rustang222

I've got an 04 Lariat 4x4 with 87k miles on it and its got a symptom that I originally thought was attributed to a bad IWE solenoid. Basically, at low speeds (under 25 MPH), turning and under load (on the accelerator) the truck seems to shudder. If feels like its coming from the front end but I really am not sure. I can say with certainty that it doesn't happen when I'm just coasting and it's at it's worst when I'm pulling into my driveway; turning and driving up a slight incline at a very low speed. Also, it's not super consistent. For example, if I'm just driving around the parking lot at work, turning and accelerating and low speeds, sometimes there is no shudder at all and the truck seems to drive just fine.

I replaced the IWE solenoid with a new OEM part and that doesn't change anything. I've also tested the system with the front wheels off the ground:

- engine off = front wheel turn without axles turning
- engine on in 2wd = front wheels turn without axles turning
- 4x4 with engine on = front wheels and axles turn
- I haven't checked the vacuum lines yet

Should I start with the lines or does the symptom sound like it might be something else?

I'm really losing my patience and would appreciate some thoughts or ideas. Thanks

jamie930

with the engine off the front hubs should be locked in. As you need the engine vacuum to unlock the hubs

alsatropine

iTrader: (2)

What Jamie said. With your engine off the wheel and axle should turn. Check your check valves coming off the iwe solenoid. Might have 2 or three. Should be able to blow through them but not be able to suck back through. If those are good, get a vaccum pump and check for leaks at the actuator If it bleeds down fast you have a bad or leaking actuator.

rustang222

My mistake. You are right. The axles turned when the motor was off. I did the test last week so misremembered.

rustang222

Alright, thanks. This is what I'll check next.

VTX1800N1

https://www.f150forum.com/f72/how-di...72/?styleid=14

rustang222

Yep... Thanks. I've read thru this more than a few times and it's an excellent write up and resource. I felt like the symptom that my truck was exhibiting didn't seem to fit exactly with what was described in the IWE diagnosis thread which is why I started this thread. However, it seems like I just need to do some more diagnostic work first in order to make sure I've checked the IWE's fully.

rustang222

I wanted to give you all a quick update. Today I spent a few hours checking the vacuum lines and the IWE's. All seems to check out... IWE's hold vacuum well and all the lines also seem to be working properly. I did pick up one of the two new check valves that I'll install tomorrow.

Assuming the new check valves don't fix the problem, what should I be thinking about next??

VTX1800N1

You said you weren't sure where the shudder was coming from. Do you have a LS rear?

rustang222

That's right. I'm not positive where the shudder is coming from. This might be a dumb question but does "LS" mean "limited slip?" If that's the case, I don't know.

Also, the check valves seemed fine. I could blow air thru them but not suck any air back thru. I also had my wife sit in the cab and rev the engine up a bit while I spun the front axles. Everything spun freely in 2WD while the motor was at higher RPM's.