I have 2000 e350 7.3 with 385,000 mi.,bought new. when temps get into 20's overnight ,i get a little hard start which is ok. but sometimes I get no power for up to 10 minutes. can only roll at 5 to 10 mph. is there a valve or something that could be sticking till warm. runs fine rest of time.Thanks for help.
In addition to what KIB said.. look at the EBP sensor and tube to make sure it is reading the exhaust pressures correctly. FORScan (they have a number of recommended adapters) is a cheap tool that will pull live data from the engine PCM. I have read a post or two here that mention under powered performance when the sensor is not working correctly.
There was another thread here somewhere in-which the OP had a malfunctioning Baro sensor that the internal gel had come apart and was pressing on (or blocking) the sensor. The incorrect readings were causing major engine problems.
The EBP valve is not really a choke... not like a gas engine. It is more of a restrictor to keep the exhaust pressure up to help with warm up. Many 7.3 owners just delete the valve all together - usually when it starts leaking oil all over the engine valley. It is my understanding that the exhaust valve is not activated until it is colder that 38*F (give or take) by the temperature sensor that is located in the air filter box. The exhaust valve is not deactivated until the oil temp comes up to 170*F. Given that you are at 40*F you may or may not have the exhaust valve operating. I drive a 97 7.3 and from my observations on the exhaust valve:
moderate to heavy acceleration - no back pressure
slowing down/steady driving - back pressure around 15 psi
startup - initially no pressure, but system kicks in after a min or two of idling (I typically don't idle to warm up, as soon as the oil pressure comes up I get the truck moving, though I try to be easy on the revs and throttle till the engine has warmed up a bit).
As for diagnosing... the valve is actuated by the low pressure oil system. Look for oil around the base of the valve - leaks may cause the valve to malfunction. I have read once of a bad solenoid. I wouldn't panic too much about a non-functional back pressure system.
so when I start the engine and it's cold and I let it idle, I assume that it's the PCM that raises the rpm's until the engine warms or I tap the brake. it hasn't been doing that on the last few mornings, (40F). I'm wondering why and if it could be a sensor. if so, would it be air, water, oil temp. or something else? thanks.
Do you have any response from the accelerator? Mine would only idle below 20* till it warmed up. I traded positions of similar power relays in the fuse box and it has never came back. Maybe a connection or relay????