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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: Yellowcat on August 05, 2025, 02:26:16 pm
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Have a 1987 chevy tbi 350 which was blowing the ECM 1 fuse soon as I turned ignition key on. It done it a few times but now I driving it for a week an nout blowing fues. What components are running on this one ECM 1 fuse? I need to trace all these wires going out from the ECM 1 fuse?
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photo of fuse box
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Does it have an AIR pump? EGR Solenoid or EGR Vacuum Regulator? Not enough info on you truck but see the attached.
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It has smog air pump if that what you mean. I just got stranded on the road again today. As soon as I turn key on it blows ECM 1 fuse please help tell me which items are going to this fuse.
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In order to help you, we need your help.
Remove the air cleaner and snap pictures of the engine from either side and front then snap a full-frame picture of the Vehicle Emission Control Information (VECI) label affixed to the radiator support or air cleaner housing. Post the pics. This will show us the emission control configuration and many of the electrical appliances powered through the ECM I (ECM Ignition) fuse.
GM routinely color codes ignition power feed (I+) wiring pink with black tracer (PNK/BLK). All of the wires protected by the ECM I fuse are color-coded PNK/BLK, designated on wiring diagrams as circuit 439 (CKT 439). However, not all PNK/BLK wires are protected by the ECM I fuse. Some PNK/BLK wires are protected by other fuses and carry different circuit numbers. In other words, all ECM I wires are PNK/BLK, but not all PNK/BLK wires are ECM I wires. This will become important as you troubleshoot.
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The photos
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The harness here has constant 12v but the green and white wire will not get any power when you turn key on to power fuel pump or relay . Tried to jump fuel pump from fuel pump relay wire and do not hear fuel pump. Forgot to mention it is not blowing any fuse under dash for some reason
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Constant 12 v on orange wire I forgot to menton
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which wires to jump to test fuel pump to make sure i did right? someone told me might be a fusible link somewhere on this model to keep power going to fuel pump relay harness?
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The items labeled with yellow text, along with the ECM, are powered by the ECM I fuse via PNK/BLK circuit 439.
To test the components for shorts, switch the ignition OFF, unplug the EGR solenoid, EAC valve, and ESC module (yellow labels), and lay the connectors to the side. Connect an ohmmeter between the two pins of the EGR solenoid and then the two pins of the EAC valve. Both should measure greater than 10 ohms. If either measures less than 10 ohms, the component is faulty. Checking the ESC module is slightly more challenging. Use the ESC harness connector to determine which two ESC module pins connect to the PNK/BLK wire and the brown (BRN) wire. Connect the ohmmeter between those two module pins (should be terminals "B" and "D" according to the factory diagram). As before, if the measurement is less than 10 ohms, the module is faulty (don't be alarmed if the ESC module measures considerably greater than 10 ohms).
If all of your resistance measurements were 10 ohms or greater, reconnect the wiring harness to the three components. Trace the harness while carefully looking for any place where the harness comes into contact with bare metal or turns a corner around a sharp metal edge. Inspect for chafing or pinching of the harness or any of its wires.
The fuel pump circuit is powered by the ECM B (constant battery power) fuse via orange (ORG) circuit 440. The ECM supplies 12 volts to control the fuel pump relay via dark green & white (DK GRN/WHT) circuit 465. The black & white (BLK/WHT) relay wire is the relay ground. When the ignition is switched ON, the relay will energize the in-tank fuel pump via the tan & white (TAN/WHT) circuit 120 for up to two seconds before shutting off automatically if the engine does not start and run. The fuel pump should continue to run as long as the engine is cranking to start. The fuel pump relay connector has a 3" long RED/WHT pigtail with a brown connector. Jump the short RED/WHT pigtail to battery positive (B+) to bypass the relay and power the fuel pump directly for testing purposes only.
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The ESC module tested out with a fluke meter only staying on OL. The wires you had said was different colors here on B and D. Why is the Fluke meter staying only on OL when I touch the two pins B&D is it supposed to do this?
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I touched the probes on all different pins of the ESC just to see if anything would happen...... it every time it just stays on the letters OL. I done all these three separate tests with the ignition key switch off
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Also as I have stated before the wires going to the fuel relay do not have power when turning the ignition key on the only wire that has constant power when the key is off is the orange wire
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Don't be alarmed by the 'OL' measurement on your meter. OL means overload, indicating the circuit is effectively open from the perspective of the ohmmeter. The ESC module, unlike the EGR solenoid and EAC valve solenoid, contains an integrated circuit with very high internal impedance that conducts microamps of current. The EGR and EAC solenoids are electromagnets with moderately low impedance flowing approximately 1 amp each. That's 6 orders of magnitude difference. The primary concern was to discover whether the ESC module is shorted. It is not.
Simply for the sake of interest, recheck the ESC pins reversing the probe polarities to see if there is any difference and let us know.
Regarding the fuel pump, will the engine start and run?
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You didn't say if the EGR and EAC solenoids measured greater than 10 ohms...?
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What does the meter indicate if you touch the two ohmmeter probes together?
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The multimeter buzzes and goes to 0 when the probes are touched.. the EGR and EAC tested both at 37ohms. The truck will not start and run because I can't get power to fuel relay like it's suppose to have or power to the pump when I tried to jump it from the pigtail on the fuel relay. Why is there no power to the green and white wire on e fuel pump relay when you turn ignition on??
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See below.
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The truck cranks today and runs after cranking for 10 seconds or more. Still the fuel pump relay us nit getting all the signals. I post a link to videos to watch it. Still the pump is not priming like it did for 2 seconds
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https://youtube.com/shorts/3pHSupQrGhI?si=GTz1wP2Y-YJmjgrm
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https://youtube.com/shorts/3pHSupQrGhI?si=zqMyS2clF9DZK1x-
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The green and white wire going to the fuel pump relay is coming only from the ECM? If it is and the ECM is faulty?
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With the fuel pump relay connected to its wiring harness, will the fuel pump run as long as you feed B+ to the RED/WHT pigtail? Using an incandescent test light clipped to a good, clean ground (not your voltmeter), probe the DK GRN/WHT wire connected to the relay and start the engine. While the engine is cranking and running, does the DK GRN/WHT wire illuminate the test light?
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The fuel pump will not run when I put B+ to the pigtail when engine is not running. When I grind the engine10 to 15 seconds to finally get it running I probe the red and white striped pigtail wire it is hot. I posted a video of this. I probed the green/white when engine us running and it does not illuminate the test light. https://youtube.com/shorts/v3nxZngrtwk?si=O65XhmUublzyfdTf
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Reference and familiarize yourself with the diagnostic charts that I previously posted. Verify perfect power and ground continuity to the ECM. Check continuity of the DK GRN/WHT wire between the ECM and fuel pump relay. Clean the harness connections to the ECM using some DeoxIT D5 or CRC QD Electronic Cleaner, etc. You may need to very carefully re-tension the terminal connections to the ECM and verify that none of the terminals are distorted, broken, or heavily corroded.