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equality72521's Avatar
 
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Boost pressure sensor

Does anyone know what the voltage output of the OEM pressure sensor is for a 1979 turbo? Mine doesn't work anymore and I need to get another sensor to tie into my LC-1/SSI-4 so I can log boost along with AFR, and RPM. I need to decide if I should use an OEM sensor or buy aftermarket. I need a 0-5v output.
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Old 11-18-2008, 01:59 PM
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You should probably use a GM or equivalent map sensor. They are cheap. The factory boost sender doesn't work on a 0-5V reference like most modern sensors.

It works by changing resistance to ground. which is why it only has one wire

You need a sensor w/ 3 wires. 5V+, ground, and output. there are 3-4 different GM mapsensors. If you are running 1 bar of boost or less, you can use a "2 bar" map sensor as the map stands for "manifold absolute pressure" Meaning, it starts at 1 bar, as that is atmospheric pressure typically, then add 1 bar of boost = 2 bar absolute manifold pressure...

Hope this helps
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Last edited by rsrmike; 11-18-2008 at 02:10 PM..
Old 11-18-2008, 02:06 PM
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There are many MAP sensors that are available, the GM just popped in my head first,

try www.clewett.com for the sensor and appropiate GM "weatherpack" connector

Perhaps Innovate sells a separate MAP sensor??
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Last edited by rsrmike; 11-18-2008 at 02:12 PM..
Old 11-18-2008, 02:09 PM
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Hey Mike this brings up a good question, what's the innacurate part of our factory guages ? the sender or the guage ?
Oh and do the other senders fit the OEM sender hole?
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Old 11-18-2008, 02:26 PM
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Thanks Mike. I just looked at clewett and I'm not sure by looking at the picture how I would install the MAP sensor.
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Old 11-18-2008, 02:27 PM
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Innovate has this one: http://www.innovatemotorsports.com/xcart/product.php?productid=16202&cat=265&page=1
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Old 11-18-2008, 02:42 PM
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I'm not sure which part is the innacurate part. It probably stems from years of corrosion on the multiple wire connections between the sender and the gauge, as well as the grounding of the sender. Throw in the age factor of the sender and who knows.

As far as the other MAP sensor plumbing, you would need to tie into a vacuum hose. I would probably tie in to the vacuum hose going to the control pressure regulator (WUR) so you are reading boost pressure in the manifold. It probably doesn't matter, but that would be eaisest. Just use good quality hose and a solid vacuum "T" so you won't run the risk of loosing your boost enrichment if WUR looses it's boost signal. I believe there is a plug on the rear of the original BOV assembly that is 10mmx1.0? You could also use a banjo fitting and banjo bolt from a CIS fitting and tie it in there. I probably have one lying qround somewhere
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Old 11-18-2008, 02:46 PM
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1/8"npt is REAL clost to 10mmX1 so that might screw into the plug hole I mentioned earlier... $110, though, ouch, how much was the GM map sensor? EDIT nevermind, I just looked $95 for 2 bar sensor plus $8 for connector

Also, you don't need a 0-100 psi range. That's going to give you little resolution on your 0-15 psi boost range (assuming you are running 1 bar or less)
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Old 11-18-2008, 02:49 PM
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[QUOTE=9dreizig;4311365]Hey Mike this brings up a good question, what's the innacurate part of our factory guages ? the sender or the guage ?QUOTE]

BOTH!!
Old 11-18-2008, 02:50 PM
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the GM would probably be more accurate considering the smaller operating range
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Old 11-18-2008, 02:51 PM
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[QUOTE=jimmcc;4311416]
Quote:
Originally Posted by 9dreizig View Post
Hey Mike this brings up a good question, what's the innacurate part of our factory guages ? the sender or the guage ?QUOTE]

BOTH!!
What about the connections Jim? it's not like there is much current draw to overcome a dirty connector(s)... LOL don't worry, I know better than to argue w/ you over electronics!!
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Old 11-18-2008, 02:52 PM
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Quote:
Originally Posted by rsrmike View Post
As far as the other MAP sensor plumbing, you would need to tie into a vacuum hose. I would probably tie in to the vacuum hose going to the control pressure regulator (WUR) so you are reading boost pressure in the manifold. It probably doesn't matter, but that would be eaisest. Just use good quality hose and a solid vacuum "T" so you won't run the risk of loosing your boost enrichment if WUR looses it's boost signal. I believe there is a plug on the rear of the original BOV assembly that is 10mmx1.0? You could also use a banjo fitting and banjo bolt from a CIS fitting and tie it in there. I probably have one lying qround somewhere
Thanks a bunch Mike. It looks like that's the best option.
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"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
--clutch-monkey
Old 11-18-2008, 03:13 PM
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[QUOTE=rsrmike;4311423]
Quote:
Originally Posted by jimmcc View Post

What about the connections Jim? it's not like there is much current draw to overcome a dirty connector(s)... LOL don't worry, I know better than to argue w/ you over electronics!!
A dirty connector would probably create more of an intermediate problem (gauge bouncing) than an inaccurate reading unless the connection was really dirty. Having the connection tight and clean will help.

I ran a curve on the stock sensor from my 1980 (original sender I would assume) and if I recall it read about 7 ohms at atmosphere and around 130 at the upper limit. I looked for that data earlier and can't find it at the moment but was surprised at how quickly the gauge hit the upper limit. I'll look for it later tonight. What I did notice was excessive wear at the low end as I slowly ramped up the pressure. That is probably why the tach gauge shows little at the bottom and then jumps to about .2 bar.

I should pull both the sender and tach out of the car and set them up on the test bench and determine which component contributes the most to the error. Know where I can borrow a newer one for reference?

Depending on what boost level is desired the GM based sensors are a relatively inexpensive way to go. Output is 0-5v. As rsrmike pointed out the 2 bar sensor is good for 1 bar of boost and the 3 bar is good for 2 bar. The only loss is a bit of granularity in the measurement but that is not a problem.

rsrmike is welcome to argue anytime. He's usually right!
Old 11-18-2008, 03:44 PM
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I found my notes on the stock 930 boost sensor.

993 606 103 00

0.0 Bar 5 - 13 Ohms
0.9 Bar 117 - 129 Ohms

I believe I was using a digital pressure gauge to measure the applied pressure but this was two years ago and my mind is foggy. As I recall it maxed at .9 bar which I thought to be early. The variance in the ohm readings indicate the value range I received while going alternating between 0 and .9 bar using a quality Fluke meter.

These numbers should only be used to determine if the sensor is dead as I was not concentrating on accurately mapping the sensor but wanted to know the range boundries.

Jim

1980 930
1995 993 (is that correct now Mike?)
Old 11-18-2008, 04:11 PM
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