Knock sensors?????

[glass3222]

I am trying to find out if knock sensors can go bad or what is going on with my truck.

About a week ago I noticed that I am getting some ST knock retard at WOT (all RPMs). It has been ranging from 3 to 5 degrees. I never had that before, so I thought maybe I got some bad gas. I took it easy and ran that tank to almost empty and filled it up with Sunoco 93 octane. Give it a couple WOT runs, still getting 3-5* ST KN. I think, ok maybe try one of the canned tunes instead of the custom 93 tune that I have been running for a while. Install the 91 octane tune DS canned tune, same thing. I return the truck to stock, no tune with 93 octane in the tank, still getting 3-5* ST KN.

Any ideas what is going on?

 

[Redtruck-VA]

The manual says they are bolted to the outside of the block under the exhaust manifold. Do you have anything touching the sensors. Maybe try unbolting them? Or maybe just unplugging them first. Just guessing .....

 

[glass3222]

The manual says they are bolted to the outside of the block under the exhaust manifold. Do you have anything touching the sensors. Maybe try unbolting them? Or maybe just unplugging them first. Just guessing .....

Thanks. I might give that a try tomorrow. It is just not making any sense cuase if they were loose or something was touching them, I would think I would be getting kn at part throttle, which I am not. I watch the throttle percentage on my trinity and I get no kn even at 90+%, but as soon as I hit 100% I get 3-5* pulled.

 

[DaKing]

My harness for two of the knock sensors on the passenger side got burned from the exhaust. the harness was not secured to the transmission, and it rubbed the hot headers. Check your harness.

 

[Redtruck-VA]

Possibly a level of knock is being tolerated until the PCM actually reads 100% thottle and then ******* because the throttle postion at WOT has a parameter that nolonger will tolerate any knock. What does your A/F look like? Stock tune using 93 octane should be clean with no knock. Header noise affecting sensor??? I have heard header ping will affect the sensors

 

[Redtruck-VA]

My harness for two of the knock sensors on the passenger side got burned from the exhaust. the harness was not secured to the transmission, and it rubbed the hot headers. Check your harness.

DaKing, what happens when the sensors are disconnected?

 

[DaKing]

DaKing, what happens when the sensors are disconnected?

I caught the issue before the wires completely milted. They did short out, a bit, but nothing bad.

 

[glass3222]

Possibly a level of knock is being tolerated until the PCM actually reads 100% thottle and then ******* because the throttle postion at WOT has a parameter that nolonger will tolerate any knock. What does your A/F look like? Stock tune using 93 octane should be clean with no knock. Header noise affecting sensor??? I have heard header ping will affect the sensors

I am not sure what my a/f is right now, don't have a wideband hooked up.

I will crawl under my truck tomorrow and see what I can find out.

If I unhook the knock sensors, what will happen????

 

[truckin151]

Have you checked it with Sean to have him look at your logs?

 

[OklaHemi]

just bypass the knock sensor its ******** any way. get a small piece of wire about 2" and strip of the ends then loop it on the business endof the sensor wires and you truck will run fine.

 

[truckin151]

Dont bypass them

 

[glass3222]

Sean told me to log the sensor voltage to see if one side is more than the other or if I am getting a false reading.

 

[OklaHemi]

Dont bypass them

why not

 

[glass3222]

Well, I crawled under the truck, everything seems tight, no wire damage that I could see. I also checked for exhaust leaks since Sean said that could cause a false reading, and I have none.

I sent Sean a log, I am waiting to see what he says.

Anyone have any other ideas?

 

[OklaHemi]

i was not asking that to be a smart ass i really dont know. all i know is that my sister in laws cars stopped running shop said it was the knock sensor and wanted a couple hundred dollars to replaace it. i asked a buddy who is asce certified and he told me how to bypass it. the car has ran fine for the last 3 years

 

[glass3222]

i was not asking that to be a smart ass i really dont know. all i know is that my sister in laws cars stopped running shop said it was the knock sensor and wanted a couple hundred dollars to replaace it. i asked a buddy who is asce certified and he told me how to bypass it. the car has ran fine for the last 3 years

+1. I know it is there to save the engine from detonation, but if it is giving false readings, what would be the problem with bypassing?

 

[truckin151]

Well lets say they are false readings right now so you bypass them, what happens when or if it is doing it for real

 

[glass3222]

Well lets say they are false readings right now so you bypass them, what happens when or if it is doing it for real

I guess then I would get some knock/detonation? This is what I am trying to find out, this is really the first vehicle I have modded that has all of these fancy sensors and **** like that. Before I was always an old school chevy guy building small blocks or big blocks that did not have sensors or any computer controlled stuff

 

[Off_Road_Teacher]

Are you getting any LT knock retard?

 

[Redtruck-VA]

A vehicle that was only transportation and never saw WOT I would consider bypassing. A performance vehicle I would not bypass as it serves as a good indicator that the fuel trim/timing is not right and could well save a piston. Hemi's have a narrow first ring land and detonation can damage the piston. I look at it as just another indicator of what the engine is doing. Same as wtr temp, trans temp and oil pressure.