The Evo’s 4G63 pulled willingly to its 26 PSI max and let off a sensory-pleasing swoosh from its Turbosmart Type 5 Dual-Port blow-off valve. The sound was intimidating and the turbo responded more quickly with the BOV on call. Life was great for many miles, but then the performance started to slowly fade.

The Evo developed a finicky flutter from its blow-off valve. Instead of being greeted by a sonic rush of air the valve was pulsating; under lighter loads at first then even under more significant boost, the valve couldn’t muster a full discharge. Soon the wavering gremlin raised its ugly head during closed loop operation at highway cruising speeds as the car was going up a slight hill. As the vacuum gauge neared zero the fluttering hit. This became more than a nuisance as we were worried the resulting compressor surge would hurt the turbo, which had upwards of 110,000 miles of boost on it. Further, the engine would shudder in a most discerning manner.

We adjusted the tension of the unit’s spring to no avail. We then decided to call in the cavalry, Marty Staggs of Turbosmart. He enlightened us that blow-off valves require routine maintenance, and in dirty environs a six-month interval was in order.

In absorbing this revelation we realized living in the woods means there are all manner of airborne contaminants floating around. Heck, we had seen water puddling in the trumpet of the valve. So we were in trouble. In the Evo IX, the blow-off valve is positioned with the trumpet facing upward. This exponentially increases the chance of contamination and markedly decreases the required maintenance interval.

Additionally, the car’s hood grille is directly above the valve, so there are all kinds of reasons for the hiccup in performance. Staggs talked us through the process and recommended a Turbosmart video if we needed a more visual explanation.

We loosened the hose clamp on the downward portion of the valve that is plumbed into the turbo inlet hose between the air filter and the turbocharger. After removing the boost reference hose on the top of the unit, there was one more step to go.

We found the recirculating part of the blow-off valve was threaded into a fitting that was more permanently installed in the recirc hose. So, it was a simple matter of unscrewing the blow-off valve to free it from the engine bay.

Upon first inspection we quickly confirmed we were in trouble, as the brass piston was totally covered in gunk.

The red top of the valve is where you control the unit’s performance. By turning the top, spring pressure can be altered, changing the opening characteristics of the valve. This is labeled as ‘harder’ or ‘softer’ on the valve top. Unscrew the top enough and it will separate from the valve body. Be sure to keep pressure on the cap, as it is under spring tension and will want to jump off the body.

The internal parts of the blow-off valve consist of the spring and a piston. Usually, or at least in the videos we’ve seen, the piston cooperates fully and drops out with little more than gravity acting upon it. Not so in our case.

Some of the grit we saw in the outlet had worked its way between the piston and cylinder wall. We knew this was the cause of the performance fall-off because the piston wouldn’t budge. We sprayed it with WD40 and poured some Marvel Mystery Oil on the piston top in hopes it would seep in.

We eventually used a socket and a mallet to convince the piston out of the bore. Staggs recommended Marvel Mystery Oil as the maintenance video calls for using a hydraulic or sewing machine type of oil.

We examined the valve body bore and the outer surface of the piston for scarring, pitting, and wear. We could feel some roughness at the top of the cylinder and worked some Marvel Mystery Oil in as well as we could with a microfiber shop towel. After reinstalling the piston into the bore, we saw some improvement. In talking with Staggs after the fact, we discovered it would have been wise to use some steel wool or a Scotchbrite pad in this situation to clean up the bore scratches, and we plan to do so the next time the unit needs maintenance.

We checked the base O-ring and the cap O-ring for integrity, wiped them down, and then cleaned the threads. With everything spic and span, the project moved into the reassembly stage. We applied the Marvel Mystery Oil on the piston and inner bore of the valve body, put the piston in the bore, and actuated it by hand. We then took it out and added more Marvel Mystery Oil prior to reassembling the unit.

The Evo was having another issue. We were getting CELs that indicated a code P0401, ‘insufficient flow through the Exhaust Gas Recirculation valve’ or EGR valve. In doing some research, we found that this was most often due to a hose coming loose on the EGR and not a defective EGR solenoid that our Actron AutoScanner Plus called out as a possible culprit.

We originally thought the fluttering of the BOV and the vibration it caused contributed to the hose coming loose, but later realized it was most likely the pressure not escaping the BOV getting rerouted to the EGR and popping off the hose.

The fix is a two-pronged solution; spraying hairspray on the inside of the hose end and/or using a zip-tie like a hose clamp to help secure the hose. Since we zip-tied the hose, performed our blow-off valve maintenance, and cleared the codes, we are happy to report all has been quiet on the CEL front.

Turbosmart released a new version of this blow-off valve at SEMA called the Smart Port. “This new-and-improved model has a check-valve on the VTA port to minimize any dirt and contaminants getting on the piston,” says Staggs. “In addition, the piston is now made of hard anodized aluminum that is then Teflon coated. The result is a near bulletproof design that will require far less (if any) maintenance.” We like how the vents on the trumpet of the new valve are closer to the piston, which helps eliminate the puddling we have experienced with the Type 5.

It is always satisfying to clear the workbench and get down to business making your car perform better. We’re actually looking forward to future blow-off valve maintenance. Stay tuned…