hi, i wanted to know if hot weather temperature can cause engine knock, the temperature im talking about is 94 degrees Fahrenheit during the afternoon.
sometimes my car is perfect without knock and sometimes its knocking, i have noticed that on cooler days or in the evening it doesnt knock.

is hot weather causing the knock or just crappy fuel?

 

hot weather can result in knock. your intercooler will be less efficient in warmer weather. they work off temperature delta, so with a higher ambient temp, there is less delta so the ic wont be able to shed as much heat. this will make your intake temps higher.

 

 

Yes. In contrast, in cool weather our cars knock less and become slightly faster due to more dense air.

 

Temp changes (especially temp increases) shouldn't really cause knock if the car is properly tuned. With temp increase, boost goes down due to the air being less dense, AFR also richens due to air being less dense (less O2). So, one issue could be the timing and fuel maps aren't setup well, or the tuner is being too aggressive, or a combination.

The only time my car has ever knocked due to temperature changes was if it was on pump gas, and the weather was really cold, causing over boost (car was seeing ~28psi instead of the 25ish it was supposed to be at). In which case, the fuel simply can't handle the extra boost regardless of air temp, even though AFR's were still good, and the ECU was dropping some timing with the increased load (boost), it was still knocking. Lowered WGDC to get boost back down, and all was well.

 

^^^this.

i have never seen knock due to hot weather...

typically, it due to cold weather because boost goes up when it is cold.

 

To clear this up, in cold weather, meaning higher oxygenated air, depending on the tune, detonation can occur. It is not just about peak boost rise, but how air is delivered in the engine, how engine boost changes. The ecu is always trying to reach and maintain the preset afr figure at a given load point. Depending on the type of the tune, i.e how aggressive it is or how soft it is, it can compensate afr wise for ambient air changes up to a point, usually 0,2bar on a soft tune, less on a more aggressive tune, not just on peak boost but also in the way air is delivered as I previously said. This does not mean that one will not see any knock, there still might be some level of knock remaining, even if the ecu is retarding timing, surely not as much as if the ecu did not countermeasure. One may not see peak boost rise but still experience the engine knocking due to the differentiation of the air molecular structure and delivery in specific cells.


On the other hand, in hot ambient air conditions, the culprit for any engine damage, is pre-ignition. Although here the afr is usually richer as it is easily maintained and remains the same as the preset figure , but the less oxygenated air in the combustion chamber leaves un-burnt fuel on the table thus a richer afr in exhaust gas is read by the sensor, and although one might assume that since the engine runs somewhat richer it will run cooler, hot spots due to elevated engine temps because of the hotter weather, will occur.










Marios

 

iv'e been testing my car in the morning,noon, and evening...

i have come to a conclusion that it in fact does knock when its over 91 degrees outside usually from 11am till 6pm...from two days i have taken my car in the morning usually 9am and on the same stretch of road with same boost and temps at 86 degrees, and no knock.

if i take my car in the evening after 5pm with temps usually at 82-84 again no knock. but if i take my car at 12 in the afternoon with over 91 degrees it starts to knock.
i guess its a combo of really bad fuel and hot weather causing this.

 

You must have missed the now bolded, italic, and underlined sentence.

That's great that you've test it and your car does that. It points to a tune issue.

As Marios and I said, knock is much more common when temps get colder due to boost going up, and more oxygen in the charge.
If you know what you're looking at in ECUFlash, pull a degree or two of timing, see if knock goes away. Better yet, post a datalog.

 

Don't forget winter gas blend which tends to have less resistance to knock