Alero knock sensor nightmare- please help, or just shoot me!

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kozzo
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Joined: Tue Dec 31, 2013 2:40 am

Alero knock sensor nightmare- please help, or just shoot me!

Unread post by kozzo » Sun Feb 23, 2014 10:11 pm

ok I had another post on this, but found a bad head gasket, and fixed it. rebuilt whole top end, rebuilt heads, new gaskets, the works. When doing this, I found the cam sensor wires were all taped up by previous owner, from heat damage, so I replaced the plug. also one other thing to add- right before I did the heads, i got a code for the cat converter. Using my scanner, I ran some test to see if the o2 sensors were good, and they checked out, so I bought a new Cat converter

Before the head gasket, I was getting P0327, and replaced the knock sensor with an Autozone sensor, code came back so I replaced it AGAIN with a real GM knock sensor. Code came back again, and I checked for 5v at the wire- no voltage, so I checked for continuity and voltage AT the computer. I actually cut the wire and separated it from the circuit, and got nothing, but wire shows continuity TO the sensor

I finally gave up and took it to a Chevy dealer. after an hour, they called and said that the computer and sensor checked out, and they needed another hour to check wiring, at another $110 an hour. I said sure, then they called me back to say it WAS the PCM. Confused, I went up to the dealership with a used PCM that I had bought earlier, and asked them to put it in, and program to my car. They said they would but couldn't guarantee it. I had actually installed it previous to the head work, but it didn't make a difference, probably due to the bad valves, and leaking head.

It took a whole day, but the CEL came back on, and sure enough- EFFING KNOCK SENSOR! I am really at my wits end here- here's some thoughts I need confirmed
1) if the cam sensor wires were shorting out- could it have damaged the PCM? And wouldn't I have thrown a code for the cam sensor? Thinking back, I did install the new used PCM before I found the wires that were all taped up under the intake manifold, and I don't know if they were really shorting out although it was a horrible taped up mess
2) could something else in the ignition circuit (IE either of the 2 crank sensors, cam sensor, or the ICM be malfunctioning, or shorting out causing the PCM to screw up the knock sensor circuit? I know these are all part of the ignition circuit

Please help- any ideas appreciated. I'm beginning to think someone died in the car and it's haunted

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carriedi
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Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by carriedi » Mon Feb 24, 2014 3:42 am

could you give me the information on your car? year, model and engine, 4 speed or 5 speed trans? helps me find information

the dark blue wire from pin #33 (ecm connector) goes to knock sensor connector.

the knock sensor, disconnected from the harness, should ohm out to 93 - 107 ohms from the center post of the KS to ground.

if you can get your hands on a scanner you should drive your car with the scanner hooked up and watch your KS signal voltage. (along with the KS retard timing)

check your wire harness for rubbing anywhere that might short your KS wiring. A lab scope will be handy to watch your hertz reading with the engine running. Check your connector to the knock sensor. Many times the plastic connector will be worn from heat and age and the metal connector will spread apart and not give a good connection.
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carriedi
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Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by carriedi » Mon Feb 24, 2014 4:58 am

here he is talking specifically about Toyota but it goes to testing all knock sensors.

http://www.youtube.com/watch?v=L8xRJIWkHuo
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kozzo
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Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by kozzo » Mon Feb 24, 2014 10:53 am

hey thanks for the reply. Sorry in all my excitement forgot specifics. It's an 03 Alero with a 3.4, and automatic trans(think it's 4 speed). I actually was on this board earlier, and you had helped me, till I got distracted. I will check all this tonight. There was a lot of stuff wrong with this car, and really bad mechanics. I'm wondering if it's even the original engine, and maybe a different year.

I haven't checked yet- but isn't the blue wire supposed to have 5 volts present with ignition on? before I swapped computers, I didn't, haven't checked since replacing pcm

kozzo
Posts: 15
Joined: Tue Dec 31, 2013 2:40 am

Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by kozzo » Mon Feb 24, 2014 9:48 pm

the plug is relatively new, and was pigtailed onto the wire with a butt connecter. I cut the butt connecter out, and the sensor ohmed out at 99 ohms thru the connecter and sensor to ground. the connecter looked crummy, so I put a new one on and heat shrinked around it. I hav a centech harbor freight scanner, and can't seem to find a live data test for knock sensor- is it called something else?
One other thing- I still haven't driven the car long enough to be inspection ready- you think maybe I should drive the car some more to see if something else pops up that might be the cause inadvertently?

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carriedi
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Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by carriedi » Tue Feb 25, 2014 4:56 am

every scanner is different. data stream should have a couple of ways to see the knock sensor.

http://www.youtube.com/watch?v=vqj2YWbedsc

In order to go through most vehicle inspections you have to have the monitors showing ready. If you have a code before the monitors set, usually, that stops the computer for completing more monitor testing. You need to drive it around to set the monitors to ready and hopefully the knock sensor code not come on. Every time you clear the codes you set the monitors to "not ready". Gas tank has to be between 1/4 and 3/4 full. some tests may be done overnight (evap) other tests may require certain ambient temperatures. Some states will allow one or two 'not ready's' but they are getting stricter all the time.
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kozzo
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Joined: Tue Dec 31, 2013 2:40 am

Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by kozzo » Tue Feb 25, 2014 9:54 am

well, I know it's not the sensor, or the plug, and this is a different computer that has been flashed by gm. The wire is a one wire KS, so I am going to run a new wire later today, and splice it in at the pcm and the sensor- this wire just goes from the pcm to the sensor, and to nothing else, right? Would an intermittent open short cause the CEL to come on. I ask, because both a GM tech and I have checked the wire for continuity, and shorts, and found everything ok

edit, I just watched that vid, had seen it before. I guess I will run it and check for spark advance, but I can say, the car doesn't run bad- nothing noticeable at least, and the engine isn't particularly noisy for a car with 95000 miles on it

kozzo
Posts: 15
Joined: Tue Dec 31, 2013 2:40 am

Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by kozzo » Tue Feb 25, 2014 8:05 pm

I think I have fixed it. I ran a new wire from the pcm to the sensor. I also ran a ground wire from the bell housing to the ground strap at the battery. I soldered and heat shrinked both splices. Drove it around for about an hour and a half- so far no CEL. I noticed that I am still not "inspection ready" because of the egr, cat, and O2 sensors- wonder how long I need to drive it to get those to pass?

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carriedi
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Re: Alero knock sensor nightmare- please help, or just shoot

Unread post by carriedi » Wed Feb 26, 2014 12:13 am

sometimes they can reset in a day. sometimes, if temperature is too cold it may take a while.
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