The Diesel Stop banner

1 - 3 of 3 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter #1
I recently had a couple of situations where my ’93 7.3 would not restart when hot. Glow plug indicator worked ok and the starter turned the engine over plenty fast enough that it should have started. If I waited a few hours, it would start right back up. I brought it to the shop thinking maybe IP failure (185,000 miles on the clock). The next day, the shop calls to say the engine wouldn’t turn over and did I know I had a battery with a bad cell? I knew I was having to keep the truck on a trickle charger so the news didn’t surprise me and I said put in new batteries. The next day, the shop informs me that the alternator is not putting out more than about 12.3 volts. So we replace the alternator. Next day with batteries and alternator replaced, they try to replicate my hot start problem but after 30min idle, no problem. Long idle and then drive on the road for a while, still no problem. They said they kept trying but no issues. I’ve had it back for a day and the one hot restart I tried had no issue. I can’t think of a low voltage issue that would prevent a hot restart if the engine cranks fast enough - which was the case despite the low voltage/bad cell. What am I missing? Is my hot restart problem solved or is it probably still there waiting for an inconvenient time to resurface?
 

·
Registered
Joined
·
11 Posts
I'm not an expert, like some folks on here, but my 1988 7.3 recently would turn over a little slower, and not start. The batteries were ten years old and started fine two months ago, but would not turn the engine over fast enough now. New batteries fixed the problem. On a diesel, the engine has to turn over fast enough to compress the air to a pressure that raises the air temperature high enough to ignite the diesel spray when it happens.

This can fail if the compression is bad, (rings leaking), or the cranking is too slow and the air has a chance to cool, or the glow plugs are not getting hot enough. Pretty simple, but sometime it can be hard to sort out.

Seems to me your shop did a good job. Once the batteries were changed, the immediate problem was solved, but the new batteries would have died soon if the alternator didn't do it's job.

tom
 

·
Registered
Joined
·
14 Posts
Discussion Starter #3
Tom - Assuming there is nothing that senses low voltage when hot and prevents a start, I agree with your analysis. I was Coast Guard trained on GM6V53 models and understand that compression will typically be less on a hot engine and even a slightly slower starter spin can be just enough too little for a restart. The IDI being more complex than the GMs I am more familiar with, I was unsure whether three was a low voltage sensor of some kind getting in the way. With new batteries and alternator, the hot restart problem is, hopefully, corrected. - Rich
 
1 - 3 of 3 Posts
Top