Checking VSV for the EGR without removing the VSV itself (1 Viewer)

[roncruiser]

I've been getting the dreaded CEL: code 71. Booooo! To verify the operation of the VSV, I took my inspiration for an easy way to test the VSV for the EGR from this thread:
https://forum.ih8mud.com/80-series-tech/211364-checking-vsv-egr-easy-way-p0401.html

I've attached a few photos:

1: Disconnect 8 pin connector. For a '93/'94, this is an 8 pin connector.
For the '95-97, it is different. I believe it's a 4 pin connector. You'll have to verify for yourself which pins to connect to for a '95-'97.

2:The pins you are interested in are the two bottom left pins of the male side of the 8 pin connector. Test resistance across these two pins. According to th manual, you should normally be reading 30-34 ohms of resistance. Mine measured 25K ohms. Bad!

3:Attach wires to the two bottom left pins of the male side of the connectors. Attach the wires to the battery to activate the VSV. You can hear an audible click of the relay switch on the VSV when connected to the battery.

 

[roncruiser]

4: Disconnect the two vacuum hoses attached to the VSV. They are pretty easy to reach. Disconnect the vacuum hose on the left fender side and attach a long hose to the VSV. This hose should be long enough for you to easily blow through.

5: To reach and disconnect the vacuum hose on the throttle body side, you will have to remove the EGR modulator.

6: If the VSV is good, you should be able to blow through the VSV easily when it is NOT connected to the battery. With the VSV connected to the battery, you should NOT be able to blow through the VSV.
With the VSV connected to 12V, you should not be able to blow through the VSV. My VSV is stuck open. Boooo! High resistance equals BAD. Connecting to 12V did not close the valve. My new VSV is on it's way.

 

[skibob]

ok, so, this weekend I removed my vsv, took it apart, cleaned it, put it back together, it's working as described now.
I didn't take pictures because I was in the zone and it was cold out.
What I did do;
if you look at the picture above, the one with the big red arrow,
Use a phillips screwdriver to remove the vsv from it's bracket,
Get a large cookie sheet to catch any little bits that might fall out work over the cookie sheet to reduce frustration
Use a flat bladed screwdriver to carefully pry the bent metal clamp part away from the black plastic vaccuum cap slightly. Be gentle, but it went pretty easy.
After you have loosened it a bit you can get hold of it with a pair of dykes and straighten it a bit more. It needs to be pretty straight for the next line to work.
place the cap to the side in a safe place. There will be one o-ring. Don't lose it.
Straighten the four small metal tabs and gently separate the bracket from it's other half.
There will be a small metal cap sort of looks like a mushroom cap with a silicone skirt attached.
The silicone skirt is permenantly molded, don't pull or abuse it.
Under the mushroom cap is a small spring and an o-ring.
Clean everying with a toothbrush and some carb cleaner
Put it back together using care to not pinch the o-rings or other soft bits.
Use a large plyers to squeeze the metal tabs, don't beat on them. This will offer better results and reduce the chance of breaking something. Make sure the vaccuum ports are pointed the way they belong before you put it together or you will have to risk a second round of tab bending.
apply 12V to the terminals while blowing through, air should pass through until you hit it with 12V. The click is not very loud, but it's there.
Like I said, mine works like it should now, it was pretty nasty inside.
I also did the relocate thing since it really is in a stupid place from the factory.

 

[LCHardriver_02]

I have a '95 with a 0402 code (excessive flow), could this valve cause this code too? I have looked at the EGR diagram, but I have not played with the system yet. Next on my to-do list. Thanks.

 

[ybhc]

Now I know the VSV is primarily for the EGR

So say, I have completely removed the EGR valve and associated flying saucers, and put nice plasma-cut steel plates over the top of the EGR passages in the head and the intake. How much of the vacuum tube nightmare that is the VSV could I remove..?

 

[skibob]

I don't have the diagram, but I would think that if this valve is stuck closed, a condition where no air can pass, and everything else is good, your egr would likely post an excessive flow error.
I don't have a known good modulator so I can't comment on that. I did pop the cap to look under the felt filter, it didn't have a bunch of carbon in it.
All of the ports flow freely on my modulator, which may very well mean it's toast.
Maybe someone can enlighten me as to it's proper flow characteristics, it doesn't seem right that all ports would be open.

 

[thestunts]

Thanks for posting. subscribed to reference here in a little bit.

 

[LCHardriver_02]

Here is the schematic from the '96 FSM. Looks like the VSV valve directly controls the EGR opening, with the vacuum modulator varying the EGR position controlling the amount of flow through the EGR.

Someone post up if I am reading this incorrectly.

Thanks much. I feel like I am making headway in understanding this system to best troubleshoot my issue. Well, at least one of them.

 

[skibob]

So it looks like the vaccuum modulator is designed to allow manifold vacuum to leak until it reaches a certain level, then the diaphragm pulls to close the vaccuum port from vsv to egr.
This causes the egr to open. When the ecu senses that egr is not appropriate it sends 12V to the vsv, closing it to deactivate egr.
my vaccuum modulator has free flow from all four ports, is this correct or should the bottom right be closed in order to pull the diaphragm? Maybe I'll take it apart to see how it works next. If it's anything like the rest of this truck, I will be able to get it back together with very little evidence of tampering.

 

[roncruiser]

Before removing your VSV, test it first. It's relatively easy compared to removing the VSV. My VSV was toast. High resistance. Basically, an open circuit.

 

[roncruiser]

The tab broke off of the connector shown in the first photo above. The tab keeps the connectors locked together. Instead of replacing the connector, ive zipped tied them in place.

 

[skibob]

On my rig the vacuum modulator is toast.
The diaphragm is leaking.
Remove it from the car to test.
On the schematic above there are four vacuum ports on the modulator.
1 up from the bottom, the rest clockwise from there 2, 3, 4.
port 1 apply vacuum, it should not leak
port 2, apply vacuum, should leak until you cover 3 & 4, then no leak.
ports 3&4 are activated by 2, if 2 works, 3&4 will work.
This part works on the pressure differential between the exhaust manifold and intake manifold.
Under light load with part throttle, high exhaust flow and high vacuum will cause the valve to close (not mine) and the egr to open. There must be some conditions where this pressure differential is present and the egr is not warranted, so the vsv activates, closing that port and not providing vacuum to the egr valve.
The modulator is not available aftermarket from what I can tell.

 

[roncruiser]

FYI: Passed CA smog test.

 

[Bob_Garrett]

I was getting a recurring P401, so I tested my vsv as outlined above and it tested good. I then pulled the vacuum modulator and tested as per skibob's instructions above and it failed. Picked up a new one at the Toyota dealer installed it and so far, no more P401.

 

[LCHardriver_02]

NICE! I need to try this!

 

[masyam]

Thank you for posting this test method. The VSV on my 94 tested good that saved me time and hassle of removing. However, I'm still getting the error code 28. Can someone tell me if I should be seeing a vacuum between the EGR valve and VSV when engine is hot? I see no vacuum with a vacuum gage in T connection. Would it be possible that the EGR valve is not opening and giving me the error code 28? The EGR valve and modulator are brand new just installed. The CEL (code 28) comes on when the engine reaches normal operating temperature after driving several miles.

 

[ppc]

The operation/conditions/testing of the VSV is documented in the FSM.

 

[masyam]

Thanks, it seems that the condition is complex.

 

[ppc]

That is precisely why I referred you to the FSM. That said the EGR is not that complex just follow the table and also read up on the 28 error causes and repairs.

 

[masyam]

Thanks for your suggestions. I was able to test the VSV per FSM procedure. Funny thing is that the VSV does not turn ON/OFF at all unless the vehicle is being driven. Maybe the gear has to be engaged or something. At any rate I observed that the vacuum comes on and off at the EGR valve while I'm driving once the engine warms up, i.e. the EGR valve is properly functioning (it's a brand new valve I just installed). The vehicle runs quite nicely with smooth idling, acceleration and enough power. Yet, I still get the error code 28. Checked sensor wiring continuity and they are all good. My troubleshooting continues............