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GM 3.4 Lacks Power
Posted to Technical Discussion Forum on 10/19/2012 25 Replies

This vehicle came in with a lack of power on acceleration. After the usual checks (Exhaust BP; MAF; Fuel Pressure, etc.) I noticed the scan tool was showing 12-14 degrees of knock retard during medium to heavy acceleration. There are no unusual engine noises that I can hear while this is happening. Vehicle has been running premium gas and has same problem. This car has 265000 miles on it, but has been maintained and is in excellent shape. The engine didn't sound any worse than other 3.4's when revved up in the stall but I noticed timing chain was somewhat noisy, so replaced it. No change. If the KS is disconnected, the car runs and drives perfect (but the MIL is on, of course). Owner does not want to spend lots of $$ for major engine work. I tried to "fake out" the system by removing the KS from the block, reconnecting it, and mounting it away from the engine with a good ground, but the system is too smart. Apparently on these engines, the PCM looks for "normal noise" when idling to determine if the sensor is connected and working. So right now, it looks like two choices: Vehicle runs and drives good but MIL is on or Vehicle lacks power but MIL is off. Any other ideas on solving this?

Mario Schwarz
Educator/Instructor/Technical Writer
Santa Fe College
Gainesville, Florida, USA

25 Replies Received (View Replies)


car Vehicle Data

2002 Chevrolet Venture LT 3.4L

Engine3.4 L
Trans4-speed Automatic (Electronic)