2003 Chrysler PT Cruiser, 2.4L N/A, Auto, 200,000 miles
New battery 20,000 miles ago
New alternator 20,000 miles ago with OEM pulley.
Original PCM
Here’s where I’m stumped. At idle, I get 13 volts. At 2,000-2,500 RPM it reads 11.8 volts. When I slow to a stop the voltage goes back up to 13. There is only a 0.10 voltage difference under full accessory load.
Apparently there is no external voltage regulator on this car. I think regulation is done via the PCM.
First, measure the voltage with a “real” meter at the battery, have a helper rev the engine.
How old is the belt? Does it look clean and in good shape? It could be slipping.
Where’d the replacement alternator come from? There are many poorly remanufactured ones out there.
If the belt isn’t slipping then the alternator is causing the problem. The brushes might the cause of the problem or there is a faulty connection inside it. This isn’t a common type of problem with alternators but it does happen.
Ok, thanks for the quick response. I got the Excel 10603 alt and GOODYEAR 395K5 belt from RockAuto.
I’ll check for a voltage drop by RPMs at a standstill. The belt was changed with the timing belt 20K miles ago.
I’ll check the tightness of the belt again. There is no squeaking but we did estimate the tone of the belt since our DRBIII was sold.
I guess it could be that the belt has settled (after 20,000 mi).
I would certainly check both ends of the battery connections, and possible shorts. Let’s say because of a bad ground, at idle there is less draw, and the voltage is good. While driving it needs more amps for whatever reason, and the connections do not allow that to happen, thus the reduction in voltage reading. This is a wag, but feasible.
Sounds like an alternator problem to me. Increasing rpms cause a higher current drain, if only b/c the spark plugs are firing faster. The alternator should of course be able to easily keep up. In fact one clue is that you should be getting more than 13 volts at idle. And it shouldn’t drop off with rpm. Even though more current is required, the alternator is spinning faster, so that should be a wash. I measure in the high 13’s, like 13.6 to 14 volts when I measure this on my Corolla at idle.
Could be bad connections at the battery, the belt, grounding problems, other electrical problems too o course. Me, I’d just take it to a place that could test the charging system. I suspect one or more of the alternator diodes is on the fritz.
One caution, while diagnosing this, don’t remove the battery cables while the engine is running. The battery must remain in the circuit at all times. Removing the cables while the engine is running will almost certainly give you problems that you don’t want to have.
Well boys and girls, we have a winner! Circuitsmith nailed it. The top set bolt was not tight enough and over time the tension bolt had worked itself loose. It’s all good now.
LOL. That’s a true Fluke user talk’in there @circuitsmith. I purchased a 8060 not too long after they first came out when I saw the one my boss at the time had purchased. That was a lot of years ago now. It was the standard of the industy for a lot of years. Copied, but never equalled.
I have a Fluke 88 myself, and it’s definitely the industry standard for auto mechanics
What I like about Fluke is that they stand behind their product forever
I’ve had mine calibrated a few times over the years (because it wasn’t giving me accurate readings).
The company didn’t make me pay anything, and the turn around time was fairly quick. In fact, they even replaced the seal separating the two case halves. They told me I can send it in yearly for calibrations, even if everything’s been fine.
Try getting a free calibration with your Snap On, Blue Point, etc. DMM
The fluke was initially more expensive than some other meters, but when you consider the free lifetime support, it’s actually a pretty fair deal
That’s a good testament @db4690. I have an 88 also. In fact I just got it out last week after years of sitting in my closet to make a current measurement on my son’s car.