Chevy & GMC Vans

Any guesses as to the genesis of my RF noise appreciated...

VEH:
89 Astro
Z vin engine

I'm getting RF noise on my ham radio(s).
Here's the specifics -

Noise is only on ONE freq, 146.52 MHz.

Noise happens on the vehicle installed ham radio
OR
on an HT (Handheld portable radio) or any ham radio that's near or in the vehicle. It doesn't have to be connected to the vehicle power and or antenna. If I move my HT around inside the cab of the van, the noise is greatest (worst) when the HT is in the driver/passenger area. Noise on the handheld radio stops when I move into the rear compartment or outside the van. As if the noise was eminating from somewhere near the dog house.

Noise is in synch with VEHICLE SPEED, not ENGINE SPEED. ie, moving along at 5-10 MPH, trans in neutral, revving the motor makes no difference. The noise seems to synch with wheels or drive shaft.

Noise happens only when ign key is on or running. Engine doesn't have to be running, but ign has to be on.

Seems to have started after one of my jaunts into the desert, bouncing around on some pretty rough desert washout roads. But that may be pure coincidence.

MY GUESSES?
Speedo sensor on the transmission? Anyone ever have a sensor go bad?
My speedo and odometer seem to read ok, not dysfunctioning.

Doesn't seem to be the usual culprits (fuel pump, plugs, wires etc) since it
varies with VEHICLE speed not ENGINE speed.

Any guesses, similar experiences, secrets of life or margarita recipes greatly appreciated.

Thanks -


Craig 'Lumpy' Lemke

http://www.n0eq.com

Nice camo van, and welcome to the site!

Sounds like you have it figured, I'd unplug the speed sensor and see what happens. You could also pull the gauges fuse (I think) and see if it is the speedo.

Weird problem. Good luck!

My RFI noise problem was indeed the VSS.

Pulled the connector and that killed the noise. So, pulled the VSS, found a cracked housing (leaking a bit of ATF on the driveway) and the inductor poles were worn to nearly nothing.

10mm bolt and a twist pulled the VSS from the transmission. It comes out easier if you put the trans in neutral. Replacement sensor was 30 bucks at Pep Boys.

Slip in the new, dab some contact grease on the connectors, tighten the bolt, test drive.

Result:
No RFI noise. Seemed to cure some "slippery" shifting I was experiencing. Might even cure the minor oil (ATF) leak I was seeing on the driveway.


Lumpy

You Played on Lawrence Welk?
Yes but no blue notes. Just blue hairs.

http://www.LumpyMusic.com

Good deal!

Well, I THOUGHT that replacing the VSS cured my odd RFI. It didn't.
Now, just to add to the confusion, the RFI comes and goes. I can completely
unplug the VSS and the sound may or may not be present, just depends on
the phase of the moon, how I hold my mouth, current gold prices, whatever.

For those wishing to try and diagnose, please remember the RFI occurrs
in synch with the VEHICLE ROLL SPEED, not engine speed. Rev the engine
has zero effect. Slowing the vehicle at a stop sign, no matter what the
engine is doing, results in
BWAP...BWAP......BWAP.........BWAP............BWAP...............BWAP....................BWAP

I can "sniff" around the engine with a portable radio and find the
RFI nearly everywhere under the hood, under the dash, seems like
near any GROUND on the vehicle. ie I can go to a frame bolt in the
rear of the van and hold my sniffer antenna near the bolt/frame
and hear the RFI.

RFI is present only when the ignition is on.

Unplug the big connector under the hood (that goes to ECM and sensors)
and the RFI stops.

What about the Torque Converter Solenoid? That's about the only other thing
that sits on or near the drivetrain.

Or what about the ECM itself? Nothing is throwing any trouble codes on the van.
Can the ECM go bad and NOT show trouble codes?

Thanks in advance from this increasingly frustrated shade tree mech.

Craig 'Lumpy' Lemke

http://www.n0eq.com

Possibly the DRAC module located under the dash to the right of the steering column?

I'm not 100% certain, but I don't think an '89 has a DRAC module.

Could be the speedometer itself? On my '87 there is a device in the speedometer housing that converts the mechanical action from the cable into a speed signal that then gets sent to the ECM. But your van sounds like it might be different if you already replaced a speed sensor on the trans. I don't have that on mine.

6spd_monte wrote:I'm not 100% certain, but I don't think an '89 has a DRAC module.

Could be the speedometer itself? On my '87 there is a device in the speedometer housing that converts the mechanical action from the cable into a speed signal that then gets sent to the ECM. But your van sounds like it might be different if you already replaced a speed sensor on the trans. I don't have that on mine.

Roger x 2. No DRAC, no mechanical speedo.

Currently wrestling with the Rancho MyRide controller install.
Weird little airline connectors.

Lump

you have a DRAC because your van has an electronic dash. If you had a good old fashioned mechanical speedo then you would not have a Drac. I would check for worn wires under the dash. The other thing to check is the ground on the computer located in the passenger side kick panel. Failing that could you put some sort of insulation under the carpet to dampen any magnetic fields that might be coming off the engine.

Slightly off-topic, Lumpy, but what kind of rig are you running?

Kidhauler wrote:you have a DRAC because your van has an electronic dash. If you had a good old fashioned mechanical speedo then you would not have a Drac...

I'll keep looking. It's not in the space between radio and AC controls as
most places suggest. I've been "up in there" under the dash and haven't
seen any gizmos that I'm not able to identify.

I was hoping I did. Gives me a good excuse to get bigger tires.


Lump

They are hard to see in there some times. I looked for for one on my 90 van for hours and never did find it.

The DRAC module is behind the steering wheel. It has been a white box with a single connector on it on any of the vans I have worked on.