Solenoid valve resistance different 1

[doug54]

During a retrofit I have a new solenoid valve (automotive 12V)that has a coil resistance value of 12.2 ohms. The solenoid valve is actuated by the ECU. The original solenoid valve for this ECU had a resistance value of 10.3 ohms. It doesn't appear the new valves are funtioning. Installing the earlier valve is not practicle. Is the resistance value difference enough that the ECU can not operate the new valve? Is there a way of making the new higher resistance valve work? Thanks!

 

[BrianPetersen]

A higher resistance coil will draw less current, all else being equal, and usually that's in the direction of not having a problem. BUT ...

What's the application?

Some types of coils rely on a spike of in-rush current to get them to shift. If your current supply is not providing that, this might be a problem.

Other times the coil may be supplied with a reduced voltage or a duty-cycled signal. If the new coil is not designed for that (requires full voltage supply, or isn't designed for fast cycling of a duty-cycled signal), that's going to be an issue.

 

[doug54]

Hi Brian. thanks for the response. it is a solonoid valve that opens to allow oil flow to create a change in cam timing. It is supplied power by the engine ECU. We are using the original Bosch ECU and it appears the new valves are not operating. Since the new valves are 12.2 ohms and the original ones are 10.3 I wondered if the difference was enough that the ECU cant actuate them not knowing the output current capability of the ECU. Thanks!

 

[BrianPetersen]

Is the original-equipment valve duty-cycled so as to create an infinitely-variable amount of cam shifting? (Opposing example, a Honda VTEC solenoid is a "bang-bang" on/off solenoid.) Most hydraulic cam-timing-shift mechanisms other than Honda VTEC (and even including the timing-shifting mechanism on an i-VTEC DOHC engine) are designed to be infinitely variable.

If it's a duty-cycled application and the solenoid you've put in is not designed for that, it ain't gonna work.

 

[doug54]

Thanks Brian, it's a Porsche 996 and 997. Using a Porsche 996 engine in a Porsche 997 using the 997 ECU. Thanks for your help.

 

[oab]

A lot of automotive control solenoids are operated by a Duty Cycle, even if they are an on/off operation. This is so the controller can tell if the armature is responding to the signal. It uses the Inductive feedback, that varies with the armature position, to tell if the armature is moving to the position commanded or if it is stuck in one position.

 

[dgallup]

It is possible the new solenoid valve is not strong enough to open against the oil pressure. Is the internal valve geometry the same? If it is a valve designed for a different application it may not be able to open. Generally, lower impedance solenoids are stronger because they are drawing more current but that is a gross over simplification as there are many other variables including stroke & valve design.

 

[TStaples]

Doug,

I have done the 996 3.6l motor installation on my track car (with a Motec,) and I'm familiar with the solenoid you describe. It is a simple on-off solenoid, and doesn't require a PWM to operate. However, oab is correct. Many controllers use various techniques to verify the solenoid is actuating, as part of the OBD requirements for the vehicles. I am not familiar with the 997 ECU or any differences from the 996 ECU, which I did study before setting up my Motec. With all of that said, here is what is suspect:

The 997 ECU is monitoring the solenoid via inductive feedback (more than simple resistance.) The ECU is finding the solenoid to be outside it's acceptable limits, so it's not operating the solenoid at all, which is the ECU's "limp-home" mode for that solenoid. If I'm right, you should be able to diagnose this with an OBD reader, as it should be spitting out a code for a failed cam phasing solenoid.

-Tony Staples

http://www.tscombustion.com