wondering if anybody has had this problem. just bought an 01 6 spd 24v good shape but was told it needed an injector pump or an ecm. 1689 was only code at sellers house but ran and drove fine so i thought maybe the guy didnt know what he was talkin about.. ok so paid him , drove it home with engine light on.. no problems..got home, erased code still ran fine..a couple days later 1st start up engine light came on, rpms shot up to around 2k for a couple secs then came down to 900 rpms ,,, idles fine but throttle cuts out at about 1500 rpms..havent checked fuel pressure yet at pump but it has a holley pump on frame rail so im hopin its good ..so far i have went through the 1689 diagnostics from this site and each step checks out good. also checked ac voltage and cleaned grounds. also reset and done apps check per this site. it also checks good. i can erase the code but it comes back within a few seconds after startup .BUT before it comes on i have full range of throttle then as soon as it comes on  the throttle cuts out around 1300 to 1500 rpms..most searches say just to replace the vp44 but if its just a loose solder joint on the board inside the inj pump  or a bad resistor on it,i can fix that myself. i have tried a known good ecm but still same result. wiring harness and plugs all ohm out and check good. so im thinkin bad board on vp44.   HELP !!!  any info would be GREATLY appreciated!

Check for excessive AC noise from the alternator. Measure the AC voltage at the BATT terminal on the alternator. It should be 0.01 to 0.02 volts typically. 0.05 is marginal.. 0.10 is absolute failure...

How are you checking for codes? key trick or scanner? Not sure about repairing the FPCM, I have never heard of anyone able to do that. Check that fuel pressure, low pressure can kill the FPCM due to lack of cooling.