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Discussion Starter #1
2000 K-3500 7.4l, for over a year I have had a issue with very low power after startup, 1-5 minutes. Truck acts just like cats are plugged until it just instantly snaps out of it and starts running fine. This occurs on cold start and on hot start though it takes less time to clear on hot start. Cats are not plugged, fuel pressure is within spec and does not change when the truck comes to life. Intake was replaced due to a coolant leak, new coil, cap, rotor, wires. No codes or noticeable problems showing on data. I have attempted plugging the egr as well. Nothing has made any difference on this problem. Truck has 177,000 miles on it and I have had the issue for at least the last 15,000 and just let the truck run for several minutes before I attempt to go anywhere. Any ideas???
 

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When cold, the O2 sensors are warming up and have no say in the fuel delivery; the computer uses internal fuel tables to time the injector openings.
When the O2 sensors are warm, the computer switches from the internal tables to the input from the sensors. This is called closed loop.
Without any testing, I'm guessing there is a problem while in open loop, a problem that goes away when the system warms and closed loop is achieved.
Do you have any exhaust, or vacuum, leaks?
 

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2000 K-3500 7.4l, for over a year I have had a issue with very low power after startup, 1-5 minutes. Truck acts just like cats are plugged until it just instantly snaps out of it and starts running fine. This occurs on cold start and on hot start though it takes less time to clear on hot start. Cats are not plugged, fuel pressure is within spec and does not change when the truck comes to life. Intake was replaced due to a coolant leak, new coil, cap, rotor, wires. No codes or noticeable problems showing on data. I have attempted plugging the egr as well. Nothing has made any difference on this problem. Truck has 177,000 miles on it and I have had the issue for at least the last 15,000 and just let the truck run for several minutes before I attempt to go anywhere. Any ideas???
Fuel pressure?
Are both of the Injectors fireing
 

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When cold, the O2 sensors are warming up and have no say in the fuel delivery; the computer uses internal fuel tables to time the injector openings.
When the O2 sensors are warm, the computer switches from the internal tables to the input from the sensors. This is called closed loop.
Without any testing, I'm guessing there is a problem while in open loop, a problem that goes away when the system warms and closed loop is achieved.
Do you have any exhaust, or vacuum, leaks?
Bummer, I had high hopes but there was no change in condition with new CTS.
Wait it's only when cold??
 

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Wait it's only when cold??
His first post says when first started and snaps out instantly, he also says he has to let the truck run for several minutes after starting before he could drive it.

I'm assuming if it "snaps out instantly " it's at the moment it goes into closed loop.
 

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Discussion Starter #12
Happens hot or cold on startup, just takes longer to clear when cold engine. Fuel pressure is good and has been verified that way during the condition and when operating as designed. All data seems fine and no dtc's. I assumed it was ignition hence new coil, wires, cap, rotor. Just at the end of my rope as it does not seem to make sense to run so poorly then instantly be fine. I'm about at the point where I wonder if open loop parameters somehow changed. If someone where to ask me that question I would likely tell them it is not possible.
 
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