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Ignition Coil Part Number Mystery

Joined
3 November 2011
Messages
3,379
Location
Saskatchewan, Canada
I have been thinking about ignition coils ever since the thread discussing the low priced 6 coil 'kit'. I got to thinking about the coils and the front / back differences. I know that the coils are marked FF and RR and I know that Acura gives them separate part numbers. I hadn't really paid much attention to the coils beyond that.

I had presumed that the difference was due to the 3 pin (OBDII) connector orientation; but, then I recalled (and the parts diagram seems to confirm) that the connectors on the front coils are located on the lower edge of the coil and on the rear coils are on the upper edge of the coils (when they are installed in the engine). If the connectors were always on the top (or bottom) of both the front and rear coils that would make the front and rear coils different because of the connector location. The fact that the connector location changes front to back suggests that at least the top half of the front and rear coils appear to be identical. Look at the photo of the 6 coils that Kaz posted:

http://www.nsxprime.com/forum/showthread.php/184080-Coil-Pack-bad-should-I-replace-all-of-them

If you mentally rotated one of the RR coils 180 deg so that the RR is upside down, it sure seems like the RR coil is identical to the FF coil.

So, what am I missing? Did Honda do something weird like changing the assignment of the 3 pins in the connector for the front and back coils? My car is in secure storage so I can't get at it to check the location of the misfire detection connection on the front and back connectors to determine if it is different.

The reason I got off on this track is that it is the rear coils that typically suffer from the corrosion / contamination failure problem. The front coils are readily available, probably because they share a common part number with some of the TLs ('96-'98) and RLs (96-04). On the TLs and RLs, Honda uses the same coil on the front and back cylinders. It is only the NSX that has the unique part number for the rears and because of that, the rear coils are typically only available from Acura. Lots of non Honda vendors list the front coils as available. Given the production numbers for the RL and TL, there is probably a good chance that spares for the front will be readily available for a long time. Unfortunately, NSX history suggests that it will not be the front coil that you are likely to need.

If the NSX rear coils are just front coils with RR stamped on the top, then I am going to go and think about something else more important like food or beer because parts availability is not likely to be an issue. If there is a physical / fit difference between the front and rear, then I might go purchase a rear coil to have as a spare or at least think about how I could repurpose a front coil to fit on the back. So, does anybody know whether there is a material difference between the front and rear coils and what that difference is?

As another little head scratcher, Acura lists different part numbers for the front and rear coils on the pre OBDII cars; but, the price of the coils for the front and rear is the same. On the later OBDII coils, the fronts list for about $20 more than the rears.
 

Well that is interesting. Presuming that the OBDII coils are similar to your pre OBDII coils, I think I can manage to rotate the gasket 180 deg if I ever need to use a front coil on the back.

I don't think I would have ever spotted that. Were you looking for differences or just discovered it by chance?
 
Well that is interesting. Presuming that the OBDII coils are similar to your pre OBDII coils, I think I can manage to rotate the gasket 180 deg if I ever need to use a front coil on the back.

I don't think I would have ever spotted that. Were you looking for differences or just discovered it by chance?

Yes that is the difference ,I just checked my old coils that i changed out a few years ago . Otherwise the coils are identical , I love reading your posts BUT DUDE you have to get a girlfriend ,dog or have a few beers , second thought just get a dog LOL. you just made me miss some of the Sopranos rerun on HBO, can't have this in an Italian house .
 
If I can provide information and entertainment, my life is complete.

It serious winter here and the NSX is going to be wrapped up for another 3+ months, so I have to get my NSX fix by other means.
 
Well that is interesting. Presuming that the OBDII coils are similar to your pre OBDII coils, I think I can manage to rotate the gasket 180 deg if I ever need to use a front coil on the back.

I don't think I would have ever spotted that. Were you looking for differences or just discovered it by chance?

I can't take the credit for that, it was our NSXCB member britlude's work. He is a clever old stick.

It would be great if the OBDII coils could be used in place of the older coil packs, with a converter plug....
 
I can't take the credit for that, it was our NSXCB member britlude's work. He is a clever old stick.

It would be great if the OBDII coils could be used in place of the older coil packs, with a converter plug....

They probably can. [MENTION=5430]drew[/MENTION] linked this post on nsxcb.co.gb where Kaz discusses potential complications with the later coil retrofit

http://www.nsxcb.co.uk/showthread.php?11400-OBD2-Coil-Packs-Full-set-of-6-brand-new!

I think fabricating the 2 - 3 pin adapter would be a minor issue, particularly since in North America there are likely sufficient RL and TL wrecks able to donate the plugs. These guys seem to be able to magically source the oddest connectors so in a pinch they may be able to provide new plugs to make the adapter.

http://www.cycleterminal.com/motorcycle-connectors.html

As Kaz notes, the later OBDII coils likely require the later coil cover. A new set of coil covers probably changes the whole cost calculation. However, the pre OBDII coils do seem to be in short supply so conversion may become a matter of necessity at some point.
 
$195 each for the coil covers and the RR cover is only available in Japan by the look of it @ $106 each before shipping...get them while you can...

At that price, if you know someone with a set of the OBDII covers, it might be viable to have the cover scanned to obtain the dimensions and then have copies 3D printed. High heat ABS might do the trick (110 C); but, there are more exotic higher temperature high impact printable plastics such as HP's multi jet Fusion PA12. I have an older vintage Volvo and I know that people have been printing interior trim pieces in ABS that are no longer available. Just need an excuse to do an experiment. Needless to say that you won't be printing the HP stuff on the home 3D printer that you bought off the internet.

I suspect that as the OEM parts availability starts to dry up, 3D printing may become the parts source for cars like the NSX. There are companies that can print titanium and aluminum. I haven't investigated and don't know how the strength compares to a forged or cast product; but, it could be a solution for low stress pieces that are no longer available.
 
http://www.nsxcb.co.uk/showthread.php?10150-Britludes-NSX-story&p=119769#post119769

just to save wading though to page 21 lol


re.obd2 coilpacks.... looking at the relative circuits, there is a diode internally that's the other way around between the 2 pin and 3 pin coilpack (ignoring the obd2 sensor pin)... not sure if that will make any difference, or is just something that is related to the different spec spark plug.....
 
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http://www.nsxcb.co.uk/showthread.php?10150-Britludes-NSX-story&p=119769#post119769

just to save wading though to page 21 lol


re.obd2 coilpacks.... looking at the relative circuits, there is a diode internally that's the other way around between the 2 pin and 3 pin coilpack (ignoring the obd2 sensor pin)... not sure if that will make any difference, or is just something that is related to the different spec spark plug.....

Excellent catch.

A voltage is induced in the secondary of the ignition coil when the current in the primary winding changes. The spark is induced when the primary current, which maxes out around 10 - 12 amps, drops to zero when it is shut off by the igniter module. When the igniter turns on at the beginning of the dwell cycle and the coil current starts to increase, it is possible to generate a rather feeble spark because of the increasing current. Of course this spark would be way to early leading to the possibility of engine damage. The spark at the start of switching on the coil current and the spark when the coil current shuts off have opposite polarities, so to block the spark when the coil current switches on a blocking diode is inserted in the connection to the plug. That diode is reversed biased when the coil is switched on; but, becomes forward biased when the coil is switched off allowing the spark current to flow.

In the original ignition coils, it appears that the coil winding and diode are configured to generate a negative spark voltage and in the later OBDII coils the coil winding and diode are configured to generate a positive spark voltage. Theoretically, either should work and I know historically both have been used. However, the configuration in the later OBDII coils does seem to be the configuration that is commonly in use with COPs equipped with misfire detection.

I don't think the switch in coil polarity is related to a change in sparkplugs. I expect that it is related to implementation of the misfire detection circuit in the coil. The misfire detection circuit appears to be a capacitive voltage tap. Whether it is just a matter of convention or whether there are practical design reasons, I am guessing that that the misfire detection module is configured to watch for a positive voltage spike on the capacitive tap to confirm firing of the spark plug. Hence the change to the coil.

The igniter module which switches the coil currents retained the same part number right through the production run. The test values for the primary winding resistances on the early coils and OBDII coils is the same which means that the maximum obtainable coil primary current is the same (jives with retaining the same igniter). As such, everything appears to match up on the primary circuit of both coils (hold that thought for a moment).

As long as Honda achieved the change in spark voltage polarity by internally reconfiguring / reversing the secondary winding in the OBDII coils, the OBDII coils should work in a pre OBDII car - setting aside for the moment any consideration of fitment issues. However, I think it would be possible to achieve a reversal of spark voltage by reversing the primary winding connections. That would be a strange way to do things. On the pre OBDII coils, the 'a' primary terminal is connected to the +12 v supply and the 'b' primary terminal is connected to the igniter module. As long as that 'a' and 'b' terminal connections remain the same on the OBDII coils, you are good to go. I have an OBDII equipped car and service manuals with wiring diagrams; however, they are all locked up in secure storage until Spring so I haven't been able to confirm that the primary winding connections on the OBDII coils remains the same as on the pre OBDII coils.
 
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interesting..... :)

re. spark plug change... it was noted on some ford forums that use edis system, and wasted spark coils firing 2 cylinders, that the cylinders one side of the coil pack were wearing differently to the other ... so i wondered if that was the thinking behind the spec change....
 
I don't think the plug change is related to the wear issue you flagged. Wasted spark systems will have differential wear on the paired plugs. On one plug the current flows from the tip to the ground electrode and on the other sparkplug the current flow is from the ground electrode back through the spark plug tip. As a side note, wasted spark coils typically don't have the barrier diode because the two plug gaps in series presented enough of an electrical barrier to prevent sparking when the coil is initially energized.
 
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