Suburbazine

I would not recommend using sensors that have already been torqued into another engine. It's not worth the risk that they will have something out of spec, considering the time involved in replacement. Also, ensure that replacement sensors are tightened to EXACTLY 15ft/lbs. Too tight and they become too loud, too loose and they are too quiet.

@marineusmc4:

Your diagnostic was faulty from the get-go. The OP stated an issue and you went off on a wild tangent about the Limp Mode display. It's true that it MIGHT be an issue, but does not relate to the more specific issue at hand about the CEL with knock sensor codes.

Your post about the knock sensors was just wrong. You stated you assumed. The whole diagnostic in this post was also wrong and indicated you may not understand how the system works.

This test is wrong because a knock sensor does not detect knocks. No scan tool can indicate a sensor is detecting knocks in the fashion you speak of, as well. The knock sensor detects sounds/vibrations from the engine block which it converts into a linear electrical signal. This signal waveform, when timed with combustion strokes, tells the PCM that either a detonation occurred or the fuel ignited properly. This is also how the PCM determines a misfire.

bbowerman

its not a 2 hour job for me i can disassemble and re-assemble in an hour or less its pretty easy

Suburbazine

That's the average time for a practicing mechanic. 2.7 hours is the book time lol.

bluebird71

iTrader: (53)

If I get 2 new sensors, can I still use this spare wiring harness for them I have? Not trying to be cheap, but if its Im good shape and it works, I figure why not use it.

Suburbazine

Yeah, if the harness is in good shape and the connector ends and seals aren't cracked, go for it. If you're doing it yourself, make sure not to get the harness pinched between the intake and the heads. Also, put a bead of RTV sealant around the valley caps to keep water out of the knock sensor buckets.

I've seen some enterprising individuals pump half a can of non-permanent RTV into the sensor buckets after the sensor is installed to keep water off the sensor. I can't say it's a great idea though because it makes a future replacement very messy.

marineusmc4

look at the thread title. "CEL and Limp Mode" why you are so hung up on the knock sensors and the CEL is beyond me when he is also concerned about Limp Mode, as stated in the thread title.

there was no diagnostic strategy here. as u keep bringing up, it was an ASSUPMTION based off of provided information and personal experience with not only the CEL but the limp mode, again, as stated in the thread title


so what you basically said is that the knock sensor doesnt detect knocks but yet it detects sounds/vibrations (knocks)? so if an engine has abnormal sounds/vibrations and the knock sensor detects them and PCM reads that and turns on the CEL, and you hook up a scan tool it it wont come up as a knock sensor code but as a misfire or some other type of code? well maybe u should get a better scan tool than a $50 dollar one from the auto parts store cuz i have 2 scan tools that tell me everything. and you can check out those waveforms with an oscilloscope. also, read my posts closer cuz i told him to physically inspect the knock sensors for any connection or wiring issues. so anytime you wanna stop being an internet tough guy let me know, cuz id really like for this guy to get his problem resolved.

Suburbazine

1: Limp mode AKA Reduced Engine Power Mode- Engine runs on alternating sets of 4 cylinders. Engine can barely get to 2000RPM in gear no matter what you do. Bluebird has stated that this is not the case, hence, not REP mode.

2: Knock sensors detecting knocks does not make them functional knock sensors.

It's great that you tried to help. But I think you read too far into the problem in this case and pretty much skipped the issue at hand. I'm a professional mechanic. Does that make me a perfect internet board technician? Hell no. But I do have a very clear cut diagnostic path and extensive diagnostic knowledge on most of the GMT800 platform.

bluebird71

iTrader: (53)

I do see some fraying on the sensor harness wires so I'm gonna just go ahead and replace the sensors themselves no matter what they look like once I'm in there just to be safe. Hopefully that will cure my issues cause it makes my truck run worse every day. The funny thing is that I have reset my ECU a few times by unplugging the battery and doing a re-learn and before the CEL comes back on after a few miles, the truck seems to run fine. Once it comes on though its just gets worse and worse. Could this crappy running actually damage the motor over time?

03klugss

iTrader: (1)

Given that the cost of the knock sensor harness isn't too bad and what's involved in replacing the knock sensors with removing the intake, etc.... I feel it's always best to be proactive and just replace the harness anyways while you are right there and have everything apart. No matter what shape it looks like it's in.

Suburbazine

The crappy running won't damage the motor, although there's a slight chance that it will damage the catalytic converters or foul the plugs.

The truck runs fine after a code clear because it's the code setting that is making it run terrible, not the fact that the sensors are malfunctioning. If the code didn't set (triggering maximum safety mode) you run an insanely high risk of punching holes in your pistons like the one below:

http://www.arcticchat.com/forum/atta...piston_001.jpg