Jarsky Posted July 8, 2021 Share Posted July 8, 2021 Hey all, i Have a 93 Subaru legacy. My cars having a problem from 4-5k rpm with a severe lack of power. She feels like a rocket up until that point but as soon as it hits 4 i can feel the car not wanting to accelerate. I figured it would be the knock sensor so i changed it with another one that i know worked. Drove the car around and it felt great so i let it sit overnight, this morning when im leaving for work, boom check engine is back on and the weak spot seems to be back. I haven't checked the code, I'm probably gonna do it tomorrow or during lunch today, but does anyone have any idea what this could be? also of note, sometimes the check engine light will go away, the car backfires less and the weak spot is completely gone. I'm aware that those are symptoms of a bad knock sensor, retard the timing and make the car run rich hence the backfire but as i said that's been changed with a slightly used but working unit. Any help would be greatly appreciated, thank you! Link to comment Share on other sites More sharing options...
GeneralDisorder Posted July 8, 2021 Share Posted July 8, 2021 Pull codes. Could just as easily be a bad ECM as it is a bad knock sensor. Most of those old ECM's have cracked solder joints or other issues by now. GD 1 Link to comment Share on other sites More sharing options...
Jarsky Posted July 9, 2021 Author Share Posted July 9, 2021 17 hours ago, GeneralDisorder said: Pull codes. Could just as easily be a bad ECM as it is a bad knock sensor. Most of those old ECM's have cracked solder joints or other issues by now. GD ill try and pull the codes when i get the chance, are the ECM and the ECU the same or contained in the same unit? if so i might have a spare laying around Link to comment Share on other sites More sharing options...
Numbchux Posted July 9, 2021 Share Posted July 9, 2021 Yep, different terminology for the same thing. CEL is trying to tell you what's wrong. Pull the codes. My crystal ball is a little hazy. Link to comment Share on other sites More sharing options...
nipper Posted July 10, 2021 Share Posted July 10, 2021 Will it get over 5K rpm? Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted July 11, 2021 Share Posted July 11, 2021 how does it run immediately after a battery disconnect reset? If badly, look for something 'physical' like a clogged exhaust or 'dropped' valve. If better, could be a bad sensor or sensor wiring.... Link to comment Share on other sites More sharing options...
nipper Posted July 11, 2021 Share Posted July 11, 2021 1 hour ago, 1 Lucky Texan said: how does it run immediately after a battery disconnect reset? If badly, look for something 'physical' like a clogged exhaust or 'dropped' valve. If better, could be a bad sensor or sensor wiring.... Thats why Im wondering about what happens over 5000 RPM Link to comment Share on other sites More sharing options...
Jarsky Posted July 12, 2021 Author Share Posted July 12, 2021 On 7/9/2021 at 11:21 AM, Numbchux said: Yep, different terminology for the same thing. CEL is trying to tell you what's wrong. Pull the codes. My crystal ball is a little hazy. gonna work on the car tomorrow as the brakes decided they didnt want to exist anymore ill take a look then Link to comment Share on other sites More sharing options...
Jarsky Posted July 12, 2021 Author Share Posted July 12, 2021 On 7/9/2021 at 11:57 PM, nipper said: Will it get over 5K rpm? yeah it gets pretty happy past 5k Link to comment Share on other sites More sharing options...
Jarsky Posted July 12, 2021 Author Share Posted July 12, 2021 On 7/10/2021 at 9:36 PM, 1 Lucky Texan said: how does it run immediately after a battery disconnect reset? If badly, look for something 'physical' like a clogged exhaust or 'dropped' valve. If better, could be a bad sensor or sensor wiring.... it runs pretty good after a battery disconnect reset. While I'm hoping its a faulty sensor, i chased down a previous problem about a year ago and spent way too much money replacing basically every sensor except the oil pressure, while it would be a relief if it was a sensor would also be annoying Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted July 12, 2021 Share Posted July 12, 2021 well, maybe the FSM has some guidelines for testing sensor signals - could be that the actual sensors are OK, but a wire is broken or a pin is pushed back in a connector. Testing resistances from the ECU's connector and comparing values with the FSM could locate the problem. If the car was OBDII, live data would be very helpful. Maybe someone else knows how to get live data from a '93. If the car also struggles to rev past 5K at idle, maybe try a squirt of raw propane, or starter fluid. maybe the fuel pump is weak???? Link to comment Share on other sites More sharing options...
Jarsky Posted July 13, 2021 Author Share Posted July 13, 2021 21 hours ago, 1 Lucky Texan said: well, maybe the FSM has some guidelines for testing sensor signals - could be that the actual sensors are OK, but a wire is broken or a pin is pushed back in a connector. Testing resistances from the ECU's connector and comparing values with the FSM could locate the problem. If the car was OBDII, live data would be very helpful. Maybe someone else knows how to get live data from a '93. If the car also struggles to rev past 5K at idle, maybe try a squirt of raw propane, or starter fluid. maybe the fuel pump is weak???? there's definitely a possibility in the wiring department, but as i said after 5K the cars a rocket and at idle as well revs past 5 with no problem. The gas tank is from a GD wrx or sti with a brand new fuel pump, so it definitely shouldn't be that. Fuel filter is also only a year or so old. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted July 13, 2021 Share Posted July 13, 2021 The knock sensor is being ignored once it goes past 5k. Too much mechanical noise for the signal to be useful. It's probably pulling timing like crazy but that could be due to a faulty sensor, faulty wiring, or faulty ECU. My suggestion would be to replace the ECU with a LINK WRX2X and then tune it speed density and ignore the knock sensor. GD Link to comment Share on other sites More sharing options...
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