near RTH: Vacuum Modulator Meltdown (1 Viewer)

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Grench

SILVER Star
Joined
Jun 15, 2006
Threads
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Location
Lincoln, NE
Not stranded. I have other wheels and the truck is in a safe place. So, I called this near RTH as I need to get a plan together before the weekend.

I wish I had a picture of the valve meltdown carnage, but the truck is 60 miles away from me right this minute. I will try to get some pictures of the valve this weekend.

Background:
1996 FZJ80 130,000 miles
Fresh head gasket
Fresh TRD Supercharger Install
Brand new EGR valve
Brand new EGR vacuum modulator valve
Hose routes right according to the SC install book
Stock exhaust

Symptom:
Blew a hole the size of a quarter through the side of my new vacuum modulator valve. The valve body/plastic got hot enough to melt/blow with bubbled plastic and holes through the side & top. The gas flowing from it was hot enough to melt the plastic wire loom around the harness extension 4" away.

Analysis so far:
The EGR valve has a side stem that provides exhaust pressure over and up to the bottom of the EGR vacuum modulator. It pushes quite a bit of pressure and if the modulator valve fails, it moves quite a bit of exhaust out under the hood.

There was enough pressure coming through the lower hose on the modulator valve to cause it to fail. Once it had failed, the exhaust continued to flow into/through the valve to heat it up to the melting point. It then failed catastrophically with curling bits of molten plastic wrapping up in lava-rock formations all over the valve. The hot gas continued to shoot out of the EGR stem acting like an ultra high temp heat gun melting the wiring looms. The wires appear to be fine (lucky me).

The first sign of failure was when the cruise control stopped working on the highway due to the vacuum loss.

So, I'm trying to understand how the EGR modulator is supposed to work. From what I can tell it balances the pressure of the exhaust vs the vacuum flow from ports on the throttle and one port that connects through the T on the EGR back to the (now) high pressure intake port. This is how the SC install guide shows it anyway so that is what we did.

I have two theories, but am interested in hearing more.

My theory 1. The stock exhaust is providing more back pressure than the EGR modulator valve was able to handle under the SC conditions.

My theory 2. The SC install book wasn't right or I interpreted it wrong. Should the EGR actually be fed off of the DS port into the tiny port on the intake (per the SC guide) OR should we reroute it back to the vacuum side of the SC? Having vacuum on one side and pressure on the other seems a bit self defeating as any vacuum fed to it through the pre-SC side would just be defeated by the pressure coming to it from the post-SC side.

What else do you guys have? I searched, but found no reference to someone actually melting/blowing holes in an EGR modulator valve.

I'll try to get some pictures Saturday when I can get back to where my truck is at. That valve looks cool. Good thing I still have the one we took off.

Grench
 
You sure it's not the EGR valve itself that's failed?

Curtis

It is a brand new out of the box EGR valve. When I supply vacuum to it and close off the other end of the T (mimicing the VSV working) it moves appropriately.
 
The EGR valve has a side stem that provides exhaust pressure over and up to the bottom of the EGR vacuum modulator. It pushes quite a bit of pressure and if the modulator valve fails, it moves quite a bit of exhaust out under the hood.

This is the part that concerns me; I don't recall that the side stem should allow near enough exhaust gas out to cause the damage you're describing.
 
Sorry to hear about this problem. I'm glad you were injured, it sounds like a dangerous problem.

I didn't replace my EGR or anything like that when I put on my S/C so I don't know how much help I could offer.

However, I did remember quadruple checking the routing of the hoses between the EGR and the throttle body and even held the instruction manual right next to it to make sure it was assembled correctly. In all honesty I was crossing my fingers that everything would function properly, so maybe I was just lucky I didn't have a problem like this.

Is there a possibility that when you put the new EGR on that it wasn't sealed properly or that the hoses were routed incorrectly? I haven't changed mine, so I don't know exactly what is involved, just throwing out some ideas.


FWIW I have never had the dreaded P0401 code or whatever it's called, guess I should probably knock on wood.
 
Sorry to hear about this problem. I'm glad you were injured, it sounds like a dangerous problem.
I'm assuming that was a typo. ;)

I didn't replace my EGR or anything like that when I put on my S/C so I don't know how much help I could offer.
Thanks for the offer. If you could tell me letter code to letter code for the two lines you have from the throttle body to the EGR modulator, that would help quell a curiosity of mine. Also, did you hose clamp the line on the bottom of the EGR modulator or just stub it in?

However, I did remember quadruple checking the routing of the hoses between the EGR and the throttle body and even held the instruction manual right next to it to make sure it was assembled correctly. In all honesty I was crossing my fingers that everything would function properly, so maybe I was just lucky I didn't have a problem like this.
We double checked. I guess we should have checked a few more times 'cause somethin' ain't right.

Is there a possibility that when you put the new EGR on that it wasn't sealed properly or that the hoses were routed incorrectly? I haven't changed mine, so I don't know exactly what is involved, just throwing out some ideas.
I've thought about this. I've also considered the possibility that our brand new EGR modulator valve was dead in the box.

FWIW I have never had the dreaded P0401 code or whatever it's called, guess I should probably knock on wood.
I had had this code a few times. Part of the reason why I'd purchased a new EGR and modulator over a year ago and swapped them out when putting in the SC.

I'm going to try to get a picture of it posted up tomorrow. You guys are going to love this one.
 
Keep in mind I am confused at which "space ship" is the EGR Modulator and which one is the valve.


I'm assuming that was a typo. ;)

Thanks for the offer. If you could tell me letter code to letter code for the two lines you have from the throttle body to the EGR modulator, that would help quell a curiosity of mine. Also, did you hose clamp the line on the bottom of the EGR modulator or just stub it in?

See below, I did not hose clamp any lines that went to the EGR Mod

We double checked. I guess we should have checked a few more times 'cause somethin' ain't right.

I guess this is one area my OCD might have saved my bacon.

I've thought about this. I've also considered the possibility that our brand new EGR modulator valve was dead in the box.

I assume it was OEM wasn't it?


I had had this code a few times. Part of the reason why I'd purchased a new EGR and modulator over a year ago and swapped them out when putting in the SC.

Still knockin' on wood. You can see mine have surface rust, but still kickin' it.


I'm going to try to get a picture of it posted up tomorrow. You guys are going to love this one.

I'm very interested to see the pics

Letter code to letter code for the two lines you have from the throttle body to the EGR modulator (Smaller green space ship?):

EGR Mod "R" line --> TB "R"

EGR Mod "P" line --> TB "E"

Also

EGR Mod "Q" line --> to T-fitting on top of the Larger space ship (EGR valve? sorry for the technical jargon) the line on the other side of the T goes to a nipple on the brass square bracket under the intake manifold. From here a line goes to the "yellow filter according to the TRD manual" or in reality the orange T fitting.

Connected to the orange T is a line supplied by TRD that goes to the third nipple on the TB (next to the "R" and "E" nipples on the throttle body)

The OEM line that was connected to the "Orange T" is the line that is connected to the intake manifold opening where the intake runner is bolted. As you can see in the picture, I just left mine there ghetto style because I read that the intake runner gasket covers the hole. I will cap it off soon.

I hope this helps
 
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And yes that was a typo, I am glad you were NOT injured ;)
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Thank you! Yes, they do look like space ships. :) I'll have more info tomorrow.
 
Figured it out. Maybe.

It looks like the modulator end of the little hose popped off, sat beside it, ran exhaust through it like a cutting torch. Nifty.

The old one is going back on with hose clamps.

Thank you for the Tbody mapping. We had it right, but it helps to know for sure.
IMGP1406_small.JPG
IMGP1404_small.JPG
 
Damn, that is crazy.

IS that an OEM Toyota part? I thought my factory one is all metal.
 
Just an update

Damn, that is crazy.

IS that an OEM Toyota part? I thought my factory one is all metal.

It is an OEM part. That is the way the new ones look. The top and bottom shell are held together with glue/press/snap.

The old factory ones are plastic top & bottom with a metal ring around the center holding them together.

I've driven it 180 miles over 3 trips since we put the old factory one back on (with hose clamps this time) and it has done the job. I'm not getting any CELs, so it looks like the EGR is doing what it should be.

So far so good.
 
Its good to hear everything is working well.

Note to self: Never touch the EGR Modulator or replace with new unless I use hose clamps.

My factory installed unit does not appear to have any hose clamps. I wonder why yours blew off without them.
 
Its good to hear everything is working well.

Note to self: Never touch the EGR Modulator or replace with new unless I use hose clamps.

My factory installed unit does not appear to have any hose clamps. I wonder why yours blew off without them.

We had it off and on there a dozen times or so as we were working out the connections in the area. It is possible that it didn't get put on snug or got it slick enough that it came off easy or was sitting in front of rather than on the stub for the modulator.

So, the most likely answer is installation error. :bang: I think the new OEM one would have been fine if we had secured it properly.

So far so good. I still have a laundry list of projects to do on it, but they will have to wait while I take care of the :princess: home list and help my :banana::banana::banana::banana::banana: brother in law who helped me with this project get his snow trucks ready for the plowing season.

My list of items still to do on the truck that I already have parts for...
  • Slee tie rod & relay rod & new OEM ends
  • Slee rear diff lock skid plate
  • Over the frame exhaust
  • Rear power
  • '91 seat belt receivers and seats
  • Landtank MAF body & sensor (Easy, but I wanted to make sure we had a solid baseline before installing it.)

At least the list is shrinking. What we did this round...

  • New head gasket
  • TRD Supercharger
  • Cruiserdan's special V6 fan & shroud modification
  • Toyota pusher fan (Currently wired through a relay run off of the low beam from the Slee wiring harness. I'll probably be changing that some time soon.)
  • Slee headlight wiring harness
  • Slee aux light harness w/ switch in cab
  • HID aux lights
  • New radiator
  • Landtank fan clutch
  • New water pump
  • New thermostat
  • new belts & hoses all around
  • Coated manifolds
  • Modified the factory wiper fluid jug so that it would ride in the corner behind the cruise control
  • Modified the cruise control plastic hood cap so that the above would fit
  • Re-wrapped the wiring harness by the EGR
  • New EGR valve
  • New and back to old EGR modulator
  • EOM washable air filter
  • Safari Snorkel
  • Grill of unknown year ('94 maybe?) that says 'TOYOTA' instead of the sombrero with modifications to fit my big marine switches and the pusher fan.
  • Put a thimble on my winch cable so it doesn't get flattened by the hook
  • Slee transfer case skid plate

That is probably enough for the moment.
 
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On my third EGR modulator valve

After adding this one to another EGR thread, I realized that I never did post back what the results were on my EGR meltdown.

From above, you could find that I replaced the melted down EGR valve (pictured) with the old one (metal ring) and hose clamped it on.

2 weeks later it blew out the new hose (OEM) and roasted the exhaust side port right off of the 'old' valve.

Why?

Clogged catalytic converter. It was resulting in so much exhaust back pressure that something had to give. I replaced the exhaust and put a third new EGR modulator valve on it with another new OEM hose. So far so good. Third time's a charm.
 
On my third EGR modulator valve

After adding this one to another EGR thread, I realized that I never did post back what the results were on my EGR meltdown.

From above, you could find that I replaced the melted down EGR valve (pictured) with the old one (metal ring) and hose clamped it on.

2 weeks later it blew out the new hose (OEM) and roasted the exhaust side port right off of the 'old' valve.

Why?

Clogged catalytic converter. It was resulting in so much exhaust back pressure that something had to give. I replaced the exhaust and put a third new EGR modulator valve on it with another new OEM hose. So far so good. Third time's a charm.
Exactly what happened to mine. But I also just did the EGR valve check (connected directly to vacuum) and couldn't get the engine to stall so I believe I have a stuck valve. But I'm thinking it's worth investigating the catalytic converter as well so it doesn't keep happening.
 
Exactly what happened to mine. But I also just did the EGR valve check (connected directly to vacuum) and couldn't get the engine to stall so I believe I have a stuck valve. But I'm thinking it's worth investigating the catalytic converter as well so it doesn't keep happening.
To save you a whole lot of searching and consternation:
Code:
https://www.amazon.com/gp/product/B004SH8CR4
 
To save you a whole lot of searching and consternation:
Code:
https://www.amazon.com/gp/product/B004SH8CR4
Thanks for the link! I hope it doesn't come to that just yet...
I was able to get the EGR Valve to function correctly and cleaned the two TB to VM ports and put a new VM. Guess it's time to read up on how to test for clogged converters and order your link if it looks bad for me. Seems like measuring temperature before/after is one way.
 

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