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Hey everyone,

I am trying to help a friend diagnose and fix the infamous hesitation problem on his 2000 RS. It has random bouts of hesitation and surging under acceleration, but only seems to do it when the engine is warm. Also, it doesn't do it all the time and will usually last a few drives before it starts happening after resetting the CEL.

So far, it has thrown the knock sensor low voltage, misfire on cyl 2 & 4, and catalyst inefficiency CELs. The knock sensor and misfire codes were on at the same time. We originally replaced the knock sensor with a Duralast sensor, but have since replaced it with a Delphi after seeing that the Autozone knock sensors are not recommended. I also replaced the PCV and downstream O2 sensor a few months ago after a CEL was on for that. After these parts changes, the only code that it is now throwing is P0420, which I have seen on several of my older cars and generally doesn't concern me.

The previous owner replaced the plugs, wires, and coil pack last year and all are still in good condition.

After all of this, it is still happening. I am trying to find out how to diagnose this without throwing parts at it. I looked at the MAP sensor tonight, and other than a light coating of oil (which I believe is normal?) it visually looked good. I also checked the intake manifold pressure with a Bluetooth reader & Torque Pro - It seemed to be functioning properly.

It did not show any voltage on the upstream O2 sensor (Bank 1 Sensor 1), but I have seen people say that certain upstream O2 Sensors will not report voltages to torque pro. I would assume that if the upstream sensor was going out, it would be throwing a CEL, but is there any way to test it? In retrospect, it probably wouldn't have been a bad idea to change both O2 sensors at the same time.

My best guess would be something sensor or computer-related as it only seems to happen with the engine at operating temperature, doesn't happen for a few days after a CEL reset, and it being intermittent.

Any help is greatly appreciated. Thanks in advance!
 

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Discussion Starter #2
If I disconnect the upstream O2 sensor, other than the car running in open loop and probably very rich, the absence of hesitation would confirm that the O2 sensor is the cause, is this assumption correct? I am not familiar enough with this vehicle to know exactly how it will respond to having it unplugged, but in my research, I have seen some say that this is a way to verify the O2 sensor is causing it.
 

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My car knowledge is very low relative to most people on this forum, so please listen to me last lol. With that out of the way, in my research on these forums, I know that some people have claimed that a grounding kit stopped the hesitation. I do experience that hesitation, and I did buy a kit, but I never installed it (laziness, really). Based on what I am reading and what I understand, that solution seems too simple for you, but since no one has posted anything yet, I figured I would chime in. Again, me = not very car knowledgeable; I am just posting this on the very very slim chance that it might help.
 

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not helpful at all, but MY98 RS does the same thing. p0420 is the only code I get.(also no cat lmao so to be expected)

checked my coils and one of the wires was chewed through. had like 4 strands left. repaired, still hesitates.
changed out both o2s
cleaned MAF sensor
wasn't sure if it was injectors (I'm not very knowledgeable either sorry) and used some seafoam
cleaned intake (mine was filthy)

so for some reason, cleaning the intake took care of my hesitation. Also turned off my CEL for p0420.
 

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I have fought with o2 sensors for years... nothing seems to solve the sensor burning out all the time. 99-01 ECUs weren't the best for a modded car and had no tuning options until Delicious Tuning came into play. There ECU flash helped a ton with the little hesitations here and there and opened up certain parameters to not cause the timing to retard itself too much. DO the ground wire mod and it helps a ton with the flat spot on the 3500ish RPM range. I'm still fighting with the upstream o2 sensor after 18 years. There is no way to fool our particular O2 sensors because of the way our cars use a wideband sensor as a non wideband sensor. My details may be a smidge off but this is the gist of things that helped my hesitation problems.
Definitely do the bigger ground wires tho, you'll be surprised how much it helps.... if you can't get the reflashed ECU from delicioustuning.com, save money and get it done. They now offer wireless tuning with our cars and he's the only I know that even messes with the retarded 99-01 ECUs.

Hope this helps you out.

--Justin
 

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I have fought with o2 sensors for years... nothing seems to solve the sensor burning out all the time. 99-01 ECUs weren't the best for a modded car and had no tuning options until Delicious Tuning came into play. There ECU flash helped a ton with the little hesitations here and there and opened up certain parameters to not cause the timing to retard itself too much. DO the ground wire mod and it helps a ton with the flat spot on the 3500ish RPM range. I'm still fighting with the upstream o2 sensor after 18 years. There is no way to fool our particular O2 sensors because of the way our cars use a wideband sensor as a non wideband sensor. My details may be a smidge off but this is the gist of things that helped my hesitation problems.
Definitely do the bigger ground wires tho, you'll be surprised how much it helps.... if you can't get the reflashed ECU from delicioustuning.com, save money and get it done. They now offer wireless tuning with our cars and he's the only I know that even messes with the retarded 99-01 ECUs.

Hope this helps you out.

--Justin

dude... awesome. Is this the simplest solution if you still have a stock ECU? I'd love to get my RS dialed in. It's a NA/T
 
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