Expert: Ernest (Ernie) Kenward - 7/21/2007

Question
QUESTION: Ernie, Here's my problem:
2003 Suburban. Dies while driving...will not turn over as if dead battery...not turning over slow...just dead. No dome light...Jump starts with no problem. Had electrical system checked at NTB. Battery good, starter not making a drain. Alternator putting out full. 14 volts on meter. May start 10 times in a row with no sign of problem at all. Suddenly on #11, it gets no juice at all. When this happens, clock looses time...all classic signs of no juice at all. Battery cables tight and no signs of corrosion. Link looks good and is tight in small box labeled "Battery."

Would not start after church last night...got a jump and drove home with lights on with no problem...killed engine in driveway and tried to re-start. Did not even try to turn over. Jumped started today and it ran 1 miles and died. Took battery out...had it tested. It showed to be fully charged. Put it back in and it fired right up. Killed it and restarted it 5-6 times in a row. Drive it about 8 miles with no trouble.

It is a side mount battery if this helps. Any ideas?
Thanks,
Alan


ANSWER: Well-documented process of elimination!  You have pretty much cleared away the common causes.

That leaves you with what appears to be an intermittent problem, great if you enjoy challenges, which is just a euphemistic way of saying that they are a real pain!

What would I think or do, were I in your situation?  Well, if it were not for one item you pointed out, I would wonder about the possibility of an intermittent fault to ground (0V common really; electrical codes define ground differently), either in the starting contactor, or in the starting motor itself.  Any short-circuiting fault in either of those would draw considerable current, enough to pull the main bus down, killing the lights, resetting the clock and digital radio, etc.

If that was the problem, you could probably verify it by holding the key in start for a second or so, and then using an IR pickup thermometer to look for evidence of noticeable temperature rise at the contactor and at the starter.

However, you did point out that this problem also manifested itself as an abrupt shutdown on the road ... Drat - that rather shoots down the intermittent-short-in-the-starting-circuit theory!

So next, I would wonder about an intermittent open in the main bus.  That can be tricky to find, especially if the conduction is good at all times when the circuit does not open.

Time to do some idling tests while you systematically not only look at connections, cable runs, fusible links and the like, but also grasp them and move them around a bit - taking proper safety precautions, of course (wear work gloves and safety glasses to protect yourself from possible arc flash, and keep clear of belts and the fan!) - while the power is on.

Just as an aside: being one familiar with industrial electrical systems, fuses and switchgear, I am not too impressed with the fusible link approach used in most vehicles.  Quite a few years ago, I changed these out on my E250, replacing them with fuseholders to accept type AMG low-voltage high-current DC fuses.  Easier to replace if ever needed (so far not) and, as well, less parasitic voltage drop.

Time for more detective work, I guess - enjoy!

Cheers ... EGK

---------- FOLLOW-UP ----------

QUESTION: "Ernie, I appreciate your advice. I will be under the hood tomorrow. One comment that I didn't make earlier...don't think it will change anything but for about a minute prior to the engine shutting off while being driven, the AC started blowing warmer air and the blower slowed way down. The load seemed to increase on the elec system until of killed the motor. It wasn't a sudden thing...a moment...maybe two, passed prior to the engine shutting off."

Answer
This is a tricky one to assess, but that added point does appear to corroborate the idea that there is an intermittent high-current fault to the vehicle ground, one that pulls down the voltage significantly.  Any significant voltage reduction on the system would have the effects of causing the electromagnetic clutch on the AC compressor to drop out, cause the DC blower motor to slow down, and - once low enough or if sustained - probably cause the ECU to cycle off, shutting down the engine.

Heavy current draw of that type would have to have the effect of causing something to get very warm somewhere.  The fact that the current evidently is very high, along with the fact that the problem has been ongoing for a while without finally announcing itself via a burned-out conductor of connector, also along with the fact that the voltage reduction is seen on every circuit, does suggest that the problem affects a major sizable conductor such as the main bus.  That should isolate the portions of the circuit that require close scrutiny.

As suggested previously, an IR-pickup thermometer would probably find a hot spot very quickly, as could your hand, if you are careful.

Failing that, why not disconnect the battery and then do a complete physical inspection of the main leads connecting the alternator to the battery, and from the battery through the fusible links to the point(s) where most of the distribution is taken.  This should aid in isolating any fault due to cracked, rotten or physically damaged insulation on a lead running in close proximity to grounded metalwork.

Failing that, there might be one other possibility I just thought of now ... what if the main ground on the engine is intermittently becoming high resistance or OPEN?  This could have the same general effect of causing a large voltage reduction to any accessories relying on that ground point.

This might even be as simple as a loosened bolt at that main ground.

More to check out ... keep me posted ... EGK