NSX Ignition noise on fm stations 3

[BarneyD]

Hey all,
I'm a technician at an Acura dealer here in Tn. I'm working on a 94 NSX. (OBD 1) For those that aren't farmiliar with the ignition system on this car, it has individual coils on each cylinder. I'm having trouble figuring out why I have an ignition tick that is directly related to engine rpm ONLY on fm stations. I've replaced the plugs with factory NGK platinum plugs. (it originally had Iridium plugs that are commonly known to cause noise in fm stations from time to time on NSX's.) I've also put brand spanking new coils in the car. Nothing has even changed the tick noise I'm getting. It has the factory Bose stereo system.
Also, the noise cannot be heard on AM, Cass, or the CD changer. ONLY on FM stations. The car has recently had a motor replaced by another shop....so there may be something going on there. So, any help would be GREATLY appreciated.....

Barney Demonbreun
Nashville, Tn.

Barney Demonbreun
Technician for Gary Force Acura, and owner of;
Ashland Motorsports
1304 Big Marrowbone Rd.
Ashland City, Tn. 37015

 

[patprimmer]

Are you sure it is not alternator or other motor driven source.

Is it supposed to run resistor plugs.

could the compression ratio have been increased.

Have you closed down the plug gaps a little to see if it dissapears with a tight gap.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TheBlacksmith]

Is there any factory shielding or ground straps that could have been damaged or left off when the other shop replaced the motor?

 

[MacGyverS2000]

The use of Iridium (or any other) plugs should have no effect on noise level. Check the alternator and grounding straps... make sure all connections are clean and oxidation free. Check the resistance on the injectors to make sure they're within spec. Disconnect the alternator and run the engine on a battery only for a few seconds, see if the noise disappears.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[WGJ]

Is the hood properly earther / grounded?
If it isn't then try a braided earth cable, body to hood.


Bill

 

[BarneyD]

First of all....I'd like to say thanks for the responses to this thread. I'll try to answer any questions in this one reply.
I took the belt off of the alt. and ran the car. The noise was the same. As far as the compression ratio....the motor is a remanufactured motor from ?? The heads may have been shaved a slight bit when the motor was assembled. Again...I don't know this for sure becuase I wasn't part of that equation. The owner has no idea as well.
I'm about to contact the Honda / Acura tech line to see what they can come up with. I'm leaning toward a loose / corroded ground strap somewhere. As soon as I can free up from working on my other customer work I'm going to look it over and try to find a ground issue.
The injectors appear to be the factory injectors. So that shouldn't pose a problem...(how many times have I been bitten when saying that?!!) But I will keep that possibility open as well.

Thanks again guys,
Barney Demonbreun

Barney Demonbreun
Technician for Gary Force Acura, and owner of;
Ashland Motorsports
1304 Big Marrowbone Rd.
Ashland City, Tn. 37015

 

[MacGyverS2000]

If the injector resistance has decreased too much, overswing of the control signal will cause some serious EM spikes. No need to check out the current grounding straps, just connect a thick cable between engine block, alternator, and battery... if the noise doesn't disappear, it's not going to be an engine grounding problem.

Check the cable for the FM antenna... the coax grounding shield can often snap loose, both at the radio side and the antenna side. A bad shield will pull in noise from anywhere.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Fabrico]

Anything emanating from the crank or cam position sensors