Graham Rudd Posted March 12, 2002 Share Posted March 12, 2002 Can someone explain what effect replacing stock jap injectors with 550cc or bigger ones will actually do, and how it works? I can understand that replacing 440cc injectors with 550cc ones can provide more fuel. What I'm more interested in is what happens when you're just tootling along and don't need a river of fuel? If a 550 injector is open for 1ms, would it spit out more fuel than a 440 open for 1ms? If this is the case then wouldn't the ECU have to be remapped to actually make sensible use of the bigger injectors? Surely it would be running stupidly rich if it wasn't, or will the o2 sensor and the closed loop operation take care of this and adjust the pulse width accordingly? However, if this isn't the case then how do you actually get the ECU to open the injector for a longer period of time? Again wouldn't this involve remapping? (I may have answered my own question in the previous paragraph) Any insight into how it works would be great, I don't doubt the fact that replacing the injectors works fine, I just want to know how and why it works. Many thanks, Graham Quote Link to comment Share on other sites More sharing options...
Alex Posted March 12, 2002 Share Posted March 12, 2002 Answer: Buy a fuel computer - and map that to the injectors - Chris Wilson is able to provide this service. Popular Fuel Computers currently on the market: Apex'i S-AFC, HKS FCON, Fields Simple Fuel Computer, MoTeC replacement ECU!! Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 12, 2002 Author Share Posted March 12, 2002 That doesn't really address the original question though. What about those that haven't got a fuel computer? What happens when you stick the UK injectors on a J-Spec car without doing anything else? I'm assuming the ECU recognises the fact that the mixture is too rich and reduces the pulse width of the injectors. If not then where is the compensation made? In fact, if you're decatted isn't the lambda sensor removed? Just to re-iterate: I'm not having a go at anyone's setup, or doubting that upgrading injectors work. I'm just trying to find out how it all fits together for my own satisfaction. Graham Quote Link to comment Share on other sites More sharing options...
Adam W Posted March 12, 2002 Share Posted March 12, 2002 I think the engine will compensate when running in "closed loop" mode, (idling), using the O2 sensor as you describe. You will be running 20% richer than normal when driving properly though. For the Mk3, there is a nifty engine mod which involves using this very property of upgraded injectors - use larger injectors in conjuction with an equally larger air flow sensor thingy. You get 20% more air going through the engine than the ECU thinks (because you now have a larger air flow sensor but the same output voltage from it), but this is cancelled out by the 20% extra fuel at the same pulsewidth for the larger injectors, so you get the same mixture, but 20% more of it! That won't work for you though, because there isn't a handy Lexus air flow sensor you can bolt straight on in place of your stock one! Pretty useless post for you lot really! Quote Link to comment Share on other sites More sharing options...
Alex Posted March 12, 2002 Share Posted March 12, 2002 Adam - I like your thinking....how about using a VPC (Vein Pressure Converter will that do the trick?? Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 12, 2002 Author Share Posted March 12, 2002 That won't work for you though, because there isn't a handy Lexus air flow sensor you can bolt straight on in place of your stock one! Pretty useless post for you lot really! Erm.. cheers Adam Well, if what you say is true then would sticking 550cc injectors on a Jap spec car without doing anything else not be a bit cludgy? What would happen if I reduced the voltage from the air flow sensor by 20% then? Sorry about all the questions, I've got my 'just have to know' head on today. Car eh? Bloody mystery to me! Cheers Graham Quote Link to comment Share on other sites More sharing options...
Adam W Posted March 12, 2002 Share Posted March 12, 2002 What makes the Mk3 trick work is that the replacement lexus AFM is exactly the same shape and type as the original Supra one, just physically larger, and the voltage/airflow scale is the same - it even has the same multiplug connection. Unless the VPC has the same flow/voltage characteristics (ie a set percentage more airflow for any given output voltage) as your stock AFM you will be back in the realm of the fuel computer. I have no idea if this will be the case. For anyone more interested in what I'm talking about, look up the "Lexus-Riemer Upgrade" on the net for this (IMO) very elegant solution to a common problem. Quote Link to comment Share on other sites More sharing options...
Alex Posted March 12, 2002 Share Posted March 12, 2002 You can't just get the injectors... You'll need the pump and resistor pack as well. Ian C is getting some in from the states soon if you have the cash he can add you to the deal too. Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 12, 2002 Author Share Posted March 12, 2002 Quote: from Alex Holdroyd on 8:47 pm on Mar. 12, 2002[br]Adam - I like your thinking....how about using a VPC (Vein Pressure Converter will that do the trick?? Can you explain what a VPC does please Alex? (simpleton terms please) Cheers Graham Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 12, 2002 Author Share Posted March 12, 2002 Yep, I know I need a pump (got one) and resistor pack. What I really want to know is if its a good idea or not to do. I'd like a complete understanding of whats going to happen first. Just me being pedantic. Graham Quote Link to comment Share on other sites More sharing options...
Alex Posted March 12, 2002 Share Posted March 12, 2002 I believe it is a device to fool the ecu into thinking its flowing less air than it is.....so you can flow more... If you do a web search you'll probably find an explanation which answers all your q's... Quote Link to comment Share on other sites More sharing options...
GavinL Posted March 12, 2002 Share Posted March 12, 2002 Quote: from Graham Rudd on 8:55 pm on Mar. 12, 2002[br]Quote: from Alex Holdroyd on 8:47 pm on Mar. 12, 2002[br]Adam - I like your thinking....how about using a VPC (Vein Pressure Converter will that do the trick?? Can you explain what a VPC does please Alex? (simpleton terms please) Cheers Graham A VPC replaces the MAP (or is it MAF) sensor on the UK/US/Euro spec car, I think I am correct in saying there is no equivilent for the j-spec car however. Quote Link to comment Share on other sites More sharing options...
Adam W Posted March 12, 2002 Share Posted March 12, 2002 Quote: from Graham Rudd on 8:53 pm on Mar. 12, 2002[br]That won't work for you though, because there isn't a handy Lexus air flow sensor you can bolt straight on in place of your stock one! Pretty useless post for you lot really! Erm.. cheers Adam Well, if what you say is true then would sticking 550cc injectors on a Jap spec car without doing anything else not be a bit cludgy? What would happen if I reduced the voltage from the air flow sensor by 20% then? Sorry about all the questions, I've got my 'just have to know' head on today. Car eh? Bloody mystery to me! Cheers Graham Reducing the airflow sensor voltage would be counterproductive - what you need to do is increase the flow by 20% (ie the max flow), and maintain the same voltage. I think. So for a 1V output, instead of flowing 1cfm of air, you want 1.2cfm of air through the new AFM. I think Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 12, 2002 Author Share Posted March 12, 2002 Just to recap though. Will it be true that J-Spec owners with 550cc injectors and no F-CON or VPC or any other 'lets fool the dumb ass ECU' device, will be running 20% richer than stock? Cheers, Graham Quote Link to comment Share on other sites More sharing options...
Alex Posted March 12, 2002 Share Posted March 12, 2002 That's my impression... Quote Link to comment Share on other sites More sharing options...
GavinL Posted March 12, 2002 Share Posted March 12, 2002 Quote: from Graham Rudd on 9:11 pm on Mar. 12, 2002[br]Just to recap though. Will it be true that J-Spec owners with 550cc injectors and no F-CON or VPC or any other 'lets fool the dumb ass ECU' device, will be running 20% richer than stock? Cheers, Graham yep Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 12, 2002 Author Share Posted March 12, 2002 *sigh* So the only real way to go is to get a Motec? Wonder how much that would cost to get all plumbed in properly and mapped correctly? *shudder* We need a money bags volunteer to do the leg work Grahamn Quote Link to comment Share on other sites More sharing options...
mark brown Posted March 12, 2002 Share Posted March 12, 2002 550CC injectors alone on the J spec will make you run very rich. Don't count on the ECU at idle and cruise, i.e closed loop, correcting the over rich mixture. The Lambda sensor on mine was not sensitive enough and I have had to use an Apexi AFC to adjust the low throttle fuelling down. 550cc injector upgrade is only worth doing if you run Hybrids or bigger and high boost. I ran standard injectors and hybrids orginally, I only fitted 550cc injectors 'cos the injectors were running at almost 100% duty cycle with this set up. Mark Brown Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted March 12, 2002 Share Posted March 12, 2002 Quote: from Graham Rudd on 9:11 pm on Mar. 12, 2002[br]Just to recap though. Will it be true that J-Spec owners with 550cc injectors and no F-CON or VPC or any other 'lets fool the dumb ass ECU' device, will be running 20% richer than stock? Cheers, Graham Yes in open loop mode you will be running richer as the base maps will be setup for 440cc injectors, but in closed loop mode i think there is enough trim to bring the fuelling back in. I'm sure that there is some sort of fuelling computer\add-on that you could use to correct this, but as i don't know all the in's and out's of the different ones i'm not sure which is best suited. Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 12, 2002 Author Share Posted March 12, 2002 Mark, Thats partly the reason for my questioning. I've got Hybrids, ECU, Cams, HKS 'R' Spec FMIC, EVC, Water Injection, Induction kit, Exhaust... yadda yadda.. I figured at some point I'd better sort the fueling out. Would have loved to have just been able to tack 550cc injectors on there.. seems not though. Cheers, Graham Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 12, 2002 Share Posted March 12, 2002 Quote: from mark brown on 9:40 pm on Mar. 12, 2002[br]550CC injectors alone on the J spec will make you run very rich. Don't count on the ECU at idle and cruise, i.e closed loop, correcting the over rich mixture. The Lambda sensor on mine was not sensitive enough and I have had to use an Apexi AFC to adjust the low throttle fuelling down. 550cc injector upgrade is only worth doing if you run Hybrids or bigger and high boost. I ran standard injectors and hybrids orginally, I only fitted 550cc injectors 'cos the injectors were running at almost 100% duty cycle with this set up. Mark Brown I might be talking to you later, mate When I get the bits (and have sorted this gammy electrical problem I currently have). If that's OK with you, of course So that I can find this post with the search engine - ventolin. -Ian Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 12, 2002 Share Posted March 12, 2002 Quote: from Graham Rudd on 9:45 pm on Mar. 12, 2002[br]Mark, Thats partly the reason for my questioning. I've got Hybrids, ECU, Cams, HKS 'R' Spec FMIC, EVC, Water Injection, Induction kit, Exhaust... yadda yadda.. I figured at some point I'd better sort the fueling out. Would have loved to have just been able to tack 550cc injectors on there.. seems not though. Cheers, Graham Have you actually had the fuelling checked? What boost are you running? I don't want to worry you, but I have hybrids, FMIC, induction, exhaust (no WI or cams) and mine ruptured itself eventually at 1.2bar - new engine city... All down to the J-spec injectors not being able to deliver enough fuel at high rpm+high boost. -Ian Quote Link to comment Share on other sites More sharing options...
Graham Rudd Posted March 13, 2002 Author Share Posted March 13, 2002 Ian, I haven't had my fueling checked. In fact your situation is one of the reasons that my mind has turned to my fueling. I'd like to know what the max duty cycle my injectors are running at. What factors will the ECU use to determine the injector pulse width? What I'm trying to get at is this: Could it be possible that the ECU is running the injectors at a duty cycle it believes is correct for the current conditions based on the information its been fed, but it turns out that the duty cycle is too low despite the fact that there is a lot more 'slack' available to the injectors. I guess I'm saying does it boil down to the fact that the 440cc injectors may be adequate for my needs but I need bigger injectors to introduce a cludge factor that works around limitations introduced by the sensors available to the ECU? Hope that makes sense! Cheers Graham (just trying to understand!) Quote Link to comment Share on other sites More sharing options...
THOR Racing Posted March 13, 2002 Share Posted March 13, 2002 I've built a prototype injector duty cycle monitor and combined AFR (monitors the stock O2 sensor so therefore has the limitations of the stock sensor) Anyway It shows you in a range of 16 LED's how hard the injectors are working 0->100% Now on my modded car running at 18psi, H20 and hybrids on 440cc injectors I see that the duty cycle is pretty much maxed out at WOT. Whilst crusing at 80mph it's at a steady 12% (shows just how much fuel you need when flooring it!) Anyway the intention was that with the combined AFR you could simultaneously monitor the O2 sensor and the injector duty cycle. If you saw the AFR begin to lean off and the injectors were maxed out then you know it time (sharpish!) to take your foot off the pedal and get some better fueling sorted. >Could it be possible that the ECU is running the injectors at a duty >cycle it believes is correct for the current conditions based on the >information its been fed, It will always do this, yes. It only knows what you (it's sensors) tell it. >but it turns out that the duty cycle is too low despite the fact that >there is a lot more 'slack' available to the injectors If this happens then you've modded something you shouldn't. If it senses more air flow or more load it will increase the duty on the injectors. Now with a FCD you've clamped one avenue open to the ECU as it still thinks you're at 15psi but other systems are telling it it needs more fuel. They are just not as accurate. This is why 18psi is the recommended absolute max (and even then only on cold days with good high octane fuel inside) Do this on a hot day with the same car and no extra charge cooling and start to worry.... In the end the ECU will increase the duty to maximum on WOT but the question is.... is the maximum it can deliver enough? Pete Quote Link to comment Share on other sites More sharing options...
Ian C Posted March 13, 2002 Share Posted March 13, 2002 Quote: from Graham Rudd on 2:47 pm on Mar. 13, 2002[br]Ian, I haven't had my fueling checked. In fact your situation is one of the reasons that my mind has turned to my fueling. I'd like to know what the max duty cycle my injectors are running at. What factors will the ECU use to determine the injector pulse width? What I'm trying to get at is this: Could it be possible that the ECU is running the injectors at a duty cycle it believes is correct for the current conditions based on the information its been fed, but it turns out that the duty cycle is too low despite the fact that there is a lot more 'slack' available to the injectors. I guess I'm saying does it boil down to the fact that the 440cc injectors may be adequate for my needs but I need bigger injectors to introduce a cludge factor that works around limitations introduced by the sensors available to the ECU? Hope that makes sense! Cheers Graham (just trying to understand!) With your levels of modification, I would say that you will need a better fuel delivery system. At the end of the day, before shelling out on injectors, pumps, AFCs, et al, you need to check the fuelling as it currently stands when the engine is under load, like Chris Wilson did for me. The proper way appears to be a sensor probe in the centre section of the exhaust, near the downpipe. With no CATs in place. If it's running unpleasantly lean at full throttle under high boost conditions, you need better fuelling. How that's done is the next step, not the first My AFC was cranked up to +50% fuelling, but it made no difference, ergo the injectors were flat out already. If the reading is lean across the rev range, even at idle, then maybe you have a low duty cycle issue with the ECU, but that seems a remote possibility. -Ian Quote Link to comment Share on other sites More sharing options...
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