Charging system question

[CBLEGUY]

Hello all,

I've got a 90 Turbo. I just rebuilt the top end in the garage. I know I have to finish setting the timing, its a little off. I have another problem and I am almost positive what it is, but I need some reassurance before I start replacing stuff. My battery is not charging, and when I jump it, it runs with the cables on. When I take the jumper cables off, the car dies. It is a brand new battery only a week old. I was reading the TSRM and the testing procedures are crazy confusing. It even tells you how to rebuild alternator.

I am assuming the alternator is bad due to the fact that it will not run on its own charging system. any input, anything I forgot? Any help or input I would be grateful.

thanks,

Scott

 

[Boss302]

get a volt meter and stick on the battery that should tell you. but 99.999% alty is gone to charging heaven.

 

[jetjock]

Do as suggested but if the battery is in good condition the engine should not die when you remove the jumper cables. In fact the ECU even adjusts to a low battery so something goofy is going on there. In addition to testing the ALT have the battery tested and check the wiring. Sounds to me like a problem in the main ground path.

 

[CBLEGUY]

The battery is already dead, because I left the key on the night before. I am sure the battery is good, after I jumped it for a minute, the car still ran for about 30 seconds before it died. I could see the lights start dimming and the car started sputtering. seems to me like the alt is bad, but I'll check the ground as well

 

[jetjock]

Hmm, those aren't minor details and should've been in your first post. Check the voltage across the battery at idle. Should be around 14 volts. If you ran the battery down dead you've already impacted it's service life. All it takes is one time. If you now go and rapid charge it you'll do even more damage. Best to remove it from the car and do a slow charge before using it again.

 

[CBLEGUY]

Sorry about the details. I had a vapor lock when I originally posted. I slow charged the battery yesterday, and last night. I'll be testing everything today. I have to put my new downpipe on today as well, the old one cracked. I am also going to break out the timing gun today and time it. I read some posts about it, and they say it should be at 10deg. we'll see how that turns out. I have another question about the stock boost gauge. typically, how accurate are they? It is showing boost, but never over 1 to 2 psi. I am going to get a elec boost controller and new gauges, probably in the next couple months.

Hmm, those aren't minor details and should've been in your first post. Check the voltage across the battery at idle. Should be around 14 volts. If you ran the battery down dead you've already impacted it's service life. All it takes is one time. If you now go and rapid charge it you'll do even more damage. Best to remove it from the car and do a slow charge before using it again.

 

[Boss302]

I have another question about the stock boost gauge. typically, how accurate are they? It is showing boost, but never over 1 to 2 psi. I am going to get a elec boost controller and new gauges, probably in the next couple months.

boost leak...

 

[jetjock]

The problem is probably not the gage but to answer your question the stock gage is electric, powered by a pressure transducer on the left fender. They're usually reliable but if you don't trust it you can verify boost with another gage. Any cheap boost gage from an auto store will work. Sears also sells an ok compound mechanic's gage for cheap. Anyone who works on cars should have one. Just run the hose into the car or tape the thing to the base of the windshield. You can also verify the stock gage by pressurizing the transducer. You'll need a regulated source of compressed air so it may be more trouble than you want to go to unless you happen to have a compressor and a small regulator lying around.

 

[CBLEGUY]

I have a compressor and a regulator. I replaced all of the gaskets when I put the car back together. It could be leaking because it is slow to boost when I accelerate. I thought that was due to the timing being off.