Engine bucking after car is warm - Subaru Outback

DarkPhoenix · 05-01-2010, 11:10 PM

I just bought a 97 Legacy OBW and I am pulling my hair out trying to figure this out.

I noticed that the bucking happens after the car reaches normal operating temp, and it gets worse under load, like going up hill. It seems to be "governed" at 3K RPMs. I will try cleaning out the MAF and the throttle body to further TS.

Okay, I went to the local auto parts store and they pulled the following codes from my OBW.

P0136 - o2 Sensor Circuit Malf. (B1, S2) - This one is pretty self explanatory and will hopefully fix that hesitation issue.

P0340 Camshaft position sensor circuit malfunction

The front o2 was changed by the previous owner and I changed out the Cam and crank sensors. It has new plugs, PCV and fuel filter, and will be getting new wires today when I get home. This has me perplexed. I took the car to Grand Prix to see if there were any ECU recalls for my car, but there was nothing. I am not sure what else to do at this point, but it has to be a sensor or ECU issue, as it only happens after the ECU goes into closed loop.

I have replaced the following items:

Plugs
Wires
MAF
Cam and Crank Sensors
Front O2 Sensors
Coil Pack
EGR Valve and I also blocked the EGR as well.
PCV valve (with OEM Subaru)
Fuel Filter (with OEM Subaru)
ECU (will be replaced on Monday once it arrives)
I have moved the knock sensor off of the block and to the air intake bracket.
Air filter
There was a butt connector on the pigtail for the Cam sensor, so I replaced the wire and soldered everything in.

Today I drove about 30 miles and for the first 5-10 miles, the car was strong, and then it started cutting out, like it was losing spark. When ever I changed the throttle input at all, it would buck. It got to the point where I went to WOT and the car had no power and was missing. The car backfired through the exhaust.

It is driving me NUTS because the car runs great when it is cold, so I know there is no mechanical issue.

Any ideas out there in the Outback?

Blacky · 05-01-2010, 11:17 PM

Temperature sensor?

DarkPhoenix · 05-01-2010, 11:24 PM

I never get a temp sensor code, ever. The rear O2 sensor, I am not really worried about as that doesn't affect the way the car runs, and I know why the I am getting that code because the wire was taped together.

Wouldn't disconnecting the temp sensor just keep it in open loop?

**nipper** · 05-01-2010, 11:43 PM

I would go with the temp sesnor too. there are a couple of sensors that never throw a code. Trouble codes are not the answer (even if they do not exist), just a tool to help solve a question. Knowledge is still required to do a proper diagnoses.

RobLog · 05-01-2010, 11:58 PM

Probably nothing ... but warmed up and 3000 rpm is when the EGR system normally kicks in. But the symptoms are more consistent with an EGR valve stuck in the open position, not blocked off.

Related thought: could be a vacuum leak that only occurs when the engine is warmed up and 3000 rpm ... the EGR solenoid valve opens about 3000 rpm and allows vacuum through to the EGR valve ... if the vacuum hose to the EGR valve is leaking ... ?

Just guessing.

ETC · 05-02-2010, 03:03 AM

My first guess would be Engine Coolant Temp sensor too since it's Open/Closed loop temp related.

Other option is that there is a blown fuse or relay that powers those sensors and when the car reaches temp and goes in to closed loop, the sensor value isn't there so it goes in to "limp mode" to protect the motor. I had a bad fuse connection that killed a relay and gave me intermittent power to the sensors in my truck, something to check.

DarkPhoenix · 05-02-2010, 01:39 PM

Quote:

Originally Posted by nipper

I would go with the temp sesnor too. there are a couple of sensors that never throw a code. Trouble codes are not the answer (even if they do not exist), just a tool to help solve a question. Knowledge is still required to do a proper diagnoses.

Okay, I ordered an ECT from my local auto parts store.

OT:Where in O'Side do you live? I grew up in Long Beach and my ex grew up in O'Side?

Quote:

Originally Posted by RobLog

Probably nothing ... but warmed up and 3000 rpm is when the EGR system normally kicks in. But the symptoms are more consistent with an EGR valve stuck in the open position, not blocked off.

Related thought: could be a vacuum leak that only occurs when the engine is warmed up and 3000 rpm ... the EGR solenoid valve opens about 3000 rpm and allows vacuum through to the EGR valve ... if the vacuum hose to the EGR valve is leaking ... ?

Just guessing.

I checked for vacuum leaks in the car, but there was nothing that I could find with that. The EGR is blocked off now because I thought it was the EGR as well.

Quote:

Originally Posted by ETC

My first guess would be Engine Coolant Temp sensor too since it's Open/Closed loop temp related.

Other option is that there is a blown fuse or relay that powers those sensors and when the car reaches temp and goes in to closed loop, the sensor value isn't there so it goes in to "limp mode" to protect the motor. I had a bad fuse connection that killed a relay and gave me intermittent power to the sensors in my truck, something to check.

Hmm, that is something to think about. Time to break out the Haynes to find where all of these fuses are.

Thanks for the responses guys. This has been driving me nuts for the past 3 weeks and I would like the car to run right before i start doing any mods to it.

DarkPhoenix · 05-02-2010, 03:43 PM

A new wrinkle in the saga.

I was checking the voltage of the TPS sensor, and I am getting 5 volts regardless of throttle position. I disconnected the harness from the sensor, and it was reading 5.12 volts at the pigtail. The wiring looks good, but it am unsure if there is a relay or fuse for the TPS. unless the ECU is bad and is giving off a bad signal.

DarkPhoenix · 05-02-2010, 07:11 PM

Okay, after reading online, the Haynes manual is retarded and gave me the wrong wire to check the voltage on. I adjusted the TPS and it is reading correctly now.

I took out the ECU to look at it and I noticed some oxidation on one of the chips. A friend of mine works with electronics and he did a continuity check on the chip that is oxidised and one of them basically kept the circuit closed. I will change out the ECU tomorrow when I get it.

As for the ECT, where is it on the engine? I see one sensor on the block itself, just behind the alternator that has one wire going to it. That wouldn't be the ECT, would it?

miker104 · 05-02-2010, 07:18 PM

its on the coolant pipe that runs between the heads, under the intake manifold. There was a thread on here somewhere that showed a photo. Its kind of hidden. There are two sensors in that area, the single wire one is for the temp guage and the other one is the ECTS.

Not sure if this is exactly for your car but there is a photo on this thread by Porcupine73 that shows it:

uh oh... low idle, almost stall

"As for the ECT, where is it on the engine? I see one sensor on the block itself, just behind the alternator that has one wire going to it. That wouldn't be the ECT, would it?"

that is probably the oil pressure switch for the low oil pressure light.

05-01-2010, 11:10 PM	#1 (permalink)
DarkPhoenix Registered User Join Date: May 2010 Location: Hicksville, NY Car: 2002 DSP Outback AWP w/ 5 speed Posts: 126 Feedback Score: 0 reviews	Engine bucking after car is warm I just bought a 97 Legacy OBW and I am pulling my hair out trying to figure this out. I noticed that the bucking happens after the car reaches normal operating temp, and it gets worse under load, like going up hill. It seems to be "governed" at 3K RPMs. I will try cleaning out the MAF and the throttle body to further TS. Okay, I went to the local auto parts store and they pulled the following codes from my OBW. P0136 - o2 Sensor Circuit Malf. (B1, S2) - This one is pretty self explanatory and will hopefully fix that hesitation issue. P0340 Camshaft position sensor circuit malfunction The front o2 was changed by the previous owner and I changed out the Cam and crank sensors. It has new plugs, PCV and fuel filter, and will be getting new wires today when I get home. This has me perplexed. I took the car to Grand Prix to see if there were any ECU recalls for my car, but there was nothing. I am not sure what else to do at this point, but it has to be a sensor or ECU issue, as it only happens after the ECU goes into closed loop. I have replaced the following items: Plugs Wires MAF Cam and Crank Sensors Front O2 Sensors Coil Pack EGR Valve and I also blocked the EGR as well. PCV valve (with OEM Subaru) Fuel Filter (with OEM Subaru) ECU (will be replaced on Monday once it arrives) I have moved the knock sensor off of the block and to the air intake bracket. Air filter There was a butt connector on the pigtail for the Cam sensor, so I replaced the wire and soldered everything in. Today I drove about 30 miles and for the first 5-10 miles, the car was strong, and then it started cutting out, like it was losing spark. When ever I changed the throttle input at all, it would buck. It got to the point where I went to WOT and the car had no power and was missing. The car backfired through the exhaust. It is driving me NUTS because the car runs great when it is cold, so I know there is no mechanical issue. Any ideas out there in the Outback?

05-02-2010, 07:11 PM	#9 (permalink)
DarkPhoenix Registered User Join Date: May 2010 Location: Hicksville, NY Car: 2002 DSP Outback AWP w/ 5 speed Posts: 126 Feedback Score: 0 reviews	Okay, after reading online, the Haynes manual is retarded and gave me the wrong wire to check the voltage on. I adjusted the TPS and it is reading correctly now. I took out the ECU to look at it and I noticed some oxidation on one of the chips. A friend of mine works with electronics and he did a continuity check on the chip that is oxidised and one of them basically kept the circuit closed. I will change out the ECU tomorrow when I get it. As for the ECT, where is it on the engine? I see one sensor on the block itself, just behind the alternator that has one wire going to it. That wouldn't be the ECT, would it? __________________ 2002 BH Outback - EJ251 w/ 5 Speed 2002 GG Impreza - EJ251 w/ 5 Speed (Stormtrooper)

Thread Tools
Show Printable Version Email this Page
Rate This Thread
Rate This Thread:

05-01-2010, 11:17 PM	#2 (permalink)
Blacky Registered User Join Date: Jul 2007 Location: Lac Ste. Marie, Quebec Car: 1997 SVX Bordeaux 2012 OBW 6 speed 1992 SVX Ebony 1992 SVX Claret Posts: 687 Feedback Score: 0 reviews	Temperature sensor?

05-01-2010, 11:24 PM	#3 (permalink)
DarkPhoenix Registered User Join Date: May 2010 Location: Hicksville, NY Car: 2002 DSP Outback AWP w/ 5 speed Posts: 126 Feedback Score: 0 reviews	I never get a temp sensor code, ever. The rear O2 sensor, I am not really worried about as that doesn't affect the way the car runs, and I know why the I am getting that code because the wire was taped together. Wouldn't disconnecting the temp sensor just keep it in open loop?

05-01-2010, 11:43 PM	#4 (permalink)
nipper Super Moderator Join Date: Jan 2007 Location: Oceanside, NY Car: 2005 OBW 2.5L, 1989 Subaru Justy, RIP Blu Posts: 7,233 Feedback Score: 0 reviews	I would go with the temp sesnor too. there are a couple of sensors that never throw a code. Trouble codes are not the answer (even if they do not exist), just a tool to help solve a question. Knowledge is still required to do a proper diagnoses.

05-01-2010, 11:58 PM	#5 (permalink)
RobLog Registered User Join Date: Nov 2008 Location: Oregon Car: 1997 OBW 2.5L Auto and 1991 Ford F150 Posts: 1,242 Feedback Score: 0 reviews	Probably nothing ... but warmed up and 3000 rpm is when the EGR system normally kicks in. But the symptoms are more consistent with an EGR valve stuck in the open position, not blocked off. Related thought: could be a vacuum leak that only occurs when the engine is warmed up and 3000 rpm ... the EGR solenoid valve opens about 3000 rpm and allows vacuum through to the EGR valve ... if the vacuum hose to the EGR valve is leaking ... ? Just guessing.

05-02-2010, 03:03 AM	#6 (permalink)
ETC ;} Join Date: Jan 2007 Location: Southern Ca Car: 00 outback Posts: 5,199 Feedback Score: 0 reviews	My first guess would be Engine Coolant Temp sensor too since it's Open/Closed loop temp related. Other option is that there is a blown fuse or relay that powers those sensors and when the car reaches temp and goes in to closed loop, the sensor value isn't there so it goes in to "limp mode" to protect the motor. I had a bad fuse connection that killed a relay and gave me intermittent power to the sensors in my truck, something to check.

05-02-2010, 03:43 PM	#8 (permalink)
DarkPhoenix Registered User Join Date: May 2010 Location: Hicksville, NY Car: 2002 DSP Outback AWP w/ 5 speed Posts: 126 Feedback Score: 0 reviews	A new wrinkle in the saga. I was checking the voltage of the TPS sensor, and I am getting 5 volts regardless of throttle position. I disconnected the harness from the sensor, and it was reading 5.12 volts at the pigtail. The wiring looks good, but it am unsure if there is a relay or fuse for the TPS. unless the ECU is bad and is giving off a bad signal.

05-02-2010, 07:18 PM	#10 (permalink)
miker104 Registered User Join Date: Feb 2009 Location: N KY Car: 1999 30th Anniversary Legacy 2.5L 4EAT Posts: 653 Feedback Score: 0 reviews	its on the coolant pipe that runs between the heads, under the intake manifold. There was a thread on here somewhere that showed a photo. Its kind of hidden. There are two sensors in that area, the single wire one is for the temp guage and the other one is the ECTS. Not sure if this is exactly for your car but there is a photo on this thread by Porcupine73 that shows it: uh oh... low idle, almost stall "As for the ECT, where is it on the engine? I see one sensor on the block itself, just behind the alternator that has one wire going to it. That wouldn't be the ECT, would it?" that is probably the oil pressure switch for the low oil pressure light.

Remove Advertisements Sponsored Links
Subaru Outback Forum Advertisement