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Discussion Starter · #1 ·
Hey guys,
So I've been digging for weeks now and I am unable to find any pertinent info relating to my issue save for the MK2 ST.
So here's the deets:
Under any circumstance, the car is randomly going into limp mode (limited boost, wide open wastegate, and cut power), but can be reset by restarting the car. Sometimes it will even through a CEL with the P0234 DTC (Generic overboost code). I have been unable to figure out what's causing it, the car is bone stock with 175,000 miles on it so my best guess is that the wastegate actuator is going out, or one of the two vacuum control solenoids is going out. My next move is to verify vacuum on the aforementioned components, but honestly I'm just shooting in the dark here. Also as a side note, I checked over all the vacuum lines and nothing appears out of the ordinary. I also have a Boomba BOV, but I made sure to install it correctly so I highly doubt that's it, since I've had it in the car for months and never had an issue until randomly one day it threw the CEL. I'm also thinking it could maybe be a loose charge pipe, but doubtful.
Any insight on this whatsoever would be greatly appreciated, since like I said, I haven't been able to find anything pertaining to this. Any questions, feel free to shoot a reply, and hopefully we can figure this out! I miss driving this thing, so it's killing me seeing it parked all the time.
 

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Hey guys,
So I've been digging for weeks now and I am unable to find any pertinent info relating to my issue save for the MK2 ST.
So here's the deets:
Under any circumstance, the car is randomly going into limp mode (limited boost, wide open wastegate, and cut power), but can be reset by restarting the car. Sometimes it will even through a CEL with the P0234 DTC (Generic overboost code). I have been unable to figure out what's causing it, the car is bone stock with 175,000 miles on it so my best guess is that the wastegate actuator is going out, or one of the two vacuum control solenoids is going out. My next move is to verify vacuum on the aforementioned components, but honestly I'm just shooting in the dark here. Also as a side note, I checked over all the vacuum lines and nothing appears out of the ordinary. I also have a Boomba BOV, but I made sure to install it correctly so I highly doubt that's it, since I've had it in the car for months and never had an issue until randomly one day it threw the CEL. I'm also thinking it could maybe be a loose charge pipe, but doubtful.
Any insight on this whatsoever would be greatly appreciated, since like I said, I haven't been able to find anything pertaining to this. Any questions, feel free to shoot a reply, and hopefully we can figure this out! I miss driving this thing, so it's killing me seeing it parked all the time.
The bushing on the waste gate actuator is a failure point. Try reaching back there, get a hold of the actuator arm and see if the is any play in the bushing. If it is worn the waste gate flap won't seal properly and it will also leak around the bushing as it will be wollowed out.
 

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2014 ST3. Garrett GTX2860R Gen 2. FBO
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Along with what ddfred said, if that bushing is causing binding, that would certainly cause an overboost in certain conditions.

Otherwise i would use a Mityvac, starting at the wastegate canister and apply pressure and see if it holds. If not, theres your overboost (the gate is mechanically staying closed). Then verify the vacuum lines and hoses are all sound. At that point its a possible solenoid issue as you'd mentioned. Or the BOV is sticking closed when its trying to vent under part throttle (stock ECU map uses bov to vent excess boost pressure under part throttle, so if you're driving around and the BOV sticks closed, turbo will build a few psi more than the ECU is commanding and this code will set.
 

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Discussion Starter · #4 ·
Alright guys, I really appreciate the insight. I’m off Thursday and Friday this week, so I’ll check out as much as I can as per what you’ve suggested, and I’ll report back with the findings. As for the BOV, I know it’s not sticking because it’s brand new and I can hear it venting as normal. I’m interested to see what’s up with the wastegate bushings, as I’m leaning towards that being the issue.
 

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Discussion Starter · #5 ·
Update! So I got antsy and dug into the car today, and I found something interesting... So the wastegate actuator is fine, I verified vacuum and the bushings. Now here's the interesting part, I took it for drive because I really wanted to drive it and something weird happened, because I have a loud exhaust I could hear the wastegate opening and closing a bunch while under moderate boost. I was just cruising on the highway at like 4,000 RPM about 1/4 throttle and I could hear the exhaust getting loud then soft then loud then soft, all while not moving the throttle at all. So now I'm definitely leaning towards a solenoid issue. The question is, which one? I know the one on top of the engine is for the BOV and such, so I would have to assume it's the one that mounts on that little plate that goes over the BOV, since it has a vacuum line that directly goes to the wastegate actuator. Can anyone confirm this?
 

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Update! So I got antsy and dug into the car today, and I found something interesting... So the wastegate actuator is fine, I verified vacuum and the bushings. Now here's the interesting part, I took it for drive because I really wanted to drive it and something weird happened, because I have a loud exhaust I could hear the wastegate opening and closing a bunch while under moderate boost. I was just cruising on the highway at like 4,000 RPM about 1/4 throttle and I could hear the exhaust getting loud then soft then loud then soft, all while not moving the throttle at all. So now I'm definitely leaning towards a solenoid issue. The question is, which one? I know the one on top of the engine is for the BOV and such, so I would have to assume it's the one that mounts on that little plate that goes over the BOV, since it has a vacuum line that directly goes to the wastegate actuator. Can anyone confirm this?
The one by the Bypass Valve controls boost.
 

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Update! So I got antsy and dug into the car today, and I found something interesting... So the wastegate actuator is fine, I verified vacuum and the bushings. Now here's the interesting part, I took it for drive because I really wanted to drive it and something weird happened, because I have a loud exhaust I could hear the wastegate opening and closing a bunch while under moderate boost. I was just cruising on the highway at like 4,000 RPM about 1/4 throttle and I could hear the exhaust getting loud then soft then loud then soft, all while not moving the throttle at all. So now I'm definitely leaning towards a solenoid issue. The question is, which one? I know the one on top of the engine is for the BOV and such, so I would have to assume it's the one that mounts on that little plate that goes over the BOV, since it has a vacuum line that directly goes to the wastegate actuator. Can anyone confirm this?
Don't get ahead of yourself. You need to log WGDC and make sure this isnt being commanded.

Normally your BOV would vent under these conditions to control excess boost since the minimum boost able to be controlled by wastegate is 5psi. Under that, the engineers built in the BOV cycling to bleed boost below that.

I guess i never asked, the BOV isnt routed to natural vacuum is it?
 

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Don't get ahead of yourself. You need to log WGDC and make sure this isnt being commanded.

Normally your BOV would vent under these conditions to control excess boost since the minimum boost able to be controlled by wastegate is 5psi. Under that, the engineers built in the BOV cycling to bleed boost below that.

I guess i never asked, the BOV isnt routed to natural vacuum is it?
That was quick; I went to take a shower after posting and thought to myself that the bypass valve cycles to control boost at lower speed part throttle situations and you jumped in before I could get back to edit...
 

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Discussion Starter · #9 ·
Don't get ahead of yourself. You need to log WGDC and make sure this isnt being commanded.

Normally your BOV would vent under these conditions to control excess boost since the minimum boost able to be controlled by wastegate is 5psi. Under that, the engineers built in the BOV cycling to bleed boost below that.

I guess i never asked, the BOV isnt routed to natural vacuum is it?
Yeah I figured as much, and I knew that, but doesn't the BOV only crack once throttle is released? To answer your question, it is not routed to natural vac. I didn't set it up like that since I've heard of that making the BOV pop at a higher boost level since there's a stronger, less controlled vacuum source, and I didn't want that since the car is high mileage and I didn't want to put more stress on it than what would be considered stock.

As a side note, when I was first looking into this, all signs pointed to a boost control solenoid issue. Also, what is WGDC? I've heard that term thrown around and I don't quite understand what it is. Is that something you can only log with a tuner? Because I'm not buying an Accessport just for that, and have it not be the issue. So should I just buy a new solenoid and see what happens? I seriously doubt it's the wastegate actuator. I also know it was the wastegate cycling because you can literally hear the exhaust get loud then quiet, the BOV would make an audible whoosh since I have a boomba. Am I just crazy? lol.
 

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Discussion Starter · #10 ·
Yeah I figured as much, and I knew that, but doesn't the BOV only crack once throttle is released? To answer your question, it is not routed to natural vac. I didn't set it up like that since I've heard of that making the BOV pop at a higher boost level since there's a stronger, less controlled vacuum source, and I didn't want that since the car is high mileage and I didn't want to put more stress on it than what would be considered stock.

As a side note, when I was first looking into this, all signs pointed to a boost control solenoid issue. Also, what is WGDC? I've heard that term thrown around and I don't quite understand what it is. Is that something you can only log with a tuner? Because I'm not buying an Accessport just for that, and have it not be the issue. So should I just buy a new solenoid and see what happens? I seriously doubt it's the wastegate actuator. I also know it was the wastegate cycling because you can literally hear the exhaust get loud then quiet, the BOV would make an audible whoosh since I have a boomba. Am I just crazy? lol.
Also going to throw out the fact that the boomba has been in for a long time and has never caused an issue. Something has failed, I'm simply trying to figure out what.
 

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WGDC (WasteGate Duty Cycle) is the PCMs command of the EBCS (Electronic Boost Control Solenoid) displayed as a percentage. Ideally you would need an accessport to take a datalog and review it once you were done with your drive. I know you know what you're talking about as far as correlating the exhaust volume to wastegate actuation, you are correct there, but my point in this matter is if this wastgate oscillation is intended or not. If your WGDC % is cycling up and down, then you know this system is doing what it is being told.

Ford and a lot of other manufacturers use the BOV to bleed off boost pressure below 5psi where the wastegate cannot control. This happens under cruise and part throttle conditions. These conditions will also set your overboost code if it wants the BOV to bleed this small amount of boost and it is not. Overboost doesnt always happen at wide open throttle. Boost control is extremely complex on these engines.
Blow off valves are exposed to the elements and typically are recommended to be disassembled, cleaned, and re oiled with sewing machine oil every 6 months because of this exposure. So just because it started happening and because you can hear boost dump at peak pressures now does not mean your BOV piston isnt sticking under lighter conditions...

I don't recommended throwing parts.
 

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Discussion Starter · #12 ·
Holy crap that was a lot of info, but I understood all of that, and it all makes sense now. I really appreciate the articulation of thought here, and I think I see what you’re implying. So I guess what I should do now is take out the BOV, and clean it and see if that helps. It would make sense because I noticed today when I was in there that the BOV has some greasy engine oil crud on it, presumably from some type of oil leak. So it wouldn’t surprise me if that’s the issue. I’ll report back once I’ve done that, thanks again!
 

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Holy crap that was a lot of info, but I understood all of that, and it all makes sense now. I really appreciate the articulation of thought here, and I think I see what you’re implying. So I guess what I should do now is take out the BOV, and clean it and see if that helps. It would make sense because I noticed today when I was in there that the BOV has some greasy engine oil crud on it, presumably from some type of oil leak. So it wouldn’t surprise me if that’s the issue. I’ll report back once I’ve done that, thanks again!
No problem! We'll get it sorted.

Don't be opposed to sticking the stock BPV in the meantime to totally rule out the BOV. Unless, of course, it suffered a tore diaphragm that a lot of the stock units experience.
 

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Discussion Starter · #14 ·
No problem! We'll get it sorted.

Don't be opposed to sticking the stock BPV in the meantime to totally rule out the BOV. Unless, of course, it suffered a tore diaphragm that a lot of the stock units experience.
Yeah, I was thinking about doing that just to see what happens. I’m 90% the stocker is fine, so I’ll likely put that in and drive it and see if it’s ok. I should have time tomorrow, if not then I should have an update come Thursday.
 

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Discussion Starter · #15 ·
Alright, so update time. TurboGT, you were right! I got in there today and put the stock bypass valve back in, drove it around it it was fine, 0 issues. Now the boomba was DISGUSTING, I took it apart, cleaned it, and greased it per boomba's maintenance video, put it back in and it was fine. I drove the car for roughly 45 minutes or so and no issues. But then I was on the highway, and it went into limp mode again. So I'm not sure if it was just a fluke or what, but otherwise it was fine. Thoughts? I made sure to put plenty of grease in there and I cleaned it super thoroughly so maybe it just needs to set in and wear through the excess grease...
 

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Alright, so update time. TurboGT, you were right! I got in there today and put the stock bypass valve back in, drove it around it it was fine, 0 issues. Now the boomba was DISGUSTING, I took it apart, cleaned it, and greased it per boomba's maintenance video, put it back in and it was fine. I drove the car for roughly 45 minutes or so and no issues. But then I was on the highway, and it went into limp mode again. So I'm not sure if it was just a fluke or what, but otherwise it was fine. Thoughts? I made sure to put plenty of grease in there and I cleaned it super thoroughly so maybe it just needs to set in and wear through the excess grease...
Yeah the valve only needs a couple drops of sewing machine oil. A very tiny amount to just put a thin film on it. Grease is a no-no, as it in itself will cause the piston to stick in the bore when its fully closed, as well as attract an hang onto dirt. (Not familiar with their cleaning video but i really hope they didnt actually recommend grease).

The issue with our cars is the placement. The thing sits right inside the wheel well so its constantly getting crap thrown at it.
 

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Discussion Starter · #17 ·
Yeah the valve only needs a couple drops of sewing machine oil. A very tiny amount to just put a thin film on it. Grease is a no-no, as it in itself will cause the piston to stick in the bore when its fully closed, as well as attract an hang onto dirt. (Not familiar with their cleaning video but i really hope they didnt actually recommend grease).

The issue with our cars is the placement. The thing sits right inside the wheel well so its constantly getting crap thrown at it.
Oh crap alright gotcha, yeah the specifically recommend using synthetic grease, being very specific about saying that you need to apply a even amount of it. I copied their video one-to-one by only using a small glob on my finger and spreading it around the inside of the piston cylinder. I drove it some more after replying, and it’s been fine so that one time might have been a fluke. If you really think it might become a problem, then I’ll just clean it again and use some sewing machine oil. My best guess is they recommend the use of grease due to the fact that there’s literally 3 o-rings inside, and I can’t see oil doing a good enough job and sufficiently lubricating everything. I could be wrong though lol.
 

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Oh crap alright gotcha, yeah the specifically recommend using synthetic grease, being very specific about saying that you need to apply a even amount of it. I copied their video one-to-one by only using a small glob on my finger and spreading it around the inside of the piston cylinder. I drove it some more after replying, and it’s been fine so that one time might have been a fluke. If you really think it might become a problem, then I’ll just clean it again and use some sewing machine oil. My best guess is they recommend the use of grease due to the fact that there’s literally 3 o-rings inside, and I can’t see oil doing a good enough job and sufficiently lubricating everything. I could be wrong though lol.
If you made sure to use a non- petroleum based grease then you might be alright. If it's petroleum based it will cause the orings to swell and deteriorate.
 

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Discussion Starter · #19 ·
If you made sure to use a non- petroleum based grease then you might be alright. If it's petroleum based it will cause the orings to swell and deteriorate.
Alright gotcha, yeah it’s Mobil 1 Synthetic, it’s lithium based. It’s actually the same grease they use in their video. I’m sure it’ll be alright, I’m not too worried, but maybe next time I service it I’ll try the sewing machine oil.
 
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