Author Topic: U12 Misfires under load, but idles fine....  (Read 4516 times)

0 Members and 1 Guest are viewing this topic.

Offline LoW GLi

  • antrx.com junkie
  • *****
  • Posts: 608
  • Karma: +12/-2
  • Gender: Male
  • Dble Up!! 2.0L 4 Cyl (Pinnie)... 4.0L V8 (180sx)
U12 Misfires under load, but idles fine....
« on: Jun 28, 2010, 10:38AM »
Hey Everyone...
Quick run down of what happened just for reference sake. Driving home late saturday night, over took a car in 3rd on the highway, just as i went to back off and put it back in 5th i heard a slight pop, tacho needle drops to 0 and no dash lights come on... Still managed to drive the car home, but wasnt able to put my foot down... As soon as i did put my foot down, the car would sound like the fuel had been cut to the motor, drop a cylinder and would start decelerating rather quickly....

Have looked inside the dizzi (2nd hand dizzi with a new cap) all appears to be fine, have pulled out spark plugs and cleaned them (havnt put new ones in for a while - could be problem) swapped coil leads over to see if it was a dud coil.. still no love...

Still need to look at more things such as replacing spark plugs, and also checking spark leads.

Am a bit concerned as to why the tacho isnt working as the car idles fine....

Should i be looking at things such as o2 sensor and things like that?? Anyone else got any ideas?? Wont get around to looking at the car again till this arvo, but also have all day tomoz to sort it out...

Offline SSS

  • Administrator
  • post whore
  • *****
  • Posts: 8279
  • Karma: +5020/-3
  • Gender: Male
Re: U12 Misfires under load, but idles fine....
« Reply #1 on: Jun 28, 2010, 10:39AM »
Change the ecu.

Offline LoW GLi

  • antrx.com junkie
  • *****
  • Posts: 608
  • Karma: +12/-2
  • Gender: Male
  • Dble Up!! 2.0L 4 Cyl (Pinnie)... 4.0L V8 (180sx)
Re: U12 Misfires under load, but idles fine....
« Reply #2 on: Jun 28, 2010, 10:45AM »
Can i ask how you came to that conclusion? Cause if it was the ECU wouldnt it be running shit all the time? not just under load?

Offline SSS

  • Administrator
  • post whore
  • *****
  • Posts: 8279
  • Karma: +5020/-3
  • Gender: Male
Re: U12 Misfires under load, but idles fine....
« Reply #3 on: Jun 28, 2010, 01:11PM »
Because you have no tach signal, and it misfires under load. Tach signal comes from the ecu, not the coil.
Pity you didn't have consult on the CA's, that would tell you straight away.

I had a problem where my KA would miss at 5000rpm at WOT but ran fine everywhere else; an ecu swap solved the problem. I swapped the bad ecu back in and the problem was back immediately until I put the good ecu back in.

Offline LoW GLi

  • antrx.com junkie
  • *****
  • Posts: 608
  • Karma: +12/-2
  • Gender: Male
  • Dble Up!! 2.0L 4 Cyl (Pinnie)... 4.0L V8 (180sx)
Re: U12 Misfires under load, but idles fine....
« Reply #4 on: Jun 28, 2010, 06:13PM »
Maybe i should of mentioned that this is an aftermarket tacho that DOES run from the coil, i installed it myself....

I will try another ECU tomorrow and see what happens. Thanks

Offline LoW GLi

  • antrx.com junkie
  • *****
  • Posts: 608
  • Karma: +12/-2
  • Gender: Male
  • Dble Up!! 2.0L 4 Cyl (Pinnie)... 4.0L V8 (180sx)
Re: U12 Misfires under load, but idles fine....
« Reply #5 on: Jun 29, 2010, 11:11AM »
Problem isnt ECU.. going to try the basics and then move onto the ignitor for the coils...

Offline LoW GLi

  • antrx.com junkie
  • *****
  • Posts: 608
  • Karma: +12/-2
  • Gender: Male
  • Dble Up!! 2.0L 4 Cyl (Pinnie)... 4.0L V8 (180sx)
Re: U12 Misfires under load, but idles fine....
« Reply #6 on: Jun 29, 2010, 12:27PM »
Problem solved, appears to be one of the ignitors (i think thats what it is) on the coil pack... after installing new plugs it was doing the same misfire.. so i undone all the coil pack wiring, and as i went to remove the  coil mount, i noticed it was attached to the car still, when i installed the tacho wire, i didnt realise the plugs for the coil wire into the ignitors on the coil mount.. so i switched the plugs and problem solved... also advanced the timing on the dizzi and now she pulls harder than ever before!! haha stoked

Offline SSS

  • Administrator
  • post whore
  • *****
  • Posts: 8279
  • Karma: +5020/-3
  • Gender: Male
Re: U12 Misfires under load, but idles fine....
« Reply #7 on: Jun 30, 2010, 10:26AM »
Good stuff, i'm guessing you had a spare ecu laying around? It's usually the easiest to check that first, your symptoms sounded similar to mine before you mentioned about the tacho driven off the coil.


Offline LoW GLi

  • antrx.com junkie
  • *****
  • Posts: 608
  • Karma: +12/-2
  • Gender: Male
  • Dble Up!! 2.0L 4 Cyl (Pinnie)... 4.0L V8 (180sx)
Re: U12 Misfires under load, but idles fine....
« Reply #8 on: Jul 2, 2010, 12:43PM »
I did have a spare ecu, but i couldnt find it, so i just limped it over to the wreckers (not even 5 mins away) and chucked one in... Today its decided to carry on and misfire again... getting over this shit! lol
Its running ok now, had a fiddle with the spark leads, i think one was a bit loose from when i put in the new ones  :-\
Might see if i can buy new ignitors...