[Burple]

My 01 PT Cruiser suddenly started exhibiting detonation under load w/no codes present or past. Replaced knock sensor and tried higher octane gas, started in middle of tank, no help. Any ideas are welcome.
THANX, Roger

 

[ImperialCrown]

Is the PCM stuck on maximum advance? This may be internal to the PCM. No ignition timing marks, but the cam sprocket marks could be used with an advance timing light. Always diagnose first.
From the Wiki:

 

[Gerry G]

Additional information posted on chryslerforum.com

My 01 PT Cruiser suddenly started giving signs of detonation. Replaced Knock Sensor although no codes were indicated. 180K w timing belt replaced twice, E3 spark plugs w/maybe 20K.Tried higher octane, have used fuel injection cleaner w/every service @ 3K since new, original owner.Where do I look next? Don't understand problem w/no codes. Regularly get emission codes related to PCV hose, have to regularly tighten clamps on hose (added when first code showed). hose replaced at least twice.. I only mention this to indicate code system is functioning. HELP, need a direction to look.
THANX, Roger

 

[ImperialCrown]

Not everything will or can set a fault code. That is why the troubleshooting procedure book has a 'no code' section.
Common causes are advanced timing, high combustion chamber pressures/temperatures and lean mixtures.

 

[Burple]

Not everything will or can set a fault code. That is why the troubleshooting procedure book has a 'no code' section.
Common causes are advanced timing, high combustion chamber pressures/temperatures and lean mixtures.

Where can I reference the book you referred to? Timing in the ecm and possible lean mixtures were my thoughts as well but feel the need to confirm source before throwing more parts at it. I am considering a scan tool w/live data but am unsure what I am looking at. Currently considering a "FIXD", any suggestions?

 

[ImperialCrown]

A tool with data recording that is graph-able later on a laptop is useful for diagnosis. Watch ignition advance and the upstream O2 sensor (or fuel injector pulsewidth) for mixture.
The knock (piezo-electric) sensor should also generate a voltage under detonation that (should) retard spark advance.

Instead of buying an expensive tool, consider paying a shop diagnostic fee (usually the minimum charge of 1 hr) or borrow one (unless you really want the capability for your tool inventory).

 

[Skinpine]

First place to check is the EGR valve and system since you have already changed knock sensor.

 

[ImperialCrown]

An EGR does lower the peak flame temperature (pressure) in the cylinder during combustion.
I would think an EGR malfunction would set a fault code, but they can be checked manually:

How to Test an EGR Valve: A Simple Procedure

Learn how to check an EGR valve in a few minutes to confirm you actually need a new replacement.

axleaddict.com

 

[Gerry G]

An EGR that does not fully close could lean out the air/fuel mixture and not set a dtc. The EGR would be able to open sufficiently to pass the EGR test, just would not close completely.

 

[Burple]

Thanks, after more research and head scratching, I've come to agree w/EGR diagnosis and have one ordered. This is my newest vehicle by far, so my preferred shop does not have needed live data scanner. Really not trusting of most other local shops, especially local Dodge and Chrysler dealers. Will report back w/results. Thanks to all who answered.

 

[ImperialCrown]

The black, plastic transducer comes with the valve. Make sure that you can pass air through the metal tube and head passages.
The bottom half of the transducer diaphragm was fed by exhaust gas to measure back-pressure and meter the amount of EGR accordingly.
The electric solenoid allowed EGR when the engine reached a certain temperature. You don't want or need EGR on a cold engine.

 

[Fast Eddie]

A tool with data recording that is graph-able later on a laptop is useful for diagnosis. Watch ignition advance and the upstream O2 sensor (or fuel injector pulsewidth) for mixture.
The knock (piezo-electric) sensor should also generate a voltage under detonation that (should) retard spark advance.

Instead of buying an expensive tool, consider paying a shop diagnostic fee (usually the minimum charge of 1 hr) or borrow one (unless you really want the capability for your tool inventory).

Back in the 60's and 70's at the Chrysler Tech Center we used to do Octane Testing for all our production engines like this. We would bring in 5 gallons of gas of each octane from 80 to 102 using only the even numbers for actual testing into the dyno test cell. This was back when the dyno operator was in the cell right next to the engine. There were NO walls of any kind for protection. We would start the test at 800 rpm at WOT and go up in speed every 400 rpm till we got to 4800 rpm. While the dyno operator ran the dyno the engineer would plug in one of the cans of gas and advance the spark till he could hear the engine knocking. He would stand right next to the engine as close as possible to hear the initial pinging. Then he would unplug the gas can and plug in the next octane and repeat the procedure. Every time you would unplug the quick disconnect gas would splash out. By the time you got to 3200 rpm or so the exhaust manifolds would be red hot. It was truly amazing through all those years nobody got hurt or there were no fires or explosions. From 3200 rpm and on the sound of the engine was incredible. Of course we wore ear muffs for sound deadening but they didn't help much. Around the 1980's OSHA came in and said that will be enough of that and sound proof walls were built and the operator and the engineer were in another room. Around the late 70's we got Scopes and pressure transducers so we could actually see the detonation and the pressure spikes more safely. At the end of the test we had spark curves for each speed and octane and that's how they determined what the spark advance would be.