Join Date: Oct 2013
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newbie here. I purchased a 2000 F250 used with about 240,000 miles back in July. I have added about 4,000 miles since then, and have had no problems with the engine. Yesterday and today I noticed on the way to work a hissing sound from the other side of the firewall. It wasn't so bad yesterday, but did it all the way to work today on and off. My trip is about 20 miles one way, cruising at 55-65 MPH. The noise doesn't start until the engine is warmed up into the "normal" range. Sorry, I don't have any gauges yet. The engine warms until it is just at the bottom of the normal range, and stays there. That's when the noise starts. A hissing comes on quickly, along with a slight but noticeable drop in power. The noise really sounds like a boost leak. It will last anywhere from about 10 seconds up to several minutes. Then it will stop just as quickly as it started, with a whistle sound just as it stops, sounding almost like a waste gate on a WRX or something. When it stops, the power comes back. It will then happen again after a short time. The temperature recently dropped out here, and this morning on my way to work it was 32 degrees. It happens while cruising in overdrive at constant speed, 55 mph (about 1,700 rpm) to 65 MPH (about 2,000 rpm). It does it with cruise control on and off.
I checked all the red and green lines, and all the intercooler lines. Nothing appears to be loose or disconnected. I read the sticky about the exhaust back pressure valve. The sensor was replaced by the dealership before I bought the truck. I want to think that this noise is the exhaust back pressure valve opening and closing, but I am confused. It just started when it got cold outside, making me think it is the EBPV, but why is the noise not starting until AFTER the engine is warm? And why is the noise happening on and off for the entire trip? Wouldn't the valve be closed to start until the engine is warm, then open, and stay open? Is this normal, or may I have a sensor or something that is bad? Or is it not the EBPV?
1996 F250, 7.3L, auto trans, 4x4, eclb, TS Performance 6 position chip
Last edited by delta99; 10-04-2013 at 01:39 PM.