07 5.3 Knock Sensor Issue

[Kwing]

So my 07 Tahoe, with it's new engine, came up with the left bank knock sensor low voltage code. I tried to look online, but everything i'm finding is for the previous gen 5.3 with the sensors under the intake. Mine are on either side of the block by the motor mounts. Since I can't find anything online for mine, I'm here to look stupid again.

I replaced both knock sensors. Truck ran grest, light went off (i reset the computer). 20 minutes later, truck lost it's power and the light czme back on.

Connectors are clean looking, wires up to the rest of the ECU harness look good.

I don't want to cut open the harness to check the whole length of wire if i don't have to.

Suggestions?

 

[Kraig]

Truck lost it’s power—like it went into limp mode, or it shut down?

 

[Kwing]

Truck lost it’s power—like it went into limp mode, or it shut down?

Like accelerating feels like a type 1 VW that needs a tune up pulling a fully loaded trailer up a hill.

You push the pedal and there is literally no reaction for 3 or 4 seconds, then from there to speed i can just hear the poor girl chanting "i think i can, i think i can".

Once it's up to speed it's ok, but again if i accelerate to pass or something it has no balls.

My mileage after the engine swap was 14.7mpg, now it's 11.4.

The problem is better the colder it is outside. Much worse on hot days. Engine temp, however, does not seem to effect it. Only ambient temp. That could just be coincidence.

The knock sensor is the only code.

 

[Kraig]

What brand knock sensors did you use? Did you torque them to spec or crank to tight enough?

 

[Kwing]

AC Delco's. I ordered them from Rock Auto.

I torqued them per the manual using the new bolts that came with the sensors.

The fact that the re-failure was pretty much instant, that it's consistent (not intermittent), and that it stayed on the left bank before and after the sensor swap makes me think the root cause is somewhere other than the sensor itself...

 

[swathdiver]

So my 07 Tahoe, with it's new engine, came up with the left bank knock sensor low voltage code. I tried to look online, but everything i'm finding is for the previous gen 5.3 with the sensors under the intake. Mine are on either side of the block by the motor mounts. Since I can't find anything online for mine, I'm here to look stupid again.

I replaced both knock sensors. Truck ran grest, light went off (i reset the computer). 20 minutes later, truck lost it's power and the light czme back on.

Connectors are clean looking, wires up to the rest of the ECU harness look good.

I don't want to cut open the harness to check the whole length of wire if i don't have to.

Suggestions?

Did you try swapping sensors and swapping in the old known good sensor on both sides? Are you getting P0327 or P0332?

From the shop manual:

DIAGNOSTIC AIDS
 Inspect the KS for physical damage. A KS that is drop or damage may cause a DTC to set.
 Inspect the KS for proper installation. A KS that is loose or over torqued may cause a DTC to set.
 The KS mounting surface should be free of burs, casting flash, and foreign material.

CIRCUIT/SYSTEM TESTING
P0325, P0327, P0328, P0330, P0332, or P0333
1. Ignition ON, engine OFF.
2. Disconnect the appropriate KS harness connector.
3. Measure for 2-3 volts between each of the following circuits and ground on the ECM side of the harness
connector.
 The KS signal circuit terminal A
 The KS low reference circuit terminal B
 If less than the specified range, test the circuits for a short to ground or an open/high resistance. If
the circuits test normal, replace the ECM.
 If greater than the specified range, test the circuits for a short to voltage. If the circuits test normal, replace the ECM.
4. If all circuits test normal, replace the KS.

 

[Kwing]

Swath, thank you for the diagnostic proceedure. I will have to give that a try.

The code is P0332.

I know the torque is right, but I hadn't thought of burrs or debrit on the flanges. I'll have to pull them back off and check the condition of the surface(s).

I would think if the ECU was bad there would be other issues and/or symptoms. Wouldn't it?

I'll just have to run the tests and see I guess.

 

[gpracer1]

Almost sounds like fuel pump low pressure or fuel starvation/filter, runs lean under acceleration then you get knock and it goes to limp.

 

[Kwing]

Almost sounds like fuel pump low pressure or fuel starvation/filter, runs lean under acceleration then you get knock and it goes to limp.

If it was actually an issue with detecting too much knock, would it really throw at "low voltage" code?

I thought voltage went up with a knock detection. I very well could be wrong though

 

[BG1988]

So my 07 Tahoe, with it's new engine, came up with the left bank knock sensor low voltage code. I tried to look online, but everything i'm finding is for the previous gen 5.3 with the sensors under the intake. Mine are on either side of the block by the motor mounts. Since I can't find anything online for mine, I'm here to look stupid again.

I replaced both knock sensors. Truck ran grest, light went off (i reset the computer). 20 minutes later, truck lost it's power and the light czme back on.

Connectors are clean looking, wires up to the rest of the ECU harness look good.

I don't want to cut open the harness to check the whole length of wire if i don't have to.

Suggestions?

could be bad gas

bought 87 and got 85 octane


Get some octane booster

 

[Kwing]

could be bad gas

bought 87 and got 85 octane


Get some octane booster

This has been going on for months with many hundreds of gallons of gas from several different stations. Arizona does not have 85 octane available anyway, so if that happened the delivery truck would be WAY of course

 

[BG1988]

This has been going on for months with many hundreds of gallons of gas from several different stations. Arizona does not have 85 octane available anyway, so if that happened the delivery truck would be WAY of course

(secondary fault )
engine coolant temperature sensor could have an issue it's staying at the correct temp ?? right? 99C

 

[Doubeleive]

have you done any mods or changed anything from stock under the hood?, a knock sensor detects knock wherever the source may be...
I have seen bad maf sensors cause a whole slew of other issue's also, just something to possibly consider
could be a bad (new) knock sensor also like James mentioned

 

[Kwing]

have you done any mods or changed anything from stock under the hood?, a knock sensor detects knock wherever the source may be...
I have seen bad maf sensors cause a whole slew of other issue's also, just something to possibly consider
could be a bad (new) knock sensor also like James mentioned

Bone stock. No mods of any kind anywhere, not even cosmetic.

If it was the temp sensor or MAF, would i see a fault code?

It is holding temp just fine BTW

 

[kbuskill]

I didn't realize the torque on these was that crucial... when I swapped mine i just tightened them up to what i thought would be good... not overly tight but good and snug so they wouldn't rattle around... no issues with mine after install so i must have guessed correctly... lol

 

[Doubeleive]

Bone stock. No mods of any kind anywhere, not even cosmetic.

If it was the temp sensor or MAF, would i see a fault code?

It is holding temp just fine BTW

a bad or failing maf wouldn't necessarily throw a code in the beginning it would eventually, I have seen them cause misfires, rough idle, loss of power, transmission shift problems, cause 02 codes, cause throttle body codes, surging, just all kinds of problems, a bad knock sensor would MOST likely just throw code and maybe cause some pinging, I think it would be unlikely to cause much if any loss of power like you are describing (maybe it could) but I have never seen it happen, seen plenty driven around for quite a while with no noticeable problems other than a check engine light. I'm not saying run out and buy one, but maybe get a can of MAF cleaner and clean it and the throttle body and swap those knock sensors and see if the problem follows the knock sensor and/or if the power issue re-occurs.