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Thank you for the response college man.
I unplugged the throttle body connector a few months ago to check the throttle body to see if it was dirty. The car sat for about 5 months since then. I tried doing a idle relearn by following the steps listed in the FSM and even on a obd2 app called car gauge pro but nothing changed.
heres an update on this car so anyone with a similar problem can know what the fix was.
the misfire was due to a bad ecu. it wasn’t sending a signal to trigger the coil pack in cylinder 3. apparently the maf, misfire code, etc was all due to the bad ecu. it seems to be a fairly common problem on these sentras. I found a company that rebuilds them online and shipped it out to them. i just got it back, installed the ecu in the car and it started up without any misfires. also replaced all 4 coil packs as per the company’s instruction. the car runs decent now but is idling higher than normal and rpms jump up and down by a few hundred sometimes. the car probably needs the idle relearn procedure done and i’ll double check for any vaccum leaks. hopefully thats the end of the problems with this car.
I did try swapping the coil packs around and the problem did not follow. the coil packs fire on cylinder 1 and 4 always. cylinder 3 has a wiring problem with the connector. i fixed that. Cylinder 2 & 3 is where the problem is. I’m not getting spark in those two cylinders. Sometimes ill start the car and ill have spark in cylinder 2, but sometimes i wont. this makes me think its a wiring issue on that coilpack connector too, but i tested all 3 wires and the first one has power and the other two have ground so I have no idea whats going on right now. I can assume that all my coilpacks are good though because they have spark as soon as i put them in another cylinder. I’m using an inline spark tester to check for spark btw. Do you guys think this could be due to a failing cam/crank position sensor? thats the only thing i can really think of.
update: so the car is idling and i discovered why one of the cylinders is misfiring. the misfire is on cylinder 3 and one of the wires on the coil pack connector is broken. theres not enough wire to solder the wire back together so ill figure out how to fix that tomorrow.
the next problem is the idle goes up and down BUT when i disconnect the coil pack wiring for cylinder 2, the car idles normally and doesn’t go up and down. The car actually runs smoother with that coilpack disconnected and doesnt shake and misfire as much. I disconnected the coil pack wiring for cylinder 1 and 4 and the engine starts to misfire and shake as expected instead What can this mean for cylinder 2? bad injector, just a simple vaccum leak?
Hopefully this is the last problem i have to fix on this car.
update: i got the car to idle. the wiring on the egr valve was damaged. I repaired the damage section and the car now idles without shutting off. i believe that was putting the car into limp mode and not allowing it to idle but it wouldnt throw any codes.
I just have a few more problems to solve now. the car idles high at 2k rpms and it seems to misfire even though it has no codes for a misfire. im thinking it needs an idle relearn procedure done and the spark plugs that were in there are ACDelco 41-986. I looked up the part number and those are not gapped for a 2001 sentra. I’ll get some NGK plugs, a new pcv valve and report back.
Thank you for all the replies and comments guys! They’ve been really helpful.
I only had a few minutes to work on the car today, but i confirmed that the maf is getting 12v, ground, and 5v from the computer. I couldn’t test the signal wire to determine the actual status of the MAF because the car wont idle. I also checked the TPS and it is getting 5v and ground from the computer. The voltage on the signal wire also changes when i open the throttle manually so i assume thats good. I pulled the spark plugs and saw that it was black so i assume the car was running rich. I managed to do a compression test on 2 cylinders before the rain started pouring down. the fsm states 168 psi is the minimum on a fully warmed up engine. I did it on a fully cold engine and got 150 and 130ish. I will do another test another day. I assume the engine has good enough compression to keep it running though because the car was running and driving on the test drive for a couple miles and it started right back up after it stalled out.
I also took a video of how the car tries to idle with the maf unplugged. the previous owner did install an aftermarket exhaust so thats why it sounds so loud. here is the link: https://www.youtube.com/watch?v=fypmaq1xke0
Any ideas on what my next step should be? I’ll check pcv and fuel pressure as soon as I can and report back.
Thank you for the reply!
I will take a video of the problem tomorrow and post it. I’ll pull the spark plugs and do a compression test as well. I haven’t really done much testing due to no time to work on the car. I should have a good hour or so to do some testing tomorrow though. My scanner is basic and cannot read live data so i’m limited to using a multimeter to test the MAF.
I’ll try to do a compression test, check the maf, pcv, tps and o2 sensors tomorrow and report back with my findings.
I have done some research on this specific generation of Sentras and it seems it is a common problem that is usually resolved by replacing the MAF. However, some people reported having to change their ECU in order to fix this problem. I’m hoping that isn’t the problem with this car, but we’ll find out eventually. Thank you to everyone for all the replies so far!
Thanks for all the replies guys! let me provide some more information
I just bought the car one week ago and it would stall out a few times during the test drive, but it started right back up after. It also had a hesistation. All of this made me think it was just a faulty maf sensor. The next day i started the car and it wouldn’t even idle. It would start, then shut right back off. If i held the gas pedal and rev’d it up, it would idle but the engine would be running rough like it was misfiring badly. I just put in an idle air control valve after discovering how dirty it looked. It did not help the problem. The car will still start right up then the idle will drop and the car will shut off. I do have codes for the MAF, but its codes that i created because i tried to run the car with it unplugged. any ideas on what I should check next? I checked the fuel lines and there is no leaks. I also tried to hold the key but it didnt help.
is there a way to temporarily bypass the egr so i could see if that is the problem?
Also, I would like to add that the same problem occurs when i start the car without the MAF plugged in.