I own a 1988 3/4 ton Dodge passenger van with a 318 engine. The fuel system is a throttle body injection controlled by a smec.
The smec also controls the field circuit from the alternator.
I replaced the alternator as a maintenance
precaution. Taking short trips in town(2 or 3 miles max)there was no problem. I took a little out of town and the engine check light came on and it was obvious the alternator had started to overcharge.
After digging thru wiring and hooking a volt meter to the battery and test driving I found the connection into the smec from the alternator field was intermittent and the alternator was not always charging. I repaired the connection and have 14+ volts
as soon as the engine starts and all seems fine.
My question is was the overcharge condition
a result of the engine controller going in a limp mode once the intermittent connection started working.
What light came on indicating a obvious overcharge condition?
The statement “I replaced the alternator as a maintiance precaution” is rather odd.
Then your story changes from a overcharge condition to a intermittent no charge condition, Is there a connection between the two pieces of info?
Then you link a “limp mode” condition. Do you feel there is a change by design in alternator output when a vehicle is in “limp mode”.
Did the vehicle exibit normal symptons of limp mode operation? (limited vehicle speed and limited automatic transmission gear range avialable)
Have you found any technical info on what happens by design when a 88 Dodge goes into limp mode? How do you know that “limp mode” was a feature in 88? (I am not saying it wasn’t) I just haven"t found any reference in my books. Also no reference of “smec” control of alternator output (also I am not saying it is not the way it is)
How high did the alternator output actually get?? A normal output should be anywhere between 13.5 to 14.5 volts.
transman
My reference shows fuel injection (TBI) for the 318 ci engine. The charging diagram for a 318 ci with FI, Fig. 8 shows a wire from the smec to the alternator: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528007fe1f
Follow the wires from the alternator, note and compare the wires, to the wiring diagram.Results?
Output voltage, of the alternator, is best measure with engine speed of 1,000 rpm plus.
The van has 121,000 miles on it and my son needed to use it for a trip so I changed out the battery, rear brakes, and alternator just for piece of mind and I have no desire to get rid of the vehicle any time soon. The alternator was just preventive
maintenance.
The engine check light came on and the onboard fault code was 46(engine has been running more than 6 minutes, engine temp above 160 and rpm above 1500)(the check engine light is activated when the voltage exceeds 1 volt over control control voltage for over 35 seconds). This is as described in the dodge service i bought when I purchased the van in 1989.
The service manual does address a limp in mode for low battery voltage by the smec on page 8A-21 but only a check engine light for overcharging.
There is no description of what happens in the limp in mode,and the vehicle drove fine except for the extra bright lights.
You are right that there is no connection between overcharging and no charging, that is what has me perplexed. The alternator field is not shorted the only the problem I found was the poor connection into the smec alternator field which now fixed is working fine.
I hope to find out if overcharging is a result of the smec going into limp in mode,
the service manual is no help.
Yes I think the limpin
In order for you to notice a “extra bright light situation” you would sure need tp be more than 1 volt high.
I wonder what this parameter is designed to protect, I have investigated many check engine lights,by far they were emission related, the charging system warnings were left to a light,a ampmeter,or voltmeter, and a “limp mode” that doesn’t cause the car to “limp” I have driven vehicles in “limp mode” there is no question that the vehicle is inhibited in performance.
OK I see, no effect on driveability for “high voltage detected” just turns on the “check engine” light
Since you did notice the lights get brighter the over charge must have be significant, is it possible this broken wire you found could have full fielded the alternator?
The voltage across the battery was significant (19+ volts).I actually burned out the high beams. I hooked a Radio Shack 15 volt Panel meter into the 12 volt outlet (cigarette light) and mounted it to the dash so I could monitor the system voltage.
I discovered that the vehicle was running on the battery at start up,( no charge) when I went over some railroad tracks(only a short distance from home) the voltage went from 12 to 14 volts. This was after I had pulled connectors from the smec pushed back in, after returning home I started “wiggling” the field wire into smec with engine running and the alternator kicked in and out. That’s when I fixed the (intermittent)connection.
I am still using the meter on the dash and the alternator is working perfectly. I really have no idea why the alternator overcharged since there was no short from the field wire. Bad alternator? bad smec? Limp mode feature?
I’m going to drive the van more see what happens.
Thank you for the input and advice.
Dodgeg