Eagle Posted March 8, 2019 Share Posted March 8, 2019 22 hours ago, JMO413 said: And if I'm reading this right mine is rich beacuse the 746 injectors are 20.2/lb and stock injectors are 23.2/lb? So the ECM is compensating? Sorry too high Jack your post. Just want to understand this fuel trim thing. I have always read that the Renix 4.0L injectors are 19.x lb/hour. The 746 injectors, at 20.2 lbs, should be close enough that the difference wouldn't show up in practical application. All of which begs the question of whether the flow rates are measured at the same pressure ... Link to comment Share on other sites More sharing options...
hakukamana Posted March 8, 2019 Author Share Posted March 8, 2019 Wouldn't the ECU read the data from the sensors MAP, O2, CTS, and adjust accordingly especially if we are talking about fuel delivery? To little fuel longer duration of the pulse width, to much fuel shorter duration of the pulse width. If a given injector delivers x amount of fuel per hour at a given pressure, and the fuel delivery is to much or to little isn't that what the ECU is suppose to compensate for? Link to comment Share on other sites More sharing options...
Jeep Driver Posted March 8, 2019 Share Posted March 8, 2019 I would think the range in which it is able to compensate would be very limited. Link to comment Share on other sites More sharing options...
JMO413 Posted March 8, 2019 Share Posted March 8, 2019 Understand now. Link to comment Share on other sites More sharing options...
Ωhm Posted March 8, 2019 Share Posted March 8, 2019 9 minutes ago, Jeep Driver said: I would think the range in which it is able to compensate would be very limited. Its range of authority. O2S is boss. MAP, TPS, ECT & MAT values are used at every given time to determine INJ pulsewidth (ms). This determination goes to a lookup table and picks the correct INJ PW (ms) value for each engine condition. Rate of change also plays into this lookup (MAP & TPS). This type of fuel strategy is called Speed Density. Only the O2S through STFT & LTFT can add or subtract time (ms) from the fixed lookup values. Link to comment Share on other sites More sharing options...
Jeep Driver Posted March 8, 2019 Share Posted March 8, 2019 6 minutes ago, Ωhm said: Its range of authority. O2S is boss. MAP, TPS, ECT & MAT values are used at every given time to determine INJ pulsewidth (ms). This determination goes to a lookup table and picks the correct INJ PW (ms) value for each engine condition. Rate of change also plays into this lookup (MAP & TPS). This type of fuel strategy is called Speed Density. Only the O2S through STFT & LTFT can add or subtract time (ms) from the fixed lookup values. Let's assume a given injector has a specified flow rate @ 41psi, your fuel pressure is (for whatever reason) @ 36psi. Fuel is not atomized appropriately, excess fuel cannot be burned, O2 senses rich condition. Just how much can the ECU adjust or compensate? IOWs you are operating outside a given set of parameters? Link to comment Share on other sites More sharing options...
Ωhm Posted March 8, 2019 Share Posted March 8, 2019 9 minutes ago, Jeep Driver said: Just how much can the ECU adjust or compensate? IOWs you are operating outside a given set of parameters? Regardless of the cause, ECU uses 0-255, starting at 128 (STFT or LTFT) to determine if it needs OPEN loop or if engine can stay at CLOSED loop (with O2S feedback). Link to comment Share on other sites More sharing options...
WahooSteeler Posted March 8, 2019 Share Posted March 8, 2019 3 hours ago, JMO413 said: If I'm reading this correctly 0 is ultimate rich and 255 is ultimate lean. This is a screen shot out of the Renix infection manual. So hopefully it right. And if I'm reading this right mine is rich beacuse the 746 injectors are 20.2/lb and stock injectors are 23.2/lb? So the ECM is compensating? Sorry too high Jack your post. Just want to understand this fuel trim thing. JMO, that info I posted on stock injectors running at 23.2/lb is incorrect, unfortunately I don't even remember where I came across that as I was reading multiple sources of info on different forums when I was researching 746 injectors. As Eagle pointed out above, the correct rate on stock 1-hole injectors is 19+/lb. Sorry to add to your confusion. Link to comment Share on other sites More sharing options...
hakukamana Posted March 8, 2019 Author Share Posted March 8, 2019 OK, as of 3/8/19 Scan of 89' renix O2 data. LTFT has readjusted during a drive cycle. Link to comment Share on other sites More sharing options...
Ωhm Posted March 8, 2019 Share Posted March 8, 2019 Good (only in sense of the) recording showing movement on LTFT. Does the ECU retain that value after a KEY OFF or say the next day? Link to comment Share on other sites More sharing options...
hakukamana Posted March 8, 2019 Author Share Posted March 8, 2019 I will let you know. We have the data, now let's see what it does. Link to comment Share on other sites More sharing options...
JMO413 Posted March 8, 2019 Share Posted March 8, 2019 LTFT should store unless you unhook the battery. I had mine unhooked today and it reset to 128. Mine LTFT was at 90 before. I drive it 40+ miles today after I hooked the battery back up. There LTFT is back at 90. I don't know where but I read somewhere, if you drive 20 minutes at 40+ mph it was the learn for the Renix ECM. Not sure if that's true but it's far enough to set a new LTFT. Which truck is the scanner video from? Just wondering you data is very similar to mine. Link to comment Share on other sites More sharing options...
hakukamana Posted March 9, 2019 Author Share Posted March 9, 2019 Scanner is a MT2500 with the primary cartridge GM-Chrysler-Ford-Jeep, and the trouble shooter cartridge that is labeled the same Link to comment Share on other sites More sharing options...
hakukamana Posted March 9, 2019 Author Share Posted March 9, 2019 The truck is my Eliminator, the 89', 4.0L, automatic. Just checked mine again, LTFT is at 97. I did do a key off, after checking, and then started up again stayed the same 97. I don't think I drove 40 miles over 40mph. Link to comment Share on other sites More sharing options...
JMO413 Posted March 9, 2019 Share Posted March 9, 2019 It is from the 89 or 87. Really just wondering is it a stick or auto? I have the same scanner set up. It's by far my favorite thing I have bought on eBay. Money well spent. Link to comment Share on other sites More sharing options...
hakukamana Posted March 9, 2019 Author Share Posted March 9, 2019 It's the 89 auto Link to comment Share on other sites More sharing options...
JMO413 Posted March 9, 2019 Share Posted March 9, 2019 Link to comment Share on other sites More sharing options...
Ωhm Posted March 9, 2019 Share Posted March 9, 2019 28 minutes ago, JMO413 said: LTFT should store unless you unhook the battery. I had mine unhooked today and it reset to 128. Must have some kinda memory, possibly KAM. Yours is a 90 ECU? Link to comment Share on other sites More sharing options...
JMO413 Posted March 9, 2019 Share Posted March 9, 2019 Yep. Still wondering if LTFT at 91 is rich or lean? Link to comment Share on other sites More sharing options...
Ωhm Posted March 9, 2019 Share Posted March 9, 2019 Too me, LTFT of 91 means O2S sees RICH and LTFT 91 is taking fuel away (decreasing INJ PW time (ms)). Link to comment Share on other sites More sharing options...
hakukamana Posted March 9, 2019 Author Share Posted March 9, 2019 Ok just got back average speed 45 mph, for about 30 minutes. LTFT is now 91 down from 97 Link to comment Share on other sites More sharing options...
hakukamana Posted March 9, 2019 Author Share Posted March 9, 2019 JMO413, & OHM are you both saying your LTFT is 90, 91 and now mine is 91 what are the chances of that being random versus something that was designed into the fuel mapping? Link to comment Share on other sites More sharing options...
Ωhm Posted March 9, 2019 Share Posted March 9, 2019 Its just you and JMO413 that's tracking LTFT. These numbers are real world stuff. Random, I don't know, but yes it could be ECU characteristic. Link to comment Share on other sites More sharing options...
JMO413 Posted March 9, 2019 Share Posted March 9, 2019 Interesting question. I don't know it could be coincidence or part of the programming. I do have a 90 ECM in mine and I believe 89/90 are there same ECM. Have you modified anything from stock? I have 746 injectors and a bored throttle body. Link to comment Share on other sites More sharing options...
hakukamana Posted March 9, 2019 Author Share Posted March 9, 2019 I have the 89 ECU, 746's, and a 60mm TB. Stock airbox, stock sensors, now running the Bosch O2. Stock plugs, coppers. Link to comment Share on other sites More sharing options...
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