McChalium Posted March 23, 2015 Share Posted March 23, 2015 My 2.2l Legacy engine will slow down below a normal idle to about 500 RPM and then quit suddenly, usually while waiting at a stop sign or light. 240000 miles, o2 sensor maybe never changed. (I am not the first owner, just the latest) Fuel pump and strainer is new as is the fuel filter. Fuel pressure is about 35 PSI, 40 psi when vacuum hose is disconnected from the regulator. Problem is more acute when the weather is wet, either rain or dew. New plugs and wires. Engine will rev freely to redline and pulls like a tractor over 2000 rpm. Below that, it is subject to quick jerks that I interpret as momentary stalls and below about 1200 RPM it will stall out suddenly, usually at stops while in gear. I have an automatic transmission. The ECU reads out a 13 DTC which should be a faulty cam position sensor, but as mentioned before the engine is strong and does not seem to misbehave above 2000 RPM. Also the alternator recently died while enroute from work to home and the whole shebang died and left me in the dark on a back country road. When the engine finally died during that episode it could have caused the ECU to store a DTC 13. It never lit the check engine light. No complaints in the ECU about anything else including the O2 sensor or MAF sensor. Under load such as driving uphill the engine starts to shake at about 60 MPH and smooths out about 70 or if you back off the throtle. Had the wheel balance checked, it was okay. I plan to reset the DTC to see if the 13 code comes back before replacing the expensive CAM Position Sensor, but I am planning to replace the O2 sensor on general tuneup principles soon. I have noticed in other cars I own that an old O2 sensor can cause driveability problems, some that you might not suspect are related to that sensors function. Maybe clean the MAF also. Does anyone out there have experience with these kinds of symptoms? I would like to hear from you is so. Quote Link to comment Share on other sites More sharing options...
nipper Posted March 24, 2015 Share Posted March 24, 2015 What brand wires? Is there any oil on the spark plug boots? Have you checked for voltage leakage at the coil towers? Crank sensor is ignition timing, cam is fuel injection (throttle body) reference. try something simple for now, unplug and plug back in the cam sensor and see if it is as simple as a dirty connection. If it is just doing that usually cleans the contacts. Quote Link to comment Share on other sites More sharing options...
montana tom Posted March 24, 2015 Share Posted March 24, 2015 I just helped a neighbor with a similar problem,turned out the maf had an intermittent problem . Cleaning maf did nothing. I switched a working one from my 94 to his 96 and problem was gone. I was told here at usmb that there is a poor solder connection inside that is known to cause this kind of problem. New /original equipment maf are expensive , used ones could have the same issue pending. We went with the 50$ china copy on ebay. So far after over a month no problems, car idles and runs normal again! Quote Link to comment Share on other sites More sharing options...
McChalium Posted March 24, 2015 Author Share Posted March 24, 2015 What brand wires? Is there any oil on the spark plug boots? Have you checked for voltage leakage at the coil towers? Crank sensor is ignition timing, cam is fuel injection (throttle body) reference. try something simple for now, unplug and plug back in the cam sensor and see if it is as simple as a dirty connection. If it is just doing that usually cleans the contacts. Wire brand unknown now but they are grey with red plug boots and the wires are marked made in USA. There is no oil present on the boots. Other than listening and looking for arcing I have not checked for leakage at the coil towers. The idea that moisture was getting in there is what prompted me to replace the wires. I used silicone grease to seal the towers to the wires. I'll give your unplug/plug idea a go tonight after work. I wondered why there were two different speed sensors on the engine and speculated that the cam sensor was igniton since it runs at same speed as distributors in older cars. Judging from the way the engine reacts when these events occur I suspected fuel delivery from the beginning, but did not suspect the cam sensor because I thought it was for ignition. They sure leave a lot of useful info out of the Chilton Manuals. I'll never buy another of those. Quote Link to comment Share on other sites More sharing options...
McChalium Posted March 24, 2015 Author Share Posted March 24, 2015 I just helped a neighbor with a similar problem,turned out the maf had an intermittent problem . Cleaning maf did nothing. I switched a working one from my 94 to his 96 and problem was gone. I was told here at usmb that there is a poor solder connection inside that is known to cause this kind of problem. New /original equipment maf are expensive , used ones could have the same issue pending. We went with the 50$ china copy on ebay. So far after over a month no problems, car idles and runs normal again! I also cleaned my MAF with the special (?) CRC MAF cleaner and compressed air but it had no effect as well. Thanks for your tip about EBAY, easier than going to pick and pull. What about the O2 sensor? Mine may be as old as the car. Quote Link to comment Share on other sites More sharing options...
nipper Posted March 24, 2015 Share Posted March 24, 2015 Crank is ignition so the engine knows exact moment of TDC of #1 piston. Getting this timing wrong can cause engine damage. Cam for fuel as thats less critical and manged differently. It also probabaly has something to do with making a robust ECU and all the coding, and signal noise from an engine. These cars HATE cheap wires. Cheap wires the silicon breaks down very quickly and you get voltage leakage. Subarus are very pickey on wires and plugs, so i bet the wrong plugs are in there too. Get yourself a Haynes manual, they are the best for your car. Quote Link to comment Share on other sites More sharing options...
montana tom Posted March 24, 2015 Share Posted March 24, 2015 Yup a haynes manual is as good as it gets but.... Use it for general information ,big grain of salt for following their "procedures" better to ask here for real world experience. I like to replace sensors one at a time, try the tune up , then the maf and last I would try the o2. No sense spending all your $ rite away! Quote Link to comment Share on other sites More sharing options...
nipper Posted March 24, 2015 Share Posted March 24, 2015 replace one part at a time with the exception of a tuneup or timing belt job. If the new part doesnt resolve the issue, put the old part back on. No reason to add new variables. This sounds like a simple high voltage leakage problem. technically known as Sparklies. Quote Link to comment Share on other sites More sharing options...
McChalium Posted March 24, 2015 Author Share Posted March 24, 2015 Let's see, new plugs (NGK), new wires, new gas and air filters, cleaned MAF, checked fuel pressure w/wo vacuum applied to the regulator, what else could one do for a tuneup when everything else is computer controlled? While I can't say 100% for sure, I do not think I am plagued by "sparklies" due to the fact that the wires are new and sealed with silicone grease. I have thought that maybe the coils are breaking down but decided no because the engine runs strong anywhere above 1200 RPM and I don't think a coil that was breaking down would support that. I've gone looking for vacuum leaks but haven't found any. As you might guess I am frustrated by this because I like to find an actual failure before I replace something. Anyone know what kind of signal levels I should see coming from the crank and cam sensors using an oscilloscope? Quote Link to comment Share on other sites More sharing options...
nipper Posted March 24, 2015 Share Posted March 24, 2015 The dreaded spray bottle. At dusk with the engine running (dont touch the car with any part of your body, trust me I know) spray the coil and ignition wires with water and look for sparklies. That is the definitive test. Wires look new they can still be crap wires. NGK plugs thats good. Air filter, fuel filter, plugs, wires, PCV valve are all part of the modern tuneup. Do you have a vacume gauge about? Quote Link to comment Share on other sites More sharing options...
montana tom Posted March 25, 2015 Share Posted March 25, 2015 Try the spray test & see if you have a problem with sparking. If not try to find a donor car you can borrow the MAF from, easy ,easy to R&R if your problem changes you have your answer , if not keep looking. I personally have never had cam or crank sensor send bad signals , they either worked or did not . Again if you can find a willing donor car you can easily swap those out for a few minutes to see what effect that may have. Keep looking you will find it! 1 Quote Link to comment Share on other sites More sharing options...
McChalium Posted March 25, 2015 Author Share Posted March 25, 2015 The dreaded spray bottle. At dusk with the engine running (dont touch the car with any part of your body, trust me I know) spray the coil and ignition wires with water and look for sparklies. That is the definitive test. Wires look new they can still be crap wires. NGK plugs thats good. Air filter, fuel filter, plugs, wires, PCV valve are all part of the modern tuneup. Do you have a vacume gauge about? LOL! I never thought about deliberately spraying the wires. Will try that tonight. I do have a couple of vacuum gauges, one very good one and several that I would class as general purpose. What is the test you are thinking of? Quote Link to comment Share on other sites More sharing options...
McChalium Posted March 25, 2015 Author Share Posted March 25, 2015 Try the spray test & see if you have a problem with sparking. If not try to find a donor car you can borrow the MAF from, easy ,easy to R&R if your problem changes you have your answer , if not keep looking. I personally have never had cam or crank sensor send bad signals , they either worked or did not . Again if you can find a willing donor car you can easily swap those out for a few minutes to see what effect that may have. Keep looking you will find it! There is a guy I know near where I live who may have a MAF I can borrow for that test. I'll ask him. Quote Link to comment Share on other sites More sharing options...
McChalium Posted March 29, 2015 Author Share Posted March 29, 2015 Good evening. Well it pretty definitely isn't the MAF sensor. I swapped another in yesterday out of a newer Legacy and got exactly the same symptom. I haven't looked for the sparks yet but may do that this evening. A local shop that deals in Used Subarus and repairs them as well suggested that the Air bypass valve could be the problem, but its 219 bucks so I'm gonna go for the O2 sensor first. The guy that runs the local shop lent me his 1992 Legacy Factory Shop Manual so I could study and learn more about it. How's that for friendly? 1 Quote Link to comment Share on other sites More sharing options...
nipper Posted March 29, 2015 Share Posted March 29, 2015 A vacume gauge can tell you many things. Sorry for the delay in answering just been a very rough few months. http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm It is an underused and underated diagnostic tool. Quote Link to comment Share on other sites More sharing options...
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