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MYSTERY MISFIRE ISSUES ... 2002 Legacy Wagon 5sp MT

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HELP!

I am new to this Subaru forum and I am hoping to get some help or advice from experts with Subaru’s. I am not a mechanic. I work with wood for a living, but have a good mechanic I trust.

This is my first Subaru. It is a 2002 Legacy Wagon AWD 5 speed MT. NOT AN OUTBACK.

My car is experiencing misfire issues. Below 2500 rpms. My mechanic and I have exhausted everything we can imagine it may be.

Here is what it’s doing. When the car gets heated up, it’s misfiring when it’s below about 2500RPMs.

When I try to take off in first gear it bogs and sputters and misfires, until I get up to about 3500 RPMS, then it takes off like I am trying to drag race. Same happens when I get into 2nd gear and so forth. While driving the misfire would make a passenger think I don’t know how to drive a shift. A lot of shaking back and forth, so I have to keep revved up around 3000 RPMS.

I think its heat related for some reason? My mechanic thinks I am crazy. When it’s cold in the mornings it doesn’t do this very often. When the engine gets hot, or the day gets warmer, the issues start. At a stop light, the engine will slow down around 500 rpms, then begin to sputter and stammer… but the engine fan will turn on, then it will rev back up to 750 rpms, and idle well. This makes me think heat has something to do with this.

This really has my mechanic scratching his head too. We don’t know what to look at next.

I get a check engine light and it’s a code OBD2 – FUEL SYSTEM TOO RICH

This is what we have fixed/replaced so far.
 

  • Valves have been adjusted
     
  • New ignition coils and cables. New Spark plugs
     
  • New MAP Sensor
     
  • Ran fuel injector cleaner thru a full take of gas a couple times in the past month.
     
  • Changed to a better quality gas
     
  • Timing belt appears to be fine.
     
  • New air flow housing and air filter.

Other repairs that I have done that I don’t think are related:
 

  • Replaced the transmission
     
  • New clutch
     
  • New rear driveshaft when replaced transmission.
     
  • Replaced front axels


I am hoping for suggestions on what to look at next. I love this car. I want it to run for quite a while. I’m a single dad with two kids that gets out in the PNW a lot.

Any suggestions to look at next or shops you can recommend???

Thanks
 

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there is an engine temp sensor - separate function from the temp gauge, though, in soobs after the 90s, it shares the same physical part.

 

Maybe it is holding your car in 'choke' mode? It's located on the coolant crossover I think. Not sure about resistance reading or testing but, it could be bad and not throw a code. maybe you mechanic can test it.

Edited by 1 Lucky Texan

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All of the work done has been OEM parts.

my mechanic won’t used aftermarket parts.

We are really scratching our heads. I’ve decided to take this online here for suggestions.

thanks

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If the code is P0172 for fuel system too rich, it definitely can cause those issues. 

Start with checking fuel pressure. If it's too high, fix that. 

 

If you want to throw another part at it, it likely needs a A/F ratio sensor (upstream O2) and to reset the fuel trims. 

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Quote

TB appears fine

....how old are the timing components?, what about the timing itself? check for timing a tooth off - set the marks and find the tooth count for yor engine.

 

also, check inside the vacuum line from the fuel pressure regulator - it should be dry.

 

 

Edited by 1 Lucky Texan

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The timing belt and components are older (I have not replaced them) but appears to be in good working condition.

my mechanic doesn’t think that’s a place to troubleshoot cause it’s nit misfiring at all times.

He suggested maybe checking the camshaft sensor?

I wish I knew more about cars.

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He needs to monitor the A/F ratio sensor and downstream O2. 

Until he does that you have no idea what's going on inside the combustion chamber when it's acting up. 

It is rich, lean, or correct? 

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maybe get the car down to Superior Soobie and Import (Milwaukie/Gladstone area?) - let our own General Disorder take a look at it?

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Thanks for everyones input.

This forum is great. I called Superior Soobie and they are great.

Seem to have found what the issue was. Replaced the Air Fuel Ratio Sensor (145$) and it seems to have solved my issues.

Appreciate the help.

  • Like 1

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Haa haa.

best part is this guy at Superior talked to me on the phone for about 30 mins. He described what my car was doing as if he had been driving it for the past month. He said if I took it to him that would be the part he would replace.

Went back to my mechanic and we did just that and it seems to have been the missing link.

I'll pay it forward friend.

Thanks again

  • Like 1

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Thanks for the follow up..

The problem was the Air Fuel Ratio sensor.  Was a $141 part.  Once we replace that its been running good.  Mechanic said this sensor was an 'open loop' so  the car would mix fuel at a correct default level when it was cold.. when the heat got hot, up above 600 degrees, it would rely on this sensor and that's when I would see it was malfunctioning.

Imagine trying to take off in 3rd gear from a red light all the time. That's what the experience was like. This sensor fixed the problem

 

Have a good one

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