Detonation - 01 Disco

nolift911

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Feb 19, 2006
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01 Disco - been trying to resolve this for some time. Pinging and detonation (sounds like drivers side) marbles when accelerating, worse when warm out. No noise at idle or revving. I replaced a number of accessories thinking that might be the culprit. I use 92/93 octane. Have never heard detonation like this. No codes. Unplugged a knock sensor, no change and no codes - is that possible? Had head gaskets done and new heads 10k ago, no issues then except now have the detonation that has been going on for a month or so. Runs fine otherwise. Something in the heads? Other causes? Do knock sensors go bad? What should they read with a meter?

Thanks in advance
 

jastutte

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Nov 10, 2009
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are you sure there are no codes? i almost always have a knock sensor code but it doesn't trigger the SES light.
 

jymmiejamz

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You could try swapping the knock sensors from side to side. I recently ran into a RRS where a tech replaced the engine and had plugged the knock sensor harness connectors on the wrong banks. When it was detonating the PCM was making corrections on the wrong bank.

If swapping the knock sensors doesn't change anything I would check the wiring to the PCM. Outside of a sensor or wiring issue, I don't see how it is possible for a modern engine to detonate excessively.
 

nolift911

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Feb 19, 2006
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Thanks for the replies. After 2 indie mechanics and a trip to the dealer (with some seasoned techs) everyone is stumped. No codes, no running issues, lots of power, great gas mileage (350-375) per tank, no other obvious issues, knock sensors working, no MAF issues. Had an upper engine intake cleaning, injectors done as well and fresh plugs gaped correctly, always run 92/93/94 octane. I do have a theory. See if this holds water. The engine is a remaned from AB, top hat etc. After I got the engine the HG's started to leak so I had a shop redo the heads. They sent out the heads to be decked just to be sure. So with a remaned block, and decked heads is it possible that these to pieces have been decked more than once or twice or three times and now I have a high compression issue? In that the motor is now running higher compression due to both surfaces being cut - too much. What should stock compression be on these motors? Am going to try and put in a mix of race gas to see if that calms it down a bit. I have been looking for a colder plug for the motor as well (without much luck) to see if I can get the detonation to subside. Does anyone have a colder range plug they recommend other than a NGKBR6ES?

Thanks -
 

Swedjen2

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Sep 12, 2018
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"Unplugged a knock sensor, no change and no codes - is that possible?" How about - no signal.

Then you said in your post taday that - "knock sensors working"

So the 2 indie and dealer techs confirm you knock sensors are working?
 

nolift911

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Feb 19, 2006
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Good points - so I took the knock sensors off and tested them with a meter, they are doing something. If that something is what they should be doing, I don't know it seems they are hard to test. I have gotten mixed feedback from techs on if an unplugged knock sensor will throw a code or not - general consensus is they will not throw a code, unless they are "bad". The other general consensus is that knock sensors rarely go bad. They didn't seem to think that was the issue - so when 3 techs look at the car and look in another direction so do I.

At this point I am open to suggestions for sure. If you guys unlplug the knock sensor on your trucks does it throw a code? Do they go bad a little bit as in wear out or just bad as in works or doesn't?

The other line of thinking is that are these trucks on the ragged edge of detonation all the time as in the computer constantly checks for detonation and in the absence of a properly functioning sensor the truck detonates all the time? I always thought in extreme heat or poor quality fuel situations the knock sensors kick in and then retard the timing until the detonation goes away.

So in other news I thought $45 in spark plugs was worth a shot and installed the Champion RN8WYPB3 plugs which is a "colder" plug. I think stock is an 11 or 12 heat range. Didn't fix the issue but definitely helped. Not sure what that means in the grand scheme.

Certainly open to suggestions and appreciate the feedback.
 

p m

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The other line of thinking is that are these trucks on the ragged edge of detonation all the time as in the computer constantly checks for detonation and in the absence of a properly functioning sensor the truck detonates all the time?
I seriously doubt that, given the minimal difference in power and fuel consumption between Lucas 14CUX, GEMS, and Bosch trucks. Bosch trucks do run hotter, somewhat.
 

jymmiejamz

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I think at this point I would want to put an oscilloscope on the knock sensors to confirm it is in fact detonating and also to determine which cylinders are detonating. If you have someone hook a scope up to it (every Land Rover dealership should have a Picoscope at this point) they need to put a probe on an injector or plug wire to have a reference point of what is the start of the firing order. From that point you could determine if there is a faulty knock sensor or something else. It seems very unlikely to me that a modern engine management system would allow much detonation.

Here is an example waveform (zoomed in) of detonation. If you look at the bottom right corner you can see the knock sensors picking up each time a cylinder fires and also when it is detonating in-between combustion events.
 

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nolift911

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Feb 19, 2006
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So knock sensors, when I tested them they did spike in voltage when I would tap them when hooked up to my meter (that was my "they are doing something" observation) at $63 for two, I ordered the knock sensors, at 312,000 miles I think I am due anyway and can rule that out.

The biggest observation I have thus far is that the colder plugs made a big difference. I think if I had one step colder it would probably eliminate all together. Does anyone know of a coder plug other than the Champion RN8WYPB3? The cross reference charts are dizzying - NGK plugs are the opposite, the lower the number the hotter the plug, but its hard to tell within the family of plugs which are the coldest that still fit the truck. I also ordered a new set of wires (not that I think that is the issue) but in replacing plugs and testing this and that I have two that now have pulled through boots - ugh.

I would like for someone like PTSchram to weigh in on the compression theory with all the motors he has seen - either not possible or could be?

Any good sites for plugs?

Thanks again for the info -
 

rovercanus

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Apr 24, 2004
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I'm running 4.0 pistons on 4.6 rods for high compression and don't get detonation. If your heads and motor were skinned enough to cause compression problems your lifters would probably be extremely unhappy with the pre-load.
P.T will just tell you how big a genius he is and will tell you to ship the truck to him then call you a cheap fuck for not wanting to spend eleventy-billion dollars to fix it.
 
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Run away from all of the techs you spoke to.

Knock sensors are so easily tested, it's laughable. Bang on a valve cover with a deadblow hammer, your knock sensors should recognize that as knocking.

As for the compression issue, if that was truly the case, the EMS would have detuned the engine to such an extent you wouldn't be experiencing the fuel economy you claim. The whole reason we have knock sensors is to allow these engines to operate at their peak potential (yeah, I laugh too), if one increases the compression enough, the knock sensors will take care of you jsut fine!

I doubt you have detonation but suspect it is something else that sounds like detonation, could be an exhaust leak, busted cat, even loose heat shield around a cat, detonation-unlikely unless you're badly overtemp, VERY poor fuel, disconnected knock sensors (FWIW, I have screwed knock sensors in wherever I could find a handy spot with no repercussions), OR something mysterious, but BAD happened in one cylinder/combustion chamber that is causing a localized hot spot.

When I hear hoofbeats, I look for horses, not zebras and I think you're chasing a zebra here.
 

nolift911

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Feb 19, 2006
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OK. Its detonation. If I put colder plugs in it almost goes away. Still there just less severe. Its not a cat, or an exhaust leak. I don't have heats shields, those rusted away at 280k. Same for the starter heat shield. I am not a master tech but I know what detonation sounds like.

What is a "hot spot" on a cylinder? What would that look like on a scanner?
 

jymmiejamz

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I doubt you have detonation but suspect it is something else that sounds like detonation
This is exactly why I think at this point someone needs to put a scope on it.

The waveform I posted was one I took to prove an engine was detonating when our foreman was convinced it wasn't. That vehicle got a new motor (replacement of the replacement), two cats, and a supercharger because no one took the time to actually diagnose it.