Is the Decel Tune Safe? - Ford Powerstroke Diesel Forum
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Old 02-14-2012, 05:38 PM Fanatic

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Is the Decel Tune Safe?

I just got my DP tunes hooked up including "Decel" and was searching around the internet and found PHP doesn't offer it saying it can be unsafe under larger loads. Anyone with experience good or bad? Of course I see this right after I got it. Here's from their website.....

Do you offer a "decel" or "exhaust brake" calibration? Simply put, no, we don't because it goes against our business philosophy which, in part, is to provide safe, reliable products to our customers.

For those who don't know, this is a calibration that uses the EBV (Exhaust Backpressure Valve) as a makeshift exhaust brake. While this setup may work reasonably well for lightly loaded vehicles, we generally do not recommend this type of calibration... at least not for automatic transmission vehicles. There are a few reasons we don't recommend this.

First, in order to transfer the energy of the moving vehicle to the engine during deceleration, two things must occur: the torque converter must remain locked, and the coast clutch must be engaged. The problem with this is that the coast clutch on a stock transmission only has 3 friction plates, and these are smaller than the standard forward clutches. On 2001 and later transmissions, you also run the possibility of damaging the intermediate sprag or "diode," which will result in an immediate transmission teardown. Again, lightly loaded vehicles would have less of a problem with this, but the general idea of an exhaust brake is to be able to slow larger loads without overheating the standard brake system. It is these types of loads that can cause transmission damage. Obviously, a manual transmission would be free from these types of situations.

Second, whenever you increase exhaust backpressure, you need to make sure that the exhaust valve springs are capable of preventing the pressure in the exhaust system from lifting the exhaust valve from the valve seat, as this would result in a collision with the piston. Normal valve spring seat pressure is 70-75 PSI for NEW valve springs and deteriorates from there. Given that the surface area of the back of the exhaust valve is approximately 1.9 square inches, it would take only 40 PSI of exhaust pressure to lift the valve off the seat, even with new valve springs.

To put it simply, if you plan to use an exhaust brake, either through the use of the EBV or by purchasing an aftermarket stand alone unit, you will need to consider the condition of your transmission and exhaust valve springs in order to ensure safe, reliable operation.

I guess i'll use this rarely, but under loaded conditions. Hope i'm GTG.

Last edited by WA_PSD; 02-14-2012 at 05:46 PM.
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Old 02-14-2012, 07:15 PM
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I saw that too when I was looking at PHPs site. Near as I can figure is that assuming your truck brakes are in at least decent shape and you have a decent set of trailer brakes on the trailer, why would you need an exhaust brake?

Semis, I can see. Up to 80,000lb is a lot harder on friction parts than our trucks can be.
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Old 02-14-2012, 08:03 PM
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Or you can buy upgraded valve springs and run it all the time.......
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Old 02-14-2012, 10:53 PM
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The weakest link is probably your transmission if you have a auto. I run a manual TC lockup and manual EBP exhaust brake which is basically the same thing as a decel tune. I couldn't immagine running without it when towing, it really saves the brakes.
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Old 02-15-2012, 01:50 PM
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I've been using my decel tune on my DP for over 4 years... the trans was rebuilt at 150K miles, tork converter went out at 175K, was replaced, and now at 220k, it's starting to act up again... but concidering how I use the truck, towing, hauling, driving it hard, I doubt the decel tune is the sole culpret in the trans issues I'm having... the 4R100 is the weak link no matter how you look at it, decel tune or not... and the fact that the rebuild only cost $1500 when it was done in 2007, I'm not complaining. I'll gladly have the same guy rebuild it again in the near future, and continue to use my decel tune.
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