misfire question

[shippy8907]

okay just a few days ago my car was running great no misfires or anything. I let it set for a few days in the garage and drove my other car. When i went to start it a few days later it now has a misfire in it. almost like when i had a bad injector, but i checked with the long screwdriver technique and can hear all the injectors firing. so i am assuming that it is in the ignition somewhere. so i tried to unplug the coils and see if one didn't change the misfire but I could not really tell any difference between any of them. at this point i am assuming ptu/ptu harness is bad. im not really sure if mine has ever been changed because mine is a 90 model. i'll be calling the local dealer here tomorrow and see if they can tell me. but i just wanted to ask you guys to see if that is what it sounds like to you too? also is there anyway i could ohm test the coils? what should they read if they are in good condition?

[Milton'Z Nissan'Z]

Often some of the connector contacts become corroded causing a poor connection. Pull the ones with the spring clip (PTU, CAS, Coolant Temp Sensor, Injectors, AAC, FICD, TPS) and check for green discoloration. Often all that's needed is to scrape it off and apply a good quality contact cleaner to fix the problem. This is a common issue on these cars because of the poor connector design.

[shippy8907]

all connections are good and clean. i found out that if i uplug my number 5 coil nothing changes. so i swapped in a known good coil and it still does the same thing. could it be the ptu not firing that cylinder?

[NissanFairladyZ32]

or could be a plug not firing

[shippy8907]

okay i figured out that the number 5 is just getting a very very weak spark. i hooked up a coil with a plug in it and watched to see if it fired. you could barely see the spark at all. im assuming that has excessive resistance somewhere along the line or its grounding out. i found a wiring diagram and i figured out which wire controls number 5 spark but i don't know where the wire goes once it comes through the firewall. i have a feeling it is pinched somewhere.

[shippy8907]

does anybody have a continuity test diagram i could see for the s2 ptu? only one i can find is for the old style.

[robomatic12]

Have you tried swapping coilpacks to eliminate that as the cause for a weak spark?

[shippy8907]

yeah that was the first thing I thought it could be. it still had the weak spark. i finally figured it out though. it was a dead channel on the ptu. 5 out of the 6 had voltage when running and 1 was completely dead. i have never heard of a series 2 ptu dieing but this one def. did.