sundance - computer problems common?

Hello,

1990 Plymouth Sundance

I just replaced my alternator a few months ago when the car completely died
and it WAS happy for awhile. Now my check light is back, but erratic and
doesn't always stay on. When it comes on, the battery meter shows it being
lower than normal (and sometimes tickers back and forth) and the RPM sits
under 1 (generally it idles higher, at least 1 RPM). I diagnosed it via the
ignition trick and the code that came up was 41. Now the light is staying
on, battery indicator always low and today it showed fault code 16 as well.
They tested the voltage of the battery and alternator and it seemed normal
to them. I have been told this can be my alternator again or a computer
replacement needed. Can anyone one advise if replacing the computer is
common? I have found a few things on google but it all contradicts. This car
is such a money pit but I can't help loving it Thanks if anyone can help.

Kendra

 

On some models, don't know anything specific about yours, if the grounds can
corroded it makes the car nuts. I would check for bad grounds first. Also
a faulty battery or dirty terminal can make the computer act nuts.

 

41: Alternator field circuit open or shorted
16: Loss of battery voltage while engine running

These point to (surprise!) a problem in the alternator field circuit. Have
you verified that the two field terminals are firmly attached to their
studs on the back of the alternator? Tell us about this replacement
alternator you installed: Was it used (probably fine) or a
"remanufactured" hunkajunk from the parts store (definitely suspect)? If
everything's OK in the wires between the engine computer and the
alternator field terminals, then the computer's internal voltage regulator
has probably failed.

Loss of voltage regulation function is pretty much the primary failure
mode, and it's not incredibly common. You needn't replace the computer
just because the voltage regulation has failed, however. Here. This sounds
hokey, but it works just fine:

Take the easy and cheap way out. Use a NAPA Echlin VR1001 voltage
regulator. The terminal on the end of the regulator's short wire The
nut-and-stud terminal on the regulator body gets switched 12V from the
ignition switch, and the terminal on the end of the new regulator's short
wire gets connected (via a length of wire that you supply) to one of the
alternator's two field studs. It does not matter which of the alternator's
two field studs you connect this wire to. Then, using another length of
wire, connect the *other* alternator field stud to ground. The vehicle's
original two field wires get REMOVED from the alternator and taped off.
(on some '90 and later vehicles, this will cause the "Check Engine" light
to remain illuminated. Placing a resistor between the vehicle's two
original field terminals prior to taping them off will prevent this.)

-Stern

 

It is a refurbed from an auto source store; I was warned that these are not
very reliable by the mechanic that put it in but was not willing to pay his
outrageous markup. It has a 5 yr warrenty which is good if this is the
problem...except the labour is on me I have had several people check the
alternator and they did poke around the wires, tightened the belt, etc. and
didn't say anything. It will be removed and tested independent from the car
tomorrow and I will know if I can eliminate that from my search in what is
wrong or not!

Thank you for the suggestion. Reactions to computer problems so far have
been - trash the car or buy a used one, no one has said anything about
getting around it. This is my first vehicle so I know next to nothing about
cars except what I learn when something goes wrong with this one, but I will
ask whoever works on it to give your idea a try.

You've given me a little hope now Thanks again!

 

If it turns out to be a failed voltage regulator in the computer
Daniels work around repair works perfectly. We did this on a friends
car back last winter and haven't had a bit of problem since. He saved
my buddy along the lines of $400 for a replacement computer.

You really weren't paying your mechanic for his outrageous markup
(entirely).. Your paying for a quality product as compared to an
inferior product. If its an easy to replace alt I use the cheapies
myself but if you can't swap it yourself his labor charges to change
it out when it fails are going to outweigh the value of that five year
warranty pretty quickly.

Steve B.

 

I am expecting to have to do this at some time. How much resistance needs to
placed across the two field terminals to turn off the "check engine" light?

Also, will a 1/4 watt resistor of the specified resistance work?

-Kirk Matheson

 

I never remember. Resistors are cheap, buy a few different values and try
'em.

Should be fine.

 

An easy sure bet way to determine the resistor value would be to
measure the field current on a [correctly] functioning system and
use ohms law to calculate what resistor is needed.

 

Agreed, except my mom and I got our nails dirty and now we can remove and
replace the alternator ourselves

It wasn't the problem so we got a 20 dollar computer from a pick your parts
place and the light went off, it worked fine. However, I drove the old
computer home and it completely failed half way so my battery is dead

We tried a computer from a different source and rec'd the same error as my
current one so I have a feeling this is more common than one might think.
80% of the cars of this engine size had their computers missing.

I just wanted to thank everyone who replied