Tech Talk - RFI Troubleshooting

(603) 226-DYNO

How can I reduce ignition noise?

Electromagnetic Radio Frequency Interference (EMI or RFI) from the test engine’s ignition can be a major problem when trying to capture data via sensitive electronic instrument running adjacent to a high compression spark-ignition engine. EMI symptoms include bad dyno tach readings, erratic servo operation, Personal Computer lock-up, and holes or spikes in the captured data.

Interference worsens as the engine’s throttle is opened - this is due to the rise in spark voltage that accompanies any increase in cylinder pressure. Supercharging, turbocharging, and many race modifications that increase cylinder charging drive up ignition energy demands, often creating severe interference problems. As RPM increases (raising the EMI/RFI frequency) the number of interfering "pulses" generated goes up proportionally. The worst conditions often occur right around peak torque output (both cylinder pressures and RPMs are high) and the resulting EMI is often known to crash (blue screen) even a high quality PC running nearby.

Fortunately, there are steps that can be taken to reduce the interference at the source and also to harden the dynamometer's electronics and your PC from this ignition "noise." Taking one or more of the following preventive measures will generally allow testing of even the wildest combinations. EMI  problems are not in any way specific to the DYNOmite, so your ignition system’s manufacturer may have other suggestions you can follow.

1) Run all ground leads to either the engine’s battery (or block if no battery is in use) or to a clean common junction connected by a heavy-gauge ground cable to the engine’s battery. Ideally this battery's negative terminal and/or dynamometer's frame itself should be connected directly to a quality earth ground (e.g. buried large-diameter 8' copper ground rod) via a heavy-gauge wire (for a very low resistance connection). Avoid multiple ground points as this often creates a “ground loop” (where RFI can get onto the circuit).

CAUTION: Always hook up all the ground leads before hooking up any of the power leads for the DYNOmite Data Acquisition module, its accessories, or the engine. Failure to follow this precaution can lead to circuit damage not covered under warranty!

2) Try using resistor sparkplugs (or caps) and also run graphite ignition cables (or genuine MAGNECOR brand Race Wires). These components tremendously reduce the level of RFI generated by the ignition. Subduing the noise at the source of generation is much more effective than chasing down every dyno harness lead that might be receiving these unwanted random signals.

CAUTION: Spiral wire wound “suppression” ignition cables are not nearly as effective (at reducing EMI) as true graphite core cables. The cheapest set of graphite wires will “out-suppress” the most expensive wound metallic wires. The only effective EMI suppression wires (other than the preferred graphite or carbon core) used in the high end automotive racing world are manufactured by MAGNECOR. For some straight talk about the pro's and con's of various type sparkplug wires, read "THE TRUTH ABOUT IGNITION WIRE CONDUCTORS" or "A Brief Overview of the Performance Aftermarket Ignition Wire Industry in the USA".

Tip: Keep an inexpensive set of graphite core cables in the dyno cell for troubleshooting problem ignitions. You don’t need expensive high temperature 8+ mm silicone jacket wires with high quality boots to survive on the dyno. Even installing just a graphite core coil lead may do the trick. New graphite cables will not reduce the engine’s power.

3) Keep the ignition wires (and coil wire) as short as practical and avoid routing the DYNOmite’s harness leads parallel or near to the ignition wires.

Tip: The EGT probes have extra shielding on them to allow operation near the ignition. Conversely, the Engine Temperature leads are quite sensitive to RFI, keep them away from the ignition if you can.

Tip: Temporarily iinstall braided metal shielding, such as Aeroquip stainless braid hose (grounded at one end to the engine block) over all the sparkplug (and coil) wiring. This trick was used on early Corvettes and many marine applications where the fiberglass engine cowling provided poor RFI suppression.

4) If EMI is interrupting communications between the DYNOmite Data Accusation Computer and your PC running DYNO-MAX (via a RS-232 serial port connection) the use of Land Sea's special shielded and filtered cables may help. Symptoms include dropped data packets or random data spikes that worsen in intensity as the throttle is opened (increasing cylinder pressure and spark intensity). Avoid using USB adapters as they just add another point of EMI sensitivity - instead use a computer with built-in RS-232 ports (or add an RS-232 port bus card) so that there will be an uninterrupted grounded shield from the DYNOmite to the PC..

Tip: In extreme cases fiber-optic RS-232 serial "cabling" is available. Such hook-ups use a converter at each end that translates the normal hard-wired connection into a light signal that runs along the fiber optic link. However, be sure to select models that do not require power from the PC or DYNOmite RS-232 signal to operate! If you go fiber optic, order 100' long leads so that you can run one test with the PC far away from your engine - if the problems go away during the remote test, its your PC (so jump to suggestion #7 below).

5) Modern computers have gotten lighter and less expensive - and plastic housings are part of the reason. Unfortunately, plastic offers much less EMI shielding that the heavy metal cases used for early PCs. Toady, even many of the most expensive model PCs and laptops are very poorly "hardened" against the levels of EMI present near a spark ignition engine. If you can, try a few other models (or brands) to find the most robust computer.

6) Most modern PCs are no longer grounded via their power cords or chargers. In certain cases running a large gauge (#12 or 10) wire to ground the PCs case helps - try it both ways. Moving a problem PC further away from the engine is always a good idea. Sometimes, simply reorienting  the position of the PC (rotating it 90 degrees), moving the angle of the power cord, etc. may uncover a less sensitive position (just as moving a radio's antenna effects its ability to pick up a weak station).

7) Place your PC and monitor inside an EMI shielded enclosure to harden it against the interference. You do not necessarily need a $6,000 military specification EMI housing - something like the DYNOmite RFI/EMI Shielded PC Cabinet should do the trick.

For DYNO-mite dynamometer technical assistance - telephone or e-mail: sales@land-and-sea.com
© 02 Sep 2008 Land & Sea, Inc. 25 Henniker Street; Concord, NH 03301-8528 USA  +1-603-226-DYNO