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<h1>2G Baro Input Workaround</h1> <div class="level1"> <p> The baro input of the 2G ECU may not be compatible with aftermarket sensors. The 2G ECU has a 3.3K ohm pull-down resistor (R39 on 1995 EPROM ECUs), which may (probably will) put more load on the sensor than it can drive properly. </p> <p> For example, a GM 3-bar sensor can only drive this input to 1.76 volts at maximum pressure. The GM 3.3-bar sensor seems to have a bit lower output impedance and will drive the 2G baro input a little higher, but it's still unsuitable. </p> <p> Short of removing that resistor from the ECU (described below), the 2G baro input is suitable for use only with very low impedance sensors (even a 50-ohm output impedance will produce a little over 1% of voltage offset). Since most sensor designs have a resistor in series with its output for protection, the 2G ECU's baro sensor input is probably not suitable for use with most sensors. </p> <p> <b>OMNIPOWER NOTE:</b> The <a href="http://www.ecmtuning.com/product_info.php?cPath=28_30&products_id=47" class="urlextern" title="http://www.ecmtuning.com/product_info.php?cPath=28_30&products_id=47" rel="nofollow">OmniPower 4-bar sensor</a> that we sell on our website *does* work fine on the 2G baro input. This sensor incorporates a buffer circuit that drives the 2G baro input just fine. </p> <p> <b>GM MAF CABLE NOTE:</b> Also note that our GM MAF cable's "baro" <a href="/wiki/doku.php?id=gmmafiatbaro" class="wikilink1" title="gmmafiatbaro">breakout wire</a> includes a buffer circuit as well. So any sensor connected to a GM MAF cable's "baro" wire will work fine as well without having to deal with the 2G ECU's baro input resistor configuration. </p> <p> The 1G baro input doesn't seem to suffer from this problem. It has an input impedance similar to the 2G MDP sensor input's 100K ohms). </p> <p> <b>12/19/2007:</b> Instead of this process, you can also consider using the <a href="/wiki/doku.php?id=ecuinputdata" class="wikilink1" title="ecuinputdata">buffer circuit</a>. </p> </div> <h1>Process</h1> <div class="level1"> <p> If you're really looking to maximize inputs, you can consider removing R39 from the underside of the ECU board. Best to use a couple small-tip soldering irons for this. Heat 'em up, apply one to each side of the resistor and slide it right off. I'm including a picture of the location of the resistor of interest below. I have verified that this does allow a GM 3bar to drive the baro input just fine. Once you have done that, you can use either the baro or the intake air temp inputs for whatever you want. </p> <p> <a href="/wiki/lib/exe/fetch.php?tok=6b2991&media=http%3A%2F%2Fwww.dsmlink.com%2Fimages%2Fforums%2F2gbaro.jpg" class="media" title="http://www.dsmlink.com/images/forums/2gbaro.jpg"><img src="/wiki/lib/exe/fetch.php?tok=6b2991&media=http%3A%2F%2Fwww.dsmlink.com%2Fimages%2Fforums%2F2gbaro.jpg" class="media" title="www.dsmlink.com_images_forums_2gbaro.jpg" alt="www.dsmlink.com_images_forums_2gbaro.jpg" /></a> </p> </div>