Altanator and/or Cable Problem?

[lars1]

What would cause(s) the tachometer and speedometer needles to bounce while attempting to start? My 1994 GMC Suburban (6.5TD) started after disconnecting and reconnecting the battery negative terminals.

The starter was slow and strained and the alternator gauge reported in or near the red zone.

The passage side battery went from +14 to +11-volts on a second back-to-back check.

The cable to battery mounting hardware was replaced earlier. The terminals were cleaned and the cabling visually looked okay. The batteries are about three years old.

Would it be reasonable to start by replacing the battery cables?

Suggestions would be appreciated. Thanks in advance!

1990 GMC K2500 Pick-up (6.2L NA)
1994 GMC K2500 Suburban (6.5L TD)
2003 GMC K2500 Duramax

[rustyk]

The symptoms are, as you suspect, of bad connections. Recheck all, including the positive commections and chassis grounds

[DennisG01]

I'm not sure what you mean by your "back to back" comment? It's normal for the battery gauge to dip like that when the glow plugs are working.

I agree with Rusty - start by cleaning and tightening all connections - don't forget to check at the starter and the alternator.

[phantom309]

My 94 had the same problem,.
the solution has been covered here ad nauseum,.
I put 3 big ground cables from batterys to motor,. motor to firewall,. all 1 guage stuff,.i also did the positives,.
made a huge difference,.:cool:
I also added a dedicated larger guage cable from alternator to dr side battery

I cut open the cable from pass side battery to starter,. it was full of the green monster,.
The old girl whirls over pretty quick now,. enough that she has been starting with about 4 glow plugs working because i,m too damn lazy to change them out and add a harness,.:D

Nick

[Robyn]

The previous advice is ++++++

New cables with soldered eye ends on both and usea stud and nut setup at the batteries.

Another good mod is to add a Ford Starter relay to manage the solenoid on the starter.
This can be located up by the RH battery on the inner fender. Just extend the existing solenoid wire.

Use the existing Solenoid small wire to run the relay and feed the relay off the RH battery. Run a fresh wire from the relay to the solenoid. Use #10 wire.

The solenoids on these rigs draw a lot of current and the ign switch takes a beating and over time can go south.

The relay takes a very small draw.
This mod adds life to the starter too.

Be sure you make up a new alternator feed line and connect from the alt to the LH battery ++

The battery voltage should be nearly identical at both batteries as well as the Alt and the junction block when things are in good order. 14v to 14.5v with engine running and the system stable. (its possible with full batteries to see 13.5-13.8)

Be sure to replace the + feed cable that runs from the RH battery to the junction block stud up by the AC BOX ON THE FIREWALL.

This new cable can be routed on the RH inner fender instead of down along the frame as was done by the factory.

Once these mods are done you will see a drastic improvement.

Do the grounds as well with soldered copper eyes on all ends.

THE GREEN GUNGE gets into any crimped cable thats not soldered and will render it worthless.
The green is caused by electrolysis. Moisture and electrical current and add time = green crud.

Sadly, from the outside, things look fine, but until you cut them open you can't see the crud.

The old factory stuff was so so, but the new replacements are junk, as are the parts house stuff.

Welding cable and copper eyes. Use rosin core solder only.


Goo luck

Missy