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SOHC - 2.3L & 2.5L Lima Engines Discussions and Topics specific to the Lima 4 cylinder engines

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Old 02-01-2016
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dual plug head question.

Been asking around to see what people thought, I have an 89 ranger with 2.3 lima dual plug head, now I have read that with the Ford factory firing order the exhaust side plugs fire on the exhaust stroke to help burn emissions. Quick little tests confirm this, switch plug order around and now you have 2 plugs firing every compression stroke. Now for the question I keep hearing at high rpm gap plugs smaller, low rpm gap bigger, what if you gap one at 10 over and the other 10 under, would that produce better then one or the other?
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Old 02-01-2016
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I think you misunderstand the Ford Waste spark system.

Each spark plug fires on the compression stroke and the exhaust stroke, single or dual spark plugs.

With dual spark plugs you always get 2 sparks on compression stroke and 2 spark on exhaust stroke.

The way it works is that all engines have "matched pairs" of pistons/cylinders, firing order tells you which are the matched pairs.

2.3l firing order 1-3-4-2
You divide it in half, 1 - 3 and 4 - 2 then put one above the other
1 - 3
4 - 2

So 1 and 4 are a matched pair, both will be at TDC at the same time
2 and 3 will be at TDC at the same time

The firing order on 2.3l with coil packs is 1/4-3/2-4/1-2/3, for both coil packs

Say you have a 3.0l V6, firing order is 1-4-2-5-3-6
So matched pairs would be
1-4-2
5-3-6

1-5, 4-3 and 2-6, look at 3.0l coil pack

TDC is either compression stroke end or exhaust stroke end, valves decide that not pistons.

Each Ford coil pack has the matched pairs wired in series, so when 1 fires 4 fires, when 4 fires 1 fires, doesn't matter how you mix them around both spark plugs still fire.

One heads up, on this dual spark plug setup only the exhaust side coil/spark plugs are working when starter motor is turning engine, when engine reaches 400rpm(engine started) then the other coil and plugs will start working, this is a function of the ICM(ignition control module).
This often lead people to think if they rearranged the wires on the coil(coil mod) they would get better performance, doesn't work that way, although people will swear it does work.


Spark plug gaps are changed for "coil recovery time" and heat up, the time it takes coil to build up another charge and the heat generated.
Larger gaps require larger spark so coil has less recovery time, smaller gaps more recovery time.

If you gap spark plug wider then you will notice more misfiring at higher RPM as coil fails to build up enough of a charge, but it will be easier to start and run cold.

Smaller gap eliminates high RPM missing, to a point, lol, but smaller gap can cause engine to misfire cold or make it harder to start.

Using 2 different gaps on a dual spark plug cylinder could cause pinging/knocking from delayed spark, but you can try it, pretty sure you wouldn't see any gain.
Exhaust side plugs would be best with wired gaps since they are used for starting.

Pinging/knocking noise is caused by two(or more) separate ignition points in one cylinder, the noise is the 2 explosions wave fronts meeting.
Common cause of pinging is pre-detonation, the air/fuel mix self ignites before spark plug can ignite it, when spark plug fires it creates the second explosion and you get the ping noise.
This occurs more often when engine is under higher load because cylinders heat up with the load and regular gas can self ignite at higher temps.
Diesels often sound like that because they only use compression to heat up the air/fuel mix so often get 2 or more self ignition points in a cylinder, but they are built to withstand that issue, gas engines are not, so pinging will melt pistons and damage head gasket ring, also reduces power.

Last edited by RonD; 02-02-2016 at 05:26 PM.
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Old 02-03-2016
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if so when you unplug the intake side plugs or coil how come it wont run? in the factory plug orientation.
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Old 02-03-2016
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It should start and run with just the exhaust side coil and spark plugs connected.
Intake side isn't used at startup.

If you find the opposite is true than perhaps your system wiring is reversed, or maybe yours only uses Intake side on startup, I haven't tested every year made, lol, Ford engineers do what they like.
But it wouldn't change anything as far as 1-4 and 2-3 spark plugs firing at the same time on both coil packs after engine is running.
If you look at the wiring there are only 3 wires connected to each coil pack, a 12v wire, and 2 Grounds, so there are only 2 coils inside each coil pack, but 4 spark plug wires, 1 and 4 are on the same coil in that pack, and 2 and 3 are on the other, you can reverse 1 and 4 or 2 and 3 wires but both still spark when ICM cuts the Ground on that 1 coil.

The separate ICM(ignition control module) controls the coil packs directly and is connected directly to the Crank position sensor(CKP), in 1994 and older engines.
In 1995 and up the ICM was in the computer(the first year of the EEC-V computer)

The ICM can control basic spark timing on its own, it doesn't need the computer, the CKP tells ICM when #1 is at TDC and it fires 1 and 4 spark plugs at that time, then 2 and 3 180deg later, so compression/exhaust stroke doesn't matter.
Computer connection is for injector timing and does allow computer to modify spark advance and retard based on driver input which is faster/better than RPM(or vacuum) based advance/retard.

Until the CPS(cam position sensor) was added the computer, or ICM, had no way to tell if a cylinder was on compression or exhaust stroke.
But it didn't matter with Waste Spark system, CPS was added for better Sequential Fuel Injection, most fuel injection engines ran on Batch Fire injection prior to CPS being added.
On a 4cyl that means 2 injectors opened at the same time, like Waste Spark, since this happened on the intake stroke of just one cylinder "most" of the sprayed fuel would end up in the one cylinder, but some would coat the inside of the intake, so lost MPG like we had with carbs.
Sequential injection cuts down on that "lost" fuel, Direct injection cuts it out completely.

Last edited by RonD; 02-03-2016 at 12:16 PM.
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