persistent knock sensor code-kind of fixed?

Post by **darrylrobert** » 11 Feb 2021, 04:14

Im still trying to solve these knock sensor signal high codes, i did mistakenly tighten them thinking they were loose but i now know they are very sensitive to torque. Ive tried several times to torque them to 20nm and still getting codes and slight loss of power.

One thing i remember doing is "fixing" the crankshaft alignment when i replaced the timing belt (my car has a fixed intake timing pulley) as it was way off at the red mark (picture), i moved it back to the green mark. Did a previous owner/mechanic adjust it like this for a reason? as timing effects the knock sensor, does anyone know if this would advance or retard the timing?

: correct timing marks; correct timing.jpg (168.13 KiB) Viewed 2418 times

Post by **abscate** » 11 Feb 2021, 04:38

You’ve advanced the cam timing by moving the cam from red to green in that picture

I don’t think we have ever seen the knock sensor fail here,it’s always something else. I think I’m the only idiot here who bought a new sensor for a knock code, which didn’t solve it.

Post by **darrylrobert** » 11 Feb 2021, 04:44

OK so its currently at the green, if i move it towards the red i would be retarding the timing? I will try this after i check my spark plugs and get the injectors cleaned. Ive read that bad spraying injectors can cause performance issues.

Post by **abscate** » 11 Feb 2021, 04:59

You want those marks aligned, crank amd cam. Playing with this more than a tooth or two runs the risk of bent valves from valve-piston contact. Ouch
I’m not sure what is the correct crank park in your picture. Research that and get that sorted, Mate

Good-day...

Post by **RickHaleParker** » 11 Feb 2021, 05:16

Playing with the timing advance to "cure' a knock code is a kludge. It does not fix the root cause and may damage the engine.
Time it with the blue mark aligned with the green mark then hunt down the source of the knock code and fix it at the root cause.

Post by **RickHaleParker** » 11 Feb 2021, 05:26

darrylrobert wrote: ↑11 Feb 2021, 04:44 OK so its currently at the green, if i move it towards the red i would be retarding the timing? I will try this after i check my spark plugs and get the injectors cleaned. Ive read that bad spraying injectors can cause performance issues.

Too low of fuel octane and carbon buildup in the combustion chambers can cause knocking. Carbon buildup raises the compression ratio. If the buildup is heavy the compression ratio can exceed the octane rating of the fuel.

Try a full tank of high octane fuel and see if the engine quits knocking. If the knocking does quit you got a diagnostic clue.

Post by **erikv11** » 11 Feb 2021, 09:50

You have already corrected the timing by aligning blue and green marks, good move there (and great photo!). Nothing to do or mess with as far as timing. Checking the plugs is a good idea. I'd be surprised if the injectors were dirty but it's possible.

I'd also look very carefully at the connector on the knock sensor harness, make sure no oxidation or other corrosion in there. Check the wiring on that part of the harness too.

Post by **darrylrobert** » 12 Feb 2021, 21:47

thanks for the suggestions, i have been only using high octane premium gas 98RON (93PON) in this car, i could try an octane booster or aviation fuel? I am leaning towards the knock sensors being "too sensitive" or carbon build up?.i will experiment with different locations, the car idles very smooth so hard to believe its a "worn" engine.

UPDATE kinda fixed well no knock code from the rear sensor only one from the front but no hesitation felt due to timing being pulled, i changed the location of the rear sensor one cylinder towards the front (close to the front sensor) i also put a thin copper washer on it. i will further experiment with moving it back to its original location with the copper washers.

My upper engine mount rubber (square type) moves inside the bracket or upper strut is knocking, i can hear it sometimes while coasting however i find it hard to believe this is triggering the knock sensor?

Post by **SuperHerman** » 12 Feb 2021, 23:15

I ran my 2001 XC/70 with standard USA 87 octane and never had an issue with knocking/pinging during the 40-50k miles of ownership.

A few years back I had a 2005 V50 awd and Volvo changed its recommendations from high octane to 87 as it solved some running issues.

Have you done a compression test or leak down test on the engine?

How long have you owned the car, and when did the problems manifest themselves? Do you have the right knock sensor on there? I just don't see a car that was working correctly having knock sensor issues in the direction you are taking - increasing the gap - it would make sense the other way.

Carbon build up would increase the compression ratio (would have to be pretty thick), but that explanation makes more sense.

As I understand knock sensors, it picks up vibrations that are consistent with detonation issues. By adding a spacer I suppose the theory would be you are decreasing the sensitivity of the pick up. This would mean you still have the detonation issues, assuming you have them.

Post by **jonesg** » 13 Feb 2021, 04:00

darrylrobert wrote: ↑12 Feb 2021, 21:47
My upper engine mount rubber (square type) moves inside the bracket or upper strut is knocking, i can hear it sometimes while coasting however i find it hard to believe this is triggering the knock sensor?

An old test used to be tap the block with a hammer, knock sensors would pick it up and cause the idle to blip.
I'd suspect the mount is the problem.