2014 - Mileage loss 4A vs 2H

[SteveIdaho]

My 2014 Expedition (107k miles) was in the shop a couple weeks ago to replace four struts and install new front end stabilizer links.

After getting the car back, I've got a front end grinding noise in 2H that lasts less than a second under light acceleration, typically 15 - 25 mph. I figure this is an IWE problem with a vacuum line leak. The reduced engine vacuum during acceleration is causing loss of vacuum in the front hubs, causing the springs to slowly engage the front hubs.

The noise does not happen in 4A (vacuum is released and the hubs are always engaged). I've been driving in 4A since getting the car back.

Yesterday we did two freeway trips in 4A, each about 35 miles on the same freeway, one east-to-west and the other west-to-east. I reset the mileage computer when entering the freeway both times. We got 18.2 mpg on the freeway both directions.

QUESTIONS:​

1. How much mileage reduction is typical when driving in 4A vs 2H?
2. Is it worth having the IWE repaired so 2H works properly? (ten year old car with 107k). I don't have a quote yet to repair it. It might be as simple as re-attaching a disconnected vacuum line to the hubs, replacing vacuum lines in the IWE system, or replacing the solenoid and check valve.

If I drive the car another 50,000 miles, get 15.8 mpg average highway / in-town, suffer a 5% reduction in mileage, and gasoline costs $4.00/gallon, I would pay an extra $680 for fuel.

If I suffer a 2% reduction in mileage and gasoline costs $3.50/gallon, I would pay an extra $245 for fuel.

I don't like broken things, but it is hard to justify a big IWE repair bill.

 

[99WhiteC5Coupe]

My 2014 Expedition (107k miles) was in the shop a couple weeks ago to replace four struts and install new front end stabilizer links.

After getting the car back, I've got a front end grinding noise in 2H that lasts less than a second under light acceleration, typically 15 - 25 mph. I figure this is an IWE problem with a vacuum line leak. The reduced engine vacuum during acceleration is causing loss of vacuum in the front hubs, causing the springs to slowly engage the front hubs.

The noise does not happen in 4A (vacuum is released and the hubs are always engaged). I've been driving in 4A since getting the car back.

Yesterday we did two freeway trips in 4A, each about 35 miles on the same freeway, one east-to-west and the other west-to-east. I reset the mileage computer when entering the freeway both times. We got 18.2 mpg on the freeway both directions.

QUESTIONS:​

1. How much mileage reduction is typical when driving in 4A vs 2H?
2. Is it worth having the IWE repaired so 2H works properly? (ten year old car with 107k). I don't have a quote yet to repair it. It might be as simple as re-attaching a disconnected vacuum line to the hubs, replacing vacuum lines in the IWE system, or replacing the solenoid and check valve.

If I drive the car another 50,000 miles, get 15.8 mpg average highway / in-town, suffer a 5% reduction in mileage, and gasoline costs $4.00/gallon, I would pay an extra $680 for fuel.

If I suffer a 2% reduction in mileage and gasoline costs $3.50/gallon, I would pay an extra $245 for fuel.

I don't like broken things, but it is hard to justify a big IWE repair bill.

I can’t answer your question on the MPG reduction.

Your IWE issue may be something simple such as the IWE vacuum check valve or the IEW solenoid, or one of its attachment hoses. Rarely does the IWE vacuum reservoir tank go bad, unless the vacuum line nipple is cracked. You can easily check and replace the items. They are inexpensive.

You can crawl under the truck, or put it on ramps, and check the hard plastic IWE vacuum lines. They are also easy to replace.

Since you had the front struts replaced, I would be the mechanic broke or disconnected a vacuum line, which is causing your IWE grinding issues.

 

[eddytheexpy]

yep that's the hallmark of an IWE vacuum leak somewhere. Could be the check valve, cracked vacuum line, maybe a poorly seated hose on the IWE or even maybe a bad IWE all together. If you are able to track down a vacuum leak but believe you've really beaten on the IWE from this issue they are ~$90 at auto zone and only require taking off the tire, taking off the brake caliper bracket, removing the UCA and tie rod from the knuckle, and then the CV shaft out of the hub. So just 7 nuts/bolts on each side. After that the knuckle folds out and then there's 3 small bolts holding the IWE in. If you have deep sockets going up to 22mm, a floor jack and 2 jaw pullers, you're ready to do the job!

Sure, the 4a might sound like a solution but it's more of a stop-gap. You're engaging the front axle so your front diff is going to be working wayyyyyy more than its designed to (the wheels turn it in 4a instead of it turning the wheels in 4h) so you'll have to consider the cost of increased maintenance on that since it looks like you're already starting a cost analysis. If the front diff goes down and you can't use 2h, you now have an inoperable vehicle. Also, you may have already noticed your steering binding up in 4a. You can't make hard turns on pavement with your front axle engaged. So if you are expecting around-the-town driving, good luck trying to use a parking lot. BTW this impacts the health of your front diff as well.

you can replace the entire vacuum line (this is what I used for mine) for $65 and that's way more expensive than the check valve so nothing here is particularly pricey. It's a super easy job too, you literally only need a screw driver and needle-nose pliers. You don't even have to raise the vehicle! If you don't ever expect to use 4x4 and don't really care about the IWEs being a little damaged, just leave the old ones in (assuming they aren't the source of the problem). Honestly, replacing them would just be a peace of mind thing for me but I use 4x4 regularly.

 

[ExplorerTom]

Experienced the EXACT same thing on my 2014.

I replaced the vacuum check valve under the brake booster. Didn’t help.

I hooked up a vacuum pump, vacuum gauge to various parts of the system and tried troubleshooting the system. I couldn’t find anything wrong. Except the noise was still there.

I bought the RCV lockouts. My hubs are always engaged.

I’ve tracked 92k miles of driving for my MPGs. Not sure off hand how many of those are with the RCVs, but it’s roughly half. My overall average is 14.9. My best is 19.1.