Two dead cylinders... What drives them?

[everpresentnoob]

Ok, so I have two dead culinders. Checked out the PTU, and it is fine. chased the PTU wires back to the ECU, those are fine... How do I check to see that the PTU is in fact sending the signal to the coils? I know the coils are good, pulled one and plugged it into a different coils harness and shocked the ever loving crap outta myself... Checked voltage, and they have good ground and voltage, so it has to be they are not getting the signal to fire. Is that from the ECU? Or the PTU?

Ok. Yea... Service manual wiring diagrams are helpful. signal comes from ECU to PTU then to Coils. Ok. Its dark outside right now but tomorrow I will go chase the other side of the PTU wires to the coils and see if those are good....

[z.Leinbach]

Check the injectors too

[everpresentnoob]

I did. Injectors ohmed out fine. Pulled the offending coils and plugged them into the harness from working cylinders and they had good spark when putting a spare spark plug into them and grounding to the plenum. Cylinders 3 and 4 dont seem to be getting the signal to fire. when the coils are plugged into their propper harness, no spark. Putting a working coil from cylinder 1 into the harness for 3 or 4 that coil has no spark. Has to be in the harness between the PTU and the coil. Looking in the FSM one side of the PTU goes to the ECU, the other side goes to the coils.

Tomorrow I plan on checking the signal wires from the PTU to the coils and see if I have continuity through them. If not I am going to take my spare sub harness and solder new wire onto it and create my own PTU to Coil harness and solder it into the dead cylinders signal wires and see if I can get spark. Just bypass the main engine harness.

[budget300zx]

Its possible your harness is just wore out, Id check from the terminals of the ptu then check the values against the ecu harness side.

EDIT: in case you haven't read this already
dead-cylinder-can-t-figure-out-why-read ... 64452.html

[everpresentnoob]

This is embarrasing... Im normally better than this. So I was reading on here about reconnecting the computers main plug. How you cant put to much force on it or you can damage the connectors. So in the intrest of NOT putting to much pressure, I apparently didnt put ENOUGH pressure on it. relooked at it and noticed that it didnt seem seated fully. tightened the screw down until the little red plastic thingy started raising and was flush with the white plastic guides on either side and tried again. VIOLA! all 6 cylinders are firing once again.

now back to the previous issue....