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99 Suburban only runs for an hour

Ok so this is something I can’t quite wrap my head around. I have a 1999 K1500 Suburban, 5.7L. I have only owned it a few months. The thing is, shortly after I got the truck, we took it out of town, where it died after a little over an hour of driving at highway speeds. I had punched the odometer to watch the gas mileage, and we had run it about 70 miles when it died. We got it to our friend’s house, where we were headed anyway, and stayed over, planning to look at it in the morning because it was later than part stores stay open in our rural area. Thing is, in the morning it fired right up. So we headed home, and once again, after about another 70 miles, it shut down and refused to crank.

This time it happened as we were coming back into town, and on a hunch I said that something must be overheating for the problem not to be present until after an hour of road time. So we pushed it a safe distance off the road, and went and grabbed something to eat. After about an hour we made it back to the truck and success! It cranked back up and we made it the rest of the way home. Since I have driven it to town and back, and to my parents a few times, but never more than thirty or forty miles away. It never hesitates to crank, and sounds ok running. Although I will say, I have not owned a truck before or a V8, but it seems to not have the power it should (my thunderbird with a 3.8L had more punch), and I did noticed both times this happened that that problem seemed more pronounced right before it died. But I don’t know if I just feel that way just because I am used to driving cars, and the truck is heavier. When it dies, you hear the starter relay click, and that’s it. So my question is, where should I be looking? I haven’t done a lot of mechanic work, but I kept my own car running when I was in school and replaced a lot on it on my own. I am just not real good at diagnosing things, and don’t have a ton of money, so I don’t really want to throw parts at it. I gave it a basic tune up when we got it. I have a sinking feeling that this is fuel related, and want to see if that worry is founded.

If the solenoid is clicking and the starter motor is not cranking, my first step would be to check and clean ll connections. step 2 replace the starter motor. It may bench test fine when cold but running a long time everything gets warm, hot, including the starter motor so starter motor when it is hot from running that long is my wag.

Would the starter cause the truck to die? I thought that once the bendix engages and spins the flywheel to turn the motor over, it’s job was done. This happens when I am driving down the road.

A starter motor would NOT cause the truck to stall

It would cause a no-start

A few culprits that could fail when warmed up while driving

Crank sensor

By the way, is . . . or was . . . the check engine light on?

If so, please give us the codes

No check engine light. Sorry, I should have mentioned that. I am finding it odd that the light isn’t on. So maybe not a fuel issue? Because I’ll admit, I haven’t done that sort of work before, and it makes me uneasy. But a spark problem I could handle.

A failing crank sensor may or may not throw a fault code

It may or may not cause the check engine light come on

I’ve seen both scenarios

I’d suspect the crank angle sensor too. These often fail intermittently when they get hot, then work OK after cooling off.

If you’re so inclined, here’s how to test it yourself when the engine won’t start:

But first check for spark when the engine won’t start. If any plug is sparking, the sensor is OK.

You can buy one of these new off the Internet for as little as $16, so you could afford to replace it yourself. It’s not difficult since the sensor is inside the distributor.

Thanks! I will try this today and see how it goes.

“When it dies, you hear the starter relay click, and that’s it.”

So how does a failing crank sensor (or anything else ignition or fuel related) cause the engine to fail to crank?

I think you are losing your battery ground.