charge trek IX - 'Something Springs to Ferret's Mind'

[tim eh?]

from episode 8...

Something has just sprung to mind, can you do the following tests for me when you get a chance?

with everything connected

D+ to bat+, ignition off 12.5V
D+ to bat+. ignition on dropped fast... to 10.0V in around 5 seconds.


with D+ cable disconnected from alternator, battery attached.

D+ cable to bat+, ignition off 12.5V
D+ cable to bat+, ignition on 0.1V


with D+ cable disconnected from alternator, battery disconnected (removed).

D+ cable to bat+ cable, ignition on 12.2 ohm
D+ cable to alternator case 34.0 ohm


i've been having nightmares since seeing shogun's new site.

maybe i should do this alt cable repair for the heck of it... i have a feeling (kinda hoping) ferret's going to tell me the problem is down there anyway.

piece of cake right?


edit - here's the picture...



edit2 - wait a sec!!!!!!!

shouldn't i have 0.0V bat+ to D+ cable with ignition off????????????

edit3 - another diagram....

[bad_manners_god]

Easiest thing would be to just disconnected the cable at the alt, disconnect at the battery and run a new cable the easiest way you can, if your problems go away, you found/fixed the problem.

[Ferret]

Easiest thing would be to just disconnected the cable at the alt, disconnect at the battery and run a new cable the easiest way you can, if your problems go away, you found/fixed the problem.

I agree with this, try getting a dash bulb or the like and rigging a line from the battery + terminal to D+ with the bulb in line, see what it does.

There's something bizarre going on here, probably due to the regulator shifting 'resistance' as you power up, that and the inductance of the field coil.

Initially the bulb should have 3.16 volts across it to 8.84 volts across the regulator using the resistance values given above. (IE D+ to ground should be 8.84 volts)

However the regulator shifts as soon as you power on, as if you've got 10 volts across the bulb at power up, this means the regulator (and ABS computer) have a combined voltage of 2-2.5 volts meaning their resistance has shifted to about 4.4 ohms.

Next Test! With the battery disconnected, measure the resistance from the unplugged D+ cable to ground...

Being honest I dont think there's a major problem with the D+ voltage here, as once the alternator is started, it internally regulates and totally ignores the voltage on the D+ pin.

If you look at the internal alternator diagram on the bit you listed above, the D+ line is fed from the alternators windings once the alternator is running through a diode gate. This means that after the initial 14v spike, assuming the generation voltage doesnt drop under the 12.5 mark it doesnt need any input on D+ any more.

The only thing I can suggest is comparing readings with someone else, and my alternator's a complete swine to get at under the v8 block. I'll have a look for you this evening though see if I can get at it from above to take some readings.

Try unplugging your ABS ECU to see if it makes any difference.

[tim eh?]

Thanks for this, Ferret (et al...) - Claude has also suggested i hook up the light bulb... (bat+ -> dash light -> D+ terminal)

i initially get a reading of 12.35V across the lit bulb.

with ignition on (not running) i get 11.05V

immediately after starting, the bulb turns off and voltage drops to 0.14V.

I still get the exact same voltage readings as before. Does that rule out the blue wire?


I haven't pulled the ABS unit yet, that's next i guess.

Also tested for a voltage drop at the starter.

Tiger has suggested checking the ignition switch, but I can't find any specs on how to test it. Do I just look for voltage on the appropriate wires?

unplugged D+ cable to ground = 46.2 ohm

i have looked around... this exact problem is not super uncommon in european cars, but the solution seems to be rare enough.

EDIT:

abs control unit pulled, no change! looks brand new in there.

could this still be a loose ground somewhere?

...main relay? ....rear fusible link?

[tim eh?]

just throwing random stuff out there, sorry guys i feel like i'm almost spamming...

anything the PO may have touched is immediately suspect to me now.

what normally goes through the hole beside my power line?

[tim eh?]

well guys, i'm just about through i think.

i can't find anything wrong with the ignition switch. i have checked every single relay in the car. there were some carbon deposits in the plug at the main relay and the fuel pump relay. i switched the fpr (which had been changed at some point) with the wiper relay, no change... traced those circuits back to the 50A fusible link, changed that and connected the cable directly.... (nc), replaced both battery terminals + neg to ground, disconnected some stuff (a/c, headlight washers).

in previous episodes i have replaced the instrument cluster, battery, and alternator (3 times) + belt. everything works as it should except the system voltage drops off a cliff under heavy load once the engine has been running for a couple of minutes.

i'm sick of it - on other cars i have correctly diagnosed 2 dead batteries and a dead voltage regulator in the last 2 weeks but i can't figure out my own car!

the alternator power cable is a bit beyond my abilities i think, it's attached to the starter somewhere buried under all kinds of sensors and pipes and coverings i haven't a clue where to start there - and outside is no longer a good place to be doing that kind of thing... too cold now! so i might take it in for that... i have been recommended to a good place.

maybe all these alternators are garbage, i don't know but it's not healthy for me to start a winter here with no volts.... looks like i'm not the only one...

thanks everyone especially claude, ferret, tiger, bubba, eagle, at least i have learned a ton from you guys.
now i'm going to put on my winter wheels, i'm confident i can manage that at least!

[bad_manners_god]

I think the last step is to get a new alternator, not rebuilt.

Checl the Belt Routing and check the Tension of the belt.

Apart from this, not much else matches your symptoms.

[tim eh?]

I think the last step is to get a new alternator, not rebuilt.

Checl the Belt Routing and check the Tension of the belt.

Apart from this, not much else matches your symptoms.

from episode VI...

pic1 pic2 pic3 If I routed that wrong I will be embarrassed but so very happy. It's tight, really... it's really tight... I have tried it at different tensions and it doesn't change anything.


please tell me i routed it wrong.

[Tiger]

Tim... did you run a temporary wire from battery positive to D+ and see what your alternator output is?

[tim eh?]

Tim... did you run a temporary wire from battery positive to D+ and see what your alternator output is?

yes, with a dashlight bulb wired in and the other wire disconnected. i got these readings across the bulb.

(bat+ -> dash light -> D+ terminal)

i initially get a reading of 12.35V across the lit bulb.

with ignition on (not running) i get 11.05V

immediately after starting, the bulb turns off and voltage drops to 0.14V.

the system voltage drops as before under load.