2008 F150 Starting Issues

5

Asked by Jan 11, 2017 at 01:20 AM about the 2008 Ford F-150 Lariat SuperCrew 4WD

Question type: Maintenance & Repair

My 2008 F150 has been having intermittent no start, no crank when the engine is hot. I've already replaced the battery, starter, digital transmission range switch (neutral safety switch) but still no luck. I checked the cable connections (clean & tight), and tested the fuses and relay (good). Today I tested the continuity of the ignition switch. It appears to be working but I'm not sure about voltage-wise or if it can fail at hot temperatures. I've also read that a relay could fail intermittently?

Here's what I know, when I checked the ignition terminal on the starter, the test light did not come on. This led me towards the ignition switch. I have constant 12 volts at terminal 4 (green wire with purple stripe) but none of the other wires have voltage. Should the other wires get voltage based on the position of the switch? In my Haynes repair manual they only show the terminal 4 wire (green wire with purple stripe) and terminal 7 (red wire with blue stripe). according to the diagram, it seems like terminal 7 should only have voltage when key is turned to start. Is that correct?

I couldn't find information on what terminal 1 is (blue wire with green stripe), terminal 2 is empty,
terminal 3 (solid yellow wire) goes to multi-function switch if I'm correct, terminal 4 (green wire with purple stripe) constant hot,
terminal 5 (black wire with pink stripe) instrument panel (I think??),
terminal 6 (black wire with green stripe) I couldn't find info on,
terminal 7 (red wire with blue stripe) goes to starter when key is in "start"

Could it still be the ignition switch? Is it most likely just a break in the wire somewhere? Could it be an intermittent failing relay or fuse? How can I pinpoint the issue?

2 Answers

112,445

Lets step away form the ignition for a moment and look at a other things that would cause a no start under hot conditions. I would look at the crank position, if heated it could cause the truck not to start. You need to check the fuel pressure when the truck is cold and when the truck is hot. Look at the fuel relay test it when the truck is hot and cold.

5

The PCM ended up being bad.

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