VSV valve switch control (1 Viewer)

[jpoole]

Hello All,

I'm still in the long process of getting through the initial baselining my project '97 FZJ80. After replacing involved hoses, EGR modulator, VSV switch, cleaning intake, etc. I enjoyed months of being PO401 free but I've started seeing occasional PO401 codes recently and have commenced the troubleshooting. At this point I think the problem may be that the VSV is not getting powered up correctly but of course I may be wrong.

Important details:

-with no power to the VSV the EGR switch can't maintain vacuum and air passes through the VSV as it should
-if I power (hotwire) the VSV valve/switch it closes and air doesn't pass through it. The EGR valve can build up vacuum and open, etc. as it should.

Given the above I let the engine run until warm (187 degrees in my last test) and then with the VSV connected/plugged in electrically I test to see if the VSV valve is open or closed to vacuum/air and it's still open. This indicates to me that the VSV is never being powered up.

Questions:

-under what scenario does the VSV normally receive power? at certain temp, rpm, mph, other?
-if my VSV isn't receiving power when it should are there any usual suspects? I don't see blown fuses but didn't get into testing electrically beyond a cursory inspection.
-does this possibly point to other engine issues like knocking or something that keep the VSV unpowered and the EGR disabled?

Thanks!

 

[ppc]

I believe that the all the questions you have posed are documented in the FSM.

 

[jpoole]

I re-read a lot of the PO401 section in the FSM and it leads me to believe that the VSV won't get powered up when the truck isn't being driven, though I'm still not sure on that. When testing the VSV yesterday I ended up with a few small bits of carbon in my mouth (what I was using for vacuum/pressure testing as I switched the VSV on and off manually) and today when I test drove the truck (multiple runs above 50 with stops/off in between) the PO401 didn't recur. I assume that the PO401 came back due to a bit of carbon in the system left over from the previously failed and replaced modulator.

It's also possible that there is a short in the harness that is intermittent and causing the VSV to not get switched on correctly at certain times. I assume this possible short/break would be around the section of the harness that is heated up by the EGR piping. I'm not sure the best way to test that as I don't know how to trigger power to the VSV while the truck is in the driveway where I could wiggle the harness etc. to see if I could find/replicate a short.

@ppc I've already spent a lot of time reading and re-reading about the EGR system for the FZJ80 on this forum, other online resources (since the system is similar in a lot of other Toyota models and a common failure point) and in the FSM. I asked the question here vs. going back to the FSM because my searches here weren't turning up answers and I thought there may be a chance that someone here was familiar with what factors lead to the VSV being powered up, specifically as it relates to testing power to the VSV with the truck sitting in a driveway. I need to make time to re-read everything VSV related in the FSM at some point to try to better understand the system and figure out how to get power to the VSV while parked, if possible, but wanted to see if anyone here already knew the answer and cared to share it on the forum.

 

[Tedward]

I've read and sorta remember some of it.
Certain conditions have to be met for the EGR Valve to be opened by the vacuum switching valve.

Operating temp. in range.
Not at idle or wide open throttle, somewhere in the middle.
So when just cruising the valve opens and the reduced emissions magic happens, supposedly.

 

[jpoole]

@Tedward

That's my rough understanding as well. I'm not sure that the FSM gets very specific from some perspectives on this though getting to a better understanding of the diagnostic procedures recommended by the FSM would allow one to deduce more specifics I assume. As I recall the mass air flow meter is also involved and driving conditions are referenced as leading to high enough air flow to trigger EGR opening, etc. I'm not sure on how one might trigger the VSV powered-up scenario in a driveway or if it's possible but fortunately for this round of PO401 fixing I didn't need to figure it out. I'm hoping I don't have a short in the harness but time will tell on that.