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Old 02-28-2009, 09:45 PM   #1
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Default How much noise is typical on the MAP sensor signal?

I am running with acceleration enrichment turned off now, because the MAP signal is just too noisy to pick out acceleration events. Or at least it was.

I added a pressure snubber that I had lying around and it smoothed out the MAPdot signal significantly, but it still seems pretty noisy.

Example with snubber:


More details at this link, including traces made under similar conditions before I added the snubber.

I have a few more things to try, but I want to get an idea of how close to "normal" the readings now are.

Thoughts?
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Old 02-28-2009, 09:51 PM   #2
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Looks like electrical noise to me. Spill the beans on your setup. Tell us everything. Omit nothing. Good well focused pics of the MS also. Outline your grounding scheme. Are your battery connections clean and tight?
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Old 02-28-2009, 09:57 PM   #3
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Name:  noisegone1.jpg
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Name:  noisegone2.jpg
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Old 02-28-2009, 10:09 PM   #4
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I initially suspected electrical noise as well, but given the change in amplitude of the MAPdot signal after adding the (pneumatic) snubber, it looks like at least a good portion of the noise is on the "air" side.

Do you have a graph of your MAPdot signal? Your MAP does look smoother but it's on a different scale than mine so it's hard to estimate how much smoother it is.
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Old 02-28-2009, 10:14 PM   #5
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We use TPSdot, not MAPdot. It's much better.
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Old 03-01-2009, 12:39 AM   #6
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I need to switch to a tiny vac hose.
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Old 03-02-2009, 11:58 AM   #7
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Nobody's got a graph of their MAPdot signal handy?
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Old 03-02-2009, 12:12 PM   #8
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What grounds does the MS have?
Can someone point me to a schematic of "sensor gnd" and "power gnd" of the MS if they have them separated?
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Old 03-02-2009, 12:21 PM   #9
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My problems are with CAS signal. Is your MAP sensor connected to the rear of the intake manifold? just behind the throttle body seems to have a lot of turbulence which causes noise.
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Old 03-02-2009, 12:39 PM   #10
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I once had a problem with the CAS signal because it was routed near the ignition wires.
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Old 03-03-2009, 01:16 AM   #11
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Thanks for the trace TrickerZ, though at 29 kPa / 1300 RPM mine is just as smooth. It really gets noisy up in the 70 kPa >3000 RPM range.

Regarding the MS grounds, there is only one ground plane on the MS. I added an extra 14ga wire to the manifold on mine. It didn't affect the MAP signal at all, but it did give me a more stable IAT reading. (My IAT sensor is using the same ground the AFM used.)

My MAP signal is tee'd off of the FPR line.
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Old 03-03-2009, 01:21 AM   #12
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No screen shot now, but my map dot is butter smooth until about 45% duty cycle, then it gets messy to the tune of 150+ map dot swings. It's the low ohm injectors causing noise. I need to fix that. Or get a better ECU....
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Old 03-03-2009, 03:27 AM   #13
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How the hell is your **** so smooth?? should I be running a chunky ground wire to the ecu's ground line? should I be using some sort of signal smoother? My map signal is decent enough to not cause choppy afr's but it doesn't look anything like your guys'.
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Old 03-03-2009, 04:05 AM   #14
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Quote:
Originally Posted by kday View Post
Regarding the MS grounds, there is only one ground plane on the MS.
If so, there should be a separate wire from this ground plane, to the engine bay, to which all sensor grounds are returned. However, this won't work for sensors which are grounded through their body. Any sensors grounded through their body should NOT be connected to the above wire.

A second, thick wire should go from the ground plane, to the engine, to act as power ground.

Any other grounding scheme may not work.
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Old 03-03-2009, 08:50 AM   #15
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I thought mine was noisy untill I saw yours.
1st pic 2.5mm vac line. Attached at the front of IM(in place of charcoal canister vent)
How much noise is typical on the MAP sensor signal?-graph2.png
2nd pic same vac line with a 1mm restrictor in line.
How much noise is typical on the MAP sensor signal?-graph1.png
As you can see it made bugger all difference.........OK, NO difference.
kday, what is this pressure snubber you speak of? Nevermind.....Just saw the link.

Actually, looking at them together now, the map amplitude did reduce a bit.

Last edited by Greenie; 03-03-2009 at 09:02 AM.
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Old 03-03-2009, 09:03 AM   #16
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Quote:
Originally Posted by JasonC SBB View Post
If so, there should be a separate wire from this ground plane, to the engine bay, to which all sensor grounds are returned. However, this won't work for sensors which are grounded through their body. Any sensors grounded through their body should NOT be connected to the above wire.
That seems reasonable. I am not sure how different it is from the way Mazda wired everything up. In any event, my issue right now is with MAP noise, and the MAP sensor is mounted on the MS PCB.

If it is electical noise, the source of the noise is RPM and MAP dependent. The signal is smooth at idle. It's smooth at 3000 RPM and low MAP. It gets noisy at high MAPs above ~3000 RPM.
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Old 03-03-2009, 09:19 AM   #17
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Quote:
Originally Posted by Greenie View Post
I thought mine was noisy untill I saw yours.
1st pic 2.5mm vac line. Attached at the front of IM(in place of charcoal canister vent)
Yours is noisy in a different way than mine. My noise is higher frequency and is mostly visible on the MAPdot line. Yours is lower frequency and visible in both.

Early on I moved my vac line back to the FPR. I think it smoothed things out somewhat but it's hard to say since I changed so many other things.

Quote:
Originally Posted by Greenie View Post
2nd pic same vac line with a 1mm restrictor in line.
I think 1mm might be on the large side for this. One of the things I plan to try (as soon as the snow is gone...) is a 0.6mm restrictor. That's the smallest drill bit I have, otherwise I would make it smaller.

Another thing I want to try is the "G" spec pressure snubber which has smaller holes and is intended for air.
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Old 03-03-2009, 09:33 AM   #18
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Quote:
Originally Posted by kday View Post
Early on I moved my vac line back to the FPR.

Quote:
Originally Posted by kday View Post
One of the things I plan to try (as soon as the snow is gone...) is a 0.6mm restrictor.
Do you think these two will help me with my issue's, or am I worrying about nothing?

It is triggering AE.
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Old 03-03-2009, 10:03 AM   #19
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Quote:
Originally Posted by Greenie View Post
Do you think these two will help me with my issue's, or am I worrying about nothing?

It is triggering AE.
If AE is being triggered during steady state throttle then I do think it is a problem. If you can run TPS AE then it may not be a problem you need to solve. I don't plan on running a TPS with my 1.6 so I want to solve the MAPdot issue.

Unexpected AE caused me no end of grief when I first started tuning. I thought I had disabled AE by setting the threshold high, but the noise was enough to trigger the un-tuned AE and dump in huge amounts of fuel, but only in some parts of the map. I had a huge lean spot in the middle of my VE table thanks to autotune until I realized what was going on.
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Old 03-03-2009, 10:10 AM   #20
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Mine has not been that bad, I noticed it when looking over my logs. I do have a TB off an automatic 1.6 with VTPS. That may have to be the next job.
Good luck.
Thanks kday
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