EGR solenoid behavior

[steveo]

so i got a code 32.. cleared it.. it came back. unlike my usual practice of just deleting the damn valve and calling it a day, since i dont even have my tuning gear yet, i figured i'd poke at the EGR system and see whats up.

i've given the valve itself a clean bill of health, which leads me to the solenoid?

i've read a bit, but a detailed description of the operation of the solenoid eludes me.

i've found that apparently it's 'normally open' which means when unpowered, it should pass vacuum to the EGR, right?

so i put vacuum to the solenoid in both directions, unpowered.

the one that connects to the EGR valve just bleeds off vacuum immediately, which i suppose is to be expected; allowing the valve to close when no vacuum is supplied to it, right?

the one that connects to the intake, however... holds some vacuum when unpowered, going against the 'normally open' solenoid behavior i'd expect.

it does bleed that vacuum off reasonably quickly, 20in/hg will drop to zero in about 10 seconds.

however none of that vacuum is passing to the other vacuum port where the egr is. blocking or unblocking that port doesn't cause that vacuum to drop more quickly.

can someone confirm how this egr solenoid is supposed to behave?

do i misunderstand 'normally open'?

i have an LT1 solenoid here, it completely holds vacuum completely when unpowered, and passes that vacuum to the other port when powered. the thing looks identical. is that "normally closed"?

did someone put the wrong solenoid on here?

do i talk too much?

any help would be appreciated

[steveo]

oh, '88 fbody LO3 if anyone doesnt know already

[Scrufdog]

the solenoid valves only passes vacuum when parameters in the ecu call for it. So unpowered the intake side will hold vacuum. Sounds to me like the solenoid is functioning correct without power. The problem could be that it is not opening when called for, or EGR passages are clogged.

[brian617]

Should be normally closed, yet always have power, key on. ECM uses ground to open solenoid to supply vacuum to EGR pulling it open. Solenoid should hold vacuum throttle body side or that would be a vacuum leak.

[steveo]

well i threw the lt1 solenoid on there and it stabilized idle a bit at the very least, now to try to get it into EGR testing range.

[RobertISaar]

this is for a 88 camaro 5.0TBI. no idea what other years/engines this applies to, but it might be useful.

http://imgur.com/vjiKNYA,EknG4Sl,b6j9tHS,dHSQCHX

[steveo]

weird, doesn't seem like pwm? I'm gonna scope it. code seems like straight up open&closed with no knowledge of a duty cycle

[RobertISaar]

it may be a software-loop PWM scheme? wouldn't be the first time GM has done that in the C3 or even P4 era.

[steveo]

ahh good point!

it's weird i just dont see reference in any other service material about pwm behavior, and i thought these positive backpressure EGR valves were just kind of an 'open it and let pressure regulate flow' kind of device.

[RobertISaar]

they might be.... GM documentation has been less than accurate before.