Boost vacuum Gauge

[ThomS]

Can you tell one thing. I read that this gauge will tell you a lot about the system and what is going on. Like what ?
Same question for the AFR gauge.
Thanks for any help.

[chuckerants]

Thom,

If you had a vac/boost gauge from day 1, you'd know when you had a vacuum leak. You'd also know when your belt was slipping as well as be able to know if you weren't making as much boost as normal.

[socal pat]

Chuck took the boost/vac gauge, I'll take the AFR..... If for some reason one of your PC-Pro controllers stops working you'd see a sudden rise in AFR's. Your ears might pick it up as ping, but the AFR gauge would pick it up first. It will also tell you if you are running too rich.

[ThomS]

OK >>> Now for numbers, what are good numbers for AFR and Vacuum gauge.
I assume that the higher the number on the boost side the better
Right?

[maggie]

Boost/Vacuum...More vacuum= better fuel economy, more boost=more fun.
AFR for the peace of mind that a deaf ear might be missing the 'ping'.

[ThomS]

Boost/Vacuum...More vacuum= better fuel economy, more boost=more fun.
AFR for the peace of mind that a deaf ear might be missing the 'ping'.

I understand that, and thank you. But waht I would like to know if numbers? What should the numbers be on the boost gauge and AFR gauge.

Vacuum numbers seem to be about 19 to 20 at idle and crusing at 60 MPH, then up and down depending on how I am driving.
AFR numbers seem to be between 14 and 15 again depending on I am driving. Are these good numbers?
Thanks for your help.

[Kyp J]

Those are good. If things start running rough at idle, you can determine if you have a leak somewhere if the vacuum numbers drop off. If still high it is probably some other cause. I think if the RPMs drop for another reason, the vacuum will drop a little so you have to be careful of misinterpreting them. Just for fun pull off one of the semi non important hoses from the vacuum manifold and look at the result. Not the hose to the gauge tho.

[Tom @ Fast Forward]

Thom,

14-15 is good numbers at idle and cruise but what are you geting under boost. Foot to the floor. Boost should be 10-11 at 7000 and AFR should be around 12, more or less. I sure hope you are not saying you get 14-15 under boost? If so, don't drive it.

[ThomS]

Thom,

14-15 is good numbers at idle and cruise but what are you geting under boost. Foot to the floor. Boost should be 10-11 at 7000 and AFR should be around 12, more or less. I sure hope you are not saying you get 14-15 under boost? If so, don't drive it.
No 14 to 15 is normal cruise and at Idle. Underboos and to be honest I have not tried to get it that way too much yet, but when I did it was as high as almost 11 and under. I thinkl.

[Tom @ Fast Forward]

Whew! I was worried there for the moment.

[ThomS]

So what book can I read that will explain the number I am seeing.
What does 14 to 15 mean under normal drivng? I want to understand
why those same numbers will be bad under boost. what if someone was getting 15 to 16 or 13 to 14 at idle and normal cruise what would that mean?
These are the things I want to know.
Why should boost be about 10 or so? I know most if not all of you understand these things and I need to too. Any sugggestions on reading material?
Thanks

[Tom @ Fast Forward]

Most people thing engines burn gasoline. Actually they bur air (oxygen). Fuel is there only to hely burn/consume the oxygen. Perfect combustion occurs at 14.7 pounds of air to 1 pound of fuel. In that case all of the oxygen is consumed. To meet emission standards today, the engine computer reads the MAF to see how many pounds of air are coming in and adjusts the fuel to the appropriate fuel for 14.7:1 (pounds of air to pounds of fuel). It does this at idle and at cruise. When decelerating, the A/F goes completely lean as the air is still flowing (not much air as the throttle plate is closed, but some air) and the fuel is completely turned off. When accelerating, the A/F depends on how hard you are accelerating. A mild push to the pedal might actually try to sustain 14.7:1. A little more push might cause the computer to go for around 13:1. At wide open throttle, the computer typically tries (newer Miata engines) to hold around 13:1 to around 3000-3500RPM and then drop off to 12:1 to 7000RPM. 12:1 being richer as it is less air (only 12 pounds) to the same amount of fuel (1 pound). They add this excess fuel to try and cool the cylinder and avoid knock or melted pistons. When boosting an engine, it is even more important to ensure there is 12:1 (more or less) for the same reasons.

Hope that helps.

[Serpico]

No 14 to 15 is normal cruise and at Idle. Underboos and to be honest I have not tried to get it that way too much yet, but when I did it was as high as almost 11 and under. I thinkl.


Superchargers are not much fun for cruise and idle..... :)

[dazooom]

That's a great explanation of A/F, in simple terms, that most anyone could understand, Tom!:cheers2:

[Tom @ Fast Forward]

Thanks. :)

[ThomS]

Thanks Tom.. That helps a lot !

[Kyp J]

That's a great explanation of A/F, in simple terms, that most anyone could understand, Tom!:cheers2:

Yeah but.....! Imagine the nitpicking and eventual fights if that was on Mnet.

The only thing missing that I noticed was the part about the fluctuation at the 14-15 condition and the terminology used that you will run into in some discussions. Since I don't quite understand the terms (or how to spell them), I won't attempt to explain anything. Check out this place:

http://en.wikipedia.org/wiki/Stoichiometry

If that doesn't put you to sleep, you are more curious than I am.

[Tom @ Fast Forward]

Kyp, the Miata uses a narrow band O2 sensor. What that means is that the voltage curve for a change in A/F is very small (narrow) and drops off sramatically below 14.2 and above 15.2. It is really only accurate around 14.7. By the time the computer sees that it is 14.7 and rising (getting leaner) and makes a change in fuel, it is already over 15. Then the A/F starts to fall (getting richer) but, by the time the ECU sees it, it is already below 14.5. Then the ECU makes another correction the other way and the process starts all over again.

A lot of newer cars like the 06+ Miata use a wide band O2 for control. It is a lot faster device and has a much wider signal change for A/F. It puts out several volts over a band of accuracy from around 10 to above 17. With the wideband, those cars actually control to 14.7 fairly well without all of the oscillations. They can also do closed loop control at 13:1 or 12:1 with ease where the narrowband cars have to go open loop and simply go to a set of look up tables and pray the numbers work.

[Kyp J]

I already sort of knew why the osccillations were there, I meant for you to explain it to Thom. Now he won't read the explanation because you addressed it to me.:svengo:

(That was a joke.)

What I didn't know was that the newer cars did it with a wide band.

Does the new, soon to be released PC Pro effectively do the same if we had it? Or only while in boost? Or could it be made to take over the entire control of the injectors at all times? Or would that make it a stand alone controller and therefore become evil?

That brings up another question in general about "Stand alone controllers". I never bothered to look past the price. Do they only do fueling and leave the rest of the car under control of the ECM or do they do everything? (like turn on the AC, fans and the other odds and ends the stock ECM does.)

[Tom @ Fast Forward]

Kyp,

It depends on how much $$$ you spend on the after market stand alone.

[ThomS]

Kyp & Tom thanks for the help. I did not understand the osccillations but this all helps to understand thanks.
I already sort of knew why the osccillations were there, I meant for you to explain it to Thom. Now he won't read the explanation because you addressed it to me.:svengo:

(That was a joke.)

What I didn't know was that the newer cars did it with a wide band.

Does the new, soon to be released PC Pro effectively do the same if we had it? Or only while in boost? Or could it be made to take over the entire control of the injectors at all times? Or would that make it a stand alone controller and therefore become evil?

That brings up another question in general about "Stand alone controllers". I never bothered to look past the price. Do they only do fueling and leave the rest of the car under control of the ECM or do they do everything? (like turn on the AC, fans and the other odds and ends the stock ECM does.)

[Kyp J]

Kyp,

It depends on how much $$$ you spend on the after market stand alone.

That only answers the last question. There were up to 4 previous questions depending on the answers. Nothing important, just curious. I'm not buying anything else.....so quit tempting me. I'm going to be selling it next spring or summer if my house sells... and if I don't break it again between now and then.

[Tom @ Fast Forward]

"Does the new, soon to be released PC Pro effectively do the same if we had it?

Or only while in boost?

Or could it be made to take over the entire control of the injectors at all times?

Or would that make it a stand alone controller and therefore become evil?"

Yes.

Yes.

Yes (but I really only want to take control in boost).

Yes, absolutely. :)

I have a bad habit of answering the last question in a post with multiple questions. I am seeking professional help to cure it. So far the professional help only works sporadically. :angel:

[Kyp J]

Quote from Tom: "I have a bad habit of answering the last question in a post with multiple questions. I am seeking professional help to cure it. So far the professional help only works sporadically"

Maybe because you only remember the last thing the therapist says:
"Times up, pay on the way out."

[ROZ]

Is it therefore advisable to fit a wide band sensor?
Does the PC Pro take a WB signal and control "stuff" better?

[Tom @ Fast Forward]

Well, you resurrected a thread from a year ago. Someplace around here I posted that we have given up on the 'closed loop' function in the PC-pro. The PC-Pro does not, at the moment, take a wideband signal and control. Maybe someday but not now.

[ROZ]

Call me Lazarus!
Hey, it's only a year - I've dusted off some really old ones on the MX5OC forum over here.

So if one had a WBO2 set you'd need to have one with a NBO2 output to go to the PC Pro?

[Tom @ Fast Forward]

Well, IF the PC-Pro had an input for the O2 sensor, you would need a WB with an NB02 output. I think most of them do. I know the AEM does and the Innovate kits do as well.

Call me Lazarus!
Hey, it's only a year - I've dusted off some really old ones on the MX5OC forum over here.

So if one had a WBO2 set you'd need to have one with a NBO2 output to go to the PC Pro?