I6 / 300 - Chugging under sustained load
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From: Southwest Washington
I6 / 300 - Chugging under sustained load
I've recently started having an issue with my inline 6 where it runs fine until I'm under sustained load in which case it starts lurching/chugging. As soon as I relieve the load (i.e. letting off the accelerator or pushing in the clutch), it's fine/normal. If I'm staying on backroads/lower speed then I'm fine and don't notice any issues at all. As soon as I try to get to higher speed, or am going up a hill (I've observed in both 3rd and 4th gear), the truck starts lurching/jerking/chugging. I'm not real sure where to begin - any suggestions?
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Have you performed a good tune-up yet? A cylinder compression test is important so you have an idea of the engine health and whether it's worth tuning up in the first place. Rebuilt the carburetor?
Good hot spark at the plugs? Still running points & condenser? Checked mechanical advance for smooth operation? Get thee a Ford Shop Manual and studyeth it, verily. Go through everything, after 50+ years there will be plenty of things to straighten out. My vote is on weak ignition or defective advance & flaming out under load, but that's a WAG.
Good hot spark at the plugs? Still running points & condenser? Checked mechanical advance for smooth operation? Get thee a Ford Shop Manual and studyeth it, verily. Go through everything, after 50+ years there will be plenty of things to straighten out. My vote is on weak ignition or defective advance & flaming out under load, but that's a WAG.
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Joined: Nov 2015
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From: Angier, NC
Have you performed a good tune-up yet? A cylinder compression test is important so you have an idea of the engine health and whether it's worth tuning up in the first place. Rebuilt the carburetor?
Good hot spark at the plugs? Still running points & condenser? Checked mechanical advance for smooth operation? Get thee a Ford Shop Manual and studyeth it, verily. Go through everything, after 50+ years there will be plenty of things to straighten out. My vote is on weak ignition or defective advance & flaming out under load, but that's a WAG.
Good hot spark at the plugs? Still running points & condenser? Checked mechanical advance for smooth operation? Get thee a Ford Shop Manual and studyeth it, verily. Go through everything, after 50+ years there will be plenty of things to straighten out. My vote is on weak ignition or defective advance & flaming out under load, but that's a WAG.
How do you know what he has other than a I6 / 300? It could be a 90's truck with EFI and that new fancy electronic spark thing under the hood all run by a computer.
BTW that computer can tell us things that could be wrong.
We need more information like what year is this truck and what is it in to start with.
What trrany and at what speed does this happen and do you have a load in the bed or is it empty when it happens?
How many miles on the clock and has any major work been done to the truck or even minor work?
Dave ----
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Joined: Apr 2002
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From: Waterloo, Iowa
Well he has previously posted he bought a 1966 F100 so I went with that.
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From: Angier, NC
Dave - - - -
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From: Southwest Washington
Thanks Tedster and FuzzFace 
It is indeed the 66 F250 that I had bought previously, apologies for not having provided that detail. I picked up a compression test kit and am hoping to do that tomorrow after work. I really haven't done much with it yet since I bought it other than check to make sure it has oil in it. I will take your advice and pick up a set of shop manuals.
I very much appreciate the advice and direction offered. And thankfully I'm not on the side of the road without cell coverage
It is indeed the 66 F250 that I had bought previously, apologies for not having provided that detail. I picked up a compression test kit and am hoping to do that tomorrow after work. I really haven't done much with it yet since I bought it other than check to make sure it has oil in it. I will take your advice and pick up a set of shop manuals.
I very much appreciate the advice and direction offered. And thankfully I'm not on the side of the road without cell coverage
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6CylBill
Ford Inline Six, 200, 250, 4.9L / 300
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Aug 29, 2010 10:56 AM
