Calibration Resistor

NOTE: You do not need to know any of this if you are buying our FSD heat sync kit! The calibration resistor is already installed for you and you will never need to know it exists again, but if you are buying individual pieces, or just curious, read on!

What is a calibration resistor?

The Calibration Resistor on your 6.5L Diesel sets the maximum fuel delivery volume of the injection pump. It is analogous to the maximum fuel adjustment screw on an old fully mechanical injection pump. The resistor itself is actually surfaced mounted to a tiny printed circuit board like the one in the picture above, but the whole thing is called the calibration resistor.

Where is the calibration resistor located?

The calibration resistor actually slides into the connector of the PMD itself, and then the wiring harness plugs in on top of it - see picture below. The PMD on the right has a resistor installed; the PMD on the left has none. Looking at the picture above, you see that the calibration resistor has six drilled holes in a row - this is so the resistor can slide down over the six electrical pins of the PMD all the way down to the base of the connector. Notice that two of the holes are surrounded by silver circles. These are the contacts that allow the resistor to make connection to the pins of the PMD. Also notice the two extra holes - these are to allow you to get a hold of the resistor if you need to remove it.

How do I remove and install the calibration resistor?

Installation is easy; you can't put it in wrong. Notice the slot in the picture above to keep in from going in the wrong way - it will not go upside down or backwards. Just use a small screwdriver as in the picture below to press between the two silver circles and push the resistor down to the bottom of the connector. Be careful not to bend any pins! Removal is also easy. A snap ring pliers works great - see the pictures below. Just catch the snap ring pliers in the two empty holes, squeeze the handles, and carefully work the resistor up. If you don't have a snap ring pliers, bend a paper clip into a big "U" with some small hooks on the ends. The paper clip method takes some patience.

What value calibration resistor should I install?

As each injection pump is built at the factory, GM required them to deliver a specific amount of fuel for emission purposes. Since each pump will be a little different due to production tolerance, calibration resistors were needed. Typically, the bulk of pumps came down the line with a #4 or #5 resistor. If you do not know what resistor your truck had and want to stay as close to stock as you can, just buy a #5 resistor. Most people buy the #9 resistor - it is the highest number available, and will increase your maximum fuel delivery about 6%. Note that this will not affect mileage significantly, unless you are always at wide-open throttle! Remember this sets maximum fuel delivery, so if you are just cruising along, there is no effect, but when you are pulling a big trailer, or trying to get on a freeway, you have that little bit of extra power. Please note that your truck's computer (PCM) will only "look" at this calibration resistor occasionally, therefore, after you install a different resistor, it may take some time for it to take effect and make a difference in the way the truck drives. This is also why people are often able to go for some time without a calibration resistor with no problems. What it takes to trigger the PCM to learn a new resistor seems to vary with different years and software configurations, but most trucks will "look" after a TDC offset learn procedure performed with a scan tool, after about 50 drive cycles, or after an extended battery disconnect. If you are not in a hurry, just wait, the update will take place eventually!

Why do I need a new calibration resistor?

Our FSD kit comes with a calibration resistor already installed. The reasoning behind this is that your old diesel PMD calibration resistor cannot be removed without removing the old PMD which is nearly impossible (especially on newer trucks) without pulling the intake. This would require several hours labor and the price of the gaskets required alone is more than what the resistor costs. Calibration resistors "never" go bad, they are just too hard to get out, so we install new ones in our kits! If you are just buying a new PMD and can re-use your old resistor because you have the pump off already, have an extra one around, etc. there is no reason to buy a new resistor.

We have #5 and #9 resistors available for sale below. If you need another number, just drop us e-mail, we usually have a good selection, but these two numbers should satisfy 99.9% of your needs.

Click here if you would like to purchase our FSD Kit.