Wayward Speedo

FatBoy · #1 (**permalink**) 02-22-2009, 06:03 AM

Has anyone else experienced strange readings from their electronic Kirkham speedo?
Mine works great whilst the car is moving, but when it comes to a halt (with the engine still running) it reads random speeds, typically around 140mph, but sometimes off the scale. It also clocks up miles whilst doing this.

KMS replaced the original speedo as they believed it to be faulty, however, the replacement is doing exactly the same thing.
I'm running a toploader with a KMS supplied sender unit.
Thanks,
Paul

jrjmac1 · #2 (**permalink**) 02-22-2009, 08:38 AM

I have one that does the same thing, fine and accurate while driving. At rest or when I go in reverse the needle goes to 180 then back to 0! My built in gas gauge is erratic also. I plan to call them on Monday.

John

Ronbo · #3 (**permalink**) 02-22-2009, 05:20 PM

Just curious, do you have a ground strap from the engine to the frame? A quick test would be using a set of jumper cables between the engine block and the frame.

FatBoy · #4 (**permalink**) 02-23-2009, 12:14 AM

Quote:

Originally Posted by Ronbo

Just curious, do you have a ground strap from the engine to the frame? A quick test would be using a set of jumper cables between the engine block and the frame.

Hi,
Yes, I have an earth strap from the engine block to the frame.
Paul

xlr8or · #5 (**permalink**) 02-23-2009, 09:22 AM

Kinda funny seeing the advert next you post for those same gauges saying "No More Bouncing Needles".

I would check the ground on the sender or try replacing the sender.

Ronbo · #6 (**permalink**) 02-23-2009, 12:12 PM

Since none of the other gauges are effected and if the fuel reading is also erratic it sounds like they got a bad run of speedos.

A98Coupe · #7 (**permalink**) 02-26-2009, 05:44 AM

Paul,
Sounds like it could be the inductive speed sensor which is sending an erroneous signal to the speedo when the vehicle is stationary. Have you tried replacing the speed sensor? Failing that, you always go back to the good old reliable "bouncy Needle" mechanical Smiths unit!

Rick162 · #8 (**permalink**) 02-26-2009, 11:13 AM

We want to assure all customers that we are here to help and make sure our gauges perform as they are supposed to.

We found that some cars have more EMI (Electro Magnetic Interference) noise than others. When we heard of the problem we immediately went to work looking for the cause.

We have been unable to replicate the condition that you speak of. To date all known issues with the speedometer have been with a mechanical to electrical converter. We know of no problems when using a transmission that has a built in electrical speedometer output.

To narrow things down let us know please let us know which ignition system, transmission and alternator systems your cars have.

Our later speedometers have a purple wire loop coming at of the back of the speedometer. By cutting the purple loop more noise suppression is added to the front end of the speedometer. This should eliminate any erratic speedometer movement while the car is stopped. Do not cut this wire if you do not have a problem.

If your speedometer does not have a purple wire loop extending out of the back and you are experiencing an erratic speedo while stopped, you can try to cancel some of the excess noise by adding a 200K ohm, 1 watt resistor inline with the signal wire. Once you've done this it should solve the problem. If this sounds to daunting you can send in your speedometer and we will update the speedometer to the newer noise suppression board.

FatBoy · #9 (**permalink**) 02-26-2009, 12:30 PM

Hi,
Sorry, I've been away for a while.
Aaron has been very attentive and helpful in diagnosing the problem and we now think we have a solution. I'll report back in due course, but hopes are high.

Thanks for the suggestions.

Paul

Ronbo · #10 (**permalink**) 02-26-2009, 04:24 PM

Sounds like the input impedance on the speedo is a little high, great for isolation, bad for noise rejection.

Shielded lines to the sensors would help, auto electrical systems are inherently noisy especially as the battery ages. About the only way to clean this stuff off is to have decoupling caps hung off everything especially inductive loads. The ignition coil and alternator windings generate most of it.

Hang a capacitor off the positive side of the coil to ground and this will probably clear up. The ignition coil is the worst source as it's got a long path through small gauge wire to the main filter, the car battery.

FatBoy · #11 (**permalink**) 08-12-2009, 07:46 AM

Speedo update:

Aaron sent me the new model speedo with the purple wire loop at the back. This has been installed and after confirming that the needle still jumped around, I cut the purple wire, which appears to have fixed the issue. The needle has, so far, proved to be stable and accurate.

Thanks Guys.

Paul