An engine’s firing order is simply the ignition sequence of the engine’s cylinders is spark ignition. 5.7 Hemi, a diesel engine, has a firing sequence that relates to the sequence in which its fuel gets ejected into each engine’s cylinders.
The firing order of 5.7 Hemi engines is sequenced such that the firing impulse of the cylinders causes minimal vibrations, allowing the pistons receive their sparks in precisely calculated rhythms. This ensures efficient engine working and that backfiring issues are contained.
Looking at finding out how the firing order of the Hemi 5.7 affects the performance of the engine or why firing order is necessary, this post takes you through everything you should and why it adopts its firing order.
What is a 5.7 Hemi Firing Order?
The cylinders of the 5.7 Hemi are numbered in a front to rear order of 1,3,5,7 on the engine’s left bank and are on the right bank, numbered 1-8-4-3-6-5-7-2. In MDS mode, four-cylinder 1,4, 6, and 7 are deactivated to allow the MDS mode to work optimally.
Firing order 5.7 Hemi
The 5.7 Hemi engine is a special engine with a very systematic build which includes a firing order of 1-8-4-3-6-5-7-2. The 5.7 Hemi has 16 lifters, of which eight can deactivate the engine’s valve power, a unique camshaft, and four solenoids that enable it to initiate lifter action.
The engine also has a unique exhaust that allows it to preserve its V8 bubble when all the cylinders are fully operational.During the engine’s MDS operation, the four-cylinder is turned off, which are 1,4,6 and 7. So to maintain rotational balance, the engine shuts down every second, and the system shuts down the cylinder in the firing sequence.
You might also like to read our stunning guide on why your dodge ram won’t start just a clicks.
5.7 Hemi firing order diagram
The firing order of 5.7 Hemi follows the 1-8-4-3-6-5-7-2 sequence of engine cylinder activation as shown above.
What does the term firing order mean on 5.7 Hemi?
Firing order in the 5.7 Hemi engine simply demonstrates how the cylinders in the combustion engine are ignited, with the end result being striking operational balance, hence of the 5.7 engine and many other engine types; it isn’t a linear sequence.
Cylinder one is usually ignited first and typically always kicks off the progression.
The order of the 5.7 engine firing is crucial to the diagnostic process and gives off the information on whether the spark plug wires need a proper arrangement.
If the distribution cap is wired sequentially rather than according to the firing order will create an engine misfiring wrongly or cause it to come to a halt altogether.
For an engine like the 5.7 Hemi that has multiple cylinders, each cylinder is marked with a specific number. In the Hemi 5.7, cylinder one is located very close to the engine’s front end.
In the 5.7 Hemi, the firing order makes reference to the ignition pattern of the cylinders rather than their numerical values, which has no significance in the operation of the firing.
Cylinder one takes the opening spot of the firing sequence, immediately followed by cylinder eight.
This order of ignition is unique to the 5.7 Hemi engines, as every other engine has its unique firing pattern.
Also, number 8 in the 5.7 engine could be ideally any number, depending on the design of the engine and how the cylinders in the combustion engine are meant to operate, hence, an attempt to change the firing sequence of the 5.7 Hemi, results in misfires.
A wrong firing order will lead to spark plugs not getting spark on the power stroke.
This means that both firing order and cylinder number are essential to installing a spark plug wire.
The firing sequence is also vital for performing several kinds of diagnostics. Subjecting the 5.7 Hemi to an automotive oscilloscope will reveal each cylinder firing pattern in the sequence with which they fire, rather than their sequential numbering.
Hence, without knowing the firing order, discerning which cylinder matches a wrong pattern would be hard on the readout of the scope.
What is the purpose of a firing order?
For multi-cylinder reciprocating engines, the firing order has to do with the power delivery of the engine’s cylinders when considered singly.
For this to happen, the spark plugs have to be sparked in gasoline engines, in the right order, or by fuel-injected sequentially in a diesel engine.
For engine builders, firing order is vital to minimizing vibration and achieving smooth running. This, in turn, greatly influences the crankshaft design of the engine.
These are some of the reasons why firing order exists in combustion engines of vehicles:
01. Engine vibrations
Engines with evenly spaced firing timing have lesser vibrations. This simply means that the power stroke timing between the cylinders is spaced evenly.
Engines with even firing timing produce smoother sounds and vibrate less, and the pressure pulses they deliver are more even than engines with uneven firing intervals.
This is why you find some engines with burble growling sounds and heavy vibrations.
Engines function best at high temperatures. Cold engines cause components to wear out faster. Also, more pollutants are emitted, and the engine becomes less effective.
Having a firing order keeps this in check, which is exactly what once the cylinders are ignited, they are contained during their operation.
Therefore, the cooling system is pressured to always initiate the warm-up of the engine in a timely manner and keep the temperature constant.
03. Backpressure development
Firing order plays an essential role in developing the engine’s backpressure. Every engine has the maximum back pressure the engine can attain.
This is kept at bay with the firing order as long as the firing order is not altered to produce the wrong sequence that may cause backfiring.
Why is a Firing Order Important?
The correct order in which the engine cylinders fire is important because if the spark plug wires are mixed up, they may cause the engine not to start or even cause it to backfire or run poorly.
Engines that have two fire plugs firing sequentially require that the wires of the spark plugs are not routed close to each other.
If routed otherwise, a crossfire between the plugs can ensue since the magnetic field developed by the spark-flowing tonne plug may prematurely fire the next plug.
This ultimately causes the engine to run in a rough manner and misfire.
This is prevented from happening by the adjacent plug wires crisscrossed to have the magnetic induction canceled.
Engines with distributionless ignition systems have their firing controlled by the engine computer or ignition module.
In this method, the computer picks a signal from the crankshaft position sensor to enable it to determine whether the piston is reaching the top spot of its compression stroke.
The firing sequence is hence initiated when it fires that spark plug and, subsequently, the next. The most crucial benefit of firing order in engines is a correct firing order can limit vibrations in the engine system.
This, in turn, offers you a smoother ride, as passengers wouldn’t feel the vibrations coming from the engine.
Conclusively, these are the reasons why your firing order is important:
It’s great to have uniformly spaced power impulses. This creates a workable balance.
There’d be a very jerky power distribution if you had all the cylinders firing at once. Hence, the engines are designed to have the cylinders firing in a sequential manner, ensuring a smoother power delivery.
If pistons move in calculated rhythms, it then follows that they have to receive their sparks in calculated rhythms too. This is to ensure the engine runs smoothly.
For instance, the 1-3-4-2 firing order is preferred to the 1-2-3-4 firing order in engines with 4 cylinders. Remember that engine vibration and engine cooling are the two foremost factors that determine firing order. Hence the 1-3-4-2 order is preferred for the following reasons:
The power impulses are spread uniformly apart and are also 180 degrees apart. The firing order obtained from this spacing is hence 1-3-4
The load-balanced on two bearings would further cause the engine vibrations to be reduced.
It is necessary to cool the combustion part of the engine where this takes place by swapping the sequence. This effectively mitigates overheating problem.
This pattern provides sufficient time for the exhaust gases to move. This keeps high backpressure development under control.
How do you determine the firing order on a 5.7 Hemi Ram?
Typically, the firing order is determined by how many cylinders the engine is running on and the crankshaft alignment of each crank.
Firing orders are determined when the engine is built to have it run very smoothly and efficiently. The forces exerted on the crankshaft by the pistons are not considered.
However, the counterweight is considered. For the 5.7 Hemi Ram, when all these parameters are considered when balancing equations, a firing order with minimal vibration is determined.
All the parameters considered for the firing order of 5.7 Hemi Ram are:
- How many cylinders are in use
- Torsional vibrations
- How heat is distributed
- Cylinder arrangements
- Crankshaft alignment
For the V8 engine of the 5.7 Hemi Ram, no universal formula can be applied to determine its firing order. This solely lies on the experimental outcome and the vehicle’s precise model.
However, the 5.7 Hemi Ram uses an eight-cylinder engine, which means eight cylinders ate fired at precisely timed periods that can effectively minimize engine vibrations.
Frequently Asked Questions (FAQs)
01. What are different kinds of eight-cylinder arrangements for firing order?
Straight In-line arrangement
An arrangement like this produces a powerful impulse for every 90 degrees the crankshaft moves. For this arrangement, crank-throws have 90 degrees interval spacing to each other by how the power impulse is delivered.
There are only four angular positions relative to each other. This makes for a crank-pin phasing, arranged in pairs. This arrangement requires 5 or 9 major journals to support the crankshaft.
For this arrangement to have extra power required to pull hefty loads, the crankshaft may need to be extended with about two more cylinders.
This is, however, a dynamically-balanced design but tends to produce torsional vibrations. Some trucks, too, may not be able to accommodate the extended length.
Single-plane crankshaft with 90 degrees
The arrangement yields a power impulse every time the crankshaft rotates 90 degrees. It uses 4 crankpins structured to have both outer crankpins and inner crankpins.
Each crankpin has two big ends of connecting rods and has five main journals. These journals serve as support for the crankshaft.
90° V-8 cylinder arrangement
This kind of arrangement provides a 90 degrees equally spaced firing intervals. The numbering of the cylinders is 1,2,3,4 on the left, and on the right-hand band, they have 5,6,7,8.
The two-plane crankshaft operates with two 90 degrees-phased crank-throws. Each crankpin has two connecting rods, separately hinged to pistons in different cylinder banks.
There is the main journal, as well as a bearing situated at each end and also at adjacent crankpins.
Having two connecting rods sharing just one crankpin makes the five major journal crankshaft journals very short and operationally less complicated. This makes it a more popular option for many V-8 engines.
02. What do you know about an incorrectly sequenced firing order?
A wrong firing order causes delayed engines that don’t run properly. This is the most obvious sign of incorrect firing order.
When there is no fuel, the cylinder may get sparks even when there’s no fuel/air mixture or even before it is adequately compressed.
In worst-case scenarios, the engine does not run at all; as your turn, the engine is greeted with cold unresponsiveness.
03. How are V-8 cylinders counted?
The most common numbering pattern of a V-8 engine, such as that of the 5.7 Hemi Ram, is when facing the vehicle from its front part, the cylinder on your own right side, which is on the left part, is designated number one.
Then on your left side, the closest cylinder to you is often numbered 2.
Final Thoughts On Hemi 5.7 Firing Order
The 5.7 Hemi has to be a V8 engine and has a 1-8-4-3-6-5-7-2. The firing order follows this sequence and not the conventional numerical sequence as expected because this order is important during the engine’s operation to yield a smooth power delivery among the cylinders, which in turn causes lesser vibrations and hence, a smoother ride.