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How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue

Old 07-02-2015, 02:02 PM
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How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue

This is an ECU repair guide for the 280ZX Turbo computer, but is also generally applicable to any ecu or circuit board. If the car has ever experienced a major electrical malfunction (battery jumped backwards, wires shorted, EFI harness improperly grounded, etc) the fusible links may not save all the electronics. A fairly common problem after accidentally backwards jump starting a 280ZX, is that the car wonít start (no spark). The ECU LED will still light up, but will not output spark signal to the ignitor / coil. Other ECUís have been known to no longer send power signal or intermittently cut power to the fuel pump. If you have narrowed down the problem to the ECU, open it up and check for burnt resistors. Resistors have color bands to easily see their ohm and wattage values, but when they burn, itís not always easy to tell what color bands the resistor had. In this case I had a spare working ECU to compare. I have included high resolution images of a Turbo ECU internals for reference.

Tools needed:
  1. Normal and mini Philips screw drivers.
  2. Flathead screwdriver and/or gasket scraper.
  3. Needle nose pliers.
  4. Fine point soldering iron and thin strand solder.
  5. Bright work light so you can see what you are doing.

Procedure (82 Turbo ECU used as example):
  1. Remove ECU cover. There are two normal Philips screws on the bottom thin edge, and two mini Philips screws at the top.

  2. Remove six Philips screws from inside top circuit board. **There is a hard protective gel covering the screws and board. Be careful / gentle when removing screws.** Use a large flathead screwdriver or gasket scraper to gently GENTLY! pry up the board after screw removal, it will then fold open towards the bottom like a book. There are wire ribbons attached to this daughter-board so again BE GENTLE.

  3. Inspect all resistors. If the ECU has the no-spark issue it will likely be the resistor close to the harness wiring plugs, going to ECU pin# 5 (signal wire to ignitor / coil). It is a 22-ohm ľ watt resistor (Color bands: Red Red Black Gold). A burnt resistor should be fairly easy to spot. You can test resistance (multimeter leads on each side of resistor: testing ohms) to see if itís completely shot, or still functioning.

  4. Turn ECU over and locate the solder points of the dead resistor. Take note of direction (polarity) of the resistor for easier installation. Using a fine point soldering iron in one hand, melt the solder enough to push the wire of the resistor back up through the hole with a screwdriver or similar useful object in the other hand. A second person comes in handy here as they can pull with needle nose pliers while you are heating the solder. *No pictures of this since my available hands were taken*

  5. Once resistor is removed the solder will quickly fill the hole, so I placed a needle at the hole, melted the solder, removed soldering iron and quickly moved the needle through the hole so the cooling solder would pull free of the hole. Now there should be enough gap to slide the new resistor wire through each hole.

  6. The Resistor. RadioShack didnít have the OEM spec ľ watt resistor, but did have a Ĺ watt. The rated wattage is how much the resistor can handle / dissipate. You can go larger, but not smaller than the rated spec. Seeing as how these have a tendency to burn out, Iíd say Ĺ watt should have been used in the first place. So I got RadioShack part# 271-1103 22-Ohm Ĺ-Watt resistor. The 5-pack was $1.49.

  7. Installing the resistor. Pre-fit the new resistor into the open holes, making sure itís installed with the same polarity as before (use color bands as a reference). Turn ECU over and gently pull the wires tight so the resistor is centered and snug. Bend wires towards each other at the base so the resistor stays snug. Use soldering iron to melt solder and secure wires. Use a bit of new solder to fill any gaps but do not allow these solder points to touch any other solder points, thus the need for a fine point iron. Once cool, clip off excess wires and gently press down tips so the arenít protruding higher than the others.

  8. Turn off soldering iron and inspect solder job. Replace the daughter-board, install board screws and lightly tighten. Install cover. Install ECU back into car. Before starting, verify that ECU LED light is on and fuel pump primes. Start car and drive!

Helpful resistor color band chart and calculator:
4 Band Resistor Color Code Calculator and Chart

Attached Thumbnails How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-1-solder-sized.jpg   How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-2-ecu-cover-sized.jpg   How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-3-ecu-screws-sized.jpg   How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-4-ecu-full-sized.jpg   How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-5-resistor-close-up-sized.jpg  

How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-6-resistor-close-up-after-sized.jpg   How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-7-new-resistor-sized.jpg   How To Repair ECU - Burnt Resistor - No Spark / No Fuel Issue-resistor-color-chart.jpg  
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