NissanNismoZ Posted September 20, 2011 Author Share Posted September 20, 2011 Your ECU is designed by engineers who know what shielding is. While not impossible I find this extremely unlikely. If anything the ECU would cause interference in your speaker signal. that it did! hmm..any other ideas on what i should do? im at a loss.. thanks! Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 22, 2011 Author Share Posted September 22, 2011 Okay..so i did a lot of work and got nowhere.. Bought a newer ECU, put it in, CEL came on within half a mile. Fixed my vacuum leak (the small line at the top of the intake) and removed my intake plenum to unpinch the injector wire, foudn ot the plastic piece around it was melted, repaired it and straightened it out let the battery stay disconnected for 30 minutes, got in, let ir run, revved it some, turned it off, repeated the process 3 times, no CEL put it in reverse to pull out, not far after reversing, CEL comes on, and stays on. All the same codes with both computers. I'm at a total LOSS and have no idea what to do.. I've done all the testing, and got results (good or bad, i dont know, they seemed fine.) i dont know what to do!! Link to comment Share on other sites More sharing options...
sewebster Posted September 22, 2011 Share Posted September 22, 2011 (edited) Woo! Okay..i did it.. Here's the information i got: Pin 16 (Idle) .07v Pin 16 (2000 RPM) .10v Pin 17 (Idle) 13.17v Pin 17 (2000 RPM) 12.75v What exactly are pin 16 and 17? 16 seemed to act like the MAF (increases on throttle) 17 acted..odd. the harder i pushed on the pedal, the voltage went down?? Thanks everyone..i really appreciate the help!!! Your pin 16 results are bad. See EF+EC page 129 of the 95 FSM. If you pass the other MAF tests in the FSM by measuring resistances in the maf and by probing the maf at the connector when running, which it sounds like you do, then you have a problem with your wiring between the MAF and ECU. I don't know what pin 17 does. Edit: FYI, if you haven't read this chapter, might be helpful... http://www.nicoclub.com/FSM/pathfinder/1995_Pathfinder/ec.pdf Edited September 22, 2011 by sewebster Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 22, 2011 Author Share Posted September 22, 2011 Your pin 16 results are bad. See EF+EC page 129 of the 95 FSM. If you pass the other MAF tests in the FSM by measuring resistances in the maf and by probing the maf at the connector when running, which it sounds like you do, then you have a problem with your wiring between the MAF and ECU. I don't know what pin 17 does. Edit: FYI, if you haven't read this chapter, might be helpful... http://www.nicoclub....thfinder/ec.pdf THANK YOU!! So..got some more comments..and was told i should replace what usually goes wrong; the MAF connector.. Thanks!! Your feedback was very appreciated and i actualyl read a LOT of the link you posted.. (my FSM is missing that..for some reason..) and it helped me understand a lot more, at least.. Link to comment Share on other sites More sharing options...
sewebster Posted September 22, 2011 Share Posted September 22, 2011 (edited) Pin 17 does connect to the MAF as well, so you should ensure that wire is also good... it might be used to control the amount of current flowing in the wire (wire needs to stay in a certain temperature range). The third wire to the MAF seems to be connected to the positive terminal of the battery through a relay. I don't really understand the MAF grounding situation. Edited September 22, 2011 by sewebster Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 22, 2011 Author Share Posted September 22, 2011 Pin 17 does connect to the MAF as well, so you should ensure that wire is also good... it might be used to control the amount of current flowing in the wire (wire needs to stay in a certain temperature range). The third wire to the MAF seems to be connected to the positive terminal of the battery through a relay. I don't really understand the MAF grounding situation. Pin 17 seems to decrease on throttle, so it may be just varying to keep the temperature evened out.. so my understanding is this.. One wire connects for power (all sensors need at least 5v to operate(REFERENCE wire)) One wire is the output (SIGNAL wire) And the other wire is the ground..which, i made my own to the front of the engine.. it could even be my ground i made, but i made two just in case..im wondering if i should just snip the connector off the other pathy and put it on mine.. as long as the other connector is good, i should be able to splice into it.. right? Thanks!! I feel like we may be getting somewhere..finally! Link to comment Share on other sites More sharing options...
sewebster Posted September 22, 2011 Share Posted September 22, 2011 Hmm. I don't think any of the three wires are ground. Check the schematic again. One wire goes to pin 16 (MAF signal), one goes to pin 17 (unknown, but could be to control the wire temp) and the other wire is +12V. I think the ground is supposed to be through the maf body or something, but it sucks? If you grounded one of the wires, that could be the problem. At least according to my reading of the schematics... 1 Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 22, 2011 Author Share Posted September 22, 2011 oh! That could be my whole problem.. O.o time to redo my wiring the way they had it!! I wasnt aware of this at all..heh..thanks! Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 22, 2011 Author Share Posted September 22, 2011 So, i went ahead and fixed that problem! Now some further testing shall be in place.. Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 22, 2011 Author Share Posted September 22, 2011 (i may not have had it hooked up right) but i hooked it back up to stock..and.. it stumbled HORRIBLY like put..put..put.. i was waiting for it to stall out..so i hooked it back up how i had it, to a ground, and it started up running smoothly..so..maybe it is a ground wire? Link to comment Share on other sites More sharing options...
sewebster Posted September 23, 2011 Share Posted September 23, 2011 How does the truck run with the maf unplugged? It should go to failsafe mode and rely on the TPS to determine the mixture. RPM limit of 3000... Certainly MAF ground problems exist, but I haven't had them myself, so I don't know what is supposed to be grounded. I find the diagram confusing. Maybe when you ground one of the wires you fool the ECU that your MAF is just totally busted and it goes into failsafe mode? But when you hook it up "right" it sends the wrong signals and your engine stumbles? Guesses... Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 23, 2011 Author Share Posted September 23, 2011 with it unplugged it seems to run horribly, such as..it doesnt want to do anything at all.. i do agree, the diagram IS confusing.. Link to comment Share on other sites More sharing options...
Tungsten Posted September 23, 2011 Share Posted September 23, 2011 (edited) Hmm. I don't think any of the three wires are ground. Check the schematic again. One wire goes to pin 16 (MAF signal), one goes to pin 17 (unknown, but could be to control the wire temp) and the other wire is +12V. I think the ground is supposed to be through the maf body or something, but it sucks? If you grounded one of the wires, that could be the problem. At least according to my reading of the schematics... WRONG!!!!! From the MAF sensor side, the layout is as follows: A pin = Reference voltage circuit, +12v or battery voltage to power the sensor (B/W wire on factory harness, goes to ECCS relay) B pin = Reference ground circuit (B wire on factory harness, goes to pin 17 on ECU) C pin = Input signal circuit (W wire on factory harness, goes to pin 16 on ECU) The MAF sensor wire shielding is also grounded. First, make sure voltage exists at pin A and it matches the battery voltage. Then check continuity between the B wire terminal and pin 17 on the ECU and then check for continuity between the C wire terminal and pin 16 on the ECU. There is an error in the FSM specifying to test terminal A voltage but you actually have to test terminal C voltage for signal. Check EC-133 and then check EC-84 and you will see why. The procedure on page EC-84 asks you to test pin terminal A when you should be testing pin terminal C. The signal at pin C should match to the table found on EC-133, which is less than 1.0v with ON and 1.5v to 2.0v with engine warmed up and running. The voltage at pin A should be battery voltage or +12v. Nissan has released an extra grounding harness for the B pin on the sensor, which shortens the path of the reference ground circuit. Sometimes the wires may be broken inside or at the connector from stress due to people failing to remove the connector prior to replacing the air filter. In that case you have to cut back around 3 inches on the harness and splice in a fresh connector. You can do what I did and splice in the grounding harness connector instead of just plugging it in. Edited September 23, 2011 by Tungsten Link to comment Share on other sites More sharing options...
sewebster Posted September 23, 2011 Share Posted September 23, 2011 (edited) WRONG!!!!! From the MAF sensor side, the layout is as follows: A pin = Reference voltage circuit, +12v or battery voltage to power the sensor (B/W wire on factory harness, goes to ECCS relay) B pin = Reference ground circuit (B wire on factory harness, goes to pin 17 on ECU) C pin = Input signal circuit (W wire on factory harness, goes to pin 16 on ECU) The MAF sensor wire shielding is also grounded. First, make sure voltage exists at pin A and it matches the battery voltage. Then check continuity between the B wire terminal and pin 17 on the ECU and then check for continuity between the C wire terminal and pin 16 on the ECU. There is an error in the FSM specifying to test terminal A voltage but you actually have to test terminal C voltage for signal. Check EC-133 and then check EC-84 and you will see why. The procedure on page EC-84 asks you to test pin terminal A when you should be testing pin terminal C. The signal at pin C should match to the table found on EC-133, which is less than 1.0v with ON and 1.5v to 2.0v with engine warmed up and running. The voltage at pin A should be battery voltage or +12v. Nissan has released an extra grounding harness for the B pin on the sensor, which shortens the path of the reference ground circuit. Sometimes the wires may be broken inside or at the connector from stress due to people failing to remove the connector prior to replacing the air filter. In that case you have to cut back around 3 inches on the harness and splice in a fresh connector. You can do what I did and splice in the grounding harness connector instead of just plugging it in. I'm not sure my post was wrong exactly, you added additional information I guess grounding the B terminal is a good idea. I'm not sure if that's the one he grounded though. Also, apparently it didn't work, because he is now reading 13 volts at pin 17? There is some sort of problem, also indicated by pin 16 being out of range. Edited September 23, 2011 by sewebster Link to comment Share on other sites More sharing options...
Tungsten Posted September 23, 2011 Share Posted September 23, 2011 (edited) I'm not sure my post was wrong exactly, you added additional information I guess grounding the B terminal is a good idea. I'm not sure if that's the one he grounded though. Also, apparently it didn't work, because he is now reading 13 volts at pin 17? There is some sort of problem, also indicated by pin 16 being out of range. Once again, NO!!!!!! PIN 17 SHOULD READ -12v NOT +12v and that is a correct reading for the reference ground. Pin 16 however should read the same as Pin C on the sensor. Here is proof where Nissan screwed up: See this thread for explanation: http://www.nissanpathfinders.net/forum/index.php?showtopic=31278 Edited September 23, 2011 by Tungsten Link to comment Share on other sites More sharing options...
sewebster Posted September 23, 2011 Share Posted September 23, 2011 Once again, NO!!!!!! PIN 17 SHOULD READ -12v NOT +12v and that is a correct reading for the reference ground. Pin 16 however should read the same as Pin C on the sensor. Here is proof where Nissan screwed up: How can a potential measurement between ground and ground be -12V? If he grounds terminal B, and ECU pin 17 is a -12V then there's going to be a lot of current flowing through that wire, unless there is a resistor in there somewhere, which is not indicated in the schematics? Link to comment Share on other sites More sharing options...
Tungsten Posted September 23, 2011 Share Posted September 23, 2011 It's a computer. Ever looked at your computer's power supply? Link to comment Share on other sites More sharing options...
sewebster Posted September 23, 2011 Share Posted September 23, 2011 It's a computer. Ever looked at your computer's power supply? Not particularly Link to comment Share on other sites More sharing options...
Tungsten Posted September 23, 2011 Share Posted September 23, 2011 (edited) Good thing I showed up here on time before this turned into a MAF sensor nightmare. Also, the reason why the reference voltage for pin A is taken from the battery is because the voltage regulator for the MAF sensor is on the MAF sensor board. These sensors are not like your ordinary 4 wire MAF sensors. EDIT: Clarification Edited September 23, 2011 by Tungsten Link to comment Share on other sites More sharing options...
adamzan Posted September 23, 2011 Share Posted September 23, 2011 Link to comment Share on other sites More sharing options...
sewebster Posted September 23, 2011 Share Posted September 23, 2011 Also, the reason why the reference voltage is taken from the battery is because the voltage regulator for the MAF sensor is on the MAF sensor board. These sensors are not like your ordinary 4 wire MAF sensors. See, now you're changing your tune... before you said "reference ground" now it's a reference voltage... sounds better... but isn't that basically exactly what I said before? Are you saying to ground pin B or not? Link to comment Share on other sites More sharing options...
Tungsten Posted September 23, 2011 Share Posted September 23, 2011 No I'm not. The reference voltage is for pin A. Yes, definitely ground pin B. Link to comment Share on other sites More sharing options...
sewebster Posted September 23, 2011 Share Posted September 23, 2011 No I'm not. The reference voltage is for pin A. Yes, definitely ground pin B. Ok, so here's the thing where you lose me. If pin B is grounded, shouldn't pin 17 on the ECU also be at ground? Link to comment Share on other sites More sharing options...
NissanNismoZ Posted September 23, 2011 Author Share Posted September 23, 2011 (edited) That's why i've sort of stayed back..im trying to figure this out..OK. so..should i ground the wire coming from the harness as well? coz i just left it sitting there, but i DID ground teh wire coming from the MAF. Pin 17..im not sure if its even supposed to be grounded, because when i check for volts, i get the battery voltage... and when B is NOT grounded, it sputters and coughs and tries to stall out..so im ASSUMING B is ground. right? So..here's what im thinking, from experience... A = Signal B = Ground C = Reference voltage. Edited September 23, 2011 by NissanNismoZ Link to comment Share on other sites More sharing options...
Tungsten Posted September 23, 2011 Share Posted September 23, 2011 No, A is reference and C is signal. If you add an extra ground B at the MAF sensor you add an extra ground to pin 17 on the ECU at the same time. Pin 17 at the ECU is not exactly a ground but it works as one and sometimes doesn't if something is wrong or the wire is broken which causes funny MAF sensor issues. Link to comment Share on other sites More sharing options...
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