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Old 08-18-2007, 08:10 PM   #1
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Default Shaky MAP readings

So i've had the problem for a long time that my MAP readings are really really shaky, especially in boost..

I've checked over all my piping, and am pretty positive its all good..

The only thing i can think of is the ground to the MS.. could that couse the MAP reading to be shaky like that?
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Old 08-18-2007, 09:11 PM   #2
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It 'could' be a ground issue, if so you'll probably see noise on some other signals as well, but it's more likely that your map readings are just really, really shaky

Where are you pulling the MAP signal from? Through a bit of testing we've found the cruise control port isn't the best as it is noisy, the port about mid plenum on the fuel rail side of the plenum is much better. If you've still got alot of noise then you can get a vacuum line filter at AutoZone for like $2-3 that will help-- it's basically a restriction in the line that slows the oscillation with significantly effecting the actual pressure reading. You can find these in the vacuum 'y' connector section.
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Old 08-19-2007, 01:04 AM   #3
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Quote:
Originally Posted by FoundSoul View Post
It 'could' be a ground issue, if so you'll probably see noise on some other signals as well, but it's more likely that your map readings are just really, really shaky

Where are you pulling the MAP signal from? Through a bit of testing we've found the cruise control port isn't the best as it is noisy, the port about mid plenum on the fuel rail side of the plenum is much better. If you've still got alot of noise then you can get a vacuum line filter at AutoZone for like $2-3 that will help-- it's basically a restriction in the line that slows the oscillation with significantly effecting the actual pressure reading. You can find these in the vacuum 'y' connector section.
So you're saying the port on the back of the intake manifold is a bad place? And the port for the stock FPR is the spot you use? do you just tee off the FPR line or what?
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Old 08-19-2007, 06:53 PM   #4
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Pulling the MAP signal from this location had measurably less noise in my testing.... this was on a 94-95 manifold, I'd expect similar results on the 90-93 honestly.


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Old 08-19-2007, 11:57 PM   #5
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Quote:
Originally Posted by FoundSoul View Post
Pulling the MAP signal from this location had measurably less noise in my testing.... this was on a 94-95 manifold, I'd expect similar results on the 90-93 honestly.



cant really tell from the pics but i dont think the 1.6 mani's have that port..
i went ahead and moved it to the ports in front near the TB

Anyways, just for anyone who was interested in what was going on.. it was a ground issue, i ran three new grounding wires, one to the metal floorboard inside the car, one to the drivers side firewall, and one to the block..

Issue solved pretty much, its all smooth as butter now

thanks foundsoul for tryin to help
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Old 08-20-2007, 10:56 AM   #6
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NP-- two thoughts though...

On the grounds, keep them all together to the same point on the block, preferably where the stock ECU already grounded to which is one of two brackets near the back of the fuel rail. You don't want a ground loop situation which can happen when grounding to both the block and the chassis/bodywork. As you've found grounds are super important though...


Second-- I just got in the shop and popped the hood on our '91 (I had the 95 at home this weekend) and you're right that port isn't there, but the FPR port is in about the same spot. I haven't tested it yet but I'd expect it to be less noisy than the cruise port. I'll try to test that in the near future.
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Old 08-20-2007, 02:06 PM   #7
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my cruise port does me just fine told ya it had to be a ground issue man glad you got it figured out.
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Old 08-20-2007, 02:11 PM   #8
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It's a bit nit picky, and more obvious with a 4 bar map sensor, but back to back testing (with this being the only changed variable) doesn't lie-- the cruise port is noisier than the above pictured port on the 94-95 cars, I can promise you that. However... grounds are a HUGE deal.. much more important than most people realize... this isn't a lightbulb we're powering here
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