? on EGR valve function diagnosis (1 Viewer)

[tominboise]

I am fighting a P0401 code. I have a question about sucking on the EGR valve to test for functionality. With my engine running at idle, I pull off the vacuum hose between the EGR and the modulator, put a vacuum hose on the EGR valve and suck. When I do so, the engine keeps running. When I suck and also pinch the hose between the EGR and the VSV valve, the engine stumbles and dies. Does this point to a defective modulator?

For what it's worth, I pulled the intake manifold this weekend, cleaned all the passages and replaced the VSV valve with OEM, and inspected the hoses.

Any help appreciated.

 

[98 SNAKE EATER]

To check the modulator, I prefer removing it completely, cap the 3 upper ports and suck/blow on the bottom port.

If it doesn't hold vacuum/air, then the diaphragm is most likely torn

Had the same issue a few months back.

https://forum.ih8mud.com/80-series-...since-ive-had-mil-401-egr-code-revisited.html

 

[tominboise]

Ok, I will try this what you suggested. I don't want to just throw $$ at replacing parts without doing some troubleshooting first.

 

[rkuffel]

FYI, I just went thru this on my 91 last week. On a 91 you do not need to block the 3 upper ports when checking to see if the modulator diaphragm is torn/bad. Connect a small handheld vacuum pump to the bottom port and apply vacuum. If it holds vacuum the diaphragm is fine. If you plug all the other ports (including the small hole under the filters) and apply vacuum to the bottom port, it will hold vacuum regardless of the condition of the diaphragm. I'm learning that a handheld vacuum is a must have diagnostic tool for these vehicles.