olie05 Posted November 9, 2005 Share Posted November 9, 2005 So, i just finished rebuilding my sisters eclipse engine and i was all ready to fire the car up, but I had no good battery. So I pulled up my z and gave the eclipse a boost. Durring that boost, my friend notices that the tach in the z is going crazy, like dropping to 0 rpms and then kicking back up, but all the while the engine remains at a constant idle. Also, the car would keep blowing the 10 amp fuel gauge fuse. (im guessing because the tach was doing such crazy stuff.) After that, my tachometer would read double and never give me an accurate measurement of what the engine was doing. It even seemed to be that the car was running on the battery alone. I took the car to autozone, and they couldn't determine if it was the alternator or the voltage regulator. I took the alternator off and tested it by itself and it was only putting out 3 amps! I put in a new alternator and everything works again! It even fixed the problem i had before where the "charge" light would never turn off, and the voltmeter reads around 14 volts where before it would read really close to 16 volts. EXCEPT... there was a wierd problem, because i was at a stop light (after i installed the new alternator) and i heard some relays clicking under the dash and the engine shut off... but it started right up with no problem. I'm going to drive the car around tomorrow and see if it happens again. either way, i just wanted to report what happened, because when i searched for "double" and "tach" and all other tach related problems, i didn't come up with anything, so hopefully this will help someone in the future. BTW this is on a 1977 280z. -Oliver Quote Link to comment Share on other sites More sharing options...
Thumper Posted November 9, 2005 Share Posted November 9, 2005 I'm glad you found your problem. So was it your alternator or regulator? Usually alot of clicking noise will happen if your battery is low although you did say it started right back up. I would drive it a bit or if you have a charger put it on for an hour or two. If it does happen again then I bet you have a short. Quote Link to comment Share on other sites More sharing options...
PeterZ Posted November 9, 2005 Share Posted November 9, 2005 You may also have some funkiness going on with the ingition switch. The "Run" connections may be intermittent. If you can check an alternator by yourself you have the ability to find the problem. Good job. Quote Link to comment Share on other sites More sharing options...
olie05 Posted November 9, 2005 Author Share Posted November 9, 2005 yeah, i drove the car around a little more, and found out that the system is getting 16 volts at 3,000 rpm. I remember this problem was happening last time my regulator went out, so i will be replacing that this afternoon. Ill post the results. Quote Link to comment Share on other sites More sharing options...
olie05 Posted January 13, 2006 Author Share Posted January 13, 2006 I was reading through old posts and realized I didn't update this one. Turns out the voltage regulator AND the alternator had gone bad. I also ended up replacing the alternator (with internal voltage regulator) on the eclipse I was boosting. Very expensive ordeal, and I will NEVER boost a car straight to the battery ever again!!! Quote Link to comment Share on other sites More sharing options...
PeterZ Posted January 14, 2006 Share Posted January 14, 2006 That kind of stuff usually only happens when someone accidentally reverses the positive and negative cables during the jump. Only one touch is enough to fry the alternator diodes. Voltage spikes during cable disconnecting is also a problem on computer cars. It helps to have the headlights on for any kind of jump start. The lights give any voltage spikes a place to go other than the computers. BMW requires a certain fuse, #21 I believe, to be removed before jumping. Quote Link to comment Share on other sites More sharing options...
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