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06 Hesitation (or bucking) while cruising

7K views 22 replies 6 participants last post by  cardoc 
#1 ·
MY wife has a 07 Subaru Legacy Automatic with 101k miles that has been acting up lately. I know this is a Outback site (I drive an 02 Outback) but was hoping to see if someone could point use in the right direction on how to fix the issue. I have mechanics background and do almost all my own repairs. Her symptoms are:
About a 2 month ago she said that her radio and A/C lights flashed on and off a couple of times on her way home. That was the only time she noticed that happening so I was not overly concerned.
Last month her car started making a humming noise from the front left side and that her car felt like it was hesitating a little while cruising down the road. I diagnosed it to be a bad hub bearing so I replaced it. She said afterwards that the humming was gone but the hesitation was still there. The hesitation is very light so I assumed it had something to do with her throttle-by-wire system and she was starting to notice it more as the car aged.
Last night she was on her way down to see her grandmother and called and told me that when she turned on the cruise control the hesitation got worse for about 4 miles until the cruise control cut itself off and the cruise light started to flash. With the cruise back off the hesitation she thought was not as bad. Once she turned off her car and restarted it the cruise light was no longer flashing. She tried to use the cruise again and the same thing happened.
When she got home the same thing happened to me when I drove it. I hooked up my scanner to see if any codes had been thrown while the cruise light was flashing nothing showed up.
Currently there are no lights on the dash unless you leave the cruise on for more than a couple of miles and the cruise light will flash.
Anyone have a similar problem or have any suggestion on what it might be?
Thank you for the help.
 
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#3 ·
My thought - you have a mouse problem. Check under rear seats to see if there is any evidence of the critter. There is a wiring harness under there that is related to the cruise. My wife had a mouse chew through it when the car was just a year or two old. Only issue for us was cruise.

Tom
 
#4 ·
Thanks for the suggestions. My wife is a fanatical cleaner of her so I would not think she would have mice but she could have easily pulled a plug loose under her seat. I was wondering if the knock sensor could be going bad. My 98 Legacy GT u use to own started to hesitate but it through a code that pointed to the knock sensor. It would be nice if her Subaru would throw a code and point me in the right directions.
 
#5 ·
Hmm... I wonder if this isn't related to the speed sensor on the wheel where you replaced the bearing? If that isn't send the signal consistently it can disable cruise. I think I've read of a number of issues with after market bearings for subaru give issues with the wheel speed sensor....
 
#6 ·
I wonder if this isn't related to the speed sensor on the wheel where you replaced the bearing?
Yes!

tdelker: Your post reminded me of several similar threads here and I went back to see if there was a confirmation but, alas, it appears aftermarket replacement wheel bearing hubs were suspected but not confirmed.

Fortunately, this more recent thread (http://legacygt.com/forums/showthre...l-after-wheel-bearing-hub-change-181231.html?) starts with the same cruise control issue after replacing front hubs, and ends with confirmation that the aftermarket units just didn't work -- genuine Subaru replacements corrected the problem.

As noted by some of the posters, the general understanding had been that the wheel hubs and sensors are used by the ABS system but not the cruise control and therefore problems with the sensor signal shouldn't affect cruise; I was under this same impression. However, the empirical evidence regarding aftermarket hubs in the linked thread is sufficient, in my view, to suspect the replaced front hub in the present case.

This still doesn't address the hesitation which seems to be present even when the cruise control is off. But perhaps the bad wheel speed signal is also affecting the engine or even causing the ABS to pulse (without other apparent signs).

Perhaps the first thing is to install a Subaru hub and see if the cruise issue is resolved. Then check if the hesitation has gone away.
 
#7 ·
Thank you very much for the help. The hub I installed is a Rabestos aftermarket one. My wife claims that the hesitation was present prior to the hub being replaced. The hesitation is very light and hard for me to notice since I do not drive her care very often. I only kind of notice it at highway speeds and it feels like hitting very small cracks in the road surface. I wish I knew if the cruise was working prior to the hub change but my wife rarely uses it and could not remember the last time she did. It would be nice if it threw a code. I would be glad to return it for an OEM hub if I could prove that was the issue. Any other suggestions would be much appreciated.
 
#8 ·
Hesitation could well be unrelated. As with the other occasional electrical issues.

Either use a tool that can monitor wheel speed reported (no idea what tool that would be, but I believe it's possible) or put in the old hub and see if cruise is working again.

101k is getting close to timing belt... I wouldn't let it go long. Hesitation could be related to a tensioner/pulley issue. It's a long shot, but not an unheard of problem.

Tom
 
#9 ·
Thank you very much for all the help. I read the link to the forum about hubs and am pretty sure that is probably the issue. I am going to email the company I bought it from and see about getting it returned and getting an OEM one. I plan to do the timing belt in the next couple of months when I can find a free weekend. I was going to purchase the Gates timing belt kit. Would you recommend that one or is there another you prefer? I also need to pull the engine on my 02 OB and replace the head gaskets, seals and other gaskets while I have it apart. It has a very small oil leak that started about 8 months ago at the rear left head. What head gasket would you recommend?
 
#11 ·
Linked legacygt forum thread above shows exactly that - replaced hub with aftermarket, cruise fails, no other issues. Hub swapped for old one, problem resolved. Hub swapped for OEM, problem still resolved.

Regarding last question - Gates seems pretty standard, often bought on ebay. Some say include water pump (gates makes one with it), some not. Split opinion, so you decide. I have the same maintenance coming up, and haven't decided myself. I just change the coolant at 90k, so it seems a waste to drain now, but I'm in there, so... I keep seeing advice to change cam seals, but this makes the job much harder (can't use vice grips to clamp driver side cams), and no known issue with these seals, so I would only do it if it clearly is leaking.

No idea on Gen 2 head gaskets. For Gen 3 most say use the turbo head gaskets on the naturally aspirated engine. I'm sure there are plenty of treads in the gen 2 forum discussing this...
 
#12 ·
I am back and forth on if I should do the water pump while I am in there. Her car has been almost bullet proof before the hub went out (knock on wood). The only other issue besides normal maintenance was the brake shift lock going bad. I was not planning on doing the cams unless I see leaking when I take the covers off.
 
#13 ·
I'm right there with you... Looks like Amazon has the best prices for the TCK328 or TCKWP328 gates kits (for turbo). $50 more for the water pump. Hmm.... Suppose I might as well just do it. Gotta include more coolant and a new thermostat if I'm in there.

Tom
 
#19 ·
The system is designed for a waste spark. It fires 1 and 2 simultaneously, 3 and 4 simultaneously. A misfire would be on the compression stroke firing sequence unless there is excess fuel in the cylinder on the exhaust stroke, then the exhaust firing will cause imbalance due to a burn on the opposing cylinder.
 
#20 ·
is that why the resistance is super high on the ignition coil in cylinder 4? .... and processed that nugget. so its like a heart beat. i guess i never put the pieces into place and always thought it was sequential. how does this waste spark come about and what is it?

i changed all 4 plugs, autolite double platinums. awhile back i spent almost an entire day trying to get the plug out of cylinder 4 without taking out the battery, it went so much soother this time. i went cheap just to see if that was it and it mostly waswhile holding the gas steady, it remains steady and not like a mechanical bull. when i get new wires im going with ngk plugs too.. i guess when i first changed them, they gave me the single platinums and not the doubles.
when i take my foot off the gas i get a shimmy and also when i put my foot back on it, all gently. the suspension is shot, would that have any effect? last time i had my engine out i saw i had a few small fractures in my flywheeel and a little bluing. i couldnt afford to replace it at the time so i took some 5000 grit sandpaper to it. my friction plate was getting a little thin too. what does it feel like when you get down to the rivets?
 
#23 ·
@Jeremy97ej25dohc
After combustion there is always residual fuel in the chamber. Firing a spark burns this fuel but it is such a small burn that it does not produce enough power to affect crankshaft imbalance under normal conditions. The waste spark is to burn what would normally get pushed out in to the exhaust and therefore helps reduce HC in the exhaust.

Autolite spark plugs suck in any engine.

When the clutch is worn to the rivets it will slip. The disc will be so thin that the pressure plate cannot sandwich the disc between it and the flywheel. The rpms will rise without giving you forward motion or speed increase.

Since you mention suspension, other things that create a "bucking" would be engine and trans mounts, or the pitch stop mount. Then there's the rear diff bushings, rear diff carrier bushings/mounts, or anything that is made to keep parts stable.
 
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