teahouse Posted April 29, 2012 Author Share Posted April 29, 2012 I looked at both sensors today. I'm not sure what else to look for besides obvious abrasions in the wire and dirt on the contacts... of which there were none. So the CEL wouldn't signal a bad crank, cam, or MAF sensor? I want to specify that the car does not need gas to idle... it will idle perfectly, for any given period of time. Then, usually without even stuttering, it just shuts off instantly. It WILL stutter when I'm driving just before it dies, though... which will happen either 1 or 15 miles down the road. So I guess a fuel pump was a good one to try next, as we throw the dice. Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 29, 2012 Share Posted April 29, 2012 Crank and cam sensors typically produce codes immediately if they fail because the ECU replies heavily on input from those two sensors. Failures with these sensors are easy for the ECU to diagnose because there will be a complete break in the signal voltage, even if it is intermittent, the ECU will typically set a code. The MAF it uses in conjunction with the MAP sensor if it has it, as well as the O2 sensor, coolant temp sensor, and throttle position sensor to fine tune the amount of fuel the engine gets. Because of this the ECU has to run multiple checks against premprogrammed criteria in order to determine a fault with the MAF, unless it is wiring related, in which case it will set a code almost immediately. Honestly the way you describe it almost sounds like a bad MAF. Unplug the MAF and start the car, take it out for a drive around the block a few times. It won't run well, but it will run and drive and shouldn't stall. Quote Link to comment Share on other sites More sharing options...
teahouse Posted April 29, 2012 Author Share Posted April 29, 2012 Really? Interesting - I'll try it. I actually did unplug it a couple days ago to see what would happen, but only let it idle for a few minutes. The change I noticed was that the idle RPM kept fluctuating... but it didn't die in that time. So the effect of the MAF is such so that it could cause the engine to die completely, instantly? I'll try it tomorrow morning and post results. Quote Link to comment Share on other sites More sharing options...
teahouse Posted April 29, 2012 Author Share Posted April 29, 2012 Well I gave it a shot just now (disconnecting the MAF) and it was pretty rough - RPMs were all over the place, and the only way to keep the engine from dying was to keep on the gas. It does show me how big of an effect the MAF has... I'll try cleaning the contacts really well and see what that does. Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 29, 2012 Share Posted April 29, 2012 If it did die with the MAF unplugged the problem is likely elsewhere. The ECU goes into a fail safe mode without the MAF input, it runs off of preset air density values that will allow it to run, but it should still run on it's own. Quote Link to comment Share on other sites More sharing options...
teahouse Posted April 30, 2012 Author Share Posted April 30, 2012 It's weird - the first time I unplugged it, it actually was relatively stable, just fluctuating a little... then when I tried it again this morning it was all over the place. I just cleaned the MAF with MAF cleaner, and it actually seems like the engine is running smoother, having more of a smooth 'purr'. But... the problem persists. I drove back and forth in the driveway just now, and noticed that the CEL is coming on after it dies... so having the code reader is going to be good, when it gets here (it's in shipping). I also noticed that it runs rough when I start it right after it dies... it will sort of struggle to keep stable RPMs... then if I shut the engine off and restart it, it usually runs well again... Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted April 30, 2012 Share Posted April 30, 2012 The CEL comes on when the engine dies because the ECU no longer sees readings from the various sensors. It lets YOU know that the engine has shut off by turning on the CEL. Doesn't necessarily mean there will be a code, unless the light stays on after re-starting. Quote Link to comment Share on other sites More sharing options...
teahouse Posted April 30, 2012 Author Share Posted April 30, 2012 (edited) It does stay on, when I first start the engine after a stall... then when I shut it down and start it again, it will usually be off... It really does sound like a dying fuel pump, the more I read about what symptoms that would usually exhibit... who knows though. Would a dying pump somehow trigger a CEL? Maybe by somehow triggering a crank sensor, as an after effect, for example? Edited April 30, 2012 by teahouse Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 30, 2012 Share Posted April 30, 2012 Check the fuel pressure if you suspect the pump. It is higly unlikely given your symptoms though. Fuel pumps generally either work or they do not work. It is relatively rare for fuel pumps to put out low pressure intermittantly. Guessing will not help. Test. Verify. Replace. GD Quote Link to comment Share on other sites More sharing options...
teahouse Posted April 30, 2012 Author Share Posted April 30, 2012 It's true, but the thing is, I don't have a full raster of necessary tools -- so without an in-line pressure gauge and a way to mend the hoses that I would need to cut, presumably, I'm left in the dark. Yes, I could buy an in-line gauge... which, maybe I should have... but I've already ordered the fuel pump, so I may as well try it I guess. Hopefully the OBDII scanner I bought will give me a clue. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted April 30, 2012 Share Posted April 30, 2012 The fuel line is simply a hose over a barb fitting at the engine and at the engine bay mounted fuel filter. Take the lines loose from the fuel filter and put the gauge there - rent or borrow a gauge. It's not a wonderful job to replace a fuel pump. Besides that - an excuse to buy or learn to use a new tool should always be priority. Your problem isn't the pump and all you will get is frustrated by throwing parts at this problem. GD Quote Link to comment Share on other sites More sharing options...
teahouse Posted April 30, 2012 Author Share Posted April 30, 2012 Hmm, your right... I'll go buy a pressure gauge. It's OK to bypass the fuel filter temporarily, then, I take it? Also, what is ideal pressure, and how much tolerance is there? I read 35psi somewhere... I should be able to just get a refund for the pump, if unused. Quote Link to comment Share on other sites More sharing options...
teahouse Posted May 1, 2012 Author Share Posted May 1, 2012 (edited) Ok, borrowed a fuel pressure gauge from local O'reilly... hooked it up last night. Didn't realize until I read the manual that I could install it right before the fuel filter, just using one extra 2" piece of hose, instead of bypassing it completely (duh). Pressure was rock solid - first time I cranked it to ignition on, engine off, it primed to 15 psi... second time kicked it up to about 35. When idling, it consistently stayed around 26 to 27 psi... and when the engine died, it hadn't changed... in fact, it would instantly kick up to 35 psi when the engine would cut out. So, thank you GD - you saved me some work there, and possibly money as I may not have been able to return the fuel pump if I installed it and used it, even if just briefly. Knowing that my fuel pressure was good, I thought that it almost had to be a faulty sensor... so I started wiggling plugs all over and eventually found a correlation to the engine dying if I moved the MAF connecting harness in a certain direction. Ah! It's a faulty plug - just slightly too loose, and it is either shorting out or losing contact. So, hopefully today I will find out if there is a way to replace just the plug, since the MAF sensor it's self seems to work fine... This may very likely be the issue. I'll report back to update with results. Edited May 1, 2012 by teahouse Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted May 1, 2012 Share Posted May 1, 2012 Just go to the junk yard, grab a good plug, and solder it in - grab 3 or 4 inches of wire with the used plug and cut the old one off as close to the plug as possible. These don't often fail unless the plug has been damaged from someone tugging on it, etc. I knew you would likely find a wiring fault in the engine bay. Just a matter of which sensor has the bad wiring... GD Quote Link to comment Share on other sites More sharing options...
teahouse Posted May 1, 2012 Author Share Posted May 1, 2012 Ya, you called it - nice one. The thing that threw me is that the wires and contacts looked perfect, when I checked them. I actually had to really wiggle that thing around while the engine was running to realize that it was a bad connection. I just triple cleaned the contacts with electrical contact cleaner, and since the plug had a little bit of play, I secured it in place with two rubber bands and tightly wrapped electrical tape... sounds like a hob-job fix, but it seemed pretty ideal for securing the clip tighter. I just got back from an initial test drive, and it ran beautiful - better than it has in a long time since I've gone through the engine and replaced sparks, cleaned the MAF, etc... I'll go for another drive tonight and we'll see if indeed this was the fix that was needed, and it keeps running consistently, fingers crossed. If not, good idea to go to a junk yard and just pick up a new clip -- that's actually what the guy at O'really mentioned this morning when I returned the fuel pressure gauge. Thanks so much for the help everyone, and I'll post back once more to let you know if everything keeps running smooth... and probably many times more if it doesn't (-.-). Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted May 2, 2012 Share Posted May 2, 2012 Glad you found something to point you in the right direction. I had a MAF with an internal break that would cause the engine to cut off if the wires were wiggled just right. But it would set a code every time. It was like the key had been turned off, no stumble or anything, just off. If the car was rolling in gear, a few seconds later it would kick back on and carry on like nothing ever happened. Check the wiring under the loom and make sure none of the sockets are loose in the plug before cutting and splicing a new connector in. You might even just grab a used MAF from a junkyard and put it on to try it. Quote Link to comment Share on other sites More sharing options...
teahouse Posted May 2, 2012 Author Share Posted May 2, 2012 (edited) Ok, well... second test drive today was the complete opposite of the first one - total failure... I went about 100 yards, and it died... and I could barely get back - had to start it about 20 times before I was back to the driveway. Ha, I didn't knock on enough wood I guess. So, I do still think that the problem is in the wiring of the MAF sensor, or perhaps the sensor it's self - it's just my initial attempt at a solution wasn't adequate... I mean, who would have thought that rubber bands and tape wouldn't work - whaaa? lol. GD - you were right again, I'm heading to a junk yard tomorrow to clip a connector, if I can find one. Do most subaru's use the same clip? I.e., can I take one from a 2000 Forester, for example? Fairtax - sounds like the same symptoms I have. Good idea, checking the wiring under the loom... I didn't even think you could get under there - are there screws that I didn't notice? I'll go down and check soon. Also, I just had the thought to grad a MAF at the junk yard too - should be considerably cheaper than the $220 for a new one. Alright, I'll report back soon. **edit** - also, does any know what the fuel pressure is supposed to be on a 97 impreza? Mine was steady at 26-27... which, since it was so stable I figured that was what it was supposed to be at... and I can't find the optimal pressure online anywhere... nor is it listed in the manual. Edited May 2, 2012 by teahouse Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted May 2, 2012 Share Posted May 2, 2012 The U-pull-It I go to charges $28 for a MAF. And these hardly go bad. I've bought three or four of them and they all worked fine. Just match up the part number on the green sticker. Wire loom is the black plastic stuff that's wrapped around the wires. Just pull the tape off and pull back the plastic and you should be able to see anything that's wrong. I actually cut the top off the MAF to find the break. Just cut through the silicone with a razor knife and pried the top off. One of the solder joints had broken where the pin sticks through the connector housing. I think I had to pry something else off the top of the MAF though to see where the pins were. I had already replaced it at that point so I didn't see any point in trying to fix it. Quote Link to comment Share on other sites More sharing options...
teahouse Posted May 2, 2012 Author Share Posted May 2, 2012 Oh right, I'll check the wires under the loom... I wiggled them quite a bit, and didn't find correlation to the stalling, but it wouldn't hurt to take a look. Before I cut the MAF sensor housing, let me try just replacing the connector and MAF first... it's the black housing on top that you cut though, right? I.e., where the female part of the connector harness is attached to? I just found the optimal fuel pressure for a 1997 Legacy... 26-30 psi... so, considering that people say these engines are very similar to the Impreza, I'm guessing my PSI is within optimal range. Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted May 2, 2012 Share Posted May 2, 2012 Fuel pressure is pretty much the same for any EJ engine except for the turbos. Yeah I don't want it to sound like I recommend cutting open the MAF just to see what's inside. I was just saying that's how I ultimately figured out what was wrong with it. A used MAFs cheap from a junkyard, and only takes a few minutes to swap out. If you can't see anything visibly wrong with the harness connector or wires, just replace the MAF first and save yourself the trouble of cutting/ slicing. Quote Link to comment Share on other sites More sharing options...
teahouse Posted May 2, 2012 Author Share Posted May 2, 2012 Oh, I figured a MAF would include only the cylindrical sensor... but along with it comes the entire black housing on top? Quote Link to comment Share on other sites More sharing options...
teahouse Posted May 3, 2012 Author Share Posted May 3, 2012 Made my way through a few junkyards today, and eventually found a 93 Legacy with the same MAF sensor... unbolted it, and cut wiring to the harness about 8 inches down in case I needed that too. They charged about $52... which is still less than a quarter of new price, so I was OK with it. Put it in tonight, went for 2 test drives, and it ran great... no stalling. My harness only has 3 wires, and the one on the Legacy had 5 running to the connector, so I wasn't sure if the wiring in the receiving connector would be compatible... but, luckily, it seems to be running great... It seems at this point, then, that the problem was in the connecting wiring in the housing for the MAF sensor... which would explain why it would die when I would wiggle the connector... it wasn't the connector it's self, then, but some intermittent connection wiring behind the connector that I was wiggling... I think. Of course, it could have been a problem with the sensor it's self too, but the sensor wires looked good, and I would think that a problem with the sensor would most likely be a completely on or completely off situation. So, I'll report back again to verify that everything is working as it should. Again, much appreciation for the help... sincerely. Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted May 3, 2012 Share Posted May 3, 2012 $52 isnt too bad. People sell them for more than that on eBay. There were some differences in wiring through the years. The 5 wire harnesses make use of a built in air temp sensor in the MAF. The 3 wire harness doesn't use the temp sensor. The MAF still plugs in the same way, still works with either harness. Quote Link to comment Share on other sites More sharing options...
teahouse Posted May 4, 2012 Author Share Posted May 4, 2012 Ah, interesting - I guess they did away with the thermometer on this model, for some reason. So today I drove about 20 miles, highway and around town... with no stalls! I think the problem has been fixed. Quote Link to comment Share on other sites More sharing options...
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