95 LC80 EGR giving me a headache (3 Viewers)

[SavageRhyno]

I have read most of the forums on here. But none of them touch on what I’m dealing with.
I own a 1995 Land Cruiser (with OBDII)
If you look at the attached image, you’ll see my color coding trying to solve the issue. Green means I have tested it, and/or replaced it. Red means I’m getting no vacuum pressure.
I cleaned and check the vacuum cavity, connecting to the intake manifold. I can blow air through it easily… yet when I hook it all back up… I get no vacuum pressure. Can someone please shed some light on this. I’m at a loss.

 

[effjay80]

My two clogging passages on my 94 were the hard tunnels in the throttle body and this line coming off the EGR valve. I CAREFULLY used a long thin drill bit to clean out the passage down into the manifold. Beyond that I seem to recall there were two colors of egr modulators too and one wouldn't work. Also not sure if you checked the egr temp sensor? Sure looks like you've hit everything else.

 

[SavageRhyno]

My two clogging passages on my 94 were the hard tunnels in the throttle body and this line coming off the EGR valve. I CAREFULLY used a long thin drill bit to clean out the passage down into the manifold. Beyond that I seem to recall there were two colors of egr modulators too and one wouldn't work. Also not sure if you checked the egr temp sensor? Sure looks like you've hit everything else.

View attachment 3394778

Thank you for the response! I have cleaned that hard line as well. It’s all clear. I haven’t changed the temp sensor. I guess I’ll give that a shot. Does the temp sensor act as a valve?

 

[Somebodyelse5]

the best way to correct the egr, is to delete the egr.

 

[ToyotaDon]

An understanding of the Vacuum Switching Valve operation would be helpful here. Its job is to block the vent passage from the EGR valve. You should have vacuum at the RH side of the EGR tee when you accelerate (vacuum gauge in place of VSV). Then, if you tee into that hose with the VSV connected again, there should be vacuum as long as the VSV is operating. If the VSV is faulty, it will always be venting and the vacuum will not lift the EGR valve.

 

[ToyotaDon]

Thank you for the response! I have cleaned that hard line as well. It’s all clear. I haven’t changed the temp sensor. I guess I’ll give that a shot. Does the temp sensor act as a valve?

The temp sensor does not act as a valve. It is what tells the ECM that the EGR valve has opened.

 

[SavageRhyno]

the best way to correct the egr, is to delete the egr.

Does it still pass smog once deleted?

 

[Somebodyelse5]

Does it still pass smog once deleted?

In AZ yeah, no issue

 

[jpoole]

If all is functioning correctly then the red circuit is not going to hold a vacuum unless the EGR VSV is powered on. A static test at idle or with the engine off should show that circuit as open as your testing has found. I don't remember the parameters for when the ECU powers the EGR VSV but I think it may require a certain speed, rpm, engine temp and/or other conditions to be me.

If you have a clog in the pass-through port then you will always hold a vacuum on that circuit and you will see a PO402 which is the opposite of a PO401. PO401 insufficient EGR flow and PO402 is too much EGR flow.

Here are a few tests I'd run in your situation.

1. Plug the line that runs to the pass-through port and the EGR VSV. This will simulate an EGR VSV valve that is always engaged, and you should see solid vacuum at the EGR valve when the engine is running/revved up. This will confirm that the rest of the system is clear/functional. If you drive like this for a while you should get a PO402.
2. Power up the EGR VSV and then test to see if the vacuum circuit on that side of the EGR valve holds a vacuum. This will confirm that you have no air leaks and that the EGR VSV valve is functioning correctly and allowing vacuum to build when it should. Here's a howto on running this test:
   1. Checking VSV for EGR easy way P0401 - https://forum.ih8mud.com/threads/checking-vsv-for-egr-easy-way-p0401.211364/

You likely know this but the PO401/2 codes will only be thrown after you've driven up to a base speed (45mph to 50mph roughly, as I recall), come to a stop and then drive back to that base speed again. This can be confusing if you are expecting the codes to throw more quickly or if you don't drive fast enough, stop and then get to a fast enough speed again while testing.

If you put a vacuum on the EGR Valve while the 80 is idling, when/if the EGR valve opens the idle speed will drop and the engine may die. This is a good way to quickly confirm that the EGR valve is opening and allowing exhaust gas into the intake. If you know that the EGR Valve is itself functional then you can then dial in the vacuum controls and finally confirm that the temp sensor is functional to stop your PO401 codes.

When I was figuring this system out I found it helpful to run with a vacuum gauge that was monitoring the EGR valve control circuit. You can tuck one under the wiper arm and run the line under the hood then watch it while driving if you want. If you isolate the EGR VSV side of things you can quickly see what the vacuum levels should be a different driving conditions. When you add the EGR VSV circuit back in you can see if/when the EGR VSV is powered up, and closes that side of the system, thus allowing vacuum to build.

Some other common issues with these are clogged ports on the throttle body, clogged EGR vacuum modulator, leaky EGR vacuum modulator, leaky lines, etc.

Keep in mind that there are a few VSVs (vacuum switching valves) under the hood but you are interested in the EGR VSV when working on your PO401.

Looks like you are close to getting this sorted. Post back with more info and I'm sure we can help. It's very possible to get this system to run correctly, without codes, once you get to the bottom of understanding how all of the components work and how to test them.

 

[SavageRhyno]

If all is functioning correctly then the red circuit is not going to hold a vacuum unless the EGR VSV is powered on. A static test at idle or with the engine off should show that circuit as open as your testing has found. I don't remember the parameters for when the ECU powers the EGR VSV but I think it may require a certain speed, rpm, engine temp and/or other conditions to be me.

If you have a clog in the pass-through port then you will always hold a vacuum on that circuit and you will see a PO402 which is the opposite of a PO401. PO401 insufficient EGR flow and PO402 is too much EGR flow.

Here are a few tests I'd run in your situation.

1. Plug the line that runs to the pass-through port and the EGR VSV. This will simulate an EGR VSV valve that is always engaged, and you should see solid vacuum at the EGR valve when the engine is running/revved up. This will confirm that the rest of the system is clear/functional. If you drive like this for a while you should get a PO402.
2. Power up the EGR VSV and then test to see if the vacuum circuit on that side of the EGR valve holds a vacuum. This will confirm that you have no air leaks and that the EGR VSV valve is functioning correctly and allowing vacuum to build when it should. Here's a howto on running this test:
   1. Checking VSV for EGR easy way P0401 - https://forum.ih8mud.com/threads/checking-vsv-for-egr-easy-way-p0401.211364/

You likely know this but the PO401/2 codes will only be thrown after you've driven up to a base speed (45mph to 50mph roughly, as I recall), come to a stop and then drive back to that base speed again. This can be confusing if you are expecting the codes to throw more quickly or if you don't drive fast enough, stop and then get to a fast enough speed again while testing.

If you put a vacuum on the EGR Valve while the 80 is idling, when/if the EGR valve opens the idle speed will drop and the engine may die. This is a good way to quickly confirm that the EGR valve is opening and allowing exhaust gas into the intake. If you know that the EGR Valve is itself functional then you can then dial in the vacuum controls and finally confirm that the temp sensor is functional to stop your PO401 codes.

When I was figuring this system out I found it helpful to run with a vacuum gauge that was monitoring the EGR valve control circuit. You can tuck one under the wiper arm and run the line under the hood then watch it while driving if you want. If you isolate the EGR VSV side of things you can quickly see what the vacuum levels should be a different driving conditions. When you add the EGR VSV circuit back in you can see if/when the EGR VSV is powered up, and closes that side of the system, thus allowing vacuum to build.

Some other common issues with these are clogged ports on the throttle body, clogged EGR vacuum modulator, leaky EGR vacuum modulator, leaky lines, etc.

Keep in mind that there are a few VSVs (vacuum switching valves) under the hood but you are interested in the EGR VSV when working on your PO401.

Looks like you are close to getting this sorted. Post back with more info and I'm sure we can help. It's very possible to get this system to run correctly, without codes, once you get to the bottom of understanding how all of the components work and how to test them.

Thank you!!! I am going to test tonight and report back in a day or two. The current code is the PO401.
Is it a possibility that the temp sensor is stuck in the “on” position. Therefore leaving the VSV closed?

 

[jpoole]

Is it a possibility that the temp sensor is stuck in the “on” position. Therefore leaving the VSV closed?

It's hard to answer this question, which may not make sense. Short answer is "no" but follow up questions are: which temp sensor? Which VSV?

I assume you mean the temp sensor that is in the EGR gas flow path, located near the top/rear of the intake manifold. That temp sensor heats up when egr gasses flow and let's the computer know that the EGR system is working. I don't think that sensor has any control over the EGR VSV opening or closing.

I assume you mean the EGR VSV. It should require power to be "closed" as in no air can flow through it, which is what allows vacuum to build and open the EGR valve. I really don't know the factors that all tie into the computer deciding that it's time to power on the VSV and allow vacuum to build and the EGR valve to open. I suspect there are multiple factors like engine operating temp range, speed, etc. as I mentioned. I used to have a better sense of the operating parameters but it's been years since I've had to worry with this system so don't recall the details. Simply using a vacuum gauge while driving around will tell you more about when the VSV engages and vacuum can build. Of course, run the other test and make sure the VSV will even close and that you have no leaks, etc.

If the EGR VSV is closed all the time and all else is well then you'll get a PO402. A PO401 means vacuum isn't building up, the EGR valve isn't opening, the intake flow path for EGR gasses is clogged, the EGR temp sensor is not getting through to the ECU, etc.

 

[SavageRhyno]

Okay fair enough. I’ll leave the temp sensor alone for now. And based on what you said… it seems like no pressure is building (through the red line)

And Just to be clear with the first test…
I plug the line between the EGR and the EGR VSV or between the EGR VSV and the “T” connector?

 

[jpoole]

First test that I would do:

• pull the lines off of the EGR valve
• plug one of the two lines on the top of the EGR Valve so that no air can go in/out of it
• put a foot or two of vacuum hose on the other line on the EGR Valve
• crank the 80 and let it idle
• create a vacuum on the vacuum line going to the EGR valve to see if it opens and causes the idle to drop/stumble
  • You can create enough vacuum with your mouth to open the EGR valve and have the idle drop

Second test I would do is the EGR VSV test that I linked to in my first response. In that test you are essentially hot-wiring the EGR VSV valve to see if it closes off and stops air from flowing into the EGR Valve so that vacuum can build up.

If you pass both of those tests then you can test the Vaccum modulator, make sure the throttle body vac ports are open, etc. I don't have time to write a full step by step check of all of it, and it sounds like you've tested a lot so you likely don't need all of those tests anyway.

Also, you can hop on youtube and search for "Toyota PO401 troubleshooting" or similar to find some nice videos on how to test the system. Toyota delivered a lot of cars with very similar EGR system setups so while the location of the components may vary a little the troubleshooting is very similar.

Once you do more testing and have some results feel free to ask more questions.

Good luck!

 

[SavageRhyno]

First test that I would do:

• pull the lines off of the EGR valve
• plug one of the two lines on the top of the EGR Valve so that no air can go in/out of it
• put a foot or two of vacuum hose on the other line on the EGR Valve
• crank the 80 and let it idle
• create a vacuum on the vacuum line going to the EGR valve to see if it opens and causes the idle to drop/stumble
  • You can create enough vacuum with your mouth to open the EGR valve and have the idle drop

Second test I would do is the EGR VSV test that I linked to in my first response. In that test you are essentially hot-wiring the EGR VSV valve to see if it closes off and stops air from flowing into the EGR Valve so that vacuum can build up.

If you pass both of those tests then you can test the Vaccum modulator, make sure the throttle body vac ports are open, etc. I don't have time to write a full step by step check of all of it, and it sounds like you've tested a lot so you likely don't need all of those tests anyway.

Also, you can hop on youtube and search for "Toyota PO401 troubleshooting" or similar to find some nice videos on how to test the system. Toyota delivered a lot of cars with very similar EGR system setups so while the location of the components may vary a little the troubleshooting is very similar.

Once you do more testing and have some results feel free to ask more questions.

Good luck!

Okay.
First test passed.
Second test failed. But its a brand new OEM EGR VSV. I’m going to return it I guess. And go with the Dorman “replacement” I have seen in the forums.
I watch most of those videos. That’s why I got as far as I did.
I really appreciate your help. I hope this is the actual solution.

 

[jpoole]

I tried the Dorman unit and it only worked a year or so. I saw a similar report of the Dorman valve failing early from at least one other mud member. I replaced the Dorman unit with an OE unit and it's been 4 or 5 years without issue.

Before I ordered another new EGR VSV I would rule out a few other issues that could be causing the EGR VSV side of things to not hold a vacuum.

• Check the continuity/resistance of the new VSV at the port where you hot-wired it. If it tests open (no resistance) then the coil in the VSV may be broken or there may be a disconnect in the circuit. You want to make sure that the resistance is in spec and that there aren't wiring issues with the VSV or with your test leads. With the engine off you should hear the VSV click when it closes/engages and if you are pulling air through that circuit you should feel the air flow stop and start as you connect/disconnect the VSV power.
• Another thing to check, that is a little harder to access, is to rule out vacuum leaks or mis connections anywhere between the vacuum line at the EGR valve and the EGR VSV. There are a few junction points and some places where things could be leaking or mis-routed that could prevent vacuum from building up even if the VSV is working. It's pretty hard to work under the intake body but you can inspect some of the vacuum lines and unplug at one or two points from outside the intake. You can also remove the throttle body and then have decent access to the vacuum plumbing under the intake. You can use a length of vacuum line that you plug in a different points from the VSV working back towards the EGR Valve to see if the VSV side of things will hold vacuum and at what point that ceases to be the case, etc.

If you end up with the EGR VSV in hand I would also bench test it before sending it back. You don't want to find out that the VSV was fine and that there was a leak or routing issue causing the system to not build up vacuum.

 

[SavageRhyno]

I tried the Dorman unit and it only worked a year or so. I saw a similar report of the Dorman valve failing early from at least one other mud member. I replaced the Dorman unit with an OE unit and it's been 4 or 5 years without issue.

Before I ordered another new EGR VSV I would rule out a few other issues that could be causing the EGR VSV side of things to not hold a vacuum.

• Check the continuity/resistance of the new VSV at the port where you hot-wired it. If it tests open (no resistance) then the coil in the VSV may be broken or there may be a disconnect in the circuit. You want to make sure that the resistance is in spec and that there aren't wiring issues with the VSV or with your test leads. With the engine off you should hear the VSV click when it closes/engages and if you are pulling air through that circuit you should feel the air flow stop and start as you connect/disconnect the VSV power.
• Another thing to check, that is a little harder to access, is to rule out vacuum leaks or mis connections anywhere between the vacuum line at the EGR valve and the EGR VSV. There are a few junction points and some places where things could be leaking or mis-routed that could prevent vacuum from building up even if the VSV is working. It's pretty hard to work under the intake body but you can inspect some of the vacuum lines and unplug at one or two points from outside the intake. You can also remove the throttle body and then have decent access to the vacuum plumbing under the intake. You can use a length of vacuum line that you plug in a different points from the VSV working back towards the EGR Valve to see if the VSV side of things will hold vacuum and at what point that ceases to be the case, etc.

If you end up with the EGR VSV in hand I would also bench test it before sending it back. You don't want to find out that the VSV was fine and that there was a leak or routing issue causing the system to not build up vacuum.

So I tested the VSV with the truck off. And I can hear a small click when I give it 12v from the battery. So it must be okay.
I was really thorough when I connected all the vacuum lines the first time. But I’m going to take it apart and double check.
Only other thing I can think of is the ECU or harness isn’t sending the signal. I couldn’t find my volt reader. I’m going to get a new one tomorrow and make sure it’s sending a signal.
Fingers crossed. I’ll report back.

 

[SavageRhyno]

Okay… so I test the plug from the harness. And I’m not getting 12v. (I assume it should give 12v when it’s cold so the VSV can build pressure)
I started looking at the harness and noticed a large cord sitting on my starter not hooked-up. What is that for?
I plan on looking up a wiring schematic so I can determine where the VSV wires connect to the ECU. Any help will be appreciated!

 

[jpoole]

Hey @SavageRhyno

The EGR VSV is not going to have power when the 80 is cold, warming up, not moving, etc. You may want to re-read my earlier posts that touch on this. The EGR VSV not powering up is why I described tests where you add a vacuum gauge to the EGR vacuum circuit and then watch while driving as a final test that the EGR valve is being opened, and when. This is also why I pointed out that I first check the EGR vacuum on my 80 with the VSV side of things blocked off so that vacuum always built up, then I re-test while driving with the EGR VSV side hooked up so that I can see if vacuum builds up while driving.

If you step back and think about what the EGR system is doing this will make more sense. The EGR system is introducing exhaust gasses to your intake manifold to try to reduce emissions in certain conditions. If the EGR system tries to add exhaust gasses while the engine is idling then it will idle roughly or stall, if the engine isn't warmed up then it doesn't benefit from the exhaust gasses in terms of emissions, etc. My rough understanding is that the exhaust gasses help with emissions when the engine is warm and under load. The vacuum modulator helps control the vac side of things based on throttle position and load (this is why there is a vac port on both sides of the throttle body butterfly) while the EGR VSV gives the computer the ability to override and completely disable the EGR system if certain conditions are not met.

If you want to connect your multimeter or a test light and then drive around you can watch to see when/if the EGR VSV valve is powering up. If the EGR VSV valve is not powering up I'd guess that it's because of the ECU not seeing the conditions it needs being met vs. a shorted wire, but anything is possible. This type of "no power to EGR VSV" issue is uncommon in PO401 troubleshooting per my experience and that may be because if the ECU isn't getting the set of signals it needs you'll likely have other error codes that you deal with before you worry about the PO401, like engine temp sensor repairs or similar.

At this point the issues that are preventing the EGR VSV side of things on your 80 from holding vacuum while you are driving seem likely to be:

• A vacuum leak between the EGR VSV and the EGR valve or a line routing issue.
• The VSV valve having crud in it that is preventing the valve from closing and sealing correctly.
  • it could be worth trying to blow out the VSV valve in case there's a little chunk of carbon in there impacting operation
• The ECU is never powering the EGR VSV valve up
  • when you hot wired the EGR VSV it still didn't hold vacuum so I would not focus here until the EGR VSV holds vacuum when hot wired

Hope that helps you put together how this system works a little better.

 

[jpoole]

Oh, and that large / loose cable could be easy for someone else to identify but I'm not certain what it is. Here are some ideas for what I think it may be:

• a ground that wasn't reconnected
• a starter main power wire that was replaced/bypassed but left dangling
• a winch connection that had been installed on the starter power lug but then was left off
• a cable that had been added to connect a 2nd battery but then was left disconnected
• etc.

I would trace that wire down to see where it goes and then decide what to do with it and why it may have been left dangling like that. You may need to remove the wire/cable completely to clean things up, reconnect it to the starter or a ground point etc, fix what it is connected to and then reconnect it, etc.

I'll add that the wrapping and position of that cable makes it look like it was hot (connected to the positive side of the battery) and connected directly to the main power lug on the starter. I would trace it down and figure out what it is before blindly reconnecting it though because you could do some unintended welding or 80 roasting if it's shorted to ground and you reconnect it, etc. I also would not just leave it dangling without knowing what it's connected to because it could be hot and just waiting to touch ground and start a fire. It should also be very easy to trace that wire out thanks to it's size.

 

[SavageRhyno]

Hey @SavageRhyno

The EGR VSV is not going to have power when the 80 is cold, warming up, not moving, etc. You may want to re-read my earlier posts that touch on this. The EGR VSV not powering up is why I described tests where you add a vacuum gauge to the EGR vacuum circuit and then watch while driving as a final test that the EGR valve is being opened, and when. This is also why I pointed out that I first check the EGR vacuum on my 80 with the VSV side of things blocked off so that vacuum always built up, then I re-test while driving with the EGR VSV side hooked up so that I can see if vacuum builds up while driving.

If you step back and think about what the EGR system is doing this will make more sense. The EGR system is introducing exhaust gasses to your intake manifold to try to reduce emissions in certain conditions. If the EGR system tries to add exhaust gasses while the engine is idling then it will idle roughly or stall, if the engine isn't warmed up then it doesn't benefit from the exhaust gasses in terms of emissions, etc. My rough understanding is that the exhaust gasses help with emissions when the engine is warm and under load. The vacuum modulator helps control the vac side of things based on throttle position and load (this is why there is a vac port on both sides of the throttle body butterfly) while the EGR VSV gives the computer the ability to override and completely disable the EGR system if certain conditions are not met.

If you want to connect your multimeter or a test light and then drive around you can watch to see when/if the EGR VSV valve is powering up. If the EGR VSV valve is not powering up I'd guess that it's because of the ECU not seeing the conditions it needs being met vs. a shorted wire, but anything is possible. This type of "no power to EGR VSV" issue is uncommon in PO401 troubleshooting per my experience and that may be because if the ECU isn't getting the set of signals it needs you'll likely have other error codes that you deal with before you worry about the PO401, like engine temp sensor repairs or similar.

At this point the issues that are preventing the EGR VSV side of things on your 80 from holding vacuum while you are driving seem likely to be:

• A vacuum leak between the EGR VSV and the EGR valve or a line routing issue.
• The VSV valve having crud in it that is preventing the valve from closing and sealing correctly.
  • it could be worth trying to blow out the VSV valve in case there's a little chunk of carbon in there impacting operation
• The ECU is never powering the EGR VSV valve up
  • when you hot wired the EGR VSV it still didn't hold vacuum so I would not focus here until the EGR VSV holds vacuum when hot wired

Hope that helps you put together how this system works a little better.

I apologize. I’m trying really hard to understand the system. I keep re-reading your messages.
I think I was thinking of it backwards. (I thought it was closing the VSV with 12v to build pressure on the other side. Then opening and pulling the EGR with the built up pressure all at once) but I see that’s wrong now. I’m going to hook up some electrical wires and run it to the cab and see if the meter ever shows 12v while driving. After that I’m also going to get some extra vacuum lines and run a pressure gauge to see if it builds pressure.
I’ll also re-do my vacuum lines.
I really appreciate your help and patience.
I’ll let you know if I find anything out. Thanks.