Spark plugs and wires

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Changing the spark plugs in the SHO is not easy. The intake manifold is supposed to be removed to get at the rearmost bank of plugs. Be very sure to cover the air holes in the lower manifold with shop towels--dropping something in there would be bad news. It is possible to change the plugs without removing the manifold. Access to the rear bank is easier if the Intake Air Control solenoid valve and its surge reservoir are removed first: pull the electrical connector from the valve, disconnect the hose from the valve to the IAC motors, disconnect the hose from the surge reservoir to the intake manifold, then remove the single 12mm bolt that secures the IAC valve bracket. Use a 6" and a 2" 3/8 extension with a universal joint to get a socket on the spark plugs.

A special tool is helpful for removing the plug wires, but don't despair if you don't have one. You should be able to grab the top of the boot and pull it off with a pulling/twisting motion. Do not pull on the wire as the connection may separate inside the boot. Before replacing the boot, use a small screwdriver to place a light coating of Silicone Dielectric compound inside the boot where it contacts the plug insulator. (Note: Silicone Dielectric Compound and Silicone Heat Sink grease are NOT the same thing. SDC is available at the dealer; this is the moisture proofing goop that is smeared inside all of the underhood electrical connectors.) (Thanks to Mike Smith for this tip).

The spark plug wells on the SHO are very deep. Kawasaki has a very neat little tool that they use to change the plugs in the ZX-7 motorcycle that also helps to properly install plugs in the SHO V-6. The top of the tool comes up even with the valve cover on the SHO motor. There is a 15 mm hexagon on the end so we can use a socket on it. It has the rubber plug holder in it. Part number is 92110-1154 as per the 96 ZX-7R service manual, Cost should be around $20. (Thanks to Ron Ellstrom for this tip).

Rather than the plug socket that is mentioned and costs around $20.00, NAPA has one for $8.99. It is EVERCRAFT TOOLS extended 5/8" spark plug socket part # 775-9052. The socket is a 3/8 drive, 4-1/2" long and retains the plug. One other item. It is a good idea to use air to blow out the plug wells before removing the plugs. It gets rid of any dirt that may be there and in my case I had just washed the engine down and had water in two of the wells.

Motorcraft AGSP32PP Plugs. The only plug to use! Do not use any plugs other than the stock Motorcraft platinum plugs (Motorcraft AGSP32PP, sometimes designated AGSP32P+). Available aftermarket "alternatives" do not have the correct geometry to allow the plug wires to seal the plug well off from water and other contaminants. If you do use non-Motorcraft plugs, expect to be replacing at least your plugs and wires again in short order. Replacement Motorcraft plugs are not identical to the originally installed plugs. The replacement plugs have platinum plating on both the tip and the ground electrode of plugs. The original plugs only have plating on one surface: three plugs have plating on the tip and three plugs have plating on the ground electrode. This is a cost saving measure for Ford.

The DIS module uses three coils to fire the six plugs. Each coil fires 2 plugs at the same time. The current leaves the coil, goes through one spark plug tip, sparks to the ground electrode, goes through the block, comes up the ground electrode of the return plug, sparks to the tip, and flows back to the coil. This causes most of the wear to be on the tip of one plug and the ground elctrode of the other plug.

The ramifications of all this are if you are removing the original plugs and are not replacing them then make sure you replace the same plug in the same location or the DIS module will not see a balanced impedance and improper ignition will result.

If you still have doubts about the need for (or wish to read more on) the need for the correct plugs, read Scott Patterson's "A Plug for Motorcraft".

Valid alternatives to the Motorcraft Plug Some more history on the Motorcraft Plug, as well as some additional part numbers are provided by John Hrinsin :

The Motorcraft AGSP32PP spark plug was designed to the ISO specifications, not the SAE design which makes it's over all size approximately 2.3mm shorter from the gasket to the top of the contact. This is why most name brand spark plugs designed to the SAE specifications do not work in the SHO motor. The same can be said for Honda, Toyota, Mazda or most other Asian designed or produced engine. In fact the Motorcraft AGSP32PP spark plug was not designed or manufacture by Autolite (that's why the APP3924 plugs don't fit), it was supplied by Denso, formally known as Nippondenso. Because of this there are other spark plugs out there that will fit the SHO engine and the well seal spark plug boot and still run perfectly. This is good for several reasons. First, just encase you can't find the Motorcraft spark plugs you can use either a Denso p/n PK16PR-L11 or a NGK p/n PFR5G-11, both are double platinum equivalent spark plugs. I have tried the Denso plug in my car and they fit perfectly! A double platinum spark plug is desirable for street use because of it's improved ignitability, smoother idling due to reduce voltage requirement and reduce electrode wear which maintains consistent performance. Considering the procedure for replacing spark plugs in a SHO involves removing the intake manifold (I do not nor does my girl friend have size 4 or smaller hands with double jointed wrists) the up to 60 K miles durability is a major plus!

For modified engines that don't accumulate a lot of miles per season, (yes, we garage the SHO in winter on the North Coast) the U-groove design from Denso p/n K16R-U11 maybe a better option. The real improvement is in the reduce quenching effect of the U-groove designs. The design results in less flame dissipation, in other words the groove gives the flame kernel a place to grow in, thereby creating a larger flame front for more effective complete combustion, especially with leaner air-fuel ratios. To get a same effect with a conventional spark plug, the gap would have to be significantly increased and the ground strap would have to be tapered, which is not always possible or advisable. It's true that these non-platinum designs will not last as long, but both have larger diameter center electrodes for extended use.

For seriously modified engines, having other spark plugs to choose from has even greater advantages. For example if you are running an over bored 3.2L engine fitted with 10.5:1 pistons or maybe running nitrous oxide or a Vortech Supercharger kit (either 6 psi or 9 psi , which can run as high as 12 psi) and/or you are also running a MSD Digital DIS 4 multi-spark ignition system the spark retard dialed in, then you will need to run a spark plug that is at least one heat range colder. To the best of my knowledge, Motorcraft doesn't offer a AGSP33PP or AGSP34PP double platinum spark plugs. They do offer these colder spark plugs in a non-platinum SAE design, but they are too tall to work in the SHO motor. If you really need to run a colder spark plug, then either the Denso double platinum p/n PK20PR-L11 or U-groove p/n K20R-U11 or the NGK double platinum p/n PFR6G-11 are your only real chooses. By the way Denso also manufactures the ACCEL spark plugs. The equivalent ACCEL U-groove spark plugs are; stock heat range p/n 0786 or one heat range colder p/n 0784.

Wow! Ford is mighty proud of those Motorcraft Plugs!!! Luckily, Ford is not the only supplier of genuine Motorcraft parts. If you look around, you can probably find them cheaper thru a local parts source. A good source of the correct plugs online is Carparts - see vendors list.

Incorrect Emissions Stickers Some SHOs have the incorrect plug specified on their emissions sticker. All V-6 SHO's use the Motorcraft AGSP32PP. There is a TSB on this problem if you don't believe me!!!

Autolite Autolite plugs (APP3924) are sometimes alleged to be identical to the OEM Motorcraft plugs. While they are indeed double platinum plugs and are listed by Autolite for the SHO application, they have been measured by one SHO owner, and the finding is that the insulator is 1/16 inch too tall to allow proper plug boot seating.

Bosch A few owners have tried Bosch plugs. They do not fit correctly, and foul very quickly (within a couple thousand miles). Do not use.

Splitfire A few owners have tried Splitfire plugs. They do not fit correctly, and foul very quickly. Do not use.

Plug Seals If the intake manifold is removed for plug/wire replacement, an option is to replace the plug seals. At the very least, the original seals should be sealed with RTV. While Ford does offer replacement seals for the Yamaha v6 engine, as is often the case, they are far more expensive than the aftermarket option. Felpro makes a "seal set" - thanks to Dennis Weaver for information on the FelPro offering, as well as replacement instructions : The Fel-Pro seal set is called a valve cover set and the part number is VS 50378 R. Also, the Fel-Pro ISBN number 0 84113 57079 7, which may be of some help. The set includes the six plug tube seals, these are the seals that fit in the cylinder head covers (also referred to as valve covers or cam covers here on the list) and seal the plug wells. These seals are are $35 each at Ford which are also made by Fel-Pro, so I am told. According to the Fel-Pro kit box this seal by itself is part #94849. The entire set also includes the left and right hand cylinder cover gaskets. When I removed my cylinder covers these gaskets had hardened and stuck to the head causing them to tear apart. The gaskets are fairly sophisticated with one gasket containing a semicircular plug that fills a slot in the head itself. I would never want to have to manufacture a gasket out of RTV for the left cylinder cover because of this anomaly.

Total price for the kit from Auto Zone was $72. Doug Lewis recommended that you smear black RTV on the tops of the plug well rims before seating the cylinder cover to insure a good seal preventing the possibility of flooding the plug wells with oil if these seals should leak. Also at the corners of the semicircular cut outs in the cylinder covers be sure to put a bead of black RTV after removing the old. You can see where it was applied when assembled at the factory.

Plug Wires SHO owners are frequently surprised by how expensive a new set of spark plug wires can be. There are several alternative wire sets available for the SHO. The following sections provide some information on each.

Motorcraft These are the stock replacements, and will give good service for stock and modified SHOs. Expect to pay at least $150 for a set, unless you read on. Your Ford dealer is not the only shop that can get genuine Motorcraft parts. Chief Auto Parts, for instance, can get the Motorcraft plug wires for around $135.00. They can be had cheaper still. The part number for the 1989-1995 3.0L MTX SHO is WR-4033. The part number for the 1993-1995 3.2L ATX SHO is WRE4081.

Autolite While it was reported that Autolite wires were re-packaged OEM Motorcraft wires for awhile, that no longer seems to be the case. here's Ron Childs' take on them:

They were quite similar to the original wires except they did not have cylinder numbers like the OEM.

The coil end had black rubber sealing rings instead of gray.

The coil end had brass connectors instead of steel.

The two shortest wires, (cyl 5 6) were about an inch longer than OEM (not a problem).

The caps that snap over the coil end were a little different design, with one clip instead of two. It was easier to snake them through tight spots than OEM.

Lifetime warranty from Kragen.

The plug end and sealing cap were essentially identical to OEM.

They typically run around $85.00 per set. The part number is 86137.

Magnecor These are an aftermarket replacement from the company that John Lingenfelter uses for the wires on his hot Chevy engines. Some SHOtimers have reported that they have experienced minor fit problems with early implementations of these wires. Magnecor did a redesign and put a technical bulletin on their site for SHOs. Readers have reported no problems with recent Magnecor wires. Expect to pay at least $100 for a set.

Taylor One SHOwner replaced his stock Motorcraft wires with Taylor 8mm Spiro Pro's. Here's his take on them : I found them to be very high quality (kevlar etc,) and the fit was excellent. I paid $120 for the set locally in MN but I know places like Summit Racing carry Taylor wires as well at probably an even lower price.

Fastforce These are a non-resistor wire that is advertised in the back of Car Driver magazine. They may or may not be a good bet; here's Gary Morrell's take on them: One thing to be aware of using non-resistor wires, the resistance in the wire (and the plug) is there to reduce the radio frequency interference (RFI) that is generated by the spark discharge at the plug gap. Solid copper wires *may* generate sufficient RFI to not only degrade radio reception, but may also interfere with EEC's ability to interpret low level signals from the engine sensors, like the HEGO's and cam and crank sensors. If you install these and the engine doesn't run correctly, lose 'em. The only safe way to use solid conductor plug wires is if they have tight braid copper shields for the entire length of the wire, the braids are each connected to engine ground, effectively shielding the wire and hopefully keeping the RFI to manageable levels. Frankly, the Yamamotor isn't high strung enough for this type of ignition treatment to make any noticable differences.

I spoke with a Fastforce distributor several weeks ago and the Fastforce technical line that he was mimicking about decreasing spark rise time and reducing spark duration didn't make good technical sense to me: series inductance (that's their claim, isn't it?) in the plug wire will increase rise time, and if rise time increases, duration increases as well, therefore the spark energy is spread over a longer interval, and peak energy (which affects the temperature of the flame kernel in the plug gap) is down as well.

Until Fastforce publishes some independent tests of their wires, I will lump them in with Slick50, magnets on the fuel line, and all the other snake oil out there.