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93 c3500 6.2 electrical issues

N

NADCHaynes

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My buddies truck stopped charging so he put on a new alt then called me. Alt not getting 12 volts to charge, has the 2 wire plug and if I bybass and excite straight from batt it charges. also radio,cig lighter and gauges arent working. fuses are good and have power to them. Ground maybe? a wiring diagram would help a lot but dont have access to one so am shooting in the dark on this one. I have mechanical and electrical exp but am looking to speed this process up a bit lol. Any suggestions? Thanx in advance.
 
update. Cig lighter was half way unplugged and radio ground pin in connector to radio was crushed and not making contact. That being said it still has the initial prob of gauges inop and alt not charging.
 
The 1993's have a power distribution block on the passenger side firewall. Every wire has a fragile 20 year old fusible link just below that block. The 1993's have 2 bad spots to look out for: the bottom battery tray rubs through the positive battery cable. The main wire between the battery and the firewall block goes between the starter and manifold and it tends to loose it's insulation. You should inspect it and replace and possibly reroute it. Check all battery cables as well for acid wicking that corrodes them internally.

Make sure you measure the pulley on the old alt and compare it to the new one! The tach accuracy depends on the bigger diesel pulley. Lots of re-builders, and even new, love to give you the common gas engine pulley. How did the old alt die and is it confirmed dead? A popular mod is replacing the firecracker with a larger and more reliable CS 144.

The battery light is part of the alternator circuit. No gauges make me suspect no power to the cluster. Fuses are good on a 20 year old truck means you pulled each one completely out and cleaned or replaced the ones with corrosion on them. I would look at testing the ignition switch as well.

Important grounds are the ones by the transmission dipstick hold down nut on the passenger rear of the engine. A new ground strap between the engine and body is helpful on most GM stuff including this one.
 
Old alt prob never died, he assumed it was bad since it was not charging. Thats why we diagnose and then replace lol.

Think I found the prob, some butt head used a crimp splice (file 13 everyone ever made!) into the gauge cluster power supply on the back side of fuse block. apparently the exciter wire gets its voltage through the voltage light or gauge.
Exciter has voltage now and gauges working so should charge.

Now he tells me its been running rough and shutting off after last service. checked filter and seems to be sealing but, not sure who serviced it and whether or not they filled up filter base (pain in the butt) or ran dry and cranked till it fired back up which could have caused a nozzle to run dry and with 300k miles pushed it to fail or leak down maybe, lots of start up smoke. Acts like its sucking air somewhere (replaced filter even though was new, hate the plastic cap ones) filter base def running dry then will fill and be fine for a bit, then run dry again. smokes like its got air in fuel and obviously running rough.

Normally I would throw a site glass on it but its not a Cat 3406 or equivalent lol and Im not that familiar with the 6.2 other than basic diesel design and operation.

Filter base wires = ?
any way to by pass the filter base for diagnostic purposes?


Thanx for your time by the way, its much appreciated.
 
LP is not working.
OPS not sending power to LP.
Tank sock clogged.
Clogged line.
Air getting in somewhere.

Its a good idea to use a relay harness on LP. Check www.leroydiesel.com for more info and ideas.
 
Put a clear 1/4 " hose on the return coming out of the IP. Check for air there. LP is controlled by the OPS. Once LP is working (it will only run after the engine starts) if it still has air and it's not dripping fuel check for air intrusion leaks pre LP. The wires on the bottom of the filter are fuel heater and water in fuel sensor.
 
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