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Alternator?

3K views 4 replies 3 participants last post by  greenlight 
#1 ·
We have been having a surging problem with our van, noticable mostly when in overdrive.

I also have the dreaded death clunk at the stop sign or stop light.

My Grandfather oversees a fleet of 5 GC's ranging in years (3rd and 4th gen). He told me to check my voltage coming out of the alternator. He just had a 2002 do this exact same thing, and it was a weak alternator that would spike power and drop power, causing all kinds of electrical gremlins.

Anyone else experience this?
 
#2 ·
I haven't personally seen it on my vehicle, but a bad diode can cause all sorts of nasty waveforms coming out of the unit.

- G
 
#3 ·
Alternator is putting out 13.7 volts, which is what is at the battery. The battery, with the engine off, sits at 12.5 volts.

So, if it isn't the alternator spiking voltage, what would cause the van to surge while maintaining speed? Is there a fuel pump problem?

I do hear a sign when shutting the van off. It was easily duplicated.
 
#4 ·
Just FYI, if you remove the alternator and take it into Autozone, they'll run a load and test the alternator unit specifically for you for free. I just did it recently and found that my alternator quit putting out current to charge the battery all together.
 
#5 ·
IAfarmer - it would be good to find out if the surge is a power surge or transmission slip. Power surge can be fuel pump related.

(btw, I doubt you would see a bad alternator waveform on a normal digital multimeter - the spikes and dips come too close together.)

Transmission slip would cause RPM to slightly rise while power to wheels slightly falls. Power surge would cause a change in RPM and power together instead of opposite. Transmission slip should eventually set a "ratio error" code. If the transmission slips a lot, it can generate a lot of heat in there.

If it is a transmission slip, you could have a leaking seal or accumulator inside the transmission, or something similar. See if you can find someone (mechanic or dealer) who can pull the CVI's for the tranny and see if any are out of range, as well as any tranny codes.

If it is a power surge - hook up a fuel pressure tester to the test port on the fuel rail and run the engine - pressure should hold pretty steady.

See:

http://www.transmissionspecialty.com/parts/PDF/SC-41TE.pdf

for some information on a Sonnax kit -- it has some useful tidbits in it regarding some common issues with the 41TE transmission. Esp. see the last page of that PDF.

- G
 
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