Starting problem
06-19-2001, 01:49 AM
#1
1st Gear
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Starting problem
Recently my '86 911 developed an intermittent problem starting. The battery is fine (been tested; pulled it and hauled it to Sears) the alternator puts out fine(runs the car even without the battery). BUT, somtimes when I try to start her, all that comes on is the fuel pump. She can be hot or cold. However, when I jump her with another car, she fires off every time.
Any ideas?
[ 06-19-2001: Message edited by: 86Targa ]
Any ideas?
[ 06-19-2001: Message edited by: 86Targa ]
06-19-2001, 02:27 AM
#2
How did you test the battery?
When batteries go bad, their internal resistance increases. If you measure the voltage with something like a volt meter (with a very high impedance) the internal resistance of the battery is insignificant and almost all the voltage shows up on the meter. If, on the other hand, the battery is loaded with something with a much lower resistance (like a fuel pump), the drop may be considerable. As a guess, I would say that when your fuel pump comes on, it's dropping the voltage at the terminals of the battery low enough that the DME won't work properly. It starts OK when you jump the car because you're using a source that likely has a voltage output higher than your battery's.
Just a theory, hope it helps,
Bill Wagner
When batteries go bad, their internal resistance increases. If you measure the voltage with something like a volt meter (with a very high impedance) the internal resistance of the battery is insignificant and almost all the voltage shows up on the meter. If, on the other hand, the battery is loaded with something with a much lower resistance (like a fuel pump), the drop may be considerable. As a guess, I would say that when your fuel pump comes on, it's dropping the voltage at the terminals of the battery low enough that the DME won't work properly. It starts OK when you jump the car because you're using a source that likely has a voltage output higher than your battery's.
Just a theory, hope it helps,
Bill Wagner
06-20-2001, 02:28 AM
#3
86Targa:
Just got your email. It was listed as "private" and said if I wanted to respond, I had to do so here. If the battery is new and it really is good, the only other thing that I could think is that when you start turning the car over you are presenting the car with too much of a load (any add-ons that would draw a lot of power, like a high power sound system) or perhaps the battery is under rated. I hate to mention this one...but the battery terminals ARE on tight aren't they? How about the grounds in the car?
Just thoughts,
Bill Wagner
Just got your email. It was listed as "private" and said if I wanted to respond, I had to do so here. If the battery is new and it really is good, the only other thing that I could think is that when you start turning the car over you are presenting the car with too much of a load (any add-ons that would draw a lot of power, like a high power sound system) or perhaps the battery is under rated. I hate to mention this one...but the battery terminals ARE on tight aren't they? How about the grounds in the car?
Just thoughts,
Bill Wagner
06-20-2001, 11:27 AM
#4
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A little advise. Never disconnect your battery while the car is running. Or you can kiss your 600$ alternator goodbuy. Also, try to refrain from "jumping your carrera. You just might be on here looking for DME control unit for a 1000.00$ Have you checked your yellow wire at the starter when "engaging"? You need to jack up the car, pull the wire off the starter, put a test light on it, have someone key the thing. See if you're getting voltage. Once that is confirmed, place the wire back on, key it again, if it doesnt work, tap the starter while keying it. (just like an old chevy) You probably have a starter going bad. Good luck
