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                                          Basic LS1 troubleshooting

Basic Troubleshooting

You should hear the fuel pump come on for about two seconds and stop, when you first turn the ignition key to the “on” position. It helps to have a fuel pressure gauge hooked up to the gauge port on the fuel rail.

LS1 fuel port is located on front L/H fuel rail.           The Vortec intake fuel port is on the R/H fuel rail.

Fuel pressure should be at 50-60 PSI when the fuel lines are fully purged of air. When the engine starts and is at idle pressure should be at 53-65 PSI, anything out of this range is concern to be investigated and remedied.

The check engine lamp (known as a Malfunction Indicator Lamp-MIL) should be on with the key to the “on” position. The lamp should go out a few seconds after the engine starts. If it goes off and then comes back on in a short time, the pcm has detected a problem and this will have to be corrected.

If the engine starts and runs rough, and the check engine lamp is on, check the codes with a scanner tool to retrieve the trouble codes, check fuel pressure. Also a bad sensor can cause a rough running condition and if you are using used parts (including the injectors) suspect you may have a bad sensor. This is especially true if the scan tool points to a bad sensor.  

NOTE: A code indicates a particular problem, and may not be a specific part as all the fuel injection system works together. Some bad sensors will not activate the check engine lamp. You will need to follow recommended troubleshooting procedure for your particular YEAR and MODEL of LS1 or Vortec V8 engine.

 The DLC- the pcm’s link to the world.          The OBD II scanner is your friend in the digital world.

MAF sensor problem- If the engine idles, but will not respond with a smooth idle, disconnect the MAF sensor and tap the throttle and see if it responds better. If it does, replace MAF sensor.

TPS- Engine idles rough and is sluggish in throttle response. Shut off engine and turn ignition key to “on” position (engine off). With your scanner tool hooked up, monitor TPS position by opening and closing the throttle, it should respond smoothly from 0 to 100%. If it jumps erratically, replace sensor.

CRANK SENSOR- If this sensor is not responding correctly, it will run erratic, and the injector-coil synchronizing pulse will be incorrect. If the sensor is bad (no crank pulses detected) the engine will not run at all.

Typical Readings for a 1999 LS1 engine, automatic transmission:

·          Engine Speed- 650 rpm

·          ECT- 180 degrees F

·          IAT- 80-100 degrees F

·          MAP- 45 Kpa

·          MAF- 6-10 grams/second

·          IAC position- 10-30 counts, auto trans. In park

·          TPS- 0%

·          Injector Bank 1 PWM- 2.6 ms

·          Injector Bank 2 PWM- 2.6 ms

·          CMP sensor- Low to High (should be counting up)

·          CKP sensor- Low to High (should be counting up)

·          Spark Advance- 15-25 degrees (changing rapidly)

·          Knock retard-0 degrees

·          VSS- 0 mph

·          Ignition Signal 13-14 volts

DTC Trouble codes   OBD II-  Not all codes will apply to all models.  Courtesy of

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