Free Car Repair Advice by Professional Mechanics
Troubleshooting
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Why Does My Engine
Backfire?
Why Does My Engine Backfire?
Introduction
There are two kinds of back fires, one is produced from the engine air intake
and the other is produced from the tail pipe of the exhaust system. The cause
for a backfire condition can vary depending on the malfunction of a particular
system. Some backfires can be extreme enough to cause damage to related
components. Anytime a backfire is observed immediately diagnose and repair as
needed. If the engine is running rough it can produce a backfire. If the engine
is misfiring while it is backfiring please visit
why does my engine run rough? It is important to observe the location of the
backfire. The information below is separated into two sections; the first
section contains possible causes for backfires in the engine intake. The second
section contains possible causes for backfires in the exhaust system.
READ COMPLETELY BEFORE BEGINNING!
Car Repair Guide - Backfire In The Engine Intake System
- Step 1 - The ignition system in your car is designed to
operate at a specific voltage and amperage output. If this
voltage/amperage is forced to "spike" due to faulty or inferior tune up parts it
could cause the system to "crossfire". A crossfire condition can allow the
electrical discharge for a particular spark plug circuit to transfer to a
alternative cylinder. Depending on were the cylinder is in the combustion
process it can produce a backfire in either the intake or exhaust systems.
Always replace ignition components on a
regular
mileage schedule and use high quality replacement parts.
- Step 2 - Engine timing is to be set at a specific
degree in relation to the crankshaft of the engine. If this timing becomes
mis-aligned it can cause low power, poor gas mileage, engine detonation
(pinging) and backfiring. To check the engine timing locate the number one
cylinder of the engine. This number one cylinder will be the forward most
cylinder of the engine. On straight 4 and 6 cylinders engines it is pretty
obvious, but on "V" style of engines like the V8 it is a little more tricky.
The cylinders heads on every "V" style of engine are offset from one to the
other. One cylinder head is more forward than the other. The most forward
cylinder head is the side of the engine where the number one cylinder is
located. The forward most cylinder is the number one cylinder.
Next, locate the crankshaft timing
marks, most engines timing marks are at the front of the engine on the
harmonic balancer. Near the balancer there is a small pointer or scale to
align the balancer mark to. When the engine is running this gauge or
pointer should align with the mark on the balancer. When the engine is
running the timing light will
strobe and illuminate the balancer mark as it spins. To adjust the timing
loosen the distributor and turn slightly one way or the other to achieve the
desired setting. Once an adjustment has been made re-tighten the distributor
hold down bolt or bolts. Some engine's timing
marks are located at the rear of the engine on the flywheel. Before you
begin start and run
the engine until warmed to operating temperature. Connect the positive and
negative leads of a timing light to the battery. Observe the timing tag
either on the engine or engine compartment for the timing specification and
procedure. If the specification and instruction cannot be found consult a
car repair
manual.
- Step 3 - The ignition system in your car is designed to
operate at high voltage. If moisture is present inside of components like
the distributor cap it can cause internal ignition crossfire. This crossfire
condition can allow the electrical discharge for a particular spark plug
circuit to transfer to a alternative cylinder. Depending on were the
cylinder is in the combustion process it can produce a backfire in either
the intake or exhaust systems. To check for this condition remove the
distributor cap and inspect for moisture. If moisture is present dry
components thoroughly and reassemble. (some cars are not equipped with a
distributor)
- Step 4 - The engine in your car is designed to run on a
specific ratio of air to fuel (14 to 1). If this ratio increases by
withholding fuel it can cause the engine to back fire through the intake
system. The number one reason for this condition is a plugged fuel filter.
If your fuel filter has not been changed for over 30,000 miles it probably
needs to be changed. Remove the fuel filter and inspect if dirt is observed
replace the filter.
How
to change a fuel filter. (note: some cars fuel
filter is located in the gas tank and is not serviceable). Next the
ratio can be incorrect because of an air intake boot that has failed or
other vacuum leak. If a failure is detected replace part with new and
recheck.
Failed Air Intake Boot
- Step 5 - Your engine's fuel injection system is
designed to supply fuel from the gas tank to the engine under a specific
pressure. If this pressure is allowed to decrease intermittently or
regularly by a faulty fuel pump it can cause an engine backfire. Fuel pumps
that fail intermittently can be tricky to find.
Check fuel pump pressure.
Car Repair Guide - Backfire In The Engine Exhaust System
- Step 1 - Engine timing is to be set at a specific
degree in relation to the crankshaft of the engine. If this timing becomes
mis-aligned it can cause low power, poor gas mileage, engine detonation
(pinging) and backfiring. To check the engine timing locate the number one
cylinder of the engine. This number one cylinder will be the forward most
cylinder of the engine. On straight 4 and 6 cylinders engines it is pretty
obvious, but on "V" style of engines like the V8 it is a little more tricky.
The cylinders heads on every "V" style of engine are offset from one to the
other. One cylinder head is more forward than the other. The most forward
cylinder head is the side of the engine where the number one cylinder is
located. The forward most cylinder is the number one cylinder.
Next, locate the crankshaft timing
marks, most engines timing marks are at the front of the engine on the
harmonic balancer. Near the balancer there is a small pointer or scale to
align the balancer mark to. When the engine is running this gauge or
pointer should align with the mark on the balancer. When the engine is
running the timing light will
strobe and illuminate the balancer mark as it spins. To adjust the timing
loosen the distributor and turn slightly one way or the other to achieve the
desired setting. Once an adjustment has been made re-tighten the distributor
hold down bolt or bolts. Some engine's timing
marks are located at the rear of the engine on the flywheel. Before you
begin start and run
the engine until warmed to operating temperature. Connect the positive and
negative leads of a timing light to the battery. Observe the timing tag
either on the engine or engine compartment for the timing specification and
procedure. If the specification and instruction cannot be found consult a
car repair
manual.
- Step 2 - Some engine exhaust systems have
an air injection system designed to help dilute the exhaust gasses. This
added air is only in operation during power mode. If the air injection check
valve or sometime referred to as a "gulp valve" fails it can allow extra air
into the exhaust system causing system internal and external backfiring. To
check your systems valve remove it and check air flow. Air should only
travel one direction hence the name: "check valve". If air travels both
directions the valve has failed and needs replacement.
- Step 3 - The exhaust system of your car is designed to
remove poisonous gasses from the engine to the rear of the vehicle. If
something in the ignition system is intermittently failing it can cause
unspent fuel inside the exhaust system to ignite when the ignition system
returns to operation.
- Step 4 - Small leaks in the exhaust system can suck in cool air
during deceleration causing a popping or backfiring in the exhaust system as
well. Inspect your exhaust system for any leaks that can cause this
such as broken welds or rust holes.
WARNING! Always have the vehicle under inspection on
level ground, in park with the emergency brake on. Always wear protective
eyewear, gloves and necessary clothing before inspection or work begins. Never
crank an engine over when anyone is near the battery or engine. Always have a
operational fire extinguisher close by, obey all first aid instructions in the
event of an accident. Never stand in front or behind a vehicle when cranked over
or running. When engine is cranked over keep hands and clothing free from
rotating components.
Troubleshooting
/
Why Does My Engine
Backfire?
Additional Resources
Check Manufacturer Specific Engine
Backfires Questions and Answers
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