Cold Weather Bogging, Hesitation

[Chip Hedrick]

Up here in Maine we're finally begining to get the first truly cold weather of the season.

 

Now that it's cold, I've noticed that my '98 OBW is hesitating or bogging (I don't know which is the correct term to describe it) when I try to start off with gusto from a stoplight.

 

I'm not putting the pedal to the floor when this happens. Only 1/2 to 2/3. I have to back off the pedal to get the car moving forward.

 

I've had this car for nearly six years, and I don't recall cold weather having this effect.

 

The car has just under 99,000 miles. I cleaned the K&N air filter and replaced the fuel filter at 90,000 miles. I replaced the spark plug wires at 75,400. The platinum plugs were replaced at the recommended interval back at 60,000. I am using 5W-30 motor oil (which, by the way, the engine seems to like in cold weather--less racket when the engine is cold than with 10W-30).

 

Any idea about what I could do to remedy this bogging/hesitation?

[alias20035]

Originally posted by Chip Hedrick

Up here in Maine we're finally begining to get the first truly cold weather of the season.

 

Now that it's cold, I've noticed that my '98 OBW is hesitating or bogging (I don't know which is the correct term to describe it) when I try to start off with gusto from a stoplight.

 

I'm not putting the pedal to the floor when this happens. Only 1/2 to 2/3. I have to back off the pedal to get the car moving forward.

 

I've had this car for nearly six years, and I don't recall cold weather having this effect.

 

The car has just under 99,000 miles. I cleaned the K&N air filter and replaced the fuel filter at 90,000 miles. I replaced the spark plug wires at 75,400. The platinum plugs were replaced at the recommended interval back at 60,000. I am using 5W-30 motor oil (which, by the way, the engine seems to like in cold weather--less racket when the engine is cold than with 10W-30).

 

Any idea about what I could do to remedy this bogging/hesitation?

 

Probably the K&N filter oil has damaged the Mass Air Flow (MAF) sensor. The MAF's wires get coated in oil and don't work properly and as a result the ECU can not accurately measure the air flow causing it to put in way to much fuel, and this is what causes the engine to "bog". This problem also tends to present itself on cold days more than warm ones.

 

You can remove the MAF and clean it carefully with brake cleaner, but in many cases a new MAF (expensive) is required. Subaru issued a TSB informing dealers that MAF's would not be replaced under warranty if an non-paper fibre air filter was used.

 

There may be another cause, but since you indicate that you use and just cleaned and oiled the K&N filter, lets start with the MAF.

 

BTW: You are supposed to use very little filter oil, you probably used too much, and the excess is being sucked into the air intake and through the MAF.

 

In general you should not use oil based filters on MAF cars, the 99+ Impreza/Forester uses MAP instead of MAF and oil based filters will not harm them. In 2000, the Legacy/Outback switched to MAP as well.

[Chip Hedrick]

It's very hard to be polite responding to your reply to my post. Your condescending tone is annoying.

 

First, if you had read my post with any care you would see that I cleaned the K&N air filter at 90,000 mi. My car now has 99,000 mi. I don't see how that could constitute "just" (your term) having cleaned the filter. I did the cleaning and oiling 6 months ago and the hesitation is just now showing up.

 

Second, what do you mean by "you probably used too much" oil on the filter? Word has been out for quite some time to not over oil reusable panel filters. I heeded those warnings, used a conservative amount of oil, and allowed the filter to dry before reinstalling it.

 

There are a lot of people on this message board who offer valuable information, but it's condescending people like you who make me question whether it is worth the bother to post messages.

[Legacy777]

Chip I don't personally agree with alias's tone.

 

I am not going to say his diagnosis is wrong, nor correct.

 

There's a lot more things that it could be, and should be checked. I do agree with you that I don't see how it all of sudden started happening 9,000 miles after the filter was oiled. Filter definitely would not first on my list of causes...

 

Do you know if they changed to oxygenated gas recently? Is there anything recently you can coincide your problem with....like a gas tank fill-up...etc??

[1 Lucky Texan]

Chip, I'm not familiar with the actual failure mode for MAFs and it may be it takes a ling time for them to fail if a little oil gets on them. However, even if alias missed the 9K mile difference doesn't make his tone anything other than neutral. His posts are often very helpful and he defintely does not have a history or reputation for being condescending. His being new to the board, trying to communicate in text only, and perhaps missing a detail in your post doesn't mean he isn't respectful. I hope your MAF is OK - seems like it should be, but it can be a failure mode I suppose seperate from the oiled filter too.

[1 Lucky Texan]

Chip, how's idle other than leaving from a stop? Legacy 777 has posted good info on the IAC causing similar symptoms IIRC?

[99obw]

A lot has been said here on the USMB about carbon build up. As carbon builds up it causes increased compression ratio and hot spots in the combustion chamber, causing preignition (pinging). The knock sensor tells the ECM about the preignition and the ECM retards the ignition timing, reducing power output of the engine.

 

This may or may not be your problem, but I always recommend starting with the least expensive solution. I would fill the tank up with premium and add some Techron fuel additive. Burn that tank down to about 1/8 of a tank and fill it back up with premium and another bottle of Techron. Then reset the ECM and allow the ECM to relearn at idle for 15 minutes with all accesories off. Then burn the second tank of treated gas. If that doesn't work I would start looking at the more expensive items.

 

I faithfully run techron through our 99 every 3k miles. When I had the heads off I was shocked at the amount of carbon build up, mostly on the pistons.

 

PS: An over-active knock sensor can cause similar simptoms.

[Legacy777]

I highly recommend sea foam if you're looking to get rid of carbon deposits in the engine.

 

http://usmb.ultimatesubaru.org/forum/showthread.php?s=&threadid=7855&highlight=sea+foam+josh

[99obw]

Josh, how much is the sea foam? I may give it a try sometime.

 

I must clarify that I had never used Techron before I had the engine apart. I have seen excellent results in several engines using Techron.

 

The Techron seems to do a less than perfect job of cleaning the carbon, as the symptoms will return before too long, that's why I use it every 3k miles.

[forester2002s]

I don't find that Alias20035's tone is condescending at all.

 

I always think that his (her?) posts are always very informative and to the point. Alias obviously knows the subject, and is willing to share his/her knowledge with others. Very often replies are of interest not just to the original questioner, but also to the thousands of others who also read this board.

 

Good for you Alias, and don't let this impolite questioner stop you from posting. I for one am grateful to you.

[PAezb]

Originally posted by Legacy777

I highly recommend sea foam if you're looking to get rid of carbon deposits in the engine.

 

http://usmb.ultimatesubaru.org/forum/showthread.php?s=&threadid=7855&highlight=sea+foam+josh

 

I second the use of SeaFoam Motor TuneUp. I use a third of a can in the motor oil 500 miles before oil change. A can in a full gas tank every 3 months or so. And, a can sucked into the throttle body via a vacuum line revving the engine between 2-3K rpm whenever performance seems to be lagging - usually a couple of time a year.

 

Little under $4.00 a can at Fleet Frams here in the upper midwest.

 

Paul

[alias20035]

I was not trying to be condesending at all. I just wanted to point out that the first problem to eliminate was oil buildup on the MAF. This is an extremely common problem, and when this happens you get "bogging". I have seen this many times, and always with the K&N filter.

 

From my experience, everyone is guilty of overoiling their K&N filters. They are not supposed to be bright red or dripping oil. It is such A hard thing to oil with the spray can they provide, which is why I suggested that you MAY have over oiled it.

 

Clean the MAF and see what happens was my suggestion.

 

After cleaning you should also disconnect the negative battery terminal for fifteen minutes to reset the ECU.

[sprintman]

Chip ditch the K & N air filter. If you look at UOA's on BITOG in the Used Oil Analysis section you can guarantee that when you see high Si they will have a K & N fitted. Race cars yes, street cars you want to use OEM or similar.

[alias20035]

Just curious which K&N you have?

 

Is it the flat panel "OEM" style, or an aftermarket intake style?

 

Sometimes you will get "bogging" when the factory air box and air intake resonator is removed for better air flow (ex. with an intake tube).

 

I worked on an Impreza that had bogging, we tried everything to fix it, but could not. We then reinstalled the factory airbox/resonator and the problem was gone. We then clued into the possibility that the MAF needed some intake restriction to work properly, so we tried the aftermarket intake/filter with the filter wrapped in a dense cloth and it worked. The problem seemed to be temperature related, the problem only appeared in lower air temperatures. The end solution was to run the factory air box in fall/winter/spring and aftermarket tube/filter in summer. This Impreza required very frequent MAF cleanings, and several MAF's failed completely.

 

Oil contamination of the MAF it is progressive, I did note that you did recentely re-oil the filter which is why I questioned the amount of oil used. Seems as though you oiled it properly, but in the end I don't think the re-oiling is the issue, it is the long term oil build up.

 

As Sprintman notes, the K&N is not a good filter in terms of dust removal and I have seen the high SI (Silicon = dust) reports he mentioned. Not too serious an issue so long as you do regular oil changes.

 

1 Lucky Texan mentioned an IAC problem, but this is most likely not the cause. If it was your car would not idle properly, and from your report it idles fine.

 

Your bogging is related to a confused ECU that can't figure out air/fuel mixture. The number 1 culprit of this is a bad MAF, followed by throttle postition sensor (TPS). If your car runs fine and accelerates properly at highway speed, your TPS is likely ok.

 

The oxygen sensor is a delayed way of metering A/F ratio, so the ECU does not use it until the engine has obtained a constant speed, and not when accelerating. So I don't think it is involved here.

 

Carbon build-up/knock sensor was mentioned, and can sometimes cause some loss of power problems, but I have not seen it in such a serious state to cause bogging. Of course I am used to seeing Subaru's run on Canadian fuel which can be significantly different than US fuel (not better, not worse, just different), so I don't know whether US "reformulated" fuel would cause more serious carbon buildup than what I see in Canada.

 

BTW: search the NASIOC forums and you will find many posts related to MAF failures due to K&N (and similar) filters, and many of these posts will refer to "bogging" as a symptom. Most of these posts were related to the 98 2.5RS, so I am not sure how many recent posts would still be kicking around.

 

I have seen many failed MAF's myself and have about an 80% success rate with cleaning the MAF (I have worked on about 15 of them). The Impreza's MAF seems to be a lot more sensitive than the MAF in the Legacy, as most of my repairs are to the 98 Impreza 2.5RS. I have had this problem myself in my 93 Legacy way back in 97 shortly after I installed a K&N filter panel, and the "bogging" you describe is exactely what happened to me. I nursed the car home with the "bogging" and eventually the ECU reported MAF failure and started to ignore the MAF readings and use its predefined A/F ratio table. When the ECU started to ignore the MAF the "bogging" stopped. I cleaned the MAF and installed a paper filter and no more problem for 300,000 or so KM.

 

You could try disconnecting the MAF sensor and see what happens, doing so should flip the ECU to limp home mode and use its predefined A/F ratio table. The engine will usually run without a MAF connected, but in some cases it does not. If your bogging is affected by the disconnection of the MAF, your MAF is the likely culprit.

 

I apologize if you found my tone condesending, as I mentioned before I did not mean it to be. My initial thought was "K&N filter, here we go with MAF problems again", and perhaps a bit of my negative feelings about them came through, they were not intended to be personal.

 

I do try to add more information than is needed, so that others may use some of the information in as well.

[Legacy777]

just to throw this out....it was mentioned breifly

 

There are two types of mafs, hot wire & hot film.

 

The hot films are usually found on the imprezas, and as mentioned tend to be more fragile.

 

alias, do the hot film sensors really respond to cleaning that well?

 

I can see how cleaning the hot wire ones probably wouldn't be too bad since the wire is in the flow of air and cleaner.

 

Don't the hot film ones not have this film visible? which is why I would think it would make cleaning them more difficult.

[alias20035]

Originally posted by Legacy777

just to throw this out....it was mentioned breifly

 

There are two types of mafs, hot wire & hot film.

 

The hot films are usually found on the imprezas, and as mentioned tend to be more fragile.

 

alias, do the hot film sensors really respond to cleaning that well?

 

I can see how cleaning the hot wire ones probably wouldn't be too bad since the wire is in the flow of air and cleaner.

 

Don't the hot film ones not have this film visible? which is why I would think it would make cleaning them more difficult.

 

The ones I cleaned were usually the hot wire type, although the wire is not truly round but flattened and elongated. Some of them had what could be a film, and these had a much lower success rate with cleaning, but on occasion it did work.

 

I remember seeing a thread years ago indicating that a much less expensive MAF from a Nissan was plug in compatible with Subaru. Hopefully someone can elaborate on this.

[Chip Hedrick]

Alias--I overreacted. No offense taken and none intended.

 

The car seems to be back to normal. It only exhibited the bogging a couple of times, and one was on the coldest night of the fall after about 12 hours in a parking lot. Maybe the ECU needed to adjust to the temp?

 

Also, I wonder if the bogging had something to do with the fact that late this summer I removed what I call the "intake silencer"--the bulbous thing in the passenger side fender. Other than that and the K&N filter, the rest of the intake is stock. I wonder if in cold weather, with really oxygen dense air, more air is getting to the engine than the injectors, etc., can handle. But would that cause bogging? I would think that too much oxygen would cause a lean condition--plenty of power, but too much heat.

 

One other thing: earlier this fall (i.e., September) I installed a Pro-ECM chip. It worked fine at normal speeds, but I had to remove it after a couple of weeks because it was causing the car to stall out at virtually every stop light. I wonder if there could be some contamination of the MAF that only shows itself under certain conditions--very cold weather or with the input from an aftermarket chip.

[alias20035]

Originally posted by Chip Hedrick

Alias--I overreacted. No offense taken and none intended.

 

The car seems to be back to normal. It only exhibited the bogging a couple of times, and one was on the coldest night of the fall after about 12 hours in a parking lot. Maybe the ECU needed to adjust to the temp?

 

Also, I wonder if the bogging had something to do with the fact that late this summer I removed what I call the "intake silencer"--the bulbous thing in the passenger side fender. Other than that and the K&N filter, the rest of the intake is stock. I wonder if in cold weather, with really oxygen dense air, more air is getting to the engine than the injectors, etc., can handle. But would that cause bogging? I would think that too much oxygen would cause a lean condition--plenty of power, but too much heat.

 

One other thing: earlier this fall (i.e., September) I installed a Pro-ECM chip. It worked fine at normal speeds, but I had to remove it after a couple of weeks because it was causing the car to stall out at virtually every stop light. I wonder if there could be some contamination of the MAF that only shows itself under certain conditions--very cold weather or with the input from an aftermarket chip.

 

As I noted in my earlier reply, removal of the intake silencer can cause some bogging problems, I have seen this many times and usually in colder weather (sometimes hot weather too). So you have a K&N filter panel but no intake silencer? I would reinstall the intake silencer (perhaps for the winter only) if this happens again. If re-installation of the silencer does not correct the bogging, I would then consider cleaning the MAF.

 

As far as I know more air gets into the engine that is detected by the ECU and you end up with lean burn, which leads to detonation which is detected by the knock sensor, spark timing retardation and "bogging". Closing the throttle cuts the air and restores a more proper A/F ratio.

 

I have found that many of the add on chips cause a lot of idling and low speed problems such as the one you described.

 

The hot wire/film type MAF is a simple item that automatically compensates for air temperature and density by its design and method of operation, but if it is contaminated it gives information to the ECU that is very wrong. Only on a sustained medium/high speed drive will the ECU detect that it is running lean or rich from the oxygen sensor readings, and even then only if the oxygen sensor is in good condition. The oxygen sensor is somewhat disregarded during acceleration, since it is a lagging and somewhat slowly responding sensor.

[Legacy777]

Also, regarding the chips.....they don't really work too well with automatics. There are ones that supposedly work with autos....however after running a torquechip, I just wasn't too impressed.....all I could tell is that I was running richer.....and the peakiness of the car seemed more subdued....which would make sense since adding more fuel moves you down on the parabolic burning curve, since the factory usually tunes for emissions.