Hi All,

I have a strange intermittent issue i can’t resolve nor can a Ford dealership or independent shop. I have a 2013 F150 super crew with coyote engine. About 160k miles. Every few weeks when i start the truck it will pull left immediately after starting it. If i drive more than a few hundred feet like that it will engage traction control and will continue to do this until i shut the truck off. The vast majority of the time if i turn it off and turn it back on it magically works again. Once in a while it takes 2 or 3 tries to resolve. Once it happens I’m usually good for 3 weeks or so till it happens again.

There are no codes. Ford couldn’t replicate it and just turned me loose after 2 visits. I took it to an independent repair shop that is great. First time he couldn’t replicate and wouldn’t charge me. Second time it had locked up 3x in a row and i insisted it was likely the vacuum hub actuator as i couldn’t think of anything else. He smoke tested it and it passed and i asked him to replace anyways as i was losing my mind after 4 visits. He said the seals looked good but when he pulled it apart one of the parts inside assembly was broken. He checked the left side and that one was cracked so he replaced both. I was excited and confident we resolved it.

This past week unfortunately it happened again. Started truck. It immediately pulled left then engaged traction control. I don’t know where to go from here. Calipers have been checked and if they were sticking it wouldn’t fix itself with a restart. Electric power steering was replaced about 18 months ago not sure if that could be related. Not sure what else would intermittently make it pull left. Any ideas? Any help would be greatly appreciated.

 

Bumping this up in the hopes someone has ideas or can at least suggest some new things to check or at least confirm my logic.

Due to the fact that this is intermittent and it can be resolved by shutting off the truck and turning it back on again I think I can rule out some of the following issues:
- Alignment
- Stuck caliper or brakes in general
- Worn suspension
- Wheel bearing

Though I suppose it could be the new vacuum hub actuator is broken again (after only a few drives on it) i'm assuming I can rule that out but will have the mechanic check it again when I go back. I don't think its the electric power steering. When mine failed previously it was intermittently working but it would just be harder to steer, it wouldn't pull you in one way or the other by itself.

I still think its a vacuum issue. But its intermittent. When the mechanic smoke tested the vacuum system it all tested fine with no leaks. My guess is the drivers side only is intermittenly failiing and the hub is engaging and pulling it to the left which then engages traction control as you have the front wheels moving at different speeds. What I don't know is what actually builds the vacuum pressure, could that be electronically controlled and intermittently failing? Any advice would be greatly appreciated..i'm losing my mind on this one.

 

A quick question for clarification ... when you say "when i start the truck it will pull left immediately after starting it." Is the truck driving before it pulls or does the steering wheel jerk to the left immediately after the truck is running (still stopped and not moving)?

 

Good question, sorry for not being clear. It starts pulling left when I begin driving. Not violently left mind you, but if I let go of the steering wheel and hit the gas it will pull left by itself naturally unless I hold the steering straight somewhat firmly. This will last about 30-60 seconds before traction control kicks in. It will keep doing it again and again until I fully put it in park and turn the truck off and on again and start over. Usually it only takes one restart. There have been one or two occasions where it took 2 or 3 times restarting to resolve. I do think it has to be IWE related and i'm guessing the drivers side vacuum lines only. I can't think of what else would make it pull left.

For a bit of additional info...this only ever happens right on startup. It has never happened mid drive. My understanding of IWE is that once you start up the truck it applies vacuum pressure and pulls the IWE out of engagement (not sure how to technically explain it) forcing you into 2WD. Only when you manually select 4WD does it release vacuum pressure and engage it. So this makes me think somehow the drivers side IWE is not engaging vacuum pressure. The strange thing is it was pressure and smoke tested when I had the IWE replaced a few weeks ago and the lines tested fine. I'm thinking of replacing them anyways unless I can get some other suggestions here. i'm out of ideas.

 

To test that, jack up the front, chock the rear wheels, start the truck, put it in neutral and manually turn the front wheels. If the IWE is working the wheel will turn but the CV shaft won't.

Also, if you think it's the IWE at one wheel just pull the vacuum line at the vacuum switch to keep both front wheels engaged. Then when you drive one side won't be pulling you over.

Just a couple free tests you can do.

 

Hi Kruisr. Thanks for the advice. I know the mechanic did test the lines when he replaced my vacuum hub actuator but i'll test again. If I left the vacuum line at the switch off for the drivers side only wouldn't that automatically put that wheel in locked cv shaft? I thought the removal of vacuum would keep it in 4wd or do i have that backwards?

 

Just brainstorming on what would cause this. If it was wheel related it would have to be something that is restricting the wheel to turn like a stuck caliper. You said the calipers were checked and assuming they are fine and nothing was missed, maybe it has something to do with the ABS where it thinks the left front wheel is spinning and applying brake to it. Maybe a bad sensor, short/broken wire in the harness to the sensor or the module that controls the ABS is bad.

Just a thought.

 

I did have the caliper checked (it actually was replaced last year as it was dragging) and the ABS checked and there are no codes associated but good advice to check it again. The other thing I was thinking is the next time this happens I may come to a complete stop (without turning the truck off) and turn on 4H and then turn it back off and see if that reapplies the vacuum and fixes it without a full shutoff. If it does perhaps that definitively leads to an IWE/Vacuum issue?

 

I've never read an IWE issue causing the truck to pull one way or the other. I honestly don't think it is an IWE issue.

I still think it is something causing the left wheel to slow down and thus pulling to the left or something else. Maybe the steering is malfunctioning some how? Position sensor is bad, bad wire, loose/dirty connection and thus it is trying to "recenter" the wheels. If it goes away when you completely turn the truck off and back on, tells me it is something electrical.

 

I agree on the electrical comment. The reason i was thinking IWE is becuase if it was only failing to hold vacuum on the drivers wheel that would mean only 4x4 is engaging on the left side and not the right side. If it was locking the hub on the left side only I would imagine it would pull to the left? But maybe that is an incorrect assumption and maybe it would have no impact if the left hub only locked and the right didn't since if they both were not engaged they wouldn't be forced to spin at the same speed.