Hard Starting and Knock Sensor

SVXer95 · #1 12-16-2004, 12:14 PM

The title says it all. I have had a hard starting symptom for the last couple of weeks now. It has only happened to me a couple of times. Only a problem when engine is cold.

I pulled a code 56, egr, about two weeks ago and cleared it to see if it came back. It didn't, but another code popped up. I got a code 28, abnormal voltage from knock sensor. Would this cause hard starting? I am leaning towards no, but I'm not sure.

Other info:
replaced water temp sensor recently so this isn't the problem
recently did fuel filter
recently cleaned air filter
Not getting any other codes.

Not really sure what to do on this one. It is a bit scary when the car doesn't start for five minutes. Cranks strong, fuel pump is working (I can hear it), but I don't know what else to check. Like I said, I am not getting any other codes. Taking it into the dealer on Saturday, hopefully they don't rape me in charges.

#2 12-16-2004, 12:34 PM

A bad knock sensor would retard the timing, but would not cause a hard cold start. This is a common problem caused mainly by the temp sensor. Which temp sensor did you replace? The sensor that operates the temp guage has no affect on cold starts, so if that is the one you replaced then you need to replace the other.

Dave

SVXer95 · #3 12-16-2004, 12:43 PM

Computer temp sensor is the one I changed. The one on drivers side rear of engine. No code for the temp sensor is registering.

SVXer95 · #4 12-16-2004, 12:45 PM

I had no problems until after I installed the v4 of Ecutune Stage one. Not saying this is the cause, but anything is possible.

#5 12-16-2004, 03:02 PM

Quote:

Originally posted by SVXer95
I had no problems until after I installed the v4 of Ecutune Stage one. Not saying this is the cause, but anything is possible.

........oh. Well, try uninstalling it and see what happens. You could also try clearing the memory. Your ECU probably just needs time to adapt.

Dave

SVXer95 · #6 12-16-2004, 03:16 PM

Quote:

Originally posted by red95svx

........oh. Well, try uninstalling it and see what happens. You could also try clearing the memory. Your ECU probably just needs time to adapt.

Dave

It is just difficult to diagnose because it is so intermittent. One minute it starts fine, a week later it doesn't. Changing the chip also takes time to relearn, etc. Then all the sudden BAM, doesn't start. I am hoping the techs at the dealership will have a better idea of why this is happening.

SVXer95 · #7 12-17-2004, 12:19 PM

So can anyone get me a good price on two knock sensors?

Car goes in tomorrow. I figure I can change the knock sensors, but I am still having them look at it as far as hard starting goes. Having a wheel bearing done as well.

Beav · #8 12-17-2004, 10:07 PM

Weak cam sensor output signal is common on Subaru and will cause the situation you're describing. Really need to watch its output signal on a GMM or oscilloscope to be certain.

#9 12-18-2004, 08:23 AM

Quote:

Originally posted by Beav
Weak cam sensor output signal is common on Subaru and will cause the situation you're describing. Really need to watch its output signal on a GMM or oscilloscope to be certain.

That is true....but wouldn't it throw a code? I seem to remember a few Legacys that came in for an occasional hard start but they had a code for a bad cam sensor.

Dave

SVXer95 · #10 12-18-2004, 05:06 PM

Quote:

Originally posted by Beav
Weak cam sensor output signal is common on Subaru and will cause the situation you're describing. Really need to watch its output signal on a GMM or oscilloscope to be certain.

Hmmm very interesting...

I had the techs at the dealership check it out today. Couldn't find anything but the knock sensor. They said that it *could* be the cause of my problems. I am going to change it myself and see if my problem goes away. If not, I will look into the cam sensors.

Is anyone still offering discounts to network members?

I just had to drop $600 today for a rear bearing + hub. I'm looking for all of the breaks I can get.

Beav · #11 12-20-2004, 07:48 PM

But were those Legacys OBDll? If so the ECU may have picked up the problem. Prior to OBDll it may not. An OBDll ECU is looking for proper amplitude, not just a signal, that's why it would set a code. Pre-OBDll, I'm not certain. The amplitude can pass the threshold during some occasions and start. Other times it may not. Once the engine starts a weak sensor will have the benefit of rpm above cranking speed which will increase the amplitude and the engine continues to run o.k. That's why I suggested checking the pattern itself with a GMM at cranking speed. With a meter it would take but a couple minutes to confirm.

BigBlueSVX · #12 12-20-2004, 09:45 PM

Hey Collin,
I'm not experiencing any starting problems like you, but I do have the same codes as you do (egr and knock sensors). Hopefully the knock sensors are the cause of everything. Good luck on the install.

PS I am definitely going to get mine before you get yours

SVXer95 · #13 12-20-2004, 10:15 PM

Quote:

Originally posted by BigBlueSVX
Hey Collin,
I'm not experiencing any starting problems like you, but I do have the same codes as you do (egr and knock sensors). Hopefully the knock sensors are the cause of everything. Good luck on the install.

PS I am definitely going to get mine before you get yours

I hope this fixes all the problems too

Damn you and your 2nd day air

SVXRide · #14 12-21-2004, 03:59 AM

Collin/Big Blue,
Definitely try to take digital pics as you do your knock sensor replacement. Along with the Solenoid C, it appears that the knock sensors are another piece of hardware on the SVX that can/may "go away" without throwing a code. In the knock sensors' case, it appears that they can degrade a good deal before they actually throw a code - if they actually do throw a code.
Don't forget to disconnect the positive terminal before you move the alternator

-Bill

SVXer95 · #15 12-21-2004, 07:14 AM

Quote:

Originally posted by SVXRide
Collin/Big Blue,
Definitely try to take digital pics as you do your knock sensor replacement. Along with the Solenoid C, it appears that the knock sensors are another piece of hardware on the SVX that can/may "go away" without throwing a code. In the knock sensors' case, it appears that they can degrade a good deal before they actually throw a code - if they actually do throw a code.
Don't forget to disconnect the positive terminal before you move the alternator
-Bill

Will do. I plan on doing this xmas weekend.

Now I just need to remember....