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Dieseling in 1985 4.9L inline 6

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Old 07-11-2018, 05:30 PM
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Question Dieseling in 1985 4.9L inline 6

Hello everyone. I have a 1985 f150 with an inline 6. I recently fixed all the vacuum leaks in my truck and now I tried to time my truck to the proper rpm. Every time I shut off the engine, it diesels really really bad. I know my harmonic balancer is out and I plan on replacing it soon. The timing marks are incorrect so I time it by the tachometer and by ear. I understand that dieseling is caused by the engine being too far advanced, but I set the truck to idle at 200 rpm and it still diesels horribly. I was wondering if anyone had any idea what could cause this? I plan on static timing the truck next time I have time.
 
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Old 07-11-2018, 05:44 PM
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If your truck is all original, there is a special procedure to time it. Even by ear, you can't time it, the computer is controlling the timing. You need to find the spout connector, disconnect it, and then time it, even by ear.

Dieseling is caused by the engine getting too much air. The idle stop screw is too far open or there is a huge vacuum leak somewhere. The timing be off could aggravate this though, so try to find the spout connector, disconnect it, and then try to time it. If you follow the wires leaving the distributor, you will find there is a group of wires, and one lone wire coming from the group with a jumper connector in it. If you take this jumper connector out, then you have disconnected the spout wire.
 
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Old 07-11-2018, 05:57 PM
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Originally Posted by Franklin2 View Post
If your truck is all original, there is a special procedure to time it. Even by ear, you can't time it, the computer is controlling the timing. You need to find the spout connector, disconnect it, and then time it, even by ear.

Dieseling is caused by the engine getting too much air. The idle stop screw is too far open or there is a huge vacuum leak somewhere. The timing be off could aggravate this though, so try to find the spout connector, disconnect it, and then try to time it. If you follow the wires leaving the distributor, you will find there is a group of wires, and one lone wire coming from the group with a jumper connector in it. If you take this jumper connector out, then you have disconnected the spout wire.
How many turns should the screw be backed out on a carbed 1985 inline 6?
 
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Old 07-11-2018, 07:01 PM
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I have never seen timing to cause dieseling only a high idle but you said it was 200 rpm.
As we know you need fuel, motor turning and spark. Well key off we don't have spark so what is lighting the fuel?
What heat range spark plugs are you running? If too hot they could be glowing and lighting off the fuel.
Also carbon build up can have a glowing hot spot lighting the fuel.

Just some thing to think about.
Dave ----
 
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Old 07-12-2018, 03:51 PM
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Please explain your procedure for determining that all vacuum leaks are fixed.
 
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