SonicWeaver
Member
Looking for some help with diagnosing a 1506 code on my '98 4.6 that appears to be caused when the purge valve is open.
When the purge valve opens idle rpm jumps several hundred from around 600 or so to 900 while in gear (800 to 1100 in park) and stays high for anywhere from a few second to 20 to 30 seconds and then returns to normal when the purge valve closes and continuously cycles in this way.
Other than this problem it runs smooth and strong.
I have smoke tested from the PCV hose and show no leaks anywhere. Have also smoked the purge line from the purge valve to the canister while closing the vent. Again no leaks.
Swapped or replaced: Purge valve, MAF, IAC valve and PCV.
O2 sensors look fine.
Short term trims are fine when purge valve is disconnected but show lean when purge circuit is operating.
It was idling higher (900-1400 in park) and I had a hard time getting it to staying at a specific RPM when checking trims. Say trying to have it stay at 2000. It would rapidly ramp up and overshoot then dive back down. Replacing the MAF changed this and made it less jumpy and lowered the idle to the 900 - 1000 range with purge control on.
When the purge valve is closed is idles fine (600-700). If I unplug it I no longer get a 1506 and it idles correctly but obviously it throws an evap code.
This thing is screaming vac leak but I'll be damned if I can find it.
Here's a missing peice of info I'm looking for help with. I know that the purge valve is pulse width modulated but I can't find what the duty cycle should be. The only thing that I've found says it modulates a couple of times a second which is not at all what I'm seeing. The amount of time (seconds to dozens of seconds) it is currently staying open appears to be way too long and would explain why the idle is so spastic.
Does anyone know what this open/close cycle should be?
I've swapped and tried 2 new valves and the symptoms don't change so I think the valve is good. It seems like the computer is send the wrong control signal or a purge valve drive device that is bad.
If the duty cycle is bad what could be causing the long open signal?
Appreciate the group's insight!
When the purge valve opens idle rpm jumps several hundred from around 600 or so to 900 while in gear (800 to 1100 in park) and stays high for anywhere from a few second to 20 to 30 seconds and then returns to normal when the purge valve closes and continuously cycles in this way.
Other than this problem it runs smooth and strong.
I have smoke tested from the PCV hose and show no leaks anywhere. Have also smoked the purge line from the purge valve to the canister while closing the vent. Again no leaks.
Swapped or replaced: Purge valve, MAF, IAC valve and PCV.
O2 sensors look fine.
Short term trims are fine when purge valve is disconnected but show lean when purge circuit is operating.
It was idling higher (900-1400 in park) and I had a hard time getting it to staying at a specific RPM when checking trims. Say trying to have it stay at 2000. It would rapidly ramp up and overshoot then dive back down. Replacing the MAF changed this and made it less jumpy and lowered the idle to the 900 - 1000 range with purge control on.
When the purge valve is closed is idles fine (600-700). If I unplug it I no longer get a 1506 and it idles correctly but obviously it throws an evap code.
This thing is screaming vac leak but I'll be damned if I can find it.
Here's a missing peice of info I'm looking for help with. I know that the purge valve is pulse width modulated but I can't find what the duty cycle should be. The only thing that I've found says it modulates a couple of times a second which is not at all what I'm seeing. The amount of time (seconds to dozens of seconds) it is currently staying open appears to be way too long and would explain why the idle is so spastic.
Does anyone know what this open/close cycle should be?
I've swapped and tried 2 new valves and the symptoms don't change so I think the valve is good. It seems like the computer is send the wrong control signal or a purge valve drive device that is bad.
If the duty cycle is bad what could be causing the long open signal?
Appreciate the group's insight!
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