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Author Topic: "Engine Room" RFI  (Read 3578 times)

Posts: 2

« on: August 30, 2004, 06:09:44 PM »

BIG Questions.
1. Just what is the proper way to ground the exhaust? Running the wire from the clamps, or to the pipe itself some how?
2. Would wrapping the wire harness with "metal" tape work? Would the tape need to be grounded?
3. Does the "strap" have to be copper braid, or can one use copper wire? or maybe copper strips that are very thin?
I am driving a '97 Ford F-150 that belongs to my employer, and I am trying to get ideas of how to git rid of this high pitch sound that I only get with the engine running, and stays constant in tone and pitch no matter the RPM or vehicle speed. The noise generates mostly from the wire harness area on the drivers side. I can disconnect the antenna wire [either end] and the noise goes away.

Posts: 828

« Reply #1 on: September 02, 2004, 06:39:39 PM »

<Just what is the proper way to ground the exhaust?>
 Buy tinned metal "ground braid", this is woven mesh like a coax shield but flattened and fully tinned so it won't rot out under the car. You can also buy it as battery ground in 1-2' lengths and use them. Secure to the exhaust with stainless pipe clamps, and use NeverSeize or another anti-corrosion paste between the metals to ensure good conductivity and prevent corrosion. The ground braid if flexible, that's the key. Ground the tailpipe, maybe one in the middle. Check the engine grounds, there are usually several made of the same stuff, i.e. on the transmission, from the engine to the firewall, and one bypassing a motor mount.

<Would wrapping the wire harness with "metal" tape work? Would the tape need to be grounded? > What harness do you mean? Metal tape can shield and yes you'd have to ground it, usually at both ends. Coax shield is often used for this, or metal shield sold to protect hydraulic lines. If you get a "mobile ham" book up into the 70's they still show basically shielding everything in the car in order to try containing the noise.<G> Might be a lot of unnecessary or futile work.

<a '97 Ford F-150 that belongs to my employer,> I think there are some posts about the F150 in the "mobile" section, and Ford certainly should have some information for you. If the dealer says "Duh?" call Ford directly. Since the truck belongs to your employer...the less modding you do the happier he'll be.<G>

Posts: 114

« Reply #2 on: September 03, 2004, 11:29:53 AM »

I have a F150 and when I looked at the exhaust I didn't think that it would be good to put it directly on the exhaust considering the heat of the pipe..But the exhaust has 1/2" rods welded to it which are used as hangers So I used braided ground, some antioxidant goop and hose clamps .I assume you have grounded every other part of the truck also.I ended up with noise from the coil pack [6 cylinder] which i corrected with a Clear Speech unit.

Posts: 71

« Reply #3 on: September 09, 2004, 01:56:17 PM »

If it is constant in pitch without regard to speed, it is not the ignition and grounding the tail pipe probably won't make a difference.  It sounds like a fuel pump to me.  To tell, turn the truck off for a while then go back and turn on the switch but don't go so far as to start the engine.  If you hear the noise, it is the fuel pump bringing the pressure up.  It may stop once the pressure builds to the cutoff but of course it would run constantly if the truck was being driven.

Ford fuel pumps are notorious for this.  Ford may have a fix or you can try wrapping the fuel pump wires with toroids close to where the pump is installed by the tank.  There are a couple of articles about this on the web.

Posts: 71

« Reply #4 on: September 09, 2004, 02:00:25 PM »

I should add - a high pitched whine can also be the alternator but my test will tell that too.  Alternator whine will change pitch with speed and the alternator will not be running if you just turn on the ignition.  So, if you turn on the ignition without starting the truck and don't hear the noise, but you do hear the noise when the engine is running, suspect the alternator and attack it with grounding strap and toroids.
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