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:
http://www.boost-instruments.com/ms/...77kpa-snub.png

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?

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?

Attachment 207789

Attachment 207790

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.

We use TPSdot, not MAPdot. It's much better.

http://i39.tinypic.com/f4jo0z.png
I need to switch to a tiny vac hose.

Nobody's got a graph of their MAPdot signal handy?

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?

http://img204.imageshack.us/img204/408/mtscreen.jpg
http://img204.imageshack.us/img204/m...pg/1/w1079.png

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.

I once had a problem with the CAS signal because it was routed near the ignition wires.

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.

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....

How the hell is your shit 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'.

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.

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)
Attachment 10500
2nd pic same vac line with a 1mm restrictor in line.
Attachment 10501
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.

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.

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.

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.

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.

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

Believe me, it IS electrical noise in some form or fashion. Your map isn't really changing that much. Are you running low ohm injectors? Exactly how is everything grounded? Post your msq.

Stock 1.6 injectors. Stock grounds from ECU connector, plus one. I will post the msq later tonight.

I don't see any evidence of noise like this on any other logged signal. I would expect that noise due to e.g. ground bounce would affect small swing inputs like the IAT sensor (with a full scale range of only a volt or so). MAP is apparently sampled once per ignition event, which is 100 Hz at 3000 RPM. The log samples CLT and IAT at 50 Hz IIRC. That seems like too small of a difference for electrical noise to be present on all signals but only evident on the MAP because it samples faster. It is also surprising that the mapDOT swings so widely but the MAP trace itself does not. Hmm. I need to look at the code to see how mapDOT is calculated.

msq is here.

Looking at the code... (caveat: I have not studied the ms2 code in any detail.)

in ms2_extra_main.c
outpc.mapdot = (781L * (outpc.map - last_map)) / tmp_mapsample_time;

tmp_mapsample_time is the number of ticks since the last ignition event. Ticks are 128 us. 781 is ~100 ms in ticks.

I have the map sample point set to 50%. So tmp_mapsample_time should be approximately (1000 [ms/hz])/(rpm/60 [sec/min]) * 50%. Which is 10ms after the last ignition event at 3000 RPM.

So mapdot at 3000 RPM is

100 ms * (map - last_map) / 10 ms

or 10 times the change in MAP value since the last ignition event. (I am ignoring the map lag value here, which weights the sampled map value and the previous map value to determine the current map value.)

Spikes to 200 in the mapdot trace at 3000 RPM indicate that the MAP is changing 20 units per sample, post lag filtering. Units are kpa*10. So a change of only 2 kPa between samples results in a mapdot of 200.... ? At 1500 RPM 200 mapdot is a change of only 1 kPa between samples. Hmm. Clearly the lag filtering has to be taken into account here.

Interestingly, the code will never sample the MAP more than 100Hz. So above 6000 RPM the MAP is not sampled during every cycle and the point in the cycle when it is sampled moves somewhat.

I am surprised they are not oversampling the MAP and averaging it.

Anyway.... needs more investigation.

Try modifying it and see. If it fixes the problem, I bet a lot of people will be happy. It's possible it'll cause timing issues, though. I haven't looked at the MS2 code, but I'm sure it'd cause problems with MS1. I don't think MS2 is as strict on timing.

Some more comparison data on this page. Three runs with similar RPM and MAP values with various hose and snubber combinations. The 1/8" hose with the snubber has the least noise on the signal, but it is still higher than desirable, but only in the 3000-4000 RPM range with high MAP. I think the fact that the noisy region is isolated to only some running conditions, and the fact that changing only the pneumatic side has a large effect, rules out electrical noise as the primary issue.

I am going to experiment with different MAP sampling strategies when I have a chance.