NSX Pulser Engine Control Unit clicking

[fit2betied]

Have this awful clicking (sounds like relay chatter) from behind the drivers seat. I've tried to isolate it and think it is coming from part 39985SLO951 which is listed as the NSX Pulser Engine Control Unit. It's on the back wall between and behind the TCS and the FPRU (car has a CTSC). Clicking gets worse when accelerating, or if the A/C is on, or if I turn on the headlights. Anybody familiar with what this pulser control unit does. Do the symptoms make sense to pin back to this part. It's really hard to feel vibrations on any of the parts from the clicking - this seemed tho have the most vibration in time with the clicking. Thanks for the help - sounds like a typewriter behind my head when driving.

 

[Old Guy]

Have this awful clicking (sounds like relay chatter) from behind the drivers seat. I've tried to isolate it and think it is coming from part 39985SLO951 which is listed as the NSX Pulser Engine Control Unit.
- sounds like a typewriter behind my head when driving.

You refer to the Pulser Engine Control Unit. Where did you find the reference to 'Engine Control Unit'? In the Service Manual, I could not find any description of a devise or find any reference in the electrical schematics of a pulser associated with the ECU. The only 'pulse thing' that I am aware of is in the electric power steering system. The service manual refers to it as a pulse unit rather than pulser. The steering system pulse unit looks like the part you listed and is located in approximately the same location as you described on the inside back bulk-head. The service manual does not provide a description on the pulse unit function; but, from the EPS schematic it appears to be a signal conditioner for the speed signal that the EPS gets from the differential speed sensor.

Because it is a speed signal, it is reasonable that the frequency of the noise might change as the engine speed changes; however, from the exceedingly limited information in the service manual, it looks like the pulse unit is purely electronic so it is not apparent that it could be making any noise, unlike a mechanical relay. Because it is connected to the differential speed sensor, does it only make noise when the car is moving or does it make noise in neutral at a stop? It should be possible to confirm that it is the noise source by unbolting the pulse unit from its mount and wrapping it in some rags to provide sound damping. Test drive and if the noise is reduced, then perhaps the problem is the pulse unit. Personally, based on the very limited description in the service manual, I am inclined to think it might be something else; but, the noise reduction test should confirm it.

 

[Larry Bastanza]

I am thinking this would relate more to vehicle speeed vs. engine speed........

 

[fit2betied]

You refer to the Pulser Engine Control Unit. Where did you find the reference to 'Engine Control Unit'? In the Service Manual, I could not find any description of a devise or find any reference in the electrical schematics of a pulser associated with the ECU. The only 'pulse thing' that I am aware of is in the electric power steering system. The service manual refers to it as a pulse unit rather than pulser. The steering system pulse unit looks like the part you listed and is located in approximately the same location as you described on the inside back bulk-head. The service manual does not provide a description on the pulse unit function; but, from the EPS schematic it appears to be a signal conditioner for the speed signal that the EPS gets from the differential speed sensor.

Because it is a speed signal, it is reasonable that the frequency of the noise might change as the engine speed changes; however, from the exceedingly limited information in the service manual, it looks like the pulse unit is purely electronic so it is not apparent that it could be making any noise, unlike a mechanical relay. Because it is connected to the differential speed sensor, does it only make noise when the car is moving or does it make noise in neutral at a stop? It should be possible to confirm that it is the noise source by unbolting the pulse unit from its mount and wrapping it in some rags to provide sound damping. Test drive and if the noise is reduced, then perhaps the problem is the pulse unit. Personally, based on the very limited description in the service manual, I am inclined to think it might be something else; but, the noise reduction test should confirm it.

Thanks for the response. Could find nothing on Prime or Facebook with the part number. Found something on eBay with same part number and that was what they called the part "Pulser Engine control unit". Can not find any other info anywhere. Posted a video on NSX Facebook Owners Group (Holly Trumble) but no help there. Can't believe I'm the first to experience this. Finding it difficult to isolate the sound (very ackward spot to get to while car is moving). Does not occur while idling but does occur when revving motor without moving. Seems to have an electrical bent (things that draw current - lights, AC, acceleration (fuel pump?) seem to bring it out). Trying hard to avoid buying and trying till I find it. Really appreciate thoughts to date - but would love to resolve it (worried it's going to leave me struck on the side of the road at some point).

 

[Old Guy]

Agreed that the Acura parts web sites refer to it as a Pulser; but, not as a Pulser Engine Control Unit. That must be a little error by whoever posted it for sale on EBay. As an aside, the Pulser / Pulse unit part number is SL0 not SLO if you do go looking.

The pulse unit is in a really bad place to try and pinpoint the source of the noise. Hence my suggestion to isolate it and wrap it in some sound absorbing material. If the noise is un attenuated, then it is likely not the pulse unit. It is a kind of pricey unit so I would not be inclined to try diagnosis by replacement. If it is the pulse unit and it does fail it is unlikely to leave you stranded. Perhaps no power steering; but, not stranded. The pulse unit is driven by a speed sensor on the differential. The fact that the noise occurs while revving the motor; but, not moving makes me think that it is something other than the pulse unit. As Larry B. noted, if it were the pulse unit, and the noise was associated with speed the frequency of the noise would increase linearly with vehicle speed, not engine speed.

I think the fact that you didn't get any responses on this is a reflection of the fact that you may be the first person on Prime (and maybe ever!!!) who experienced a problem with the pulse unit. I had to dig out my electrical trouble shooting manual which showed all the components located on the back bulk head and that allowed me to back trace through the connector numbers to find the device in the power steering circuit (made me feel like George Smiley from a John le carre novel). If you do buy a replacement from Acura its probably going to come with a covering of dust!

 

[fit2betied]

Great input. Thank you. In the past I had a poor connection on a cable between my alternator (have a CTSC so they had to pigtail the alternator cable to extend it since it now runs backward) and the fuse box headed to the battery. Did an "emergency roadside repair - wonder now if that could be coming loose again causing intermittent momentary loss of power to one of the relays. Wouldn't the relays be running off the battery though - not the direct alternator current. Grasping a bit for answers here. Just went out again and when car is not moving neither lights nor A/C is causing clicking. Only when Engine hits about 2K rpm then it starts. Will get a second pair of hands tomorrow to see if wiggling connection makes it better or worse.

 

[Old Guy]

In the past I had a poor connection on a cable between my alternator (have a CTSC so they had to pigtail the alternator cable to extend it since it now runs backward) and the fuse box headed to the battery. Did an "emergency roadside repair - wonder now if that could be coming loose again causing intermittent momentary loss of power to one of the relays. .

I am really confused by the comment 'the fuse box headed to the battery' . You need to elaborate on that a bit.

The pulse unit sits right between the Traction control module and the fuel pump resistor by-pass relay. The fuel pump relay is mechanical so it can make a small amount of noise on operation. However, the fuel pump relay should not be operating at idle or low engine output. It only operates at high engine loads to increase the fuel pump speed. However, if you have wiring issues and the lead wire from the relay to the ECU is momentarily grounding out then the relay could be going on-off-on-off.... This does seem a bit of a stretch as a cause; but, it is really easy to check. Just unplug the relay and test by idling or driving around slowly. If the noise is still there then it is not a fuel pump relay problem. Don't go hammering on the throttle because the fuel pump is stuck on low speed and you could cause the engine to run lean with all the associated negative effects. However, since you have a CTSC car perhaps the fuel pump relay has already been bypassed? When you referred to the FPRU in your first post were you referring to the fuel pump relay or that add-on fuel management thingy that some CTSC installations have?

 

[Wirewizz]

Fittobetied, did you ever diagnose the clicking issue you were experiencing last year? I have the very same issue. It's intermittent, but exactly as you discribed. Thanks in advance!

 

[NAP2]

Has anyone resolved this ?

I hear a repeated click. Very annoying. Will go away. And randomly come back. Low speed high speed with headlights on and off. Ac has no influence. -__- ‘02 nsx

 

[NAP2]

What is the pulser unit

 

[Old Guy]

What is the pulser unit

It appears to be a signal modifier / conditioner that takes the speed signal from the differential VSS and applies it to the electric power steering controller.

 

[mwagner10702]

After reading this I am glad I have a manual steering rack.

 

[Old Guy]

After reading this I am glad I have a manual steering rack.

If your opinion is related to the difference in feel - fair game. With respect to the 'pulse unit' (the description in the service manual) being a power steering problem - I don't think that anybody has actually determined that the pulse unit is a problem. The OP never followed up on the problem and none of the parties reporting clicking reported problems with their power steering. Lots of things could be causing random 'clicks'.

 

[mwagner10702]

If your opinion is related to the difference in feel - fair game.

My opinion is born purely from the fact that the manual steering system is simpler than the EPS system. Less electronics = fewer issues.

 

[NAP2]

I have clicking at slow lace and fast pace (clicks( and it’s when the car is in motion and also at idle. I haven’t resolved it. The car drives fine. Power steering is fun. But those darn clicks. Sometimes it clicks and other times I can go hours without a click

 

[NAP2]

Behold i have the answer. 2 months in my alternator went out. I had it rebuilt and noticed clicking got worse. Much more rapid. At the same time noticed the voltage fluctuations. Took it out and they replaced the voltage regulator (i think that’s what it’s called). Put it in and it read consistent and no more clicks. Ever. I’m 2 months in with new alternator and no clicking.

 

[fit2betied]

Clicking remains :-(

Sorry to have gone silent so long. Replaced a couple of components with no luck yet. Certainly seems heat sensitive - much worse when engine and/outdoor weather is hot. Can pretty much go all winter without hearing it much. Do you have the part number for the voltage regulator you had replaced? My clicking is coming from the back panel between the two seats closer to the driver side. Am planning on taking it to Atlanta this summer before NSXPO and having it looked at again (last time I took it in there was a freak snow storm and it wasn't safe to drive it araound enough to get the engine good and hot). Will certainly post the results if I ever get resolution.