300 starts without starter.
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300 starts without starter.
When I drive my '84 300 until it warms up real good, I can shut it off for about 5 seconds, and then turn the key back on and without hitting the starter it will sart. So, just wondering if anyone else has experienced this or might know whats wrong.
MSEE
Joined: Apr 2004
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From: Austin, TX
That's happening because your motor is dieseling. That's bad. It starts after you turn the key back to run because the momentum of the crankshaft from dieseling (run-on) does the starter's job, all it takes to start running completely is power to the plugs, which you're giving it when you hit the key. The most common source of dieseling is high idle, a vacuum leak, or heightened combustion chamber temperature which often results from know-it-alls who rip out the EGR system.
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From: Boise, Idaho
Wow, that's definitely a strange issue. Unless you happened to get a starter that doesn't make any noise at all. 
For the engine to start, there must be some form of centrifugal force in there since a motor simply cannot start itself. Is it an automatic or a manual? I'm trying to think of odd things that could keep spinning, like a messed up torque converter or something. If it wasn't, you'd be able to start it at any time without hitting the starter. Since it's only shortly after turning it off, something is definitely still spinning.
For the engine to start, there must be some form of centrifugal force in there since a motor simply cannot start itself. Is it an automatic or a manual? I'm trying to think of odd things that could keep spinning, like a messed up torque converter or something. If it wasn't, you'd be able to start it at any time without hitting the starter. Since it's only shortly after turning it off, something is definitely still spinning.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
The only explanation I have is that your motor is dieseling very slightly, and you can't tell from inside the cab. That, and your combustion chamber temperatures are through the roof, so it takes very little to get it going again. I'm willing to bet you're not running an EGR valve or it has gone out, which would explain the combustion temperature issue (this is not the same thing as coolant temperature, so if your motor hasn't been overheating, that doesn't matter).
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It's a C6 auto. One more thing, it doesn't start every time. Actually it doesn't start more than it does but even so it's still a weird problem. When I go home tonight I'll let you know exactly how long I can wait before it stops starting.
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From: Boise, Idaho
Another thing that would cause a lot of excess heat is if your heat riser valve is stuck open. That would mean you're getting 500 degree exhaust heat under your carb constantly, and not just when it's warming up. That'll keep your combustion chambers boiling.
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The only explanation I have is that your motor is dieseling very slightly, and you can't tell from inside the cab. That, and your combustion chamber temperatures are through the roof, so it takes very little to get it going again. I'm willing to bet you're not running an EGR valve or it has gone out, which would explain the combustion temperature issue (this is not the same thing as coolant temperature, so if your motor hasn't been overheating, that doesn't matter).
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I guess I should've told you, the exhaust is quite hot. It doesn't take long and it's dang warm in that engine bay. I never really thought about it though because somebody told me it was a 300 thing.
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From: Boise, Idaho
The heat riser is easy to check. When your engine is cool, reach down to where the intake and exhaust connect and there'll be a spring with a small 1" arm on it. If you can freely rotate the arm, it's okay. If not, it's seized. Sometimes, you can free it up by tapping it gently with a hammer and dosing it with some PB blaster or the like.
On another note, I had all the emissions equipment removed on mine with the 1bbl and it never dieseled once. Then again, I took some time tuning it to run without them.
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300s are notorious for being a cool running engine. But then again, exhaust is just hot by nature. The heat riser works by actuating a heat driven spring. When it's cold, the spring is open and lets the blazing-hot-from-the-moment-the-engine-starts exhaust up underneath the carb to help atomize fuel. Once it's warmed up, the spring closes with just enough room around the closing plate to keep the carb warm. If it's stuck open, you're getting that blazing hot exhaust under the carb all day long.
The heat riser is easy to check. When your engine is cool, reach down to where the intake and exhaust connect and there'll be a spring with a small 1" arm on it. If you can freely rotate the arm, it's okay. If not, it's seized. Sometimes, you can free it up by tapping it gently with a hammer and dosing it with some PB blaster or the like.
On another note, I had all the emissions equipment removed on mine with the 1bbl and it never dieseled once. Then again, I took some time tuning it to run without them.
The heat riser is easy to check. When your engine is cool, reach down to where the intake and exhaust connect and there'll be a spring with a small 1" arm on it. If you can freely rotate the arm, it's okay. If not, it's seized. Sometimes, you can free it up by tapping it gently with a hammer and dosing it with some PB blaster or the like.
On another note, I had all the emissions equipment removed on mine with the 1bbl and it never dieseled once. Then again, I took some time tuning it to run without them.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I don't know why it wouldn't have done it in the donor truck...lots of variables there.
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From: Boise, Idaho
I completely agree that removing all of the emissions equipment is not a good idea. (Such as in my case, I only did it because there was a 4bbl upgrade and distributor recurve in the works). However, from everyone I've known that have removed the emissions equipment (myself included), have never run into a problem of them dieseling this severely from it. Just usually running too lean and the like.
That and the heat riser is an easy thing to check.
That and the heat riser is an easy thing to check.