Miss fire on #3-no spark...out of ideas-SR20DET-

[5upra]

SR20DET redtop in a 1990 240sx Well I have been waiting to get a ignitor chip...so I install it today start the car and there is still a continuous miss fire on the #3 cylinder. I have checked the wiring for resistance...nothing. I have swithed coils...nothing. I have changed plugs...nothing. I have checked voltages from ecu...fine. I can't think of anything else to do....besides junk it. I thought I was going to be a mechanic as I have completed 3 school years worth of automotive, but I can't even figure out my own car . I have been through the FSM more times than I care too. I don't get it Any suggestions would be appreciatedlook me up on aim Djclarkgm for real time talk

[NISTECH]

Have you checked your injectors? have you ran the car with the coil out and a spare plug in the boot and watched for spark. The threads on the plug should be grounded when you check for spark.

[5upra]

yes, the spark is so weak on only #3 that it won't jump anything

[NISTECH]

you need to load check the circuits. A weak spark generally indicates a bad coil but you say you swapped them and it remained. So you need to determine if 12volts are available at the coil under load and that the ground has no more then .5 volts. Then you need to do a load check on the signal circuit to make sure that wire isnt weak. My suspicions are the signal wire is ok if the coil is firing at all so you need to be sure the wires for power and gnd arent drawing excessive surrent under load. I am not sure what is on the power and ground circuits of the SR set up unless its an s-14 sr engine.

[5upra]

ok i found that the negative side has full 12v. The others read 2 thousands of a volt. What does this mean? Where does this wire go?*EDIT* I can find out what that means if I just figure out the second question.
Modified by 5upra at 8:57 PM 7/14/2006

[NISTECH]

I think you got your power ang ground readings swapped.

[5upra]

no for sure...both + and - come up with battery voltage. Trust me...I know my way around a car better than most on this site, hopefully. how can it have battery voltage on both sides? oh and by the way I did not do my wiring-just a side note.

[NISTECH]

If you are checking for voltage on the ground side with it plugged in you may see some voltage on the line but it must be no more then .02v anything higher then that is to much of a load on the wire and is taking away from the load of the coil. I am assuming you tested it pluygged in?

[5upra]

no disconnected connector reading, with car on, is battery voltage on both the pos. and neg. female pins in the connector. I am telling you I am out of ideas.

[NISTECH]

OOHH you are saying the grounds on the other coils reads .02v but #3 coil negetive reads battery voltage. Your ground is a direct line to ground. If you are seeing battery voltage on it its either wired incorrectly or shorted to power. What you can do it remove the ground terminal from the connector temporaily and wire a direct ground to that terminal and see if it functions properly. If it does then you can trace the removed wire and find its short or incorrect connection. Just by looking at the wiring diag it is simply spliced into all the other grounds for the coils. The likly hood it is shorted to power is extreamly small as they would all see 12volts. It should be the solid black wire your seeing the 12 volts on, not any other color other then the white wire which is your power.

[NISTECH]

Also note the red wire is the ignition signal wire that goes to the power transistor. you wont be checking that wire for anything as it is only a momentary ground to collapse the field in the coil to fire the plug. Without a DSO you cant really judge anything on that wire.

This is assuming you have an s14 sr motor in your car as that is the only silvia/200sx service manual I have on file.

[5upra]

Alright...I will see what I can do in the morning!

[jdm_master_X]

this happened to me once, except it was with Cyl 1. apparently the problem was that the hot wire to the coil harness was slightly exposed, and it was shorting itself out. the culprit was due to it being kinked and cut during the removal and install of my valve cover. thats something you want to check since its so simple.

hope that helps.

[5upra]

Well...did some more testing. the short is some where in the harness(SOB). So now I am going to have to cut open the harness. I really dont want to(lol). Maybe I will call the place that did the harness...maybe I can get them to do it...again.