Cord

I really don't want to get into an argument. I certainly don't have facts to back my opinion up, but this is the internet so we're all qualified to be experts.

I know that on my truck with the CAI, I can hear a whoop-pop-pop when the truck shutters. I have a boost gauge on my truck and typically it's making only a pound or two of boost when this happens. I don't see a change in the boost level when the sound/sensation happens. I'd kind of expect to see a change if it was a waste gate opening. That said, the gauge might be too slow or not sensitive enough to show the change. I know that on my full size diesel that I can bark that turbo if I jump out of the throttle too quickly. That's not the sound I'm hearing, besides I don't think a couple of pounds of boost is enough to bark a turbo.

Here's my theory: The engine the totally computer controlled. Computer throttle. Computer boost control. Everything is controlled by the computer. In 6th gear at 53 mph the engine is just loping along. Not really in vacuum (I've found that engine is almost always in boost, the only time it's not is when you are coasting), but not really making much boost either. It's almost lugging, but not quite. Although the boost levels are regulated by the computer, the spool of the turbo is not. That's a mechanical relationship based on airflow. I believe that at a certain speed, throttle position and boost level the computer sees that it's about to start to build boost. However it recognizes that the throttle position is very light and a surge in boost (power) might not be desired. I mean if the engine started to build boost, you'd gain power and accelerate... except acceleration isn't desired. So, to increase the driveability of the engine, Ford programmed it to dump boost at certain times so you wouldn't get a power surge. It's being done to help smooth out the power surges that are inherent with boosted engines. It's my theory that this happens at 53 mph with a very light throttle and light load in top gear. I've also noticed that it happens around 40 mph, but in a lower gear, 5th if I recall correctly.

Try this for a test. Typically, I find the issue shows up when you are cruising on the flat and come to a slight rise. Enough that you add just a bit more throttle to maintain your speed. If you can identify this condition, turn around and take a second pass at the hill and try some thing different; this time down shift to 5th gear. I'd put money on it that you don't get the same result. Different gear, different throttle position, different engine rpm = a different point in the program map.

Although I feel this shutter (not to be confused with the fall-on-it's face issue) might be normal operation; I do feel that Ford is fueling the issue by not issuing a bulletin explaining what the sensation is and why it's happening. To issue the memo wouldn't be difficult and would totally crush the 55mph conspiracy.

Centexguy

Turbo surge is one thing. What myself and others are describing is not that at all.

I run around with the transmission locked out of gears all day because the gears in this truck suck and I hate bogging an engine down (comes from my years of driving heavily modified diesels). I'm familiar with compressor surge and Ill buy your explanation. What I've experienced over the past few days is not that.

Cord

What's your complaint then?

Centexguy

Didn't have one. Was just curious to see what your reasoning was.

Cord

I mean, what complaint are you referencing in this post?

Centexguy

Oh. What we are calling the 55mph shudder. It's not compressor surge. Happened to me while in 3rd gear at 55mph which is above 3000rpms and more than a 1/4 throttle.

wigsmen

hey there the 55 mhp shudder is just a property of springs the vibration of the road are ampliified and you feel it as a shudder

wigsmen

Okay every one so I put the cai back int and it stopped doing the thinking but now it's back worst when it's warm out I also got the cover for the intake thought it might help plus I read it prevents the warm air from the engine bay from being sucked in well the cover came in and it's plastic thumb down and no difference in the thunk so I'm thinking maybe its my truck running lean and when I'm not feeding or stop feeding with the trottle she thunks bc if I let off slow it doesn't thunk any thoughts I'm really lost could it be that I did the intake before the exhaust air coming back up the exhaust bc it's to small?

Centexguy

You have 3 options. Trust us when we say its normal and learn to live with it. Run the factory intake. Or spend hundreds of dollars on other intakes until you find one that doesn't allow you to hear the pop.

whoareyou

Option 4: sell the intake to me for pennies on the dollar and get a book on punctuation.