Thank God an 84 Eldo has on board diagnostics

[carnut]

Wanted to relate a story that happened 2 days ago leaving work at 9 pm. I have an 84 Eldo 4100 with 78,000 miles. While driving, I heard a faint siren type noise as the throttle was moved. Entered diagnostics while driving and determined the alternator was putting out first 16.2 volts then 17.1 !! Got home verified that with a volt gauge attached to the 12 volt connector on the alternator it was, in fact, 17.1 volts. The alternator was too hot to touch! Removed unit, split it open, replaced the voltage regulator and reinstalled it. Again entered diagnostics and confirmed 13.2 to 14.2 volts after repair. Took 1 hour and a 14.00 regulator and 1 beer!. No need for a scanner, no need to guess. Proper understanding and diagnostics can be done by anyone with basic car repair skill. So, arm yourself with the factory service manual, read thru how to enter and run diagnostics and you will need to ask less questions. Or with the info gained, be able to ask more complete questions of the forum. These Cads from the mid 80's to late 90's have a very sophisticated diagnostic program which is easily accessed and understood.

[peteski]

Nice job carnut! Yes, in some instances the on-board diags can be very helpful. But in others the diage can be useless. I chased very intermittant stalling and intermittand loss of engine power for a long time and the diags showed no problems at all. It ended up being an intermittant fuel pump. The diags have no way of checking the operation of the fuel pump (except checking for electrical open or short). So, in my case the diags were useless.

Of course if our car had a voltmeter in the dash that woudl have also indicated a problem. But as you found out, it is good that we at least have access to the diag readouts.

Peteski