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81

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by bd on September 02, 2025, 06:45:33 pm »

What does the meter indicate if you touch the two ohmmeter probes together?

82

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by bd on September 02, 2025, 06:43:20 pm »

You didn't say if the EGR and EAC solenoids measured greater than 10 ohms...?

83

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by bd on September 02, 2025, 06:41:21 pm »

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?

84

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by Yellowcat on September 02, 2025, 06:38:25 pm »

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

85

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by Yellowcat on September 02, 2025, 06:13:23 pm »

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

86

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by Yellowcat on September 02, 2025, 06:09:55 pm »

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87

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by Yellowcat on September 02, 2025, 06:07:56 pm »

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88

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by Yellowcat on September 02, 2025, 06:06:59 pm »

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?

89

Engine/Drivetrain / Re: Vortec spark plugs

« Last post by Chevygold on September 02, 2025, 11:13:54 am »

Got 7 plug holes cleaned all the way down then rain stopped play, headers don't make for easy access to get anything into the threads on some cylinders!
Hopefully I'll get the new plugs tomorrow and can get them in then see how she runs with the right plugs, I imagine the recessed electrodes will have an affect on the dynamic ignition timing being buried 1/2" into the head?

Graham

90

Electrical / Re: ECM 1 fuse blowing 1987 chevy

« Last post by bd on September 01, 2025, 11:34:37 pm »

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.