It was a wierd situation, boosting upwards of 30 PSI but was very unstable and it did not seem to produce any power?
The vehicle is a '05 F350 6.0L PS SB DRW stock with the exception of a Corsa 4" Cat back exhaust and a Banks tecnicooler high flow intercooler and I live near Rockford, Il. It was a little cold (-32 F real temp) when the problem first was observed this winter. This particular day the block heater had been plugged in all night so the engine would be warm for an early morning start. The engine started normal and I let it warm up for around 5 mins, drove around town for around another 20 mins. Then when I was getting onto the tollway I noted that the temp gauges were both about in their normal range. Everything appeared normal while driving for the first 15 mins at about 70 MPH, outside temp was around -8 F. If I was to be a little picky I would have said the truck seemed a little sluggish. I noticed that the boost was running about 0 - 2 PSI. This seemed a little low but I dismissed it due to the cold air temps(the air was denser because of the cold temps and therefore less boost was needed). Normal boost at speed is around 4 to 8 PSI depending on road grade and load.This is where it gets a little wierd. If I increased the RPM only 50 to 100 RPM the boost would shoot up to 25 to 30 PSI with little or no increase in acceleration or speed and would be unstable. But I had no load on the truck, there was little or no wind and yet boost was around 25 PSI even up to 30 PSI at times. Modulating the throttle the truck seemed sluggish, not its norm. It was as though somehow the truck was working against itself . If I changed the engine speed the boost would suddenly rise significantly and fall with only 50 to 100 RPM change in engine speed. The boost was nolonger proportional to the throttle as it normally would be, just very unstable. If I slowed down to 55 MPH the boost and throttle were more the norm where boost appeared proportional to throttle.
As I got closer to the Chicago area the temp warmed up to 0 F. As I got off the highway and drove through town the boost and throttle started to respond more as normal where the boost was proportional to the throttle and the truck was responsive to throttle. Later that night I left to return home near Rockford. Once again the temp had fallen to around -8 F and the same problem showed up again, lack of throttle response, unstable and much higher then normal boost pressures at speeds of 65 MPH and higher.
Initially I though it might be sticking vanes in the turbo but I did not see how it would be related to the cold temps. After all the vanes are on the turbine side and should be around 800 F. Then I was thinking that it might be related to a sticking EGR valve as these have also been known to be problematic but again because of the engine temps in this area I could not see how it could be related to outside temps. My last thoughts were that maybe the intake air would be over cooled because of the aftermarket intercooler and the high flow exhaust and the OEM controls and programming could not control everthing properly in the extreme temps. Once again after surfing this board it appears that a couple of other members have had similar issues on their stock truck even to the point that there appears to be something magical about an ouside temp above or below 0 F. So now I'm at a loss, any thoughts would be appreciated.
Last edited by theonlypheonix; 01-20-2009 at 08:54 AM.