Suprash Posted February 24, 2003 Share Posted February 24, 2003 Guys, I need to catch up on this technical lark, so can anyone explain the following: Fuel Cut, have never hit that Im aware of, how can I check that this fitted and set/working properly, and what is it. Pre-detoantion/knocking/pinking, these terms I have heard but could someone give me an idiots guid to what all this means, how to test and what to look out for. The reason Im asking is, as far as some of you are aware, Im decatted, hitting 1.4bar. Now I know this could be causing the engine to run lean, so basically since I have had the car, I have had to drive it by the Boost gauge, ie, not letting boost go above 1bar, except that can be very difficult to drive the car by the boost gauge, hence why I finally got one of Mr Wilsons rings. I want to know if there is anything I can check/do to make sure this area of the engine is ok, far too techincal for me. I have heard of compression kits as well, are these a good idea, and where can you get them, something Halfrauds doesnt stock. I have a AFC, can this help in anyway, give any readings, as I havent had it fitted yet. This is soemthing that I have been trying to pick up and figure out for myself since being on the BBS but so far havent, simple idoit proof replies would be great......... Link to comment Share on other sites More sharing options...
THOR Racing Posted February 24, 2003 Share Posted February 24, 2003 Fuel Cut,...., how can I check that this fitted and set/working properly, and what is it. It is an ECU software feature that shuts down the flow of fuel to the injectors (hence Fuel Cut) if the manifold boost pressure rises above a threshold (set in software) You cannot fit a "Fuel Cut" Whatyou fit is a "Fuel Cut Eliminator/defencer/controller" This removes the fuel cut or in the case of a controller raises it to another level. Do a search on the web for more info on this. It's a common term (Boost Cut or Fuel Cut) More later..... food now! Regards Pete Link to comment Share on other sites More sharing options...
Digsy Posted February 25, 2003 Share Posted February 25, 2003 Detonation occurs when multple flame fronts develop in the combustion chamber, usually because the engine is running too hot, boost pressure is too high, too much spark advace, AFR is too lean or octane is too low. Detonation usually occurs after the spark fires, and the sudden rise in cylinder pressure as the flame front expands causes the remaining unburnt fuel/air mixture to combust of its own accord. The two (or several) flame front collide and the resulting shockwaves knacker your pistons / rings / combustion chamber / valves etc. Detonation (or knock) is characterised by the metallic "pinking" sound when the engine is under load. OEM knock sensors use peizo-electric transducers (a material that changes physical shock into an electric current) to sense the vibration caused by the flame fronts colliding. This is why the mounting of a knock sensor in the engine is so critical: There must be a clear path through the engine structure for the shockwaves to travel. Pre-ignition is a simpler problem where something in the combustion chamber ignites the fuel / air mixture before the spark fires. This can be an almost normal combustion process (one flame front) which is ignited by a hotspot in the combustion chamber, like a hot carbon deposit or a sharp edge or burr which cannot dissipate heat from itself. The combustion event will obviously be mis-timed in relation to the "optimum" spark event so the engine will lose power. However, if the normal spark event occurs soon enough after the pre-ignition, you can end up with multiple flame fronts and detonation. HTH. Link to comment Share on other sites More sharing options...
Suprash Posted February 25, 2003 Author Share Posted February 25, 2003 Cheers Guys....But Darren, one thing. /quote "Detonation occurs when multple flame fronts develop in the combustion chamber, usually because the engine is running too hot, boost pressure is too high, too much spark advace, AFR is too lean or octane is too low. Detonation usually occurs after the spark fires, and the sudden rise in cylinder pressure as the flame front expands causes the remaining unburnt fuel/air mixture to combust of its own accord. /quote Why is there unburnt fuel/air left over after the spark fires, surley everything would be burnt. How can you check for these things happening.....??? Link to comment Share on other sites More sharing options...
Digsy Posted February 25, 2003 Share Posted February 25, 2003 I probably could have been more clear there. In normal ignition, when the spark ignites the fuel / air mixture, it does so in one place - at the spark plug tip. The flame front advances across the combustion chamber at a finite speed, so the whole process from spark to "all fuel burnt" takes a short space of time. However, as the flame front expands, the cylinder pressure rises and temperature increases. With conditions condusive to detonation, this pressure / temperature rise can be enough to spontaneously ignite the fuel / air mixture in a region where the "normal" flame front has not reached yet: hence two (or more) sources of ignition, and two or more flame fronts, each expanding and heading for each other with desasterous consiquences. Det / knock / pinking makes a noise which you can hear. You could also hook up a visial display to the stock knock sensor (we use normal oscillascopes here). You could also hear it if you fed the signal through an appropriate amp and into a pair of headphones. The possibility of a custom made in-car display that talks to the standard knock sensor has been discussed here before. You could probably also hear it with a stethoscope or something similar - although this isn't much good for tuning! What we do here is map engines for fuel / spark by watching for knock events on the scope and listening on headphones. The guy running the engine dyno literally has two dials in his hands: one for spark advance and one for fuelling and he twiddles each one until he gets the best power from the engine at a given speed without knock, then he moves onto the next set speed, etc, etc. He ends up with a fuel / spark map (this is a gross simplification because some engines need many maps, but the principle is similar). Once the normal map is defined, the engine can run on "auto/auto" (auto spark and auto fuelling based around the nominal map but supervised by the O2 sensor and the knock sensor). The problem with testing a knock sensor, or with mapping an engine up to the limits of det, is that you actually have to make the engine det, which is not a good thing even in small quantities. Link to comment Share on other sites More sharing options...
Suprash Posted February 25, 2003 Author Share Posted February 25, 2003 Cheers Darren, thats a lot clearer now. So basically take the car to a local tunning shop and get them to test for this, right. Link to comment Share on other sites More sharing options...
Digsy Posted February 25, 2003 Share Posted February 25, 2003 Well, like I said, if you have det bad enough you will be able to hear it with the naked ear, but if you suspect you have borderline det or pre-ignition then take it to a tuners' to get it checked out. Just thinking aloud, maybe knock events are recorded in the ECU, so you may be able to interrogate that. Maybe someone else can confirm or otherwise...? Link to comment Share on other sites More sharing options...
Suprash Posted February 25, 2003 Author Share Posted February 25, 2003 I have no reason to believe this is happening, just thought I should understand then might fail safe any future problems. And seeing as I have an un-trained ear, is it a good idea to get it checked anyway, even if you have no reason to supect, after all something could be happen and I probably wouldnt be none of the wiser. Link to comment Share on other sites More sharing options...
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