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We have a 1995 Nissan Maxima 3.0 dohc in our shop with a rough idle and misfire on 2 cylinders only. 1 is on the front bank and one is on the rear bank. We have checked the following things so far:

1: Checked and replaced spark plugs as they were extremely worn (the gap was excessive)
2: Swapped coils (made no difference) misfire remained in same cylinder
3: Swapped injectors (made no difference) misfire remained in same original location
4: Check compression in both cylinders that were missing (about 100PSI running compression) same as the adjacent cylinders that arent missing
5: Check injector connectors with a noid light (injectors are receiving signal)
6: Listened to injectors open with stethoscope (can hear them open)
7: Checked for B+ at coil connectors ( have battery voltage)

We are banging our heads on the wall now any suggestions from someone more familiar with this engine/car would be greatly appreciated.

Remember im a dummy up front.
You say the injectors have power and you hear them open. Is there a way to tell if fuel is coming out, or enough fuel, when they do open? Don't ask me how to do that, I have no clue.

Just wondering if that could be it.

Rich wrote:Remember im a dumby up front.
You say the injectors have power and you hear them open. Is there a way to tell if fuel is coming out, or enough fuel, when they do open? Don't ask me how to do that, I have no clue.

Just wondering if that could be it.

We swapped an injector from a cylinder with no problems to the cylinder with misfire and it made no difference.

My bad, didnt see that. Good luck.

Next step for me would be a cylinder pressure test. I have had cars that had even compression and running compression that had a valve that did not seal good. Also would physically inspect cams for proper lift and worn lobes. Just a thought, I left Nissan about the time these engines were being introduced.

We have been messing around with this car a bit more and it seems the problem is that the coils on cylinders 2 and 3 are not firing.
The problem is not the coils, they have been swapped with other coils on the car and with new replacement coils.

The coils do have battery voltage present at the B+ terminal and I show ground on the on two terminal when the car is running.

We are going to check the wires from the pcm to the effected coils now...


Is there anything anyone can think of that would cause only two of the coils not to be getting the signal to fire?

We just checked all 3 wires from coil to pcm, all three wires have less then 1ohm resistance.
Wiring is ruled out now.

In my mind this leaves us with either a bad pcm or is it possible for some other sensor (CKP or CMP) to cause this?

Yes then it is probally a computer tap on it and see what happens

I had a ford this past week setting a maf sensor code. Followed the flow chart and replaced the MAF sensor. Still setting MAF code and part of the diag was to ohm the wires to the Pcm. I load tested the circuit and had less than 1 v on the 12 v power. Found wire near power steering pump nearly corroded in half. RE ohmed same wire and had less than 1 ohm and 12 v. Try seeing if you have the 12 v when coil is plugged in. Identifix mentions the maxima as having harness issues at the passenger strut tower. HTH. Jerry

I fixed a Lincoln LS a couple weeks ago doing the same thing. Turned out it was a bad transistor in the pcm. It would make a test light blink, but it wouldn't fire a coil. Look in the Ford section for my thread.

We are ordering a pcm from salvage yard will post fix if it works

i didn't see where you tested the coils. i would pull the coil jamb a plug into it, run a ground to the plug and crank it over. look and see if the cylinders are off setting. i would spray carb cleaner around the intake while it's running. vac leaks could be the culprit. i believe we had one of these a few years back where the rubber seat on the injector was leaking and sucking air.

We did test the coils in the very manner you were speaking of, we stuck a plug in the coil and ran a ground wire from the sparkplug tip to battery negative.

We have also tried the pcm now and still have no fire on the same two cylinders.


Im going to go recheck everything again now.

Well Im stuck. I really dont know what to do know.

I just rechecked everything.

Cylinders # 2 and 3 are not firing. The coils are ok, if they are moved to another location they fire fine.
Checked power and ground at coils # 2 and 3. Power and ground are ok.
I can actually make the coils fire at those locations by applying power momentarily at pin 3 on the coils.
These are the same results we got when first checking this car.
The pcm has been swapped with no change, cylinders # 2 and 3 still do not fire.
The wire running from pin 3 on the coils to pcm has been ohm checked and tested ok.
I even tried running new wire from pcm pin 2 to ignition coil # 2 pin 3 . Still did not fire.

This leaves me feeling like either the pcm i got to swap out in this car was defective on the same two cylinders( not likely) or for some reason the pcm is not firing those cylinders purposely.

pitcrewllc wrote:Well Im stuck. I really dont know what to do know.

I just rechecked everything.

Cylinders # 2 and 3 are not firing. The coils are ok, if they are moved to another location they fire fine.
Checked power and ground at coils # 2 and 3. Power and ground are ok.
I can actually make the coils fire at those locations by applying power momentarily at pin 3 on the coils.
These are the same results we got when first checking this car.
The pcm has been swapped with no change, cylinders # 2 and 3 still do not fire.
The wire running from pin 3 on the coils to pcm has been ohm checked and tested ok.
I even tried running new wire from pcm pin 2 to ignition coil # 2 pin 3 . Still did not fire.

This leaves me feeling like either the pcm i got to swap out in this car was defective on the same two cylinders( not likely) or for some reason the pcm is not firing those cylinders purposely.

So are the coils firing? If you pull one or both coils off, stick a plug in it and run the car, is there spark? If not, have you scoped the cam/crank signals?

The used pcm could have the same issue? Still possible

Possible. It looks like the coils will not fire by the pcm but fire if manually activated. Sounds like either a pcm or a bad input. Gotta know if the crank sensor has a good waveform.

Just thought of something. Does this car have an external transistor? I don't have much Nissan experience, but I worked on a 300ZX a couple years ago, and I just remembered it had what is called a power transistor. It houses the transisitors that fire the coils. I'm sure that this is your problem. American cars such as the Lincoln I repaired have the transistors in the PCM, but the 300ZX had a separate module.

Yep, just looked in Shopkey. Has a power transistor. I'd bet my paycheck that's your problem. (I own a shop so I don't get a paycheck BTW )

I just looked at the wiring diagram and I do not see a transistor externally. Maybe I have the wrong one.