Problems:

Non-functional speedometer
Alternator undercharging/overcharging
ABS non-functional

Suspected cause:

Bad Computer

As you all know, the computers on our engines are massively prone to failure, most likely due to them having been placed like a pig on a spit, right above the BBQ that is our engines. While other vehicles' computers enjoy a nice comfy life inside of the cabin of the vehicle, ours are enduring a constant trial by fire.

My speedometer and ABS have never worked since I bought my van, and replacing my rear ABS sensor and transmission speed sensor made no difference. Then the alternator started losing voltage at lower rpm and overcharging at higher rpm. Alternator tested good when removed and tested. Replacement of the alternator made no difference.

Reality:

I actually got around to inspecting my ABS module, after discovering that the speedometer functions through it, and not the transmission speed sensor. Discovery? Module badly corroded from battery acid, and all plugs literally burnt, carbonized to a crisp. Replacement is pending.

Anyone know if this is one of those units that requires a special tool to bleed?

Where the alternator problem is concerned, replacing my belt with a Gatorback, and my tensioner and idler pullies put my charging problems to bed. Go figure. How that could have ever caused my alternator to charge at 16 volts, I will never know.

I hope this will serve as a reference to those attempting to diagnose problems in the future.

 

No special tool to bleed the ABS - quite the opposite. You just crack the fittings and yes, brake fluid does spill out. Use lots of rags (obviously) to catch the fluid and wash the area down well when done.

After the ABS is done bleed the wheel cylinders and calipers.

When I replaced my ABS module I was able to vacuum bleed the entire system sucessfully from the wheel cylinders and calipers, but some have reported difficulty with this approach. Worked like a charm for me and saved me lots of mess and aggravation, plus I didn't have to ask the wife to pump the brake pedal for me.

Gatorback is by far the best and quietest serp belt I have found. Dayco and DriveWorks belts SUCK. I have the Goodyear belts on all my vehicles, even my Lexus, and they are awesome.

 

Been my experience too. I've been a believer ever since I first used one at 12 years old to cure a power steering loss issue on my father's Explorer. Brand new truck, with the factory belt, and it lost its power steering in the rain every single time. After Gatorback went in, no more problems.

Thanks for the tips. I will get on that bad boy ASAP. Before I do anything though, I'm getting that Optima in, so I never have to worry about acid killing the damn thing ever again.

I'll get myself a vacuum bleeder to make my life simple as well.

 

Its great you found solutions to your problems. For me it was the PCM. The overcharging is what keyed me to that issue. The place that did the repair stated simply that electrical sodder connections inside the PCM are pretty common.

Jason

 

I forgot to mention that what really had me convinced that it was the PCM was that it only did the overcharging when in overdrive range, when the torque converter clutch disengaged. I could sit there at 50mph, and play with the overcharging. Soon as the converter clutch locked up, bye bye overcharging. Soon as I touched the throttle enough to disengage OD, there went the damn overcharging back on again.

I will never understand in a million years how changing my belt/pullies got rid of that. Never.

 

I've heard good things about the performance of Optima batteries but they are the ugliest damn things ever. Can't imagine ruining a pristine engine bay in a restored muscle car with one of those bright yellow or red hunks of plastic, and it turns my stomach every time I see somebody who's done it. Perfectly fine for a van though.

 

Optima had some good years and some not so good.

All AGM batteries have more cold cranking amps than equivalent sized flooded batteries, but Optima, due to the six pac design, has less capacity than a rectangular battery.

Seeing as how the same footprint Odyssey battery costs ~~ the same, yet has ~~25% more capacity.......

The Six pac design excels in very high vibration environments, but for most vehicles, well lets just say they are marketed well, and people like to believe they bought the best, even if it is not true, or unneeded in their application.

Ignorance is bliss