Cranks hard when warm

[shadetree 59]

I have a 1970 Ford F-250 with a 390 engine and four speed transmission. It is not licensed and I use it on the ranch. It has always started and ran good. Lately it has been cranking very slow when warm to the point that it sometimes seems like it won’t turn at all. When it is cold it starts as normal. I have replaced the starter as I thought that because it is so close to the exhaust pipe that it was cooked. I replaced the fuel pump because it had a leak but didn’t think it had anything to do with this issue. Help the old guy out as I can’t take it to town to get help.

Thanks
John

Topic

[Kevin]

[quote=”shadetree 59″ post=117814]I have a 1970 Ford F-250 with a 390 engine and four speed transmission. It is not licensed and I use it on the ranch. It has always started and ran good. Lately it has been cranking very slow when warm to the point that it sometimes seems like it won’t turn at all. When it is cold it starts as normal. I have replaced the starter as I thought that because it is so close to the exhaust pipe that it was cooked. I replaced the fuel pump because it had a leak but didn’t think it had anything to do with this issue. Help the old guy out as I can’t take it to town to get help.

Thanks
John[/quote]

Vapor lock? The starter is probably just getting heat soaked from the continuous cranking. Aside from that it’s either not getting spark or not getting fuel.

[John Hugon]

Check all starter circuit connections, including; battery cables to battery for good connection and battery ground cable to engine block for a good ground.

A good test to solve the issue you’re having: http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems#VoltageDropTesting

[shadetree 59]

I bought a new battery today as it was getting to need a charge once in a while. It was old so it should be replaced anyway. I will probably find out it’s the alternator or voltage regulator before this is remedied.

John

[Mike]

Heating a wire (such as your starter wire) increases the resistance (so it can’t flow enough current). A corroded starter or ground wire effectively has it’s diameter reduced, and therefore has increased resistance. If your starter wire or battery ground wire is old and has corroded and worn out anyplace near the engine’s heat, that would be likely culprit.

You can have a starter/ground cables that run the starter fine at ambient temp, but just a few inches of wire near the engine, radiator, or exhaust can heat soak the wire once they get hot, the wire/cable will not flow enough current to let the starter turn at full speed because if the increased resistance.

Not definitely your problem, but keep it in mind.

[shadetree 59]

New battery solved the problem for now.

Thanks
John

[Author]

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