QuestionKudos to your site - well done and great information.
My problem relates to a 1995 Land Rover Discovery, 3.9 litre, w/ 110K miles. It's a great truck and we take it everywhere.
The problem is that I am getting intermittent voltage fluctuations and my RPM drops (to zero), suggesting an alternator problem. I took the alternator to a rebuilder and the only thing he found wrong was (a) dirt and (b) loose screws in the regulator, both of which he addressed. But the problem persisted (if intermittently). I later opened up the back of the alternator myself and found nothing visibly wrong with it - there was good continuity through the brush and no dirt or burns or anything, but I don't really know what a bad regulator/alternator looks like.
The failure has a pattern - when the vehicle is started cold, the electronics work well, with few RPM problems and strong voltage, even over an hour+ drive. If the vehicle is started multiple times, even over only 10 minutes, the RPM and voltage are highly unstable. If I drive to the store, everything works great. When I come home (and the engine is warm) the voltage will be a mess.
I hate to spend money on a new alternator when my gut says the problem lies elsewhere. But where might "elsewhere" be? I replaced the battery-frame ground cable, and checked the battery fluid levels, but the problem persists.
Any ideas will be greatly appreciated, and thank you for your time.
Keith
AnswerHi Keith,
interesting problem. Ever since I've owned my '95 Disco, I've always noted some small peculiar problems with the dashboard lights, headlight fluctuations, AC/heater blower fan stoppages, engine rev's. I always thought it could be electrically based but the problem never stays around long enough for me to be concerned. I always attribute it to 'looney' Lucas electrics.
In your case, do you measure the 'lunacy' by the tach only? If its strange rev's and tack failures your witnessing, it could be the alt but it could also be your TPS (throttle position sensor).
IF its just the tachometer that's acting up, its localized to the alt. IF you have rev's that dip and climb then consider your TPS. I had this happen on my '95 and it almost cost me a new ECU.
From what you describe, its sounds very much like my TPS problem. I would have extremely high rev's one morning, stop the engine, start again and watch the engine rpm's go up and down and up and down and...
Some days, the engine would rev well over 1000, other days barely 300. I checked all the ground wires, alt, battery and finally was forced to go to the dealer.
Long story short: Dealer wanted to replace the ECU but I refused. Dealer replaced TPS and 'reprogrammed' ECU...problem went away (as did the threat of a $3500 workorder).
The TPS replacement (by the dealer) cost me just under $600. It was mid-winter and had it happened in mid-summer, I would have done the job myself and saved at least $400.
Best of luck,
JohnMc
NB: thanks for the kind words. I hope this helps you out.
