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Old 03-07-2021, 10:02 PM   #1
agentclank777
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Default Un-Explained engine knock

It would seem any time I accelerate hard there is a brief moment of some kind of knock, I went out of my way to make a circuit capable of communication with the aldl port on my 1995 saturn sl2 to find out what's been going on with my car as many mechanics I have taken it to have given me false fixes and cost me great deals of money to fix nothing. I have attached an image showing that the timing throws it itself way off when the knock event occurs.
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Old 03-07-2021, 11:43 PM   #2
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Default Re: Un-Explained engine knock

If you have more info, you could get more help. "Accelerate hard" and "knock" can be hard to pin down to exacts. If you are in open loop you should rarely if ever get knock, below that it can happen from time to time for brief intervals.

What type of acceleration conditions, temp of the coolant, operating conditions, etc.... would all be helpful.


I know my SL1 would at times produce some audible knock under moderate acceleration when it was at a certain warming up temp, under coolish conditions. For some reason under those conditions it was apparent, but only for a brief window of operating conditions. I suspect it had something to do with factory programming flaws specific to that cars programming.


If you have an audio track of the conditions it might help people here. A light ping is IMHO, not a knock. But even a light ping shouldn't be a regular thing with most cars either.


I suspect you have tried the obvious approaches such as cooler plugs, higher octane fuel, etc?
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Old 03-08-2021, 12:23 AM   #3
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Default Re: Un-Explained engine knock

If you can log engine data, then post all and in a clearer format than a photo; I suggest PDF.

Without rpm and MAP it is not possible to even make a serious guess as to what spark advance and injector pulse should be, but I think that log in the photo shows 1ms for injector pulse, way too low for any kind of "hard accel" load. And, of course, the spark advance (11,500 degrees!) is way too high to be even considered. I am wondering if your data-log SW/HW is proper.
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Old 03-08-2021, 03:06 PM   #4
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Default Re: Un-Explained engine knock

*Was the coolant sensor replaced? Factory originals are round nosed plastic tipped, prone to cracking then sending incorrect temperature signals to the pcm. The flat nosed brass replacement fixes this problem.

*Was the thermostat replaced? The faulty coolant sensor results in overheating engines, melting the rubber seals used in the t-stat. Replacing the t-stat fixes this problem.

According to your graphing, 178F indicates a faulty t-stat unless you snapped this photo oon a cold engine. Normal operating temps are between 185F-200F.

*Replacing drive belts sometimes results in a longer belt. The clock spring belt tensioner applies around 50 lbs of belt tension. A longer belt may allow the tensioner to apply less tension and bang against its limit stop. Some have mistaken this knock as engine detonation picked up by the knock sensor. The belt tensioner should be somewhere in the middle of its tension range. When belt tension is released, there should be marks to indicate the range of tension between zero and maximum spring load. A worn out belt tensioner will let the belt slip and may hit its limit stop repeatedly and mistaken for engine knock.
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Old 03-08-2021, 03:11 PM   #5
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Default Re: Un-Explained engine knock

I will see about getting a better photo and an actual log of the data. Currently I can't run the software I use while driving as the laptop i'm using to gather the info has a bad battery so I can't actually get any solid data around town without the laptop shutting of after a few minutes. This issue happens whenever my vehicle is hot or cold and when I put my foot down half way to all of the way quickly, Looking in the software the throttle position sensor was reading correctly, I also say the map sensor showing as well and intend to obtain an image of all the sensor readouts showing what they are doing at the time of the issue. I am running NGK V-power plugs as well as premium gasoline as when I ran it on regular it refused to start reliably where it would act like it was only firing on 1-2 cylinders as if it were out of fuel. I will also try get an audio clip as the engine lugs down and rattles when the knock event happens despite the engine being in otherwise great mechanical condition.
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Old 03-08-2021, 03:17 PM   #6
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Default Re: Un-Explained engine knock

Quote:
Originally Posted by fdryer View Post
*Was the coolant sensor replaced? Factory originals are round nosed plastic tipped, prone to cracking then sending incorrect temperature signals to the pcm. The flat nosed brass replacement fixes this problem.

*Was the thermostat replaced? The faulty coolant sensor results in overheating engines, melting the rubber seals used in the t-stat. Replacing the t-stat fixes this problem.

According to your graphing, 178F indicates a faulty t-stat unless you snapped this photo oon a cold engine. Normal operating temps are between 185F-200F.

*Replacing drive belts sometimes results in a longer belt. The clock spring belt tensioner applies around 50 lbs of belt tension. A longer belt may allow the tensioner to apply less tension and bang against its limit stop. Some have mistaken this knock as engine detonation picked up by the knock sensor. The belt tensioner should be somewhere in the middle of its tension range. When belt tension is released, there should be marks to indicate the range of tension between zero and maximum spring load. A worn out belt tensioner will let the belt slip and may hit its limit stop repeatedly and mistaken for engine knock.
That is great information, thank you, the test was preformed with the engine below operating temps however I do have a new belt, tensioner, and idler pulley as I recently have been having belt slip issues and upon examination the tensioner moves far easier than it seems it should and the idler pulley nearby has a bad bearing as it wobbles and feels crunchy while I turn it. I did check my temp sensors and they are all brass tipped sensors rather than plastic with the exception of the air temp sensor.
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Old 03-08-2021, 05:28 PM   #7
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Default Re: Un-Explained engine knock

I think you're assessment to address the belt tensioner and idler pulley is correct. There are many ways mechanical issues are masked by error codes that distract from the overall perspective. Far too many diyers assume an error code points to one sensor when mechanical problems are ignored. No error codes exist for worn bearings, belt tensioners losing their ability to maintain tight belt tension, low oil, dead shocks, etc. Hopefully replacing belt tensioner, idler pulley and belt (if worn) will fix this issue. At the least, addressing them first removes any doubt about a slipping drive belt contributing to this problem and at best solves it.
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Old 03-09-2021, 09:36 PM   #8
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Default Re: Un-Explained engine knock

Quote:
Originally Posted by fdryer View Post
I think you're assessment to address the belt tensioner and idler pulley is correct. There are many ways mechanical issues are masked by error codes that distract from the overall perspective. Far too many diyers assume an error code points to one sensor when mechanical problems are ignored. No error codes exist for worn bearings, belt tensioners losing their ability to maintain tight belt tension, low oil, dead shocks, etc. Hopefully replacing belt tensioner, idler pulley and belt (if worn) will fix this issue. At the least, addressing them first removes any doubt about a slipping drive belt contributing to this problem and at best solves it.
I just got finished changing the belt, tensioner, and idler pulley. The rattle sound when hitting the gas seems to be gone and the old tensioner was completely shot as well as the idler. I will re-scan the car tomorrow to see what the graphs show to see if it is still showing knock or not but the car seems to be much happier after servicing the belt assembly.
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Old 03-10-2021, 09:55 PM   #9
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Default Re: Un-Explained engine knock

Quote:
Originally Posted by agentclank777 View Post
I just got finished changing the belt, tensioner, and idler pulley. The rattle sound when hitting the gas seems to be gone and the old tensioner was completely shot as well as the idler. I will re-scan the car tomorrow to see what the graphs show to see if it is still showing knock or not but the car seems to be much happier after servicing the belt assembly.
The knock sensor could pick up on that noise transmitting through the block, as the location is somewhat close compared to other components.
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