Electrical / starting issues I'm having trouble diagnosing

[MoonDog]

Hi all, I hate to ask such a dumb question like "my engine isn't turning over well..." but I'm a little unfamiliar with just how much it takes to get one of these big ol' things going. ('88 7.3 btw)

The symptoms began with the engine crankinging over a little slower each time it was started. I figured it was the batteries since they were old, and a mismatched pair of smaller car batteries off the shelf at the junkyard I bought the truck from. When starting the truck, the engine would turn over slowly but gradually increase in RPM as I cranked it, and it would eventually start. Over it's last few days cranking got progressively slower untill it would barely turn over. I replaced the batteries with a proper pair, gave them a full charge, and it slightly improved the cranking but it's still not enough to start the engine.

Now, the volt meter just barely gets out of the low red zone when the ignition is on, and one of the ground cables from a battery is badly corroded where the insulation is missing, and it gets warm to the touch after cranking.

It looks like both batteries share a positive lead, but have separate ground cables, is this correct? I would think that if one ground was bad and the other was good, I would be seeing more voltage.

Does it really take THAT much amperage to turn these engines over? Do these symptoms sound like anything anyone else has experienced?

I feel silly asking such a newbish question, but I feel it's wasteful to spin my wheels when this place is such a great resource and someone may have some insight or could point out something I might be missing

Thanks guys,
Tate

 

[The Warden]

You're right; the batteries share a positive cable but have separate negative cables. Unless the positive and the other negative cables look to be pristine, I think I would replace all three of them to be on the safe side. If the batteries haven't been well-maintained, there could be corrosion inside the insulation as well. You might also want to check the wire that goes from the positive cable to the starter relay on the inner fender; this wire powers the rest of the truck. Also, IIRC, a couple of people have had problems where the cable came loose from the positive terminal on the passenger's side battery, but it wasn't visible to the naked eye. I could be remembering that wrong, though.

Beyond that...I would pull the starter and have it tested. I have a feeling that it's bad. These starters do not like to be operated for more than 30 seconds at a time without a minute or two to cool down...and, while the symptoms you describe could be caused by bad cables, they can also be caused by a failing starter. BTW, mis-matched batteries would lead to a lower cranking speed, which in turn would put more stress on the starter...leading to premature failure.

Just some thoughts...good luck!

 

[tonkadoctor]

Does it really take THAT much amperage to turn these engines over

YES.....444 cubic inches at 22 to 1 compression ratio which is over 3 times higher compression ratio than a gasser.

I replaced the batteries with a proper pair, gave them a full charge, and it slightly improved the cranking but it's still not enough to start the engine.

Let me guess......used batteries .....If so take them to an auto parts store like NAPA, Advance or Autozone etc...... and get them LOAD tested, might as well take the starter with you too and get that tested.

Now, the volt meter just barely gets out of the low red zone when the ignition is on, and one of the ground cables from a battery is badly corroded where the insulation is missing, and it gets warm to the touch after cranking.

Replace them, sounds like a potential electrical fire brewing if you don't sending your truck right back where it came from.

 

[TLBREWER]

First, welcome to the site. Please fill out your signature so we can better help you in the future since there are differences between engines and model years. Your location also helps. We are also her to help you spend your hard earned cash.

Now that you've got a good set of batteries, get a good set of battery cables from www.custombatterycables.com. Less than half the price of new Ford parts and far superior quality. Also get your starter checked. My money is on the starter. I just went thru this exact problem last week. When the starter was put on the tester, sparks flew everywhere. A starter is about $165 from Napa plus core and $284 from Ford plus core.

Good luck. Sucks having these problems in the cold of winter.

Tom

 

[MoonDog]

Thanks for re reminder for the profile, and the input so far. Last night I cut off the corroded cable end and replaced the clamp. While under the hood I jumped the solenoid to see how it cranked (no real change) and noticed a dull orange light down on the side of the engine. The short braded cable on the starter itself was glowing after a few seconds, so I think it's getting enough juice!

Tonight after work (and a few extra hours of OT ) I'll pull the starter and grab another tomorrow. We'll see what that does,

Thanks guys!
Tate

 

[Mr_Roboto]

Yea if the cable down there is glowing, the starter is drawing too many amps. It probably has shorted windings, which will draw lots of power but the motor won't turn very fast.

 

[MoonDog]

well I picked up a rebuilt starter at Napa ($150 after AAA discount ) Installed it, went to crank it over... holy crap I didn't know a diesel could fire up that fast!!!

Thanks for the help guys, I wouldn't have thought a starter would fail like that, I'm sure glad I asked

Tate

 

[TLBREWER]

Tate

Glad to see you got it fixed. My daughter was the same way. Very excited that she no longer had to worry about whether it would start or not.

Tom