Hi Guys. I'm writing because I'm at an absolute loss with the electrical gremlin in my 2001 4.3 MPI with Alpha 1 running the 555 ECM. I purchased this boat knowing it had an issue but being pretty handy I thought it would be an easy fix. I wasn't very MCM savvy at the time....
I don't have the original engine number because it has a remanufactured GM long block but attached is the ECM details.
The most obvious symptom is that when the ignition is turned to the on position, there is no normal alarm status and the fuel pump doesn't prime for a few seconds as it should. Leaving the key in the on position, exactly 20 seconds from switching to on, the MPR and FPR energise and the alarm and fuel pump run continuously. At this point everything remains energised for approx 40 seconds at which it will momentarily stops for less than a second before running again for about 40 seconds. This cycle continues reliably. During this time the engine will start with alot of throttle and run very rough and rich. No matter the throttle position, revs will not increase above about 1500 rpm (I'm guessing as the tach is not operating at this point) like it's at a guardian rev limit. I have the ECM 555 manual and have systematically checked all ground's, 12v & 5v powers, and continuity of critical wires in the harness. I don't have a scan tool and cannot get it into a shop for 3 - 4 weeks as they are busy. I purchased a vessel view mobile module with the hope of reading some codes myself but it doesn't work correctly, something along the lines of “Error - Cannot complete initial setup. Please key on all engines and try again.” so that was disappointing. My harness didn't have the yellow topped terminal resistor so I purchased one of them to no avail.
I did have it in my local shop where I asked specifically for them to perform a scan, but apparently they knew better and just started to throwing parts and labour at it before the mechanic contracted COVID and didn't return to work. So I paid the money and picked it up in the same state I dropped it off, no scan performed. They replaced the plugs, oil sender unit (guage would max out with key on) and cleaned the injectors as it wasn't holding fuel pressure. But DIDN'T scan for codes!
I am leaning towards a fualty ECM but that's just a hunch. Also suspicious on the raw water pressure switch mounted on the power steering cooler. Would love to test but don't know the resistance values across the 3 pins.
I have seen this exact symptom on other forums/threads but unfortunately the solution is never posted....? Any help or direction would be greatly appreciated, I am sure somebody has the answer.
Thanks guys.
Chris
I don't have the original engine number because it has a remanufactured GM long block but attached is the ECM details.
The most obvious symptom is that when the ignition is turned to the on position, there is no normal alarm status and the fuel pump doesn't prime for a few seconds as it should. Leaving the key in the on position, exactly 20 seconds from switching to on, the MPR and FPR energise and the alarm and fuel pump run continuously. At this point everything remains energised for approx 40 seconds at which it will momentarily stops for less than a second before running again for about 40 seconds. This cycle continues reliably. During this time the engine will start with alot of throttle and run very rough and rich. No matter the throttle position, revs will not increase above about 1500 rpm (I'm guessing as the tach is not operating at this point) like it's at a guardian rev limit. I have the ECM 555 manual and have systematically checked all ground's, 12v & 5v powers, and continuity of critical wires in the harness. I don't have a scan tool and cannot get it into a shop for 3 - 4 weeks as they are busy. I purchased a vessel view mobile module with the hope of reading some codes myself but it doesn't work correctly, something along the lines of “Error - Cannot complete initial setup. Please key on all engines and try again.” so that was disappointing. My harness didn't have the yellow topped terminal resistor so I purchased one of them to no avail.
I did have it in my local shop where I asked specifically for them to perform a scan, but apparently they knew better and just started to throwing parts and labour at it before the mechanic contracted COVID and didn't return to work. So I paid the money and picked it up in the same state I dropped it off, no scan performed. They replaced the plugs, oil sender unit (guage would max out with key on) and cleaned the injectors as it wasn't holding fuel pressure. But DIDN'T scan for codes!
I am leaning towards a fualty ECM but that's just a hunch. Also suspicious on the raw water pressure switch mounted on the power steering cooler. Would love to test but don't know the resistance values across the 3 pins.
I have seen this exact symptom on other forums/threads but unfortunately the solution is never posted....? Any help or direction would be greatly appreciated, I am sure somebody has the answer.
Thanks guys.
Chris
