ECU B+ ripple+whack sensor reading. Topic is solved

[mrbrian200]

Does this look like a ECU problem, Alternator or potentially both to you? All seems ok at idle, then turns to whack as the engine speed is raised to 2000 RPM then smooths out again around 3000 RPM+ (not captured). I would like to think ecu internal power regulation would be able to deal with that amount fluctuation which looks only "moderate" to me.
Two MAFs on hand, identical readings from both. Intermittently settles down to normal readings at running speed (for short periods-shown at beginning), but mostly not.
Note, per previous thread, I have -not- removed/opened the ECU. The ground circuit is ok (0.2v drop between pigtail and both the chassis or ECU case). Engine grounds good. Installed a #4 copper soldered to ring terminals between the block/fender just to be certain. Starter cranks normal/fast.

As the ground circuit is ok, I'm not going to try to reverse engineer other areas (sensor input/power regulation) as the cost of a mistake could result in a 100 mile flatbed + ecu at nearest dealer and is a bit of a deterrent. I reworked the PEM successfully, but that module is plug and play, and "only" $300 (or less if good used). I would send this in.

[mrbrian200]

Interestingly-- no CEL lit. Low MAF and LTFT rich in memory but hasn't lit/active recently. Just lower than expected MPG (around minus 8-10) and sluggish at part throttle. If my let my sister drive it, accustomed to a 4-cyl base Jetta, she wouldn't think anything.

[mrbrian200]

Nevermind. Failed rectifier diode or shorted winding. It's been a very long time since I've delt with alternator issues as the last few cars were based on either Denso or Delco and factory alternators were good for the life of car or at least ticked on an obvious DTC or cluster light pointing to the issue with zero guesswork. Last time I saw this was on an '87 Oldsmobile that also used Bosch everything experienced severe drivability issues ECU didn't point to the real culprit I replaced the alternator on a haunch which solved it. Being more than 20 years ago I forgot how it was acting when the alt went bad.
Edit: Jogging memory more this is nearly identical to the '87 olds when it's alt failed- drivability/poor econ, ECU and cluster shows no indication of alt problem, Charge voltage low by just a little, a random/infrequent miss that doesn't get caught as a misfire and can't be nailed down to any specific cylinder/coil(DIS) or injector.

[mrbrian200]

Dropped off the alternator off to get rebuilt this morning. Good good local shop with several employees does alts/starters/some electronic modules. Should have it back/on car mid week. If issues persist after reinstallation then I'm pretty squarely lookin at sending the ECU in for repair correct?