Alternator or dash CPU issue?

[toyotafreak]

Read with interest your comments about dash CPU issues and wonder if it is related to my alternator/charging issue.

The first time I took the boat out, I noticed the battery voltage was low at around 12.5 volts (an running automobile should show about 14.0 volts). The interesting thing was that at higher RPMs (above 4000 RPM), the voltage would suppress and the message center flashed low voltage alarms. Easing back the throttle shut up the alarm and allowed the voltage to come back up. Worst case I saw was around 11.0 volts. The battery was original (3 yrs old), so I was looking for an excuse to replace it.

Prior to the next run to the lake, I charged the battery. Exact same indications the next day. Together the two trips were about 4-5 hours, so clearly the alternator is charging.

After installing the fully charged Optima (see other post), voltage read around 13.0 with the engine off but the key in the ON position. With the engine at low RPMs, the voltage looked to be about 13.5. Unfortunately, after crossing the 35 mph line, the alarm and suppressed voltage issue returns. It?s almost like the alternator can?t generate enough juice to keep up with eight coils firing 75 times a second, and begins to rely on stored energy.

I pulled the alternator last night after verifying serpentine belt and charging fuse are good, and intended on having the local car parts place bench-test the alternator. Unfortunately, they need test setup information and have no information for our alternator. The Toyota part number doesn?t cross and neither does the Denso. The one Toyota dealer couldn?t get over the fact that it was from a boat and said they don?t bench test alternators. However, I did get the number of a good auto-electric guy in Norco, so we?ll see what he?s able to find out.

In a nutshell, the indicators are telling me the thing can?t keep up with ignition requirements at high RPMs, the battery is new and good, and the alternator is outputting juice (engines don?t run long on battery power alone.) All signs point to regulator problems, but the discussion of computer issues intrigues me. I do know that the service guy who?s been maintaining the boat since new said that there were computer problems and that this boat has the latest patches throughout.

I?d appreciate any feedback you may have.


Derek Boyer
(714) 758-4029

[cyclone]

Unfortunately, it is normal My boat has exactly the same symptoms, as do other Toyota Epics. One issue is that there is significant voltage drop (1.5vdc) from the dash to the MDC computer which is located back by the gas tank in my Epic 22. It is behind the fill hose on the driver side. I put pics of it on the How to page. I believe that under relatively high current draw situations (High rpm driving servo gauges, etc), there is enough drop that it causes erratic readings in the gauges. If you read your battery voltage (alternator output) at the battery under high throttle, you will find that your alternator is putting out 14.5vdc or so. The gauge will bounce around at around 11 vdc or so. A bigger wire from the dash 12vdc supply to the computer would probably help quite a bit. I haven't bothered, I just ignore the gauges. You should also peek up under the dash and find the black relay box with all the orange wires attached. The DC supply for all electronics comes from the two studs on the ends. Make sure that the 7/16" nuts that secure the DC wiring are tight, they loosen pretty easily. For this and other issues, you should burn up the email of a guy named rick.cohn@toyota.com, he is supposed to be working on these issues and others, but he is more or less an ignorant jerk. He refused to warrantee my split upholstery because it got wet occasionally and was exposed to sunlight. Duh, it's a boat! This kind of attitude is one reason that Toyota never had a chance in the comp boat biz.

Keep on posting, I'll keep digging up info!

Pete

[toyotafreak]

Great news (I think ??!!).

Brad's Auto Electric just called and the alternator went all the way up to 90 Amps on his bench. So it's good and strong.

I will definitely check out the wiring issue. The V-drive computer is all the way up in the dash. For the mean time, I will ignore and be happy.

For this particular issue, it would probably be nice to have (maybe even install) an ammeter like the older cars have. Then there can be do doubt about net gains or losses in battery power.

Thanks for the help!

[Gearhead]

You might want to check the power bus under the dash to see if the voltage drop is in the circuit from the battery switch to the dash or a problem with the MDC box itself. If the power bus is running at the same voltage as your display then I would look for a source of excessive resistance (like corrosion on your main fuse or battery switch) If its shows to be accurate voltage than look for a loose connection or corrosion in the MDC connector or other wiring. Running a supplemental (fused) power feed might also help.

[toyotafreak]

Thanks, I sure will follow up on both of your receommendations.

As soon as I can convince my wife that a nine foot bimini at $1K is a beeter deal than a six foot one at $400.



She is my reality check.

[eagle1wi]

I got this modification PDF from Borg Warner instruments.
I was having problems with my Epic 21 gauges.

I think it is worth a try if your unit is still working but had intermittent problems.  Unfortunately these MDC boxes have to share power with the rest of the dash.


Craig Nelson

[eagle1wi]

Let's try the attachment again.

Craig

[Gearhead]

Yeah alternate wire runs will probably do the job but there are 2 downsides to doing it this way:

1 - your MDC will always have power and your parasitic drain will still be there even with battery switch off

2 - You should add a fuse. Unfused wires are just a bad idea.

[eagle1wi]

I agree with gearhead about putting a  fuse on the power lead - it's cheap insurance for a very expensive MDC.  I would also add an on/off switch if I didn it this way.  

My MDC was beyond repair but when my new one goes in next week I will see if it behaves the same way the old one used to - gauge wandering under electrical loads, recalibration while running etc.  
It did this for a long time before it gave up and failed after 700+ hours of service.  If the new one does the same it will have its own power lead (fused of course).

As far as I can tell the MDC always has power under its "stock" configuration - the only time it would actually power down is if you shut off the Perko switch in the engine compartment.

Craig

[cyclone]

All of this info is awesome. I will address my issues after an awesome 4th of July weekend!