misfire under load in low rpm only?

[filip9999]

hey everyone i know there are some very smart techs on here so hopefully you can point in the right direction. first let me give you some backround on me. im a tech at a honda dealership. this is my first nissan. its a 93 240 with the ka24de. i went to tech school so im pretty good with cars. been a tech for about 2 years now. so kinda stil starting out. just not so good about diagnosis so this is why i need help. i have tools and the nissan dealer gives me their cost price on parts. so this is the problem. when im going into first gear it feels like there is a misfire under load. only in low rpm. because when i reach about 3.5k-4k it smoothes out and sounds good. the only mods i have is a 3inch catback exhaust. stock intake. stock trans parts. now the parts i have replaced are plugs and distributor cap+rotor. i didn't get the OEM wires yet because even from the dealer its like 75 bucks unless this is what the problem is i won't buy em yet.. i have disconnected the AIR system. it seemed to have help the misfire but not all the way. it sounds like a wrx when i take off and smoothes out when i get higher in the rpm. i just checked the timing and its good at stock. i replaced the tps sensor cuz i had an weird idle and the sensor measured out wrong wwhen i did the resistance test. so it idles nicely 90% most of the time. i even pulled the fuel pump out to clean that white sock at the end. still no better. when i bought the car it didn't do it. i can't remember exactly what i did right before it started happening. and it was like the problem slowly started coming about. not like right away. i seafoamed the engine as well. and it seemed to help a lil too. so... where do i go from here. the plugs were changed about 8k miles ago. should i pull them out to see how they look? could it be the egr sticking? is it a weak coil? any advice would really help to point me in the right direction. i would love to hook the machine up to it that you can see peak spark and duration. i did it at school once to another car and i found a weak wire or plug. but i don't have access to it anymore and im not gonna pay someone to find this problem for me.

[filip9999]

i have an update. i also replaced the coolant temp sensor. one of the guys i work with said it might be that. it was a cheap part so i just threw it on. also. i did notice it runs much better at night and in the morning when its not as hot outside. which further leads me to believe its the coil or wires.

[Rucca]

Did you check the EGR? Check for codes. Plug wires have specified resistance values so you can check them instead of just buying them. Definitely pull the plugs to see what they look like. Check compression yet?

You can use your multimeter to rule out basically all the electrical components. Just check the FSM under Engine Controls, it shows you how to test all the components you are questioning.

[filip9999]

I have not checked the egr yet. haven't checked compression but i think its gonna be good since last night i was driving at night and i was so much smoother and the power was awesome when it didn't feel like it was misfiring.

[krazydriver]

Try the fuel filter. My car was bogging till ~3k.... swapped out the fram fuel filter for a oem 300zx TT and all is well.

[r3v_v3ng3]

correct me if i'm wrong but you disconnected your AIR system and left your EGR system? don't they have to work in conjunction with each other? so basically they need each other. also if you have less restriction on your exhaust (3 inch) your EGR will have trouble functioning.

[filip9999]

the air system does not work with the egr system. this problem starting occuring months after i put the exhuast on. so it had no effect on it when i put the exhaust on.

[filip9999]

so check this out. i started testing the ignition coil and such. and all passed. so i decided to ohm out the injectors as long as i had the dmm right there. all three passed except #4 . had 90 ohms. shoudl be at 11. so i started her up and pulling the connectors off one at a time. 1,2, and 3 all showed substantial engine loss. almost stalling out. so i tryed #4 and surely enough. nothing happend. the engine so running the same way. even with some throttle, it began misfiring like usual. so there ya have it. a dead injector.

[danielsan]

i i

so check this out. i started testing the ignition coil and such. and all passed. so i decided to ohm out the injectors as long as i had the dmm right there. all three passed except #4 . had 90 ohms. shoudl be at 11. so i started her up and pulling the connectors off one at a time. 1,2, and 3 all showed substantial engine loss. almost stalling out. so i tryed #4 and surely enough. nothing happend. the engine so running the same way. even with some throttle, it began misfiring like usual. so there ya have it. a dead injector.

if i would of seen this earlier i could of told you it was dead injector. my brothers car ran the same way. sounded cool at idle and low rpm but smoothed out getting up in the rpms and that is what confuses people. watch out for the other injectors they could go out at any moment. but yeah my brothers #4 injector went out also then went #3 soon after.

[filip9999]

well at least ill know if it happens again, much sooner

[180sxn]

ummmm...not turbo....3" exhaust...part problem...2 not at tdc...cams misaligned

[filip9999]

ummmm...not turbo....3" exhaust...part problem...2 not at tdc...cams misaligned

huh? it was a dead injector. or one that had much higher resistance values than the other three