Knock Sensor Faulty?

[davidti]

1997 Thunderbolt V with ICM and piggy-backed knock module mounted on left exhaust manifold. Runs great at wide open throttle for a good while then the timing suddenly changes and rpm must be reduced to near idle for a while before rpm can be increased. I think the knock module is bad. Can I just disconnect it? What happens if I run all day without it? Since there is no knock and no timing issues until it suddenly changes, seems module is the problem, not knocking or timing or overheating. Thoughts?

 

[itsathepete]

Why do you think the timing is being retarded? Did you put a timing light on it? Or are you basing this on symptoms?

 

[Bondo]

Runs great at wide open throttle for a good while then the timing suddenly changes and rpm must be reduced to near idle for a while before rpm can be increased.

Ayuh,..... Welcome Aboard,...... Please explain the statement I quoted,..??..??

 

[achris]

What engine is this on? (Serial number would be nice )

 

[davidti]

Why do you think the timing is being retarded? Did you put a timing light on it? Or are you basing this on symptoms?

Symptoms.

 

[davidti]

Ayuh,..... Welcome Aboard,...... Please explain the statement I quoted,..??..??

Loses power, stumbles at full throttle after its been running well. Throttle must be backed down for a period of time until problem disappears.

 

[Bondo]

Loses power, stumbles at full throttle after its been running well. Throttle must be backed down for a period of time until problem disappears.

Ayuh,..... Examine the Contents of the fuel filter for anything but clean fresh gasoline,.......

It's goin' lean,.....

 

[davidti]

Symptoms.

The purpose of the Knock module is to reduce timing to eliminate detonation. There is no detonation. The stumbling and loss of power feels like retarded timing based on my experience with a chevy 350. I think the KM is reducing timing when it should not.

 

[davidti]

Ayuh,..... Examine the Contents of the fuel filter for anything but clean fresh gasoline,.......

It's goin' lean,.....

Thought of that but then why does it perform flawlessly for over an hour then out of nowhere cut out? Then, after a period of low rpm, resume flawless performance?

 

[AKJohne]

I have the same ignition system, same year. Mine is mounted on the back of the motor, but no difference, if you think the timing is retarded based on symptoms, you need to verify with a timing light first.

You can check the knock sensor with a scope, or you can have a buddy tap on the block while holding a timing light on it, if knock sensor is working you will see the timing back off. I think I did this around 2K while on the muffs.
You can unplug the knock sensor and try it, prior versions of the TB ignition did not have knock sensor, I think it has value and a good device if working correctly.

 

[achris]

Thought of that but then why does it perform flawlessly for over an hour then out of nowhere cut out? Then, after a period of low rpm, resume flawless performance?

You know what that's a classic symptom of? Lack of fuel .. Check your filters, check the vent line isn't clogged. Next time it does it, loosen the fuel full cap, and listen. If you hear air being sucked in, it's a vent hose problem...

Timing is almost the last place any of us would be looking.

Chris....

 

[itsathepete]

Ever heard of Occam's Razor? It means when looking for an answer to a problem, the simplest explanation tends to be the right one. In other words, if it looks like a duck... Your symptoms are classic lack of fuel

 

[nola mike]

...

Timing is almost the last place any of us would be looking.

Chris....

Especially from an over exuberant knock sensor

 

[rustybronco]

Why would they mount a knock sensor on an exhaust manifold? Wouldn't it be block mounted?

 

[rustybronco]

Why would they mount a knock sensor on an exhaust manifold? Wouldn't it be block mounted?

Sorry, you were referring to the module.

 

[achris]

Why would they mount a knock sensor on an exhaust manifold? Wouldn't it be block mounted?

Sensor itself is on the back of the cylinder heads. The module is mounted next to the ignition module...

Chris...

 

[davidti]

Thank you all for your much appreciated input. Let me say first that the TITLE of this thread/post is WRONG. It should have said "Knock MODULE Faulty?". I know the SENSOR screws into the block. The MODULE was added to the TB V, screwed to the ICM mounted on the left exhaust manifold. It added a signal switch to the path between the knock SENSOR and the ICM. I also thought at first this was a fuel flow issue because there is never any sign of detonation. What puzzles me is that if it IS a fuel flow issue, why does it take so long to show up? Engine temp? No sign it runs hot. The ICM keeps count of fault signals before reacting. If the knock MODULE keeps signalling, wrongly, to the ICM that it is receiving a knock SENSOR detonation signal, eventually the ICM will send a signal to the distributor to retard the timing. This, to me, explains why the engine performs flawlessly for a long time at wide open throttle, THEN starts to act up. If, instead, it is a fuel flow rate/pressure problem, why would not that show up immediately and all the time?

 

[nola mike]

Thank you all for your much appreciated input. Let me say first that the TITLE of this thread/post is WRONG. It should have said "Knock MODULE Faulty?". I know the SENSOR screws into the block. The MODULE was added to the TB V, screwed to the ICM mounted on the left exhaust manifold. It added a signal switch to the path between the knock SENSOR and the ICM. I also thought at first this was a fuel flow issue because there is never any sign of detonation. What puzzles me is that if it IS a fuel flow issue, why does it take so long to show up? Engine temp? No sign it runs hot. The ICM keeps count of fault signals before reacting. If the knock MODULE keeps signalling, wrongly, to the ICM that it is receiving a knock SENSOR detonation signal, eventually the ICM will send a signal to the distributor to retard the timing. This, to me, explains why the engine performs flawlessly for a long time at wide open throttle, THEN starts to act up. If, instead, it is a fuel flow rate/pressure problem, why would not that show up immediately and all the time?

There are plenty of other reasons for an intermittent problem to show up. This is easy to test, just hook up a timing light.

 

[davidti]

Thank you all for your much appreciated input. Let me say first that the TITLE of this thread/post is WRONG. It should have said "Knock MODULE Faulty?". I know the SENSOR screws into the block. The MODULE was added to the TB V, screwed to the ICM mounted on the left exhaust manifold. It added a signal switch to the path between the knock SENSOR and the ICM. I also thought at first this was a fuel flow issue because there is never any sign of detonation. What puzzles me is that if it IS a fuel flow issue, why does it take so long to show up? Engine temp? No sign it runs hot. The ICM keeps count of fault signals before reacting. If the knock MODULE keeps signalling, wrongly, to the ICM that it is receiving a knock SENSOR detonation signal, eventually the ICM will send a signal to the distributor to retard the timing. This, to me, explains why the engine performs flawlessly for a long time at wide open throttle, THEN starts to act up. If, instead, it is a fuel flow rate/pressure problem, why would not that show up immediately and all the time?

FYI, I of course, will replace the fuel filter since that's a cheap fix. If that fixes it, great. If not, then I will disconnect the knock MODULE and see if that does it. If it does, then I will get a new ignition kit that replaces the ICM, knock module, and distributor altogether.

 

[nola mike]

Thought of that but then why does it perform flawlessly for over an hour then out of nowhere cut out? Then, after a period of low rpm, resume flawless performance?

Open your gas cap when the symptoms happen, this could be a clogged vent