Mechanics

Surges

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An engine surge is usually caused by a fuel system management or drivetrain operation  failure. The fuel management system utilizes sensors that monitor emission output and engine performance and are communicating with the main PCM (powertrain control module) controlling fuel mixture, timing and emission management systems. While the engine is surging the PCM is "hunting" by adjusting the fuel mixture and timing. These adjustments are made by the PCM in an isolating manner as the PCM 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:

Car Repair
Troubleshooting Guide

Step 1 - Test for DTS's (Diagnostic Trouble Codes): For this you need a trouble code scanner. The trouble code scanner is a small hand held electronic device that plugs into the vehicle's OB2 (OBD11) diagnostic connector. Locate the vehicle's computer connector (ALDL), most are on the lower driver's side. In some vehicles you might need to look around a little, on the passenger's side, and around the center console under a plastic cover. For more information, check the vehicle's owner's manual. This device gathers information that was stored in the vehicle's PCM. This information or trouble code can inform you about the system or sensor that is malfunctioning. Look up the code in our diagnostic trouble code chart. After repairs have been made use the code scanner to clear trouble codes and recheck system.


Check Engine Light Service Engine Soon Video

Step 2 - 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 car repair manual. If fuel pressure is not within specification the fuel pump needs to be replace.


Checking Fuel Pump Pressure Video

Step 3 - 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
Fuel Filter Removal

Step 4 - Check Engine for Vacuum Leaks: If an engine vacuum leak is present it will cause the sensor input readings to the PCM 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.

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-16)