Ron Boals
New member
I am aware that the power valve, by virtue of the sliding gate, changes the exhaust port height and thus gives you more torque at lower rpms and more horsepower at higher rpms. At least that is what I believe. What I don't understand is the actual operation, beyond the servo motor reeling in the cable and thus opening the gate. Does it open all the way at once, or gradually? What determines when and how far it opens, is it tied in only to the operating rpm? Beside the servo, the valve bodies themselves, the cables, and some sort of coil in the stator that generates an electrical current that I assume provides the energy for the servo to rotate, what else is involved? Does the servo reel only return because of the springs in the valve body or does electrical current reverse? I have been having some difficulties with them on my 98 SRX 700, although I'm not sure the problems were with the valves or the temp sensor, as I have been getting some confusing codes with the water temp light. Any light you could shed on this subject would be appreciated. Thanks Ron Boals
They are operated by rpm simply and done thru the cdi box. They open at approx 6500rpm if my memory serves me and they also open up fully below 1000rpm as a self cleaning feature. The electric signal to cycle the motor coming from the cdi box moves the servo and the springs help to return the valve as the servo motor is kinda in a coast mode meaning hardly any reistance in it on the return, but it does return on its own with no cables so it may reverse the current inside the servo, I am not 100 percent knowing on that without taking it apart. Again this happens with the rpm, so the motor only knows what way to go via the cdi box, which is run off the motors stator power, and any engine is rpm referanced off the stator voltage wires.
What I have seen happen almost exclusively to the 98-99 srx is the cdi triggering part of the box goes bad and the power valve servo will not cycle or act intermittent,meaning with the sled up on a stand and revving it up with the servo cover removed will show you a jerking motion and not opening the valves or no movement at all regardless of the rpm of the engine. I have replaced a good 3-4 of them because of this problem, its only in the 98-99 units!
Maybe you can elaborate on your problem??
What I have seen happen almost exclusively to the 98-99 srx is the cdi triggering part of the box goes bad and the power valve servo will not cycle or act intermittent,meaning with the sled up on a stand and revving it up with the servo cover removed will show you a jerking motion and not opening the valves or no movement at all regardless of the rpm of the engine. I have replaced a good 3-4 of them because of this problem, its only in the 98-99 units!
Maybe you can elaborate on your problem??
Last edited:
Ron Boals
New member
Thanks for your insight
This sounds like what mine has been doing, had a valve, the stem of which that has the cable slot, worn in a rectangle pattern like the cable anchor had been pulled through. Anyway tried to find a used one, ended up replacing it with a new one. I had been getting an intermittent code, on the water temp light, it was difficult to identify, ended up pulling the temp sensor and testing it in a can of water with an ohm meter. Resistance decreased with temp, tested a second out a SX and did the same. Next checked the coil as per manual, w-w/b connection, virtually no resistance. reconnected everthing back and then was getting a distinct pattern of 7 blinks and the servo seemed to be fully engaged while idling at 1800 rpm. Went to bed, next morning, it had curred itself, getting the three blinks at startup now.
The reel does however make some intermittent movement, while just sitting there idling. I got the tester in the mail yesterday, so will hook it up to the little white connector behind the airbox and belt cover and check to see if the servo cycles and readjust the free play in the power valves. It seems to me that one could also check the free play at the cable ends in the servo housing, without partially disassembling the valves, similar to how the freeplay is set with the choke cable. You mentioned having similar troubles with 98-99 SRXs', would you recomment replacing with a newer model CDI??
Thanks agan, for your time and information. I am finding that most of the service personnel at local shops, are younger than a lot of the equipment I am running. Ron Boals
This sounds like what mine has been doing, had a valve, the stem of which that has the cable slot, worn in a rectangle pattern like the cable anchor had been pulled through. Anyway tried to find a used one, ended up replacing it with a new one. I had been getting an intermittent code, on the water temp light, it was difficult to identify, ended up pulling the temp sensor and testing it in a can of water with an ohm meter. Resistance decreased with temp, tested a second out a SX and did the same. Next checked the coil as per manual, w-w/b connection, virtually no resistance. reconnected everthing back and then was getting a distinct pattern of 7 blinks and the servo seemed to be fully engaged while idling at 1800 rpm. Went to bed, next morning, it had curred itself, getting the three blinks at startup now.
The reel does however make some intermittent movement, while just sitting there idling. I got the tester in the mail yesterday, so will hook it up to the little white connector behind the airbox and belt cover and check to see if the servo cycles and readjust the free play in the power valves. It seems to me that one could also check the free play at the cable ends in the servo housing, without partially disassembling the valves, similar to how the freeplay is set with the choke cable. You mentioned having similar troubles with 98-99 SRXs', would you recomment replacing with a newer model CDI??
Thanks agan, for your time and information. I am finding that most of the service personnel at local shops, are younger than a lot of the equipment I am running. Ron Boals
to be honest with you the tester you got is gonna be of little value to you unless the servo motor itself would be faulty, what you most likely have the problem with is the cdi signal recieved by the servo motor, and the only way to check that is with the sled running. You can either have the sled up on a jackstand and test it with the plastic servo motor cover off or you can also turn the idle speed down to under 1000 rpm to see if the servo fully actuates the valves open.
What I like to do is have a permanent marker handy and start up the sled, with the servo cover off, turn the idle down to under 900rpm, the servo should open the valves, now mark the pulley and a referance mark on the servo. Readjust idle speed back up to spec. Now place rear of sled up on a jackstand and while watching the same mark you just placed rev it up over 6500rpm and watch to see if the marks line up or not. You know your getting the correct signal strength by doing this if they line up, if they dont it will 9 times out of 10 be the cdi box itself, although I have found a couple be the wiring harness chaffed thru and intermitantly shorting out the system.
What I like to do is have a permanent marker handy and start up the sled, with the servo cover off, turn the idle down to under 900rpm, the servo should open the valves, now mark the pulley and a referance mark on the servo. Readjust idle speed back up to spec. Now place rear of sled up on a jackstand and while watching the same mark you just placed rev it up over 6500rpm and watch to see if the marks line up or not. You know your getting the correct signal strength by doing this if they line up, if they dont it will 9 times out of 10 be the cdi box itself, although I have found a couple be the wiring harness chaffed thru and intermitantly shorting out the system.
Ron Boals
New member
Thanks very much for your insight. If I do need to replace the CDI, and you indicated you have found the problem primarily with the 98-99 models, can I substitute the CDI from an 01 or 02 SRX 700? Ron
unfortunately no, the 98-99 srx have the same plug and will interchange but the 2000,2001,2002 all have differnt plugs and wont interchange as well as a completely differnt ign system.