Hi. Well my mechanic said this was the only car in 20 years he could not repair.
I'm hoping it's something so simple that he is just overlooking the problem.
The car started rough idle at red lights or in traffic and progressively got worst.
It now will not stay started, unless you keep the engine revved at about 2000 rpm.
Something strange he found while working on the car was that if you disconnect the
alternator from the battery the car will run fairly smooth at idle. As soon as you plug in the
alternator the car will kill. Alternator was changed and did not fix the problem.
With the car running at 2000rpm and the alternator plugged in, I checked the voltage on
the battery and it is 13.7 volts. It seems the charging circuit is working properly, right?
With the car running on just the battery the voltage is 12.3 volts.
Why would plugging in the alternator kill the car? The fuel filter, fuel pump, distributor cap, ignition switch, idle speed motor, vacuum hoses, spark plugs and wires, and battery were all changed. He also changed the computer just as a last resort and it still did not correct the problem. He finally gave up and said he's never seen anything like this before. Car is a 1988 Chrysler LeBaron, 4 cylinder, 2.5 liter, 85,000 miles. Please Help! Any suggestions would be appreciated!

Thanks,

Trudy

Just some thoughts: I saw this post elsewhere and didn't know what to suggest then either.

Ok: This is behaving like a vacuum leak. This engine was known for head gasket problems and that should be checked out. I don't know why unplugging the alternator makes a difference like you said and that might be confusing the diagnosis.

If I recall (worry about that!) that computer is behind the passenger's kick panel and can get soaked with road water, dirt, salt and the connections can get all messed up. Was anything mentioned about that?

This or a similar model and year about 10 years ago had a respectable "terraruim" going on in there and it wasn't a rust bucket??!!

Just thoughts for now,

T
Tom Greenleaf - MetroWest Boston - USA
_________________________________________

http://www.autoacsystems.com/tomgreenleaf/

What you and your mechanic have to determine is whether the problem is the load or engine power that’s needed to turn the alternator is the cause; as in the engine not producing enough power?
Or whether it’s an electrical short between the alternators field circuit and the PCM (computer) that’s causing the PCM to make the wrong calculations?

Have you actually driven the car with the alternator disconnected; if so, did it run “normal” while the battery voltage was still up?

If the car did run ok; next I would start testing individual PCM circuits; starting with the alternators field circuit.
Connector 2, terminal 14 a dark green wire at the PCM is the alternator’s field driver; via the PCM this circuit provides the path to ground for the alternator field. In other words it’s the voltage regulator wire; where the PCM will control the on time of the charging system.

All circuits need to be tested for shorts to ground and power; very time consuming but the way it sounds, very necessary

One last thought is; there is a stamped welded wire connection inside the wiring harness where a number of dark blue wires are connected together.
This dark blue wire feeds power to a number of different systems; some of which are the alternator, ignition system, fuel injectors, PCM and engine cooling fan, just to name a few.
You’ll find this connection along the left inner fender, usually close to the battery; the biggest corrosion generator under the hood.
This connection has been known for corroding and causing high resistance, which would lower the available voltage to all the devices that it is meant to feed.
Like I said this stamp welded wire connection is inside the main PCM wiring harness; it’s a bared wire connection with tape wrapped around if for insulation.

Maybe with the alternator connected, it might be overheating this connection (if corroded) lowering the circuits voltage and then the PCM gets stupid?

Dan.

Canadian "EH"


(This post was edited by DanD on May 6, 2008, 9:05 AM)