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Discussion Starter · #1 ·
ok guys I believe I have a pretty good grasp on the fuel injection system and how it works and understand the sensors involved in controlling how the engine operates but spark timing is something i have yet to understand enough about to tell if its where it should be. Take for instance i am looking a my scanner while idling and my knock sensor is showing 19 does that mean its picking up knock if so whats that doing to my timing? what should i be seeing as far as knock and what should i be seeing as far as retard and advance? any input would help in further understanding ignition timing.
 

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ok guys I believe I have a pretty good grasp on the fuel injection system and how it works and understand the sensors involved in controlling how the engine operates but spark timing is something i have yet to understand enough about to tell if its where it should be. Take for instance i am looking a my scanner while idling and my knock sensor is showing 19 does that mean its picking up knock if so whats that doing to my timing? what should i be seeing as far as knock and what should i be seeing as far as retard and advance? any input would help in further understanding ignition timing.
The number in the Knock Counts box isn't really reliant... What you look for when tuning spark advance is if the number in the Knock Counts box CHANGES. If the number increases it means that knock has been detected by the sensor and will retard the timing so many degrees depending on how bad that knock was. You should try to tune out any spark knocks by adjusting your timing tables, decreasing timing by 1-2 degrees at whatever RPM and MAP kPa the knock occurred and then logging again to see if your still getting knocks at that same RPM and MAP range. If this is an LT1 engine, it is possible that you will get FALSE spark knocks in the higher RPMs (especially if you have headers) but you should still try to tune them out by adjusting the timing tables first before deciding they're false. My engine for example gives me false knocks occasionally around 4,000 RPM, I know these to be false because no matter how much timing I decreased in that area, it would still occasionally happen. This is a known problem with SOME LT1's and the fix usually is to replace the Knock Sensor Module with and LT4 module, as they are less sensitive to false knocks.

Hope this has helped you.
 

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Discussion Starter · #3 ·
That does give me a better understanding about it. Thank you for that answer but i have almost nothing modified at this point and am kind of scared about triing to tune myself, honestly i was talking from a stock stand point becuase i feel i need to understand what the computer is telling me with no mods before i can start adding some and see what effects that will cause,basically what are good numbers and what are bad as far as knock and timing, now what you were saying about headers I have just ordered some headers for the car and i have heard about the lt4 module do you think i will need it with everything else still being stock if so where can i get one and how much should i expect to pay, also it is an 94 lt1. Thank you again
 

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That does give me a better understanding about it. Thank you for that answer but i have almost nothing modified at this point and am kind of scared about triing to tune myself, honestly i was talking from a stock stand point becuase i feel i need to understand what the computer is telling me with no mods before i can start adding some and see what effects that will cause,basically what are good numbers and what are bad as far as knock and timing, now what you were saying about headers I have just ordered some headers for the car and i have heard about the lt4 module do you think i will need it with everything else still being stock if so where can i get one and how much should i expect to pay, also it is an 94 lt1. Thank you again
Your welcome. And even a completely stock LT1 can benefit from a little bit of spark advance. Typically on a stock LT1 you can increase the spark advance by 2 degrees across the board (i.e. ALL timing cells). This is usually good for about a 5-15 HP increase, but your unlikely to FEEL that change in the seat of your pants so to speak. In regards to the knocks, ANY spark knocks are bad (except false ones which are kinda rare). If your data logging your car and you see the Knock Counts increase AT ALL after starting the car, its bad and you need to lower the timing in the area that it occurred. Since you are buying headers for it, you may or may not need the LT4 knock module. Typically the false knocks at higher RPMs are caused by the headers being louder then stock manifolds, and since the knock sensor is located somewhat close to the exhaust manifold on the passenger side, it can pickup this louder "tick" from the header as being a knock in the engine. IF you do need the module I think they are about $40 online. I personally haven't ordered one yet because I just installed a toggle switch that bypasses the Knock Sensor when I want to race (I had a switch and wire and resistor that was needed so it was a free mod).

If you need more understand of exactly how spark advance and timing work in general, you can google that. But basically, as the piston reaches TDC (Top Dead Center) the spark plug ignites and the air/fuel combusts to push the piston back down. Now you would think you would want this spark to happen exactly at TDC, but as the engine rotates faster (RPMs increase) you actually want the spark to happen BEFORE the piston reaches TDC. This is because it takes time for the spark to happen and then for the air/fuel to combust. Thus, as you increase spark advance, you are actually causing the spark to happen before the piston reaches TDC so that the actual combustion happens right as the piston reaches TDC. Now, if you have the spark advance too high (i.e. too far before TDC) the combustion happens before the piston reaches TDC and the force of that combustion actual fights the rotation of the engine by trying to push the piston back down as its still coming up, THIS is what causes a spark knock. You also do not want the spark advance too low because then the combustion happens AFTER the piston reaches TDC and is already on its way back down, this can cause a dramatic loss in power.
 

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Discussion Starter · #5 ·
ok I will watch it before and after I start it and see what I am getting then monitor while driving then i can compare that to what im getting after the header install and look for change. Great info. Thanks agian
 

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ok I will watch it before and after I start it and see what I am getting then monitor while driving then i can compare that to what im getting after the header install and look for change. Great info. Thanks agian
Your welcome! Just remember, the number you see in the Knock Counts box will change when you start the engine (i.e. if your monitoring with with the key on/engine off and then you go to start it the number will increase, I think) but this is not spark knock, its just noise from the engine starting up. It really only matters if the number increases after the engine is running.
 

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when you first start the car while datalogging your going to see your knock count jump ALOT. thats normal.
while driving it shouldnt increase at all. I had to drop my spark advance 3* in the 4500-6000rpm range because i was getting anywhere from 1 to 8 degrees knock retard. i ended up at around 32* with no knock 33* in some areas and 35* below 4500RPM
 

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Discussion Starter · #8 ·
I installed the lt4 knock module a while back and scanned it while driving now when I installed it I disconnected the battery so I believe it erased all the counts that were there previously but after starting the car and driving conservatively and then a couple full throttle segments I only had 10 counts which show up on start up and never increased i also never seen any knock retard so I believe things are working just as they should. I haven't scanned the car any since then to see if I have anymore counts but what I understand is that it take a certain number or counts before the the PCM with begin to retard the timing any so I think I should check it again to make sure it hasn't had enough to start pulling timing. I am planning on getting turnercat soon to change few things and tinker with as I learn more about tuning but for now I just have a snapon scanner to see what the engine is doing.
 

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Way back when my car was stock, before starting mods I had a solid 5-7* 4800-5000 RPM knock/retard problem. Tried to fix it before doing cam/RR install. Tried all tricks including retarded timing 10-12* still did not go away, installed LT4 KM and problem was fixed. Then proceeded to add CAM, headers, RR's, knock never came back. Car was bone stock at that time, never could figure it out, may have been the actual sensor, but it' still installed w/o problems.

Some KC info... Knock count usually bumps thousands during cranking, will some times will wrap past 100K and start over again. As far as retard , it usually takes counts in the hundreds to retard spark and PCM will remember MAP/RPM that caused the KC bump. It will then preventively retard spark at that point for a while, even if the KC does not bump. Eventually retard will go away after a few runs if no more KC occurs at that MAP/RPM.

You can also get retard w/o KC incrementing during fast acceleration, it's called 'burst knock' PCM anticipates TB is wide open (MAS senses high % air flow change) but injectors have not delivered fuel yet due to mechanical delay. PCM will retard timing for a brief period (Ms) to prevent a lean condition knock. Lots of people tune out or lower burst knock retard table or they alter the 'burst knock enable % air flow' constant.
 

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i did some math and when i was getting around 237 knock counts it was retarding 2.3* so i think every 100 counts is roughly 1* but I could be wrong.
 
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