1998 NSX misfire on 4,5,6

[michaelwoodcock]

So, now I am curious. In your original post you stated the car idles rough. A failed misfire detection module can definitely cause invalid codes; but, should not affect the operation of the engine. Was the rough idling a mis diagnosis or did you do something else to resolve that problem?

It may have been a misdiagnosis on my part, but after replacing the module and putting in some fuel system cleaner it seems to run smoother at idle

But what if the failed mis-fire detector caused an intermittent short to the primary side of the spark system?

Interesting. My timing light did seem to not fire at times. I attributed this to a bad connection at my coil adapter. The only thing I know with 100% certainty at this point is that the codes no longer come back with the new module. are these things known to fail at times?

 

[Larry Bastanza]

Not a very common failure at all....

 

[Old Guy]

But what if the failed mis-fire detector caused an intermittent short to the primary side of the spark system?

I hadn't really thought of that angle. Perhaps possible. The schematic diagrams imply that the connection point for the misfire detection module is coupled to the coil secondary winding through a capacitor located in the coil. My initial reaction would be that the if the capacitor is relatively small the capacitor (if in fact that is what it is) should isolate the secondary winding from problems occurring outside of the coil. It is unfortunate that the service manual does not elaborate a little more on the operation of the misfire detector.

Aside from getting his problems fixed, michaelwoodcock's experience does have some general value in that it would seem to confirm that the 1300 series of misfire codes does seem to be generated by the misfire detection module. This could provide some general value for everyone when looking to find the source of a problem if the ECU generates the 1300 misfire codes; but, not the 1200 misfire codes.

 

[Larry Bastanza]

My initial reaction would be that the if the capacitor is relatively small the capacitor (if in fact that is what it is) should isolate the secondary winding from problems occurring outside of the coil.

I was thinking of this based on the signal really not being DC, since the system is firing at RPM rates. If so, the capaitor may not isolate it due to the frequency(AC nature) of the signal. Just a thought.

Regards,
LarryB

 

[Old Guy]

I was thinking of this based on the signal really not being DC, since the system is firing at RPM rates. If so, the capaitor may not isolate it due to the frequency(AC nature) of the signal. Just a thought.

Regards,
LarryB

I agree that it is a non DC waveform that the misfire detection module is monitoring. I was thinking that the capacitive tap in the coil is something like the clip on capacitively coupled pick-ups for using an oscilloscope to monitor the waveform on the high voltage side of the ignition.

https://www.picoauto.com/products/ignition-accessories/secondary-ignition-pickup-capacitive-with-bnc

The combination of the high frequencies present in the spark current (the spark waveform itself would consist of frequencies much higher than the repetition frequency associated with engine speed) and small coupling capacitance makes the impedance of the capacitive tap so high (z = 1/(jwC) ) that even if you have a ground on the sensing line I would not expect any material leakage of spark current through the sensing tap. Of course, in the absence of actual details of the misfire detection module all of this is speculation (albeit interesting at least for me) fueled by perhaps a little too much morning coffee.

 

[JayTwenty8]

I hadn't really thought of that angle. Perhaps possible. The schematic diagrams imply that the connection point for the misfire detection module is coupled to the coil secondary winding through a capacitor located in the coil. My initial reaction would be that the if the capacitor is relatively small the capacitor (if in fact that is what it is) should isolate the secondary winding from problems occurring outside of the coil. It is unfortunate that the service manual does not elaborate a little more on the operation of the misfire detector.

Aside from getting his problems fixed, michaelwoodcock's experience does have some general value in that it would seem to confirm that the 1300 series of misfire codes does seem to be generated by the misfire detection module. This could provide some general value for everyone when looking to find the source of a problem if the ECU generates the 1300 misfire codes; but, not the 1200 misfire codes.

I just had the check engine light 1300, 1301 1302 1303 & TCS. Misfires in cylinder 1,2,3. After clearing the codes multiple times, the CEL would come up typically during idle after the engine had warmed up.

After process of elimination of replacing spark plugs, coils, swapping coils front to back, still reading same codes, I finally swapped the misfire detection module. I cleared the check engine light and it hasn’t come back.

I’ll update if CEL & TCS come back, but I’d like to thank everyone for their input and experiences.

Asp fyi you can get the igniter / misfire detection module from a junk yard, from older RL,Legend. Hope this helps others.

 

[Old Guy]

The 37950P5A A01 misfire module cross references to the 1996 - 04 RL and the 1996 - 98 TL. I didn't find any cross reference to the Legend. I thought the Legend production ended in 2005 which means that it did not need to be OBD II compliant and may never have received the misfire detection module which was part of the OBD II compliance requirement. The ignitor module probably cross references to the Legend.

I have been trolling the on-line inventory in our local pick & pull watching for RLs and TLs of the correct vintage. For $20 I figure it might be a good spare part to have on hand, just because if I have a spare that seems to be a Murphy's law kind of thing that it won't fail.

 

[JayTwenty8]

I only mentioned the legend cause when I typed in the part number and saw it was “compatible” with nsx, RL, legend and a few others.

So true with Murphy’s law, lol.