EGR/Vacuum Modulator Question


Dec 23, 2004
Beaverton, Oregon
Anybody ever had their EGR valve blow the vacuum line off the bottom of the modulator?

I finally found that my mysterious exhaust leak was, in fact, coming from an unplugged vacuum line on the the modulator. There was a bunch of carbon build-up on the base of the modulator and around the hose nipple, which makes me think something's not right.

I was talking with CDan (thanks for all the help, by the way!) about it this morning and he thinks maybe the carbon plugged something up and the pressure of the exhaust coming from the EGR might have blown the hose off the modulator.

No CEL with the hose unplugged, so I figured I'll drive it for a few days and see if it throws any codes with the hose plugged back in. The engine seemed to rev up much more smoothly with the hose plugged in... gotta go see how it drives. I wonder if this has anything to do with my hard starting when warm issue?

Thanks for any input,


Mar 27, 2003
north of 49
I wonder if your egr valve itself might be blocked so as to route all the exhaust gas through that hose to create enough back pressure at the modulator to blow the hose off. You should try the FSM test for EGR of running a vacuum hose off your intake into the egr valve to see if the truck stalls.

How carboned up was the modulator filter? If it was carboned up I would replace it and check all the vacuum hose lines. No code yet means your vsv is probably still working but it won't be for long if carbon is getting into your vacuum hoses.
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