EGR issues again

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Nov 23, 2008 | 10:45 PM

nickbaize

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EGR issues again

on my 351m my egr valve isnt holding vaccum so that tells me its bad right, so i went to four different auto part stores and none there egr valves hold vaccum ethier so does the egr valve on my truck just not hold vaccum or is all there valves bad too?

Nov 23, 2008 | 11:08 PM

fmc400

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From: Austin, TX

When you say hold vacuum, what exactly are you trying to do? If you apply vacuum to the port, it should move inward. When you apply vacuum and hold it there, what is happening? Is the spindle moving back out? Please explain more.

Nov 24, 2008 | 09:43 AM

nickbaize

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well i take my vaccum gauge and put it on the port and i pump it nothing moves on the egr valve and it doesnt hold pressure

Nov 24, 2008 | 09:48 AM

fmc400

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From: Austin, TX

When you apply vacuum to the port on the back of the EGR valve, the diaphragm should move inward. If you look on the flange of the valve, there are two openings and one of them has a spindle insdie. This should move inward as the diaphragm moves inward, when you apply vacuum.

If you are applying vacuum and nothing moves, the valve is bad. If you apply vacuum and the diaphragm won't move, it won't hold vacuum either. The only possibility I can think of is maybe you aren't applying enough vacuum to overcome the force of the return spring, but it doesn't take too much to at least see 1/8" movement.

The EGR valve is a pretty simple device; it's basically a "vacuum motor" and operates the same way a vacuum advance does. There's a diaphragm inside; on one side is the port for negative pressure; the other side is connected to the spindle. As negative pressure is created, the diaphragm moves toward it and pulls the rod inward. The valve fails by the diaphragm rupturing, or the passageway inside the flange becomes clogged with carbon.

Nov 24, 2008 | 10:03 AM

Pickupmanx2

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From: Near Yosemite CA

Hold vacuum, when you apply vacuum, it moves in, but then goes back to normal after a short time? while still having vacuum applied?

Nov 24, 2008 | 07:34 PM

nickbaize

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well the problem i have with my truck is i get up to about 50 mph and my truck just starts surging like a bad out of hell and it acts like its going to die but dosent and when i step on the gas it goes no were but if i back it down to 30-45 mph it runs great so someone told me it could be my egr valve so i checked it and it dosent hold vaccum on my gauge on or off the vehclie so im pretty much just spinning my wheels?

Nov 24, 2008 | 09:34 PM

fmc400

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Joined: Apr 2004

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From: Austin, TX

That problem sounds more like a fuel pump, fuel filter, or float height issue than an EGR valve. The EGR valve does very little work at 50 mph because in most cases you have the throttle open a decent amount and ported vacuum (along with manifold vacuum) is very low at that point, so the valve wouldn't be open anyway. EGR valves don't cause surging; when they go out they usually lead to pinging, detonation and dieseling. Whoever told you it's the EGR valve does not know what he's talking about.