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Old 06-08-2009, 01:22 AM   #1
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Default MAP waves

Avast, thar be waves on the high seas ye landlubbers!

Anyone know what the hell is going on here? This is very annoying to try to drive at cruise.

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Old 06-08-2009, 01:37 AM   #2
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Cant say i've ever seen anything like this.
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Old 06-08-2009, 01:41 AM   #3
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Me either..

It's worth mentioning that this only happens in cruise. As soon as I increase or decrease the amount of throttle, everything smoothes out.
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Old 06-08-2009, 02:00 AM   #4
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That looks weird. Does it run weird to boot?
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Old 06-08-2009, 02:06 AM   #5
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It runs weird only when this happens. It doesn't always do it, but when it does it's always on the highway when I'm trying to hold a constant speed. I see the wideband display start to wag wildly between lean and rich like a narrowband gauge at idle.
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Old 06-08-2009, 03:38 AM   #6
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Have you thought about the idle valve settings? Just something to check.
I have been playing with my idle settings and the MAP sometimes looks like this when I **** it up, only at idle though not at cruise.
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Old 06-08-2009, 08:03 AM   #7
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I actually just took out my idle valve on Saturday, but it was doing this before I did that.
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Old 06-08-2009, 09:57 AM   #8
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where's your boost source hooked up? your MAPdot starts going crazy.....
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Old 06-08-2009, 10:26 AM   #9
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Given the limited info we have, I'm with Brainey here. Seems like the MAP sensor is either being fed from a point in the system where manifold pressure is unstable, or it's being fed with a line that is so large in diameter and so short in length that it's picking up discrete pulses as intake valves open and close.


I was about to see that this almost looks like an electrical issue, as AFR seems to be tracking PW a little too perfectly for my taste, but I can see that CLT and TPS are both perfectly clean, which kinda rules that out.
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Old 06-08-2009, 10:46 AM   #10
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I'll double check the MAP source today and get back to you, right now all I remember is it's hooked up wherever Ben and/or M2CC thought was a good idea.
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Old 06-08-2009, 11:26 AM   #11
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resonance! maybe you have a vibration causing your map signal line to shake and do that?
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Old 06-08-2009, 07:58 PM   #12
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A vibration like the MMR diff mounts I installed a few weeks ago? That would certainly explain how it begins softly and begins to feed on itself, like feedback. Hmm... maybe I should try zip-tying the line to other things to stabilize it on its way to the firewall. If it's not effective.. at least it's (nearly) free!

Joe, Brain: The MAP source is the 90* fitting coming off of the plenum just in front of the FPR.
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Old 06-08-2009, 08:08 PM   #13
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I always connect to the nipple on the #4 runner that is capped off.
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Old 06-08-2009, 08:16 PM   #14
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Did you check the hose diameter feeding the MAP? That waveform looks like the MAP is reading pulses, which you don't want in this application.

I would either find a smaller diameter hose or find an orifice to install. A quick and easy way is to get a tie-wrap around the hose and pinch it down. Not too much, you still want a signal.
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Old 06-08-2009, 08:17 PM   #15
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I'm thinking more and more that the location of the MAP source isn't likely the culprit, if for no other reason than because it's been this way ever since I got 'squirted and this issue is brand new.
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Old 06-08-2009, 08:28 PM   #16
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I am not referring to the source of the feed but the diameter of the hose to the MAP sensor.
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Old 06-08-2009, 08:31 PM   #17
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Yeah, we were typing at the same time.

I'll try choking it down if holding it still doesn't work, but like the location, the line has been there from the beginning and this is a new occurrence.
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Old 06-08-2009, 09:28 PM   #18
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Quote:
Originally Posted by kotomile View Post
I'm thinking more and more that the location of the MAP source isn't likely the culprit, if for no other reason than because it's been this way ever since I got 'squirted and this issue is brand new.
do a search on this same thing....move it to the back of the manifold, the port neo suggests is perfect. or teeing of the fpr.
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Old 06-08-2009, 09:35 PM   #19
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I looked at the #4 runner and didn't see anything. Is it on the underside or something?

So, I just got back from a datalogging run, tried zip tying the line every 6" on its way to the firewall, and then cinched down as much as I could on the line, neither worked.

Tomorrow I'll try going to a smaller line and see how that does, if that doesn't work, then I'll try shuffling the locations. Really appreciate your help guys, thank you!
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Old 06-08-2009, 09:36 PM   #20
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I had a similar problem a while back. Out of the blue I was getting noise like that. I had it hooked up to the unused nipple on the #4 runner. Matt suggested teeing it into the frp line. After that it was perfect.
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