99 K2500 7.4L electrical issue

[g00se]

OK. I have a '99 K2500 'Burban with the 7.4L, 4.10 gears and 99k miles. I just got back from a 3000 mile round trip excursion from MN to UT and back. Was up in the huntington, UT area at about 8,500 ft (beautiful up there). I pull a tt that weighs about 6,500 - 7,000lb loaded as well as probably 500-750lb of gear in the cargo area (well within the towing limits). It should be known that trips like this are rare and actually the first for this vehicle. Otherwise it's the wife's daily driver and sees low mileage/use.

 

A quick side-note: I couldn't believe how much power I lost when getting into elevation. OMG- the thing was almost as bad as my '02 silverado with the 5.3L when climbing hills (pulling the very same trailer). It felt like someone threw out a d**n parachute when I hit a hill. Some longer gradual hills, I could only get to 60mph or so without winding out over 4000 rpm in a lower gear (something I hate to do). Some steeper hills in sections, I could only get up to 25mph on MAX (about 6-8% grade, but sheesh- 25MPH?!?!). Is there anything (relatively cheap - $200 - $300) I can do to get more pulling power out of this ginormous engine? The stock motor has 290hp and 410ft/lb torque. Nothing to sneeze at IMHO.

 

Anyhoo- when I got there, I put it in 4lo to get up some steep dirt roads near the end (very dusty) with the tt behind me to regulate speed and go easy on the tranny. Once I got set up at my camp, I noticed that the blower motor in the cargo area was still on, even though I had the key out of the ignition. The 2wd/4wd indicator light also stays lit, and I can activate the rear defogger as well as the front blower motors all without the key in. I can't move the windows or turn on the radio though (I would have thought this would indicate a faulty ignition switch). Long story short, this caused a parasitic power drain that eventually depleted the battery and I had to charge it again. I tried removing the four relays I could find in the engine compartment (right next to the OBD II), one at a time. Each time, when taking the relay out I heard no clicking, nor did it fix the problem.

 

Nothing has changed electrically in the vehicle EXCEPT (isn't there always one of these?) I installed an aftermarket radio using factory wiring harness plugs about 3 weeks before the trip.

 

Can you think of any suggestions before I have to break down and bring this into the dealer or a mechanic and pay hourly for them to track down what could be a simple problem?

[454ss]

dont know about your electrical problem, but as far as power upgrades, get a wait4me yuned pcm from jesse bubb, $158.10. i put one in my 1997 k3500 w/454-4l80e, wow, best bang for the buck as far as im concerned. i dont have his number handy but somebody can post it for you and he has a web site.

[silverado3500]

If you haven't already, I'd suggest unplugging the radio at the factory connector, and see if that fixes the problem. If the radio isn't wired right, it could back feed the relay and power the accessory circuit. The radio receives power from both the ignition circuit (hot in run and accessory) and a constant supply from the battery (for the radio's memory and clock)

 

If not that, there should be a few relays in the "convience center" inside the cab along the firewall under the steering column. I don't have access to my service manuals right now, or I could tell you which specific relay to test. Also might be worth checking the ignition switch.

 

Best thing you can do with electrical gremlins is to try and isolate the problem.

[g00se]

If you haven't already, I'd suggest unplugging the radio at the factory connector, and see if that fixes the problem.  If the radio isn't wired right, it could back feed the relay and power the accessory circuit.  The radio receives power from both the ignition circuit (hot in run and accessory) and a constant supply from the battery (for the radio's memory and clock)

 

If not that, there should be a few relays in the "convience center" inside the cab along the firewall under the steering column.  I don't have access to my service manuals right now, or I could tell you which specific relay to test.  Also might be worth checking the ignition switch.

 

Best thing you can do with electrical gremlins is to try and isolate the problem.

 

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silverado3500: thanks for the tips. I'll check those relays under the steering column and if that doesn't work, I'll try disconnecting the radio. I will also check all the fuses with a meter on the side of the driver panel and in the engine compartment to see which ones are still energized. Maybe doing that will help me trace back to a common area that is causing the circuits to be energized when they shouldn't be. I'll post which circuits are energized and maybe that will help in conjunction with your service manuals.

[svensk]

Your 454 has huge potential in the aftermarket area. Like as was stated above get a PCM tune. That would help you the most right away and I think the 454 was really held back by GM. If that isn't enough you could get a more agressive cam which would really spice her up.

[g00se]

So if I bring the beast to a shop to get it looked at, what do you think it will run me in labor? I was contemplating taking it to a local shop by the house (non-dealer) because their labor rate is $30/hour less than the $115 that GM dealers charge. My only reservation is that the local shops may not have the resources at hand to get the problem fixed as quick as a dealership so it may be a wash anyway right?

 

What do you think? I don't want to put any more into this than I have to. I intend to trade it in on a diesel in a couple years or less.