Knock sensor is a PITA

[gp1991]

i have had an issue with the knock sensor for quite some time. The car would run normal, but when the SES light would come on, it would bog down hard, and right when that light came off, back to normal. The code was 43, for the knock sensor. I had the part replaced and the part did test to be bad using the multimeter, but now it seems as if the problem is not totally gone. Now i still pull code 43, but the SES light is nearly always on, but it does not bog down hard. However, i do feel like i am down power from before when it would run good when the old knock sensor was not fucking up. i reset the ECM just for fun with no luck. Any ideas at what i could look at next would be much appreciated.

[RobertISaar]

wiring. especially when dealing with anything that can generate a frequency around knock frequency (~5000Hz or so).

 

i can post the flowchart for dealing with the DTC43 if necessary.

[gp1991]

So i would need to replace the wiring leading to the sensor?

[RobertISaar]

possibly. but there are a lot of other things that could be causing it as well. setting the DTC requires either a lot of constant knock or the circuit itself has to be out of an acceptable range.

[Cutlass350]

Who replaced the knock sensor? If it was a real garage/dealer, have them fix it.

 

My guess is that it was not. In that case, there's a good chance that the sensor was not put in correctly. Or, a non-GM sensor was used.

 

A few very important tips on replacing a knock sensor (check your GM manual):

1) It must be installed to the correct torque. That requires a small N*m (in/lbs) torque wrench. Don't even think of using a ft/lb torque wrench - it's 100% useless at that low valve.

2) If the sensor is over torqued, or dropped, it's garbage.

3) Use, or do not use, anything else on the threads (like anti-seize) unless your GM manual says to for that year and motor!

4) The non-GM knock sensors have a high failure rate. They are a huge gamble, and often just a waste or money.

 

5) If you buy a brand-new GM engine, it does not come with a knock sensor. If you install your expensive GM knock sensor "by hand", there's a good chance that once the engine is installed and running, it'll be throwing knock sensor codes. Then, you'll end up buying another expensive GM knock sensor. Plus, you get the "fun" of having a very hard ********ing time replacing that now very buried PITA knock sensor!

 

6) There is no such thing as a "cheap" (under $50) in/oz torque wrench that is worth anything other than for the seller to make money by selling worthless garbage to someone. Other than installing a plastic intake and the knock sensor, there's not much real use or need for that tool. :-P

 

7) Amazon has good prices for stuff like that. But, you need to search Amazon using the GM part number, and it may take an additional ~1-10 days for delivery.

 

Good Luck!

Edited April 28, 2012 by Cutlass350

[Cutlass350]

and the part did test to be bad using the multimeter

??

 

You can't test your knock sensor with a DVM. The knock sensor gets an AC signal from the ECM, and the knock sensor then attenuates the AC signal based on the acoustic response of the knock sensor and any acoustics.

[gp1991]

it was replaced by a small shop that is owned and run by our neighbors brother and his son, and as far as the part they used, i have no idea if they used a proper one or not. i did give them a call back earlier today and he told me he is going to take the weekend researching more on the issue. He is a really cool guy tho, so all of this information that you guys give me i can discuss with him as well and its not like he will get pissed or anything like that. Im just trying to figure out what the hell is going on, because at least it ran better before the sensor was replaced and only shitty sometimes, now it just runs partially shitty (in comparison) all of the time.

[RobertISaar]

You can't test your knock sensor with a DVM. The knock sensor gets an AC signal from the ECM, and the knock sensor then attenuates the AC signal based on the acoustic response of the knock sensor and any acoustics.

 

you can do a basic test on the sensor... if it has a resistance too far from 3900 ohms, it will be bad no matter what.

[Cutlass350]

Im just trying to figure out what the hell is going on, because at least it ran better before the sensor was replaced and only shitty sometimes, now it just runs partially shitty (in comparison) all of the time.

 

I'm not sure what you mean by runny poorly.

 

With a bad knock sensor, the ECM will limit timing. So, the car will have less power, worse gas mileage, and poorer gas mileage.

 

One issue is that, for whatever *******ed reason, the GM Tech1 scanner does not show any value at all for the knock sensor reading. The Tech1 will show if the knock sensor "is active". BFD! So, if there's a bad wire, bad connection, etc, there's no easy way to tell.

 

 

If only one knock sensor "went bad again" after the shop installed it, it may be that they got a bad knock sensor. Don't forget, there are a lot of people that sensor will go through before it gets to the garage. As I mentioned, the GM manual has many warnings about the proper handling and installation of that POS sensor. Who knew? I know that I didn't.

 

Also, these generation sensors have only a single wire contact. Yea, besides being so delicate that they break if you look at them wrong , they have a cheap and very poor single wire design. Plus, the sensor uses the engine as ground. WTF?? For an ECM sensor, that's a very very bad idea. Still, more importantly, that terminal connection/type is a poorly design.

Really, these knock sensors look like someone designed them back in 50's when no one cared about any of this stuff, and if a sensor didn't work, no one cared.

 

From a sensor, ECM point of view, these knock sensors are joke. But, then again, "they worked well enough".

 

The new knock sensors are very different. They have multiple wires, and they use a bolt to bolt the "disk" onto the engine. No more screwing in a delicate piezo sensor into the engine block.

 

 

 

 

So,...

It could be that the shop just got a bad sensor. That's likely and does happen.

 

Or, it could be that the sensor's connector is loose. That again happens because of the poor design. Also, it's very easy to stress the single contact while removing or installing the connector.

 

Or, it could be a bad wire.

The looms that GM used where of cheap quailty staring in the 80's. For my 200 Olds, I replaced a good portion of the original looms - they either cracked, crumbled, or crumbled when I squeezed them. The point is that a poor or non-existent wire loom can cause a wire to fail from abrasion, tear, etc.

 

 

 

Hmm, I may have just remembered something...

I *think* that when my knock sensor wasn't working, it may have effected the trim values after a while.

Maybe after a bad knock sensor was detected, instead of just limiting the max timing advance, the ECM also went to a more retarded base timing? If that was the case, an engine wouldn't run as smooth, it would use more gas, and *the trim values would be modified to keep the proper A/F ratio with the retarded timing*.

But, I honestly do not 100% remember if the trims where effected at all, and I know that I would not have noticed a change in the base timing. I was more worried about having knock/detonation in my new engine without a working knock sensor. So, I didn't drive the car much until I replaced the knock sensor. (And, I used on hi-test gas.)

 

 

Good Luck!

[RobertISaar]

the tech1 may not show knock A/D, but it's easy enough to view using tunerpro and knowing the RAM location it's stored to. this being an $A1 application, i can certainly help here.

 

and yes, retarded timing WILL effect BLM/INT.

[Schurkey]

A few very important tips on replacing a knock sensor (check your GM manual):

1) It *must* be installed to the *correct torque*. That requires a small in/oz torque wrench. Don't even think of using a ft/lb torque wrench - it's 100% useless at that low valve...

 

...6) There is no such thing as a "cheap" (under $50) in/oz torque wrench that is worth anything other than for the seller to make money by selling worthless garbage to someone.

Inch/Oz is smaller than anything I've ever seen in a catalog. Sure you don't mean inch/Lb? 120 inch/lbs is 10 ft/lbs.

 

An old-school "deflecting beam" inch pound torque wrench won't cost $50, and if made by a reputable company (not the damned Chinese) are very accurate. They don't need calibration, and in fact the only downside to them is that they're inconvenient to use properly, but completely convenient to use improperly. I've got two of 'em (long story) each with a 0--120 scale, so if you want one, send me a PM for details.

 

Plus, the sensor uses the engine as ground.

Thanks for reminding me. You just saved me hours of rework. Much appreciated. Any good way of reducing the sensitivity of the knock sensor?

Edited April 28, 2012 by Schurkey

[Cutlass350]

Inch/Oz is smaller than anything I've ever seen in a catalog. Sure you don't mean inch/Lb? 120 inch/lbs is 10 ft/lbs.

 

Opps, typo.

You're right, I meant in/lbs.

For my 2000 Olds, the spec is 15 N*m or 133 in/lbs. That equals ~11 ft/lbs. In general, a torque wrench is only useful (dependable) between 20% and 80%. Some use 25% to 75%.

 

I bought a 3/8 torque wrench (low range) from Sears when I did my engine swap. IMHO, there is no way I'd trust hand tightening a plastic intake. Hand tightening a plastic intake would be asking for future problems, and could lead to a grenaded engine. So, I did have a low range torque wrench when I put the first knock sensor in my new engine. I just didn't think that knock sensors could/would be damaged by "typical hand tightening". I figured that at worse, it would be a little more sensitive. The LX5 doesn't have knock issues under typical driving. So, I didn't worry.

Edited April 29, 2012 by Cutlass350

[Cutlass350]

Any good way of reducing the sensitivity of the knock sensor?

Nope.

 

Also, you wouldn't want to. As I found out, the ECM checks to see if the knock sensor is working. It's very very vague in my GM manual. But, it's basically that the ECM looks for "some range of value" if the throttle, load, and speed are in a certain range (basically at cruise on the highway - forget about it being tested in city driving).

 

Also, if there is engine knock, you want the ECM to pull timing - asap. Knock is bad. Knock is pre-ignition/incorrect-ignition of the air/fuel mixture in the cylinder. That leads to additional stress and wear. Plus, less HP, less gas mileage, and poorer emissions.

 

Unlike the BS that Chrysler used to shovel "knock is not the sound of economy", nor a well tuned engine, nor better gas mileage, nor more power, etc. Chrysler would run their engines lean to get better gas mileage. Of course, that was before the wide spread use of EFI and the resulting years of EFI experience like we have now.

Edited April 29, 2012 by Cutlass350

[Schurkey]

In general, a torque wrench is only useful (dependable) between 20% and 80%. Some use 25% to 75%.

What I see in the tool catalogs is a % tolerance (for example, within 3%) from 20% to 100% of "full scale" or the highest marking on the wrench.

 

My 100-ft/lb 3/8 drive is supposedly accurate within 3%, for any torque within 20 ft/lbs (20% of 100) to 100 ft/lbs (100% of 100) clockwise, and accurate within 4% or 5% from 20 to 100 ft lbs. counter-clockwise.

 

Accuracy at full-scale doesn't seem to be a problem. Accuracy at the low end is.

 

Nope.

 

Also, you wouldn't want to. As I found out, the ECM checks to see if the knock sensor is working. It's very very vague in my GM manual. But, it's basically that the ECM looks for "some range of value" if the throttle, load, and speed are in a certain range (basically at cruise on the highway - forget about it being tested in city driving).

 

Also, if there is engine knock, you want the ECM to pull timing - asap. Knock is bad. Knock is pre-ignition/incorrect-ignition of the air/fuel mixture in the cylinder. That leads to additional stress and wear. Plus, less HP, less gas mileage, and poorer emissions.

Yeah, but both of my 3.4s have either got the GM-acknowledged lifter tick problems (possible, and I'm fixing that) or they've got the GM-denied piston slap. Either way, the knocking is loud as hell and I suspect that the knocking is affecting the knock sensor. My mileage is reduced, the scan tool shows timing retard; and it's NOT from detonation.

 

Unlike the BS that Chrysler used to shovel "knock is not the sound of economy",

Chrysler? That was GM; from approximately the time frame of the Vega 2.3.

[GP1138]

In any case, the knock sensor is really not that hard to get to -- remove the alternator and stick your hand down there. Likely the wiring is bad and not the sensor itself.

[gp1991]

just thought i would update this, the sensor was replaced, and after that i brought it back in and he ran resistance tests on the wires, and simply plugged them all back in, and it worked. So there must have been a loose wire or something, because it has been working good now for a week or so.