Won't start Won't crank when warm 2010 5.4
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Junior Member
Joined: May 2026
Posts: 25
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Won't start Won't crank when warm 2010 5.4
2010 5.4 No crank when warm.
Hi just joined in hope of getting some help with this. Details: 2010 FX2, 5.4. Starts fine when cool but after it runs a few minutes it won't start/crank. All electrical acc. work fine with key on. Here's what I've done, replaced the battery, replaced the starter, checked and cleaned all connections still didn't fix. Swapped #2 relay with all the other relays in the fuse box, no joy. But pulling the relay and jumping contacts it starts every time. Relay clicks. No voltage to starter trigger wire when no start occurs. Let it sit for 15-30 mins and it starts right up. Out of ideas.
Hi just joined in hope of getting some help with this. Details: 2010 FX2, 5.4. Starts fine when cool but after it runs a few minutes it won't start/crank. All electrical acc. work fine with key on. Here's what I've done, replaced the battery, replaced the starter, checked and cleaned all connections still didn't fix. Swapped #2 relay with all the other relays in the fuse box, no joy. But pulling the relay and jumping contacts it starts every time. Relay clicks. No voltage to starter trigger wire when no start occurs. Let it sit for 15-30 mins and it starts right up. Out of ideas.
Thread Starter
Junior Member
Joined: May 2026
Posts: 25
Likes: 2
2010 5.4 No crank when warm.
Hi just joined in hope of getting some help with this. Details: 2010 FX2, 5.4. Starts fine when cool but after it runs a few minutes it won't start/crank. All electrical acc. work fine with key on. Here's what I've done, replaced the battery, replaced the starter, checked and cleaned all connections still didn't fix. Swapped #2 relay with all the other relays in the fuse box, no joy. But pulling the relay and jumping contacts it starts every time. Relay clicks. No voltage to starter trigger wire when no start occurs. Let it sit for 15-30 mins and it starts right up. Out of ideas.
Hi just joined in hope of getting some help with this. Details: 2010 FX2, 5.4. Starts fine when cool but after it runs a few minutes it won't start/crank. All electrical acc. work fine with key on. Here's what I've done, replaced the battery, replaced the starter, checked and cleaned all connections still didn't fix. Swapped #2 relay with all the other relays in the fuse box, no joy. But pulling the relay and jumping contacts it starts every time. Relay clicks. No voltage to starter trigger wire when no start occurs. Let it sit for 15-30 mins and it starts right up. Out of ideas.
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Joined: Aug 2023
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Welcome.
couple basic ideas to check: interior corrosion of battery cable (mainly rust belt issue) clean, lubricate ignition switch. I’m assuming you’re jumping high side power to that relay, if so check for activation power and function.
Rereading your post you may have already done that. That seems suspect tho. good luck.
couple basic ideas to check: interior corrosion of battery cable (mainly rust belt issue) clean, lubricate ignition switch. I’m assuming you’re jumping high side power to that relay, if so check for activation power and function.
Rereading your post you may have already done that. That seems suspect tho. good luck.
Last edited by F150Mafia; May 8, 2026 at 09:16 AM.
Retired Ford Technician
Joined: Dec 2013
Posts: 762
Likes: 344
From: Lawton Oklahoma
When it wont crank test for voltage at pin 1 when key is in start position. If you dont get voltage then you likely have a bad ignition switch, or the TR sensor in the transmission is defective. I believe that is part of the Lead Frame assy.
Retired Ford Technician
Joined: Dec 2013
Posts: 762
Likes: 344
From: Lawton Oklahoma
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Retired Ford Technician
Joined: Dec 2013
Posts: 762
Likes: 344
From: Lawton Oklahoma
In the crank position power from the ignition switch is sent to pin 1 of the relay. PCM grounds the relay at pin 2 when it is OK to start according to the Neutral switch. If either the power is missing or the ground the relay wont activate the starter.
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Junior Member
Joined: May 2026
Posts: 25
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#1 Pin has power. When it's warm and won't start, I pull the #2 relay and jump the contacts with an alligator clip and it starts right up, every time. I didn't replace the ignition switch because the relay clicks when attempting to start.