Ignition & Injectors
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Contents: Basics; Shielding; Expensive Plug Wires; Coil Over Plug; Fuel Injectors; Odds & Ends;
There is one major item to keep in mind while reading this article. Radio Frequency Interference (RFI) is best cured at the source. This is especially true of ignition and injector RFI. Secondly, some forms of RFI, AFI, and EMI, may be caused by ground loops, and other poor wiring practices.
Very few new vehicles utilize high-tension ignition wiring, as most have switched over to Coil Over Plug (COP) technology in one form or another. However, a most of legacy vehicles use high-tension wiring, along with some General Motors' Gen III and IV small-block V6s and V8s. While they use individual coils (most are hidden under plastic panels), there are short plug wires from the coils, and around the exhaust manifold to the plugs.
Ignition wiring comes in many forms, sizes, and colors; in both resistive core and solid core; and at least one type with a spring core. For the most part, the wiring used by automobile manufacturers is all resistive core which minimizes RFI leakage. The core itself is made from fiberglass and/or Kevlar® and is impregnated with graphite and/or an amorphous carbon. The typical resistance varies between one and four kilo ohms per foot. Incidentally, replacing resistive wire with solid wire will greatly increase ignition RFI, not reduce it!
The outer cover can be in one or more layers of high-temperature silicon rubber although some types use space-age plastics. A few aftermarket types have an outer conductive sheath touted to further reduce RFI.
One important item to keep in mind about ignition wires, no matter who made them; they age. Automobile manufacturers often state that no tune-ups are required for at least 100,000 miles, they're not amateur radio operators! I used to replace mine every 25,000 miles or so, along with the plugs. While not an inexpensive undertaking, if you're plagued with ignition noise, this is your first line of defense. This goes for the plugs in COP equipped vehicles too.
Amateurs worry about ignition RFI a lot, but not nearly are much as airplane designers do. The reason is simple. They utilize AM exclusively and excessive RFI wrecks havoc with AM. In some cases, we can use their technology to minimize our RFI problems.
RFI shielding any ignition is not an easy task especially today as most factory plug wire sets are pre assembled. The photo on the left shows a coil jumper wire with a short piece of braid fastened by using heat-shrink tubing. Note the pigtail wire used to ground the shield. Most major amateur radio supply houses carry 1" wide tinned copper strapping which can be used to cover ignition wires. If you can find it, the round variety is preferred. The photo below right shows an application using it. By the way, higher res versions of these photos are in the Photo Gallery.
For those with less zeal (count me in!), there is another way thanks to 3M Company. Their 1181 copper foil tape is just the ticket for shielding ignition wires. All Electronics stocks the tape, and it's also available from Digi-Key. With some diligence you can even shield distributor caps and coil packs. The photo below shows how the tape is applied. It's adhesive backing is conductive, and adjoining pieces can be easily soldered as shown in the photo. You'll still need a fair amount of 
patience and perseverance as the tape has a tendency to curl when the backing is pulled off. On standard sized 6 mm wire, the 1" wide tape just encircles the wire. On 8 mm wire, you'll have to spiral the tape around the wire. A little dab of solder here and there will help keep the tape in place. If you have the funds, heat shrink tape as sold by Digi-Key is just the ticket for a professional looking installation.
It would be nice if we didn't have to go through this exercise, but alas we do in some stubborn RFI cases. If you're one of those with minimal ignition RFI, count yourself lucky.
Magnecor, among others, manufacture heavy-duty wire sets designed to improve performance, and reduce ignition RFI. In most cases, they fulfill both claims quite well. Their drawback is cost. A complete set for an average V8 is about $300, down to about $140 for a 4 cylinder. If your vehicle uses plug wires, these premium sets might just be the ticket. Personally, I think shielding works better, but I have to be honest here; the last four vehicles I've owned have been equipped with COP units, so I haven't tried any of these later versions.
In the days gone by, every internal combustion gas engine was equipped with spark plugs, ignition wirings, a coil, and a distributor. Or perhaps a magneto combining some of the aforementioned parts. There were tried and true methods to eliminate or at least reduce the ignition hash we all endured. Since the mid 70s when the first EPA rules went into effect, automobile manufactures have been scrambling to meet the ever-tightening emission and mileage standards. As a result the distributor was the first to go, and now the plug wires are disappearing and being replaced with Coil Over Plug (COP) assemblies. Eventually even spark plugs will be replaced with a combination direct injector/ignition module. All of these new devices require a unique approach to noise abatement.
Placing split beads over the control harnesses leading to the COP units does reduce radiated RFI, but does not eliminate it. I use 3M 1181 copper foil tape to further shield the COP units. Before I describe my installation, I need to cover an important item.
COP units have three primary wires in the harness. One is connected to the vehicle power anytime the ignition is turned on. One is the ground, and one is the control wire which connects to the engine control computer. In a recent Internet article, one enterprising amateur suggested placing capacitors across the control and power wires to ground. This is a very poor suggestion as placing any additional load on the engine control computer could very well seal its fate, to say nothing about the rise time integration or the possibility of short circuits. I have purposely not mentioned the URL to the article.
Before you start, clean the surfaces with denatured alcohol to remove any dirt and oil. Just make sure the surface it dry before attempting the application.
As you can see from the photos, installing the tape is easy, but be careful as the edges are sharp! Further, the paper backing is much thicker than the tape is (the foil is only 1.2 mils, 2.6 mils including the adhesive). Pulling it off quickly will cause the tape to curl making application difficult. An old tooth brush can be used to burnish the edges down.
For each COP unit, I cut one 6.5", one 3.5" and one 2.5" piece (yours may require different lengths). The 6.5" piece goes around the peripheral of the COP, the others over the top and partly down the sides.
If you not afraid to do a little mechanics work, you can remove the COP units (it takes a metric Allen wrench in most cases), and cover them like the left photo shows. Note that the shielding stops at the top of the seal. Don't go below the seal, or you run the risk of an arc over which can damage the COP units.
The adhesive used on the back of the foil is conductive. According to 3M's spec sheet on 1181, a 1" square piece (under 5 pounds of pressure) has a resistance of .005 ohms between the foil and the substrate it is applied on. My DVM measured my installation at .4 ohms average between the foil and the aluminum cylinder head, due to the conductivity through the mounting bolt which attaches directly to the cylinder head.
Nonetheless, I decided an additional ground was in order. As you can see in the photos, I used 1" square pieces of tape and a 14" long piece 5/16" flat copper braid. I soldered the braid to the squares and to a ground lug. This was easy on the front units, but soldering the rear ones was quite a chore. I added new strips of 1181 to cover the connectors while I was at it. The resistance between the cylinder head and the 1181 tape is now virtually zero.
The truth is in eating the pudding as they say, and the reduction of the received ignition noise was dramatic. In my case, nearly 6 S units on 20 meters! The remaining ignition noise level is about S1 to S3 depending on the band in question, with 20 and 17 meters being the worse cases.
Every modern engine uses some form of fuel injection, yet few people know how they actually work, or even what they look like. The ones shown at left are made by Delphi, one of the largest manufacturers of injectors. One of the best explanations of how they work can be found on Wikipedia. It is important to remember that fuel injectors utilize an electromagnet (solenoid), and when their field collapses (power is shut off to them), there is an electrical pulse generated. Although this pulse is RFI suppressed in most cases, it can still be heard in our receivers. It sounds similar to an ignition pulse, but is slightly narrower in bandwidth. Examples of these pulses are in my Noise ID article.
In the last few years, there has been great strides in the design and applications of fuel injectors for both gasoline and diesel engines. Heretofore, most gasoline injectors sprayed fuel into the intake manifold, but the latest iterations spray the fuel directly into the combustion chamber like a diesel does. Note the difference in the design of the direct injection unit at right, and those above left.
Fuel rail pressures have increased too, and in some current systems the pressure is nearly 3,000 psi (200 bar). And think about this; one future design calls for a fuel rail pressure exceeding 21,000 psi (1,500 bar)! Imagine what would happen if the fuel line failed?
As a result of this increase in pressure, solenoid power requirements have increased dramatically, and the level of RFI from them has also increased, factory suppression techniques notwithstanding. If you can read French, you can order a document here which describes the current EU requirements for RFI suppression from fuel injectors. It is far from ideal.
Unfortunately, there isn't much one can do to further suppress the RFI generated by fuel injectors. On most V style engines, the injectors are mounted below the intake manifold and are inaccessible. On some designs, they're under the valve covers! About all that can be done is to shield their control wires with copper tape (at least the parts we can get to).
Just in case you are interested, any RFI generated by transportation vehicles, are exempt from Part 15 of the FCC's Rules and Regulations. To wit:
Section 15.103 Exempted devices.
The following devices are subject only to the general conditions of operation in Sections 15.5 and 15.29 and are exempt from the specific technical standards and other requirements contained in this Part. The operator of the exempted device shall be required to stop operating the device upon a finding by the Commission or its representative that the device is causing harmful interference. Operation shall not resume until the condition causing the harmful interference has been corrected. Although not mandatory, it is strongly recommended that the manufacturer of an exempted device endeavor to have the device meet the specific technical standards in this Part.
(a) A digital device utilized exclusively in any transportation vehicle including motor vehicles and aircraft.
As stated above, spark plugs (like plug wire) age. This causes their spark gap to widen which increases the amount of radiated RFI. Regardless of 100,000 mile replacement schedules, replacing them at 50,000 miles (or more often) is prudent if the ignition RFI noise can't be reduced otherwise. If your vehicle uses spark plug wires, by all means replace them if they're older than a year or so. Standard factory wires are more than adequate, and spending $100+ for those fancy 8mm and 12mm wires will not net additional RFI reduction.
The first time I tried using split beads over the high tension wires on a Gen II V8 engine in a GMC truck, I was delighted to see the reduction in received ignition RFI. The second installation I tried it on was a Ford Contour V6. If anything, the RFI increased. Several other amateurs who tried beads also came up with mixed results. The only other case I know of where it helped reduce the RFI, the owner used 4 beads on each wire of a V8 Dodge. That's about $75 worth of beads. I suspect a new set of wires at about $40 would have done just as much.
I am sure there are other uses for 3M 1181 copper foil tape to aid and abet the reduction of radiated RFI in a mobile environment. If you come up with one, I'd be delighted to hear from you.