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Originally Posted by JohnnyOH
Ran the 30 minute test. 14 to 13 and ending at 12 volts. No charging system problems evident.
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I would think it shouldn't drop to 12-volts while idling with all that stuff running. I'll bet if you let it run longer it would probably stall out. (Note: If you do this you’ll need a battery charger to get it started again though) Can't say for absolute certainty from here but I think you may have found your problem.
With the 4-ways flashing you'll get a ~.4 volt fluctuation, but the voltage should hold fairly steady over time in the range with the flasher fluctuation. If the voltage drops over time then I’d say there is a problem. If the car drops even for a second below 12 volts it will stall. To have it idling and being that close to 12 is not good. It should be charging at around at least ~13V at all times while running, especially with that much of a load. I think even my worthless Haynes manuel states it should be charging 14-15 volts. I’ve found that it is usually around 13.4-13.7 though.
I’ve seen this intermittent bucking misdiagnosed in every way possible. It’s a tough one, but if you think about it with all the electronic gizmos on these engines they need a good firm clean source of power. If you haven’t changed your alternator in the last 50,000 miles I’d say it is a good bet.
I’ve also got a concern with that diagnosis of a “weak” fuel pump. Not sure what that means – low pressure? If that’s the case it could be a problem with fuel delivery. But what do they mean by weak? I’d say it is either giving enough pressure or it isn’t. Of course, if your alternator voltage is not up to snuff that will impact on fuel delivery via an electric fuel pump. Think about how a processor or hard drive would malfunction with intermittent low voltage drops…. (BTW-know a source for a Clevo laptop mainboard?)
I’m still suspecting the alternator at this point though, but the symptoms you describe could easily be a fuel problem as well. Since you’ve already changed your pump & fuel filters I’m thinking you’re all set there. Maybe try that voltage test a little longer to see if you drop below 12 volts and stall, at least you won’t shell out anymore $$’s for that test (except for the gas-ouch!), and if it does stall you’ll know for sure that’s the problem.
One more thing to check, did you ever do the key dance to check the codes? Sometimes when this happens it will throw a code 41, but many times it won’t. If your check engine light comes on when it is bucking then it is certainly throwing a code. Unfortunately when you disconnect the battery it clears the codes though, so if it does come on again check the codes stored. To check for codes have the car off and turn the key quickly like this without turning it to start:
On-off-on-off-on
Then watch the check engine light for flashing and count the flashes. You’ll get a series of 2 digit codes that end with 5-5. Since you just had the battery disconnected you should at least get a code for that.
