alaskanjer Posted June 9, 2011 Share Posted June 9, 2011 I have '98 O'B 5-speed, 2.5. It has this weird hesitation problem that showed up about 25,000 miles ago (190,000 on car, 115,000 on new warrantied motor (short block only)) and has steadily been getting worse. It has progressed from extremely minor to annoying and finally to pain in the arse status and has resisted everything I have tried. When I am accelerating from low RPMs, there are several consistant dead spots where the engine hesitates for a half second before resuming normal acceleration. The hesitation ALWAYS happens at the same points on the tach, with the worst occuring at about 1750, and the second worst happening at about 2100. There are a few other spots too, but they are all below 2500 rpm unless I have the gas pedal fully depressed (3rd gear trying to get up to 75 in a short merging lane.) At full throttle the hesitation is more pronounced and happens at semi regular intervals all the way to redline. I have searched and searched, and the post that makes the most sense is this one: http://www.ultimatesubaru.org/forum/showthread.php?t=115064 I have checked or replaced all this stuff (from above post) "Eliminate all external influences, such as an incorrect or dirty air filter, loose or tracked intake duct, dirty fuel filter, low fuel pressure, PVC system, or low engine vacuum that would indicate an external leak or an internal engine component. " I haven't (and don't know how) checked the timing while driving. I was occasionally getting CEL and codes for knock sensor and EGR and I have replaced them as well. I still sometimes get a code for EGR (P0403) but it usually goes away on its own after a week or so, and stays off for months. Idling in cold weather for 5 min or more is what seems to trigger the P0403, so I don't think it is related to the hesitation. A friend said it could be the TPS, but it seems like if it were the TPS then it would be more linked to the throttle position and not at all linked to specific RPMs, but I am by no means an expert. Any ideas? Quote Link to comment Share on other sites More sharing options...
idosubaru Posted June 9, 2011 Share Posted June 9, 2011 Subaru ECU's rarely fail and aren't wear items, so while it's possible it's far less likely than many other things so i wouldn't start guessing there. although if you have extra parts lying around they aren't hard to swap out. first thing is how is the basic tune up of this car: plugs and wires? are they Subaru OEM and how old/miles? have the valves ever been adjusted? timing belt condition - pulleys/tensioner all original? i would "guess" TPS or coil pack. both easy to swap out with another used one. neither fail enough to warrant the cost of new (particularly TPS). folks on the subaruxt.com forum have cleaned their TPS by taking it apart and cleaning the contacts and noted significantly smoother acceleration, etc. it's not meant to be disassembled though so most people don't do it. fuel pressure regulator/fuel injectors come to mind too but i wouldn't expect those to be as RPM driven as you're describing. Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted June 9, 2011 Share Posted June 9, 2011 Have you tried new plugs and wires? 2.5s tend to be kinda picky about those, NGK plugs and OE or NGK wires are recommended by many here. Quote Link to comment Share on other sites More sharing options...
alaskanjer Posted June 9, 2011 Author Share Posted June 9, 2011 Timing belt/idler pulleys and bearings were replace with OEM last year at 178,000. I haven't ever done any with the valves. I doubt they have been touched since the engine was replace at 75,000. Is this something that should be part of a regular maintenance schedule for this engine? Plugs/wires have about 95,000 on them. Opps, I thought I had done them more recently, thanks for making me check. They are OEM and the replacements will be too. I've read here that these engines are very picky about their plugs and wires. Any chance that old plugs and/or wires could produce a hesitation at exactly the same RPM every time? Quote Link to comment Share on other sites More sharing options...
alaskanjer Posted June 9, 2011 Author Share Posted June 9, 2011 According to my records, the injectors were "serviced" when the engine was replaced. Is this also something I should address? And sorry Fairtax4me, I didn't intentionally steal your words. I didn't see your post before I replied. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted June 10, 2011 Share Posted June 10, 2011 awesome, hopefully the plugs/wires are the culprit. interesting that it's at specific RPM's and doesn't make sense at first thought, so i'm with you on that. but i wouldn't be surprised if the plugs/wires fix it and they probably need it anyway. injectors don't need serviced unless there are symptoms. valves should be adjusted. it's not a huge risk but it happens that the valves get too tight and you burn a valve. usually an exhaust valve gets burned, there's threads on here where that has happened. unfortunately that EJ25D engine in your car is a real debacle to do a valve adjustment on - might be better to let it burn valves! just kidding, but valve jobs are really tough on those, so they're not done too often. on other subaru engines i'd say do it because they're easy, but i wouldn't probably think about it until 150k just because they're so difficult on this engine. pretty much every valve train i get into the valves are too tight and need adjusted. Quote Link to comment Share on other sites More sharing options...
alaskanjer Posted June 13, 2011 Author Share Posted June 13, 2011 grossgary, if you lived within 100 miles of here I'd be on your door step with a case of beer (or scotch or perrier or whatever). It was the plug wires. I had the point (that these cars are very picky about their plug wires) driven home when I got interrupted halfway through swapping the wires. I had just switched 1 and 3 when I needed to run to the store, and the car wouldn't even start. First I thought I must have missed a connection so I checked but they were good. I tried a few times more and it was pretty clear it wouldn't start. I didn't flog it to death but I did try 5 or 6 times for several seconds each time and nothing. So I pulled the old wires off 2 and 4 and put the shiny new expensive ones on and it started right up (despite smelling a little flooded.) And it ran better than it has in a year, at least. None of the weird hesitation that has had me pulling my hair out trying to troubleshoot. I've got plugs but I haven't had a chance to swap them yet. I didn't do them yesterday because I wanted to do it stepwise to know what change improved or fixed it. And today I got to spend some quality time with our plumbing digging my 4 yo daughter's toy watch out of the toilet. So I'm all up to date on my R-rated words in case spark plug # 4 is as ornery as they say. Quote Link to comment Share on other sites More sharing options...
Rooster2 Posted June 13, 2011 Share Posted June 13, 2011 I too have a 98 OBW, that I changed the spark plugs on a couple of years back. It is a really nasty job on the 2.5. Just so little room to work wrenches. It took several hours, and a lot of four letter cussing to complete. There is plenty written on this subject in the past, so it you pose the topic on the search function of the website, you can read what others have done and said about changing the plugs. Glad to hear that plug wires fixed your hesitation problem. Quote Link to comment Share on other sites More sharing options...
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