F40 Wastegate Amal Valve (long)

In between being on a cramped metal tube at 35 thousand feet, I finally got around to documenting my continuing F40 turbo system education while getting my car to run as it was designed.

My first 2 threads on the subject were the wastegate hat and the blow off valves:

http://www.ferrarichat.com/forum/showthread.php?t=246238
http://www.ferrarichat.com/forum/showthread.php?t=246112

Each fix resulted in dramatic benefits. i.e., getting boost, getting rid of boost, and keeping the turbos spooled up during shifts.

My F40 was running fine until one day my boost disappeared somewhat yet again. This time, I had a smooth running engine with a low, but linear, amount of boost to rpms. i.e., it acted normal in boost buildup and drop off EXCEPT for the max level of boost achieved. It only seemed to boost 7-8 psi or so. It should have boosted 17-18 psi or so.

The feeling was very different than when the wastegate (sticking hat) and BOVs were not operating correctly. Scary thing is, I’m now able to pretty much tell what’s happening in the boost system by the symptoms; a byproduct of having an issue in each of the major components. The only thing I’m missing is an actual blown turbo seal (knock on wood!!).

Long story short: I had a bad wastegate electrovalve, or Amal valve.

The rest of this thread goes into what I found during my investigation. I assume it to be pretty much correct, but I’m sure the experts among you will jump in and correct me if I’m wrong… ;-)

Tim

 

If you take a look at the F40 workshop manual on page 55, you’ll see the generic relative (boost) curves to rpm (see below). Curve “2” is the boost from the turbochargers without a wastegate active. Curve “4” is of the wastegate spring. Curve “1” is where you want the boost curve to be.

Curve “2” can be thought of as the boost when there isn’t an active wastegate. Curve “4” can be thought of as the boost curve if intake boost pressure is fed directly to the wastegate spring. i.e., the boost curve follows the wastegate spring curve.

To get to curve “1” (optimal) from curve “2” (native turbos), you need to apply boost signal pressure to the wastegate so the wastegate opens and bleeds off exhaust from the turbos thus lessening boost.

To get to curve “1” (optimal) from curve “4” (no control over wastegate signal pressure), you need to interrupt/reduce the boost signal pressure getting to the wastegate so the wastegate doesn’t open (as much) and bleed (too much) exhaust from the turbos.
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On the F40, a boost pressure signal is fed directly from the intake manifold (turbo output) before the butterfly valves (via hose part 50) to the wastegate by way of an electrovalve (part 54) controlled by the bank 1-4 ECU. See parts diagram below.

The electrovalve under control of the ECU controls how much boost signal pressure reaches the wastegate which controls how much exhaust is bled off from reaching the turbos. No signal pressure means the wastegate won’t open and bleed off exhaust which means high boost. More signal pressure means the wastegate will open according to its spring curve, thus bleeding off exhaust from reaching the turbos thus lowering boost.
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The electrovalve is an Amal valve, named after the town of Amal in Sweden where they were made by SEM (since been acquired). Like the BOVs the F40 uses, the Amal valve is an off the shelf standard part used by many turbo engines of the 90s, including Saab and Ford. They run about $50-$70 dollars overseas, $240+ from Ferrari.

The Amal valve has 3 ports/connections (see below). One (the input) goes to the intake manifold pressure signal, the second (the output) goes to the wastegate’s actuator bladder/membrane which pushes against its spring which opens the wastegate, the third (bleed) vents to open air.

When the valve is not energized (normal state), there is a direct path from the input (manifold) to the output (wastegate). i.e., the manifold pressure is operating directly on the wastegate to open it.

When the valve is energized, the bleed port is open to the in/out path and bleeds off some of the input pressure to open air. It doesn’t stop the output flow, only reduces it.

The Amal valve is a failsafe valve in that if it is NOT energized due to the ECU being dead or a broken valve wire, the valve remains SHUT (non energized) and thus directs ALL boost signal pressure to the wastegate actuator thus erroring on the side of low boost pressure to the engine (this is what happened in my case). If it is stuck open, some signal pressure still reaches the wastegate.

==> Note: It’s not clear whether the pressure still reaching the wastegate when the valve is energized is enough to activate/open the wastegate. The Ferrari pressure curves above suggest not because the “characteristic curve of the turbocharger” matches the “ideal boost pressure curve” in the lower part of the graph. If the pressure did slightly actuate the wastegate, the ideal pressure curve would never be as high as the turbo characteristic curve.
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So, back to symptoms of the Amal valve not working:

* Amal valve stuck “not actuated” (full signal pressure applied to wastegate): boost pressure curve would look like curve #4; matching the wastegate spring curve. i.e., you would get some boost, but maxing out at about 7-8 psi (as in my case). When people complain that they don’t have boost and that their wastegate is “stuck open”, I bet it’s really just the Amal valve stuck “not actuated” due to a bad electrical connection or bad coil inside the valve.

* Amal valve stuck “actuated” (signal pressure bled before reaching wastegate): wastegate would essentially be inoperable and the boost curve would be #2; matching the “characteristic curve of the turbocharger”. This in turn would allow for rapid boost pressure spool up, most likely above the optimal boost curve (probably as high as 22 psi?) which in turn would make the ECU call an “overboost” condition and shutdown the fuel. Thus, if switching to “green” ECUs (http://www.ferrarichat.com/forum/showthread.php?t=163643&highlight=f40+green+ecus) doesn’t help your overboost problem (especially with stock exhaust), look at the Amal valve for another cause.

 

Beware of bad Amal valves, even new ones!! If you have to replace it, I suggest you do the following simple test before installing it:

Simply take the unconnected Amal valve and blow into the input. All the air should come out the (wastegate) output.

Then, plug the output with your finger and blow again into the input. No air had better escape from the bleed hole!!!! I had a bad new Amal valve where the air would simply come out the bleed hole when I plugged the output port. If installed on the car, it would greatly reduce the ability to shut down the turbos and boost by not being able to fully open the wastegate!!! Not good.

If the above tests work, you can then hook up the valve to 12 volts to see if it can be actuated. When actuated, blow into the input again. This time, air should come out both the output and the bleed hole on purpose. If you plug the output, all the air will (obviously) come out the bleed.

Performing the above simple test can save a lot of grief.

 

Although you don’t (at least mortal men) have access to the wastegate ECU maps, you can still modify the wastegate and Amal valve characteristics.

The wastegate spring pressure can be changed via the spring preload screw on top of the hat.

You can also tune the Amal valve somewhat.

If the bleed hole is big enough, it will be able to bleed off all the input signal (when activated) thus keeping the wastegate closed and allowing the turbos and boost to spool up fast, possibly too fast.

Rexrcr (Rob Schermerhorn) has a thread about tuning the bleed hole by restricting it with carburetor jets. With the Amal valve activated, this allows some signal air to reach and activate the wastegate some amount, thus possibly slowing the rise in boost possibly preventing an overboost when running a free flowing exhaust (e.g., test pipes, straight pipes, etc).

See post #24 of:

http://www.ferrarichat.com/forum/showthread.php?t=17625


Okay, deep breath. That’s all for now. I need a beer… ;-)

Tim

 

Or Brian. But, not as much fun! They get to play with the actual engine. I just tinker with the external stuff which is readily accessible on that car. Plus with my travel schedule, it might take 4 months for me to actually successfully get the car into one of them! - Tim