Starter relay testing/wiring

5

Asked by Jan 25, 2017 at 12:02 PM about the 2008 Ford F-150 Lariat SuperCrew 4WD

Question type: Maintenance & Repair

My 2008 Ford F150 has been having intermittent starting issues. The battery, starter and digital transmission range switch (neutral safety switch) have been replaced. I'm trying to pinpoint this issue but I've never dealt with this type of problem before. I'm learning a lot which is nice but it's frustrating not being able to locate the problem. I think the issue is either the ignition switch, starter solenoid relay (R01), or wiring. I'm leaning towards the wire coming from starter to R01 but this is all new territory for me.
I originally would rock the truck while in park and that helped me get it started most of the time. This didn't work one time and I had to let it sit for awhile and let it cool down. I recently discovered that messing with R01 seems to help get the truck started. It seems like the relay is not making a good contact or one of the wires needs to be replaced. I tried switching R01 with R03 which is my hibeam headlights but it didn't fix the problem. I got half a crank and that lead me towards the relay not making good contact or a bad wire. When I switched the relay back I got a half crank and then while cranking and jiggling the relay it started.
I've bench tested the relay out of the vehicle and it checked out. More recently I took the relay out and checked pin-out 86 for 12V while cranking and it was there. My next step is to check pin-out 86 for 12V while the vehicle won't start but I'm not sure what else to do at this point.
Any suggestions?

2 Answers

110,735

First thanks for a such a detailed question, most people write (My car won't start, HELP !, LOL) anyway you are doing everything right and there are a few things I would look at when a trouble shooting your relay, A relay is a simple device, it may work a hundred times with no issues and there will be that one time it won't. The relay itself maybe heating internally and shorting or possible a bad connection in the plug or the back where the wires attach. I would try to get a really small file and get down in there and give the connectors a good cleaning and then add some dielectric grease and see it that helps cure the issue...

5

The PCM ended up being bad.

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