter in it). You'll then have to reset the ecu if you still have the stock ecu. Reset the ecu by disconnecting the neg batt cable and pressing on the brakes for 30 seconds or so.
So basically it's a cool name for a second oxygen sensor.
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Old 06-03-04, 11:16 PM   #13
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hey wheres my engine and what does it do?














lol j/k i have nothing useful to say....
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Old 06-03-04, 11:20 PM   #14
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Quote:
Originally posted by lopedl
So basically it's a cool name for a second oxygen sensor.
no, not that either. The computer uses it (among other sensors) to determine how much air is entering the combustion chamber so it can provide appropriate amounts of fuel.
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Old 06-04-04, 12:25 AM   #15
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I'm sorry this one made me chuckle.
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Old 06-04-04, 12:47 AM   #16
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Here's a really simplified (but essentially correct) description of how the FD's fuel injection system works:

There are sensors for intake manifold pressure and for RPM. There is a table of values where each row corresponds to an RPM and each column corresponds to an intake pressure. The values in the table tell the ECU how long to hold the injectors open for. Here are a few examples of what that data might be:

(RPM, pressure) = milliseconds to hold the injectors open
(4000 RPM, 0 psi) = 25 ms
(4000 RPM, 5 psi) = 35 ms
(4000 RPM, 10 psi) = 45 ms
(5000 RPM, 0 psi) = 30 ms
(5000 RPM, 5 psi) = 43 ms
(5000 RPM, 10 psi) = 55 ms

So you are driving, and you are at 5000 RPM and 5 psi. The engine computer senses that, looks a value up in the table, and holds the injectors open for 43 ms for each combustion cycle. As you can see from this, the computer absolutely needs to be able to sense the pressure of the intake manifold.

In reality, there are some other factors involved that the computer also senses and makes adjustments for. The temperature of the intake air changes its density (and hence the amount of oxygen it contains), so the amount of fuel injected needs to be adjusted for the change in density. This is usually done by applying some adjustment to the value looked up from the table, e.g. when the intake air is really cold at 30 degrees F, add 10% to the value from the map. There are also a limited number of cells in the table (a.k.a. your fuel map), so the computer will interpolate values between the cells. From my example data above, the computer might hold the injectors open for 50 ms when you are at 10 psi and 4500 RPM, since that is the average of the 4000 RPM and 5000 RPM cells for 10 psi [(45 + 55) / 2 = 50 ms].

One reason that upgrading the ECU and retuning for new modifications is so important on the FD is that the table has "baked in" assumptions about how much air you will be flowing at a given pressure and RPM. For instance, if you modify your car and the new setup flows 10% more air at 10 psi and 5000 RPM, you will run leaner than you did before if you don't re-tune the fuel map. Remember, the computer has absolutely no idea that you are flowing more air since it just senses the pressure and RPM and looks up a fuel flow rate from the map. Other cars use a device that actually measures air flow directly (a.k.a. "mass-air" or "mass air flow (MAF)" systems), so upgrading the ECU and retuning are less important on those cars. The FD does not measure air flow directly, so you have to re-tune (change the values in the fuel map) when you modify the car. The FD's system is called a "speed-density" fuel injection control system.

The basic idea here is not very complicated, but surprisingly few people care to learn and understand it. It helps so much to understand how this stuff works. It's worth the few minutes it takes to grok the basics. Pretend you are the fuel computer and you have to decide how much fuel to inject. How do you do it? A little ECU empathy is a good thing and will help you enjoy your car, especially if you are into modifying it.

-Max
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Old 06-04-04, 12:53 AM   #17
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Are you a moron?! 500 posts and you ask this question?!?!
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Old 06-04-04, 01:02 AM   #18
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wrong post *ignore*
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Old 06-04-04, 01:41 AM   #19
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Quote:
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Are you a moron?! 500 posts and you ask this question?!?!
You've got over 1,400, but some of the things you post make me wonder about your intelligence...
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Old 06-04-04, 01:55 AM   #20
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Quote:
Originally posted by maxcooper
Here's a really simplified (but essentially correct) description of how the FD's fuel injection system works:

-Max
Thank you for that explanation.
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Old 06-04-04, 09:27 AM   #21
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Quote:
You'll then have to reset the ecu if you still have the stock ecu. Reset the ecu by disconnecting the neg batt cable and pressing on the brakes for 30 seconds or so.
I've never had to reset the ECU after the MAP sensor line comes off.It "re-learns" on the fly.
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Old 06-04-04, 11:10 AM   #22
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Quote:
Originally posted by jimlab
You've got over 1,400, but some of the things you post make me wonder about your intelligence...
So what if I want to see which BOV is the loudest huh
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Old 06-04-04, 06:35 PM   #23
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I thought this site was intended to enlighten the ignorant. All you who are ostentatious... were you born brilliant?
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Old 06-04-04, 09:27 PM   #24
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I know it was foolish of me to have had that line unplugged. But I'm a bit concerned do you think my ignorant action could have had a negative affect on the engine? I basically had it at idle and then took it for a spin about the equivalent of a block, temp was no higher than 175 degrees and rpm was no higher than 3 1/2. I did rev the idle to 3 1/2 a couple times, but that was it. I know fuel wasn't a problem in my situation as it was running very rich to begin with due to the fact it was blowing out a constant flame. The reason I ask is I was reading of a story about a guy who blew an apex seal, because the very same vacuum line had blown off.
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Old 06-04-04, 09:27 PM
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