Convert Your 84/85 to an 86/87 ECM
Dan Smith -
The following article describes how I updated my wiring harness and ECM to the newer '86-87 ECM. This update has several advantages over the original ECM such as:
  • Greater chip availability
  • The ability to use Tweaker to program you own chips
  • Twice the available data from TurboLink (R) in Road Mode
  • The ability to use BST-001 Boost sensing option for TurboLink (R)
  • 1227148 ECM's are readily available in the "yards"
  • Electric fan control available (Optional)

I'm sure there are more reasons to change to the newer ECM, but these are the major reasons, feel free to think up your own too. <grin> I have recieved a lot of e-mail from people wondering if the car will run faster or get better ET's from the conversion. None of this will happen UNLESS it stems directly from the advantages listed above.

A few things the ECM conversion won't do is to:
  • Make a poor running car run better
  • Fix a broken fuel pump
  • unplug a fuel filter
  • Repair bad injectors
  • Fix a bad TPS
  • Fix a bad CTS
  • unplug a plugged cat converter
The Conversion
After much testing, I must suggest that you also get a 86/87 MAF part #25007866. The calibration of the 84/5 MAF is different and gave drivability problems with the 1227148 ECM, when cold weather came upon us in St.Louis. The colder air sensed by the MAT richened up the fuel air ratio, trying to compensate for the denser air, to the point that the car would belch black smoke out of the exhaust. Switching to the 86/7 MAF cured the problem.

First off I went to the U-Pullit and got a wiring harness out of a FWD GM car with a '86-87 3.0-3.8 V-6 in it. When I removed the wiring harness, I removed the relays and sensors that were plugged into it too. Then I striped the harness down and dissected it wire by wire. This way, I got all the fan relays AND the MAT sensor w/plug and wire to the ECM. The wires at the ECM plug come out with a large paper clip (or jewlers screwdriver) inserted into the release hole. If you have never had a wire out of the ECM plug before, I suggest a little practice on the OTHER harness first!

Before your car can be driven without the SES light on, the MAT sensor must be put in. I cut a hole in the bottom of the K&N right in front of the MAF sensor to sample the incoming air temperature. Then I took the sensor plug/wire and ran it to the ECM by poking thru the grommet on the speedometer cable. I use wire loom in the engine compartment to dress things up and make things look factory. I ran the wire to the ECM under the dash carefully staying away from the gas and brake pedals. The MAT uses the same sensor ground as the TPS and CTS ,so I spliced into the ground wire at the ECM (D-12 black,no stripe). The other wire from the MAT sensor needs to be plugged into pin #C-11 (tan) at the ECM, this is where the wire from the other car came into play. It should still have the clip on the end that will plug straight into C-11 on the ECM plug.

The ECM can come out of a 86 century but be sure to have the part #1227148 ECM. The dealer gave me two part #'s for the cal-pak in the ECM, they are 16036503 and 16036504. My 84 ECM HAD the 16036504 in it so I used it.

Pitch any other cal-pak with a different number. I downloaded a ROM file from the archives for the prom. Any 86-7 chip should do. Use a stocker to get things going. But with the addition of the MAT sensor,and the chips to the ECM, this will plug straight in and run.(without the MAT sensor)
As far as the electric fan setup goes,This IS an option. The fan control at the ECM is pin #D-2. This circuit grounds a relay when active. There are many ways to wire and electric fan. So I will not go into too much on it right now. I wired up the 10 min timer to come on if the car shuts off and the temp sensor in the radiator is tripped(about 195 deg) with the fan on high. The fan also runs on hi when the ECM calls for it. I have the low speed coming on with the A/C. To get more acquainted with the fan circuit (and ECM).

I went to the library and looked up all the different years in the Mitchell manual. Take a bunch of dimes and copy the pages that you are interested in, like the ECM pinout and the fan setup on several cars. I found some pusher/puller fan setups too.

As you should always do when splicing/adding wires. I use a 150 watt or so soldering gun and rosin core electrical solder to solder ANY connections you make. There is nothing more frustrating than looking for an electrical "gremlin" than to find out that YOU were the cause of it by not doing it right the first time. Get the wire good and hot so the solder can flow into it.

Also use HEAT SHRINK! Tape tends to come loose and fall off over a period of time, and get "gooey".

At the ECM , taking the wire out of the plug , stripping a small area bare a couple of inches from the plug and solder the wires together. Then, slip on the heat shrink, and make sure it shrinks good.

By following my procedures outlined here, the ECM can be changed (less fan circuit) in about 30 minutes if you have all the stuff already.

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