Q: Misfire and power loss until warm up - 1999 Chevrolet Silverado

asked by on September 02, 2016

From time to time in the past when I would drive my truck for the first time of the day as soon as I get on the road out of the driveway I would start to accelerate and the truck would kinda jerk and you could hear and feel a misfire coming from just the other side of the firewall possibly on the passengers side and it wouldn't have and power so I would back of from the gas peddle and slowly give it gas and still no change . it just kinda runs through it's little cycle of misfiring and power loss for maybe less then a 1/4 mile and then it clears up and drives fine for the rest of the day with no problems. Now for the past month or so it happens every time I drive it which is mostly only on weekends due to a company truck I drive thru the week. Now today I leave my house with two 4-wheelers and trailer in tow. WTF? You guys want a full description of my issue but only give me 1000 letters to do so!!!!! This is total bull shit! Thanks for wasting my time typing this only to be cut short

My car has 165000 miles.
My car has an automatic transmission.

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When a vehicle misfires when it is cold, it is usually because it isn’t getting enough fuel. A cold motor needs more fuel to run. Chevrolet trucks are well known for fuel pump issues. The first thing I would do is test the fuel pressure with a fuel pressure gauge. If you don’t have a fuel pressure gauge, you can rent one from many auto parts stores. The fuel pressure specification for your truck is 55-62 psi with the motor off after cycling the key on and off once or twice.

Fuel pressure issues are very very common for Chevy trucks, so definitely suspect this first. From there I would be connecting a scanner to observe all the sensor data. The main suspects would be the MAF (mass airflow) sensor, misfire counters, and the fuel trims. Based on the data from these sensors will dictate what diagnostic direction to follow.

Aside from this, ask when was the last time you replaced the spark plugs and checked the coil boots? I prefer to use a scanner to locate which cylinder or cylinders are misfiring. Then I can focus on the one or ones that are misfiring.

It is also possible for there to be a leaky fuel injector that is creating a rich fuel condition. I’m leaning away from this because you stated it clears up after it warms up. If it were a leaky injector, you would experience this every time you started your truck up, warm or cold.

It is possible there is a fuel component or induction component that is sealing once it warms. With this situation, it will be particularly important to find it before the truck is warmed up.

If you feel you need help with this diagnosis, I recommend having an expert, like one from YourMechanic, inspect the misfiring issue firsthand. Be sure to send a note to the technician explaining that is a cold misfire condition. Good luck!

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