An engine surge is usually caused by a fuel system management or drivetrain failure.
The fuel management system utilizes sensors that monitor emission output and engine
performance and are communicating with the main
ECM (engine
control module) controlling fuel mixture, timing and emission management
systems. While the engine is surging the ECM is "hunting" by adjusting the fuel
mixture and timing. These adjustments are made by the ECM in an isolating manner
as the ECM tries to satisfy its parameters. These parameters are not being
satisfied due to a system malfunction, we have listed some of the most common
problems and repairs below:
Troubleshooting Procedure
B.
Testing Fuel Pressure: Test for proper fuel pressure with a fuel pressure gauge.
Connect the gauge to the test port on the fuel rail. Fuel pressure reading's vary
depending on the system for the vehicle, most throttle body injection cars
(TBI) are between 13 psi and 17 psi and most (DPI) direct port inject systems are
between 40 psi and 55 psi. To find out the vehicle's system fuel pressure consult
a
repair manual.
If fuel
pressure is not within specification the fuel pump needs to be replaced.
C. Plugged Fuel Filter: A
plugged
fuel filter
can cause an engine to surge. Proper fuel system pressure is critical to fuel
injected engines, other wise there will be inconsistencies in performance. To check for this condition remove
the
fuel filter
and inspect, replace with new unit and recheck system.
Fuel Filter Removal
D. Check Engine for Vacuum Leaks: If an
engine vacuum leak is present
it will cause the sensor input readings to the
ECM to be incorrect
resulting in an engine surge. The system is programmed to work
at a predetermined value. When a vacuum leak is present these readings are incorrect causing
the engine to surge under power and idle rough. Inspect the air intake boot for
tears and vacuum feed lines to all accessories. Replace torn or dilapidated hose
with a new hose and recheck system. Also an IAC (Idle Air Control) valve bypass
hose can develop tears/holes mid way through the hose, inspect thoroughly (common
problem on Ford trucks and SUV's). Sometimes a vacuum leak can be detected by opening
the hood, start the
engine and
allow to idle, listen for an audible whistling sound. Inspect that area of the engine compartment to locate the leak.
Failed Air Intake Boot
E. Check for Plugged Exhaust System:
The
exhaust system in your vehicle is designed to release exhaust gases from
the engine to the rear of the car. This system is designed to have about 3 pounds
of exhaust backpressure under full throttle. This means the engine should not have
to push more than 3 pounds of pressure to release the exhaust at any given time.
If a
catalytic converter plugs or breaks apart it will plug the exhaust system causing
an engine surge.
Plugged Catalytic Converter
F. Test for Weak Ignition
Spark or Failing System: A weak
ignition system can be a sign of a failing
ignition component and can cause the engine to surge. Remove spark plug wire and insert
an extra spark plug into end of wire, attach spark plug to engine ground then crank
engine. You should observe blue spark between spark plug gap. If a yellow spark
is observed, your
ignition coil is weak and needs to be replaced. Also the spark
should flash in a constant rhythm, if the spark is
inconsistent suspect the crank angle
senor, ignition coil or ignition module.
G. Check for Automatic Transmission
Clutch Slippage: When the clutches inside an
automatic transmission start to
wear they can malfunction. This condition will deliver a surging or a tugging sensation
to the driver. Without taking the transmission apart it is impossible to check
the wear of the clutch discs. But there are tests that can help you in the diagnosis. First remove transmission dip stick and inspect the condition of the
fluid; if the fluid has a burnt smell and is dark color instead of the normal red
color the fluid is burnt (The transmission fluid is a hydraulic fluid that when extreme
heat is applied to the fluid it becomes dark in color and will smell burnt). The extreme heat
is generated from the clutch discs slipping. Sometimes a
transmission service will
help the operation by removing the burnt fluid and replacing it with new.
Automatic Transmission cut-away Image
H. Check for Standard Transmission Clutch Slippage: When a clutch assembly
starts to wear it can cause an
engine surge
sensation. This is caused by the clutch pressure plate loosing tension and
allowing the clutch disc to slip against the flywheel. The clutch assembly
is a normal service item and will need to be inspected between 60,000 and 80,000
miles. If the clutch
pedal is at the top of its travel with no free-play this is a sign the
clutch assembly is worn out and needs replacing.
When servicing a clutch
disc always replace the clutch disk, pressure plate, throw out and pilot
bearings, also have the flywheel surfaced to ensure a good surface for disc
contact (Note:
some transmissions do not use a pilot bearing). The flywheel is the component
the clutch assembly bolts to, the clutch disc is in direct
contact with the flywheel and clutch pressure plate.
Clutch and Flywheel Assembly
For exact specific repair procedures for any of the steps above visit our
online repair
manual page.
Troubleshooting
/ Engine Surges
Check Manufacturer Specific Engine
Surges Questions and Answers
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