Melted EGR Vacuum Modulator

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

JerseyCruiser

JerseyCruiser

10 Year 15 Year 20 Year
Joined
Jun 1, 2006
Threads
104
Messages
573
Location
North Jersey
After smelling some burning plastic I looked under the hood to find the
EGR modulator in an extremely melted condition and it even melted some of the hood insulation. All the hoses are connected none were loose. My question is can blocked, or melted cats be the cause of this? I've been lightly driving it since I replaced a dead #6 injector this summer that was causing the cats to glow cherry red. It was running fine when I first got it back together but now seems to lacking power so I'm guessing the cats are probably breaking down and getting clogged. Is there anything else that could cause this meltdown and at this point what else could I've have destroyed as well?

Thanks
Merry Christmas, Happy Holidays
IMG_0140.webp
IMG_0142.webp
 
I had this happen back in August

EGRmodulator2014two.jpg


https://forum.ih8mud.com/threads/it...ive-had-an-mil-401-egr-code-revisited.660812/



Replaced it without issue and figured the bottom hose just came loose and slowly melted the plastic away with hot gases, but it happened about 2 weeks after my primary cat had failed, so now I'm thinking it probably blew off when the system got backed up due to the clog :hmm:

cloggedbosalcat.jpg


https://forum.ih8mud.com/threads/ha...-the-drive-home-temporary-overheating.813602/



I have since gutted both cats and have yet to throw a code, even after 15,000+ miles :cool:

Running better than ever at 382,xxx miles :grinpimp:
 
EGR stuck open. Are you sure you aren't getting any CEL codes? Also, having the EGR modulator non-functional will affect engine performance/power.
 
clownmidget said:
EGR stuck open. Are you sure you aren't getting any CEL codes? Also, having the EGR modulator non-functional will affect engine performance/power.
Click to expand...
No codes at all but a very rich smelling exhaust, lack of power over 50 MPH, and poor fuel economy.
I think the cats are toast, dam shame they are OEM and were replaced in 09 I'm going to drive it too much until I can take the cats down to inspect them. I'm guessing the pressure vented out through the EGR.
 
98 SNAKE EATER said:
I had this happen back in August

EGRmodulator2014two.jpg


https://forum.ih8mud.com/threads/it...ive-had-an-mil-401-egr-code-revisited.660812/



Replaced it without issue and figured the bottom hose just came loose and slowly melted the plastic away with hot gases, but it happened about 2 weeks after my primary cat had failed, so now I'm thinking it probably blew off when the system got backed up due to the clog :hmm:

cloggedbosalcat.jpg


https://forum.ih8mud.com/threads/ha...-the-drive-home-temporary-overheating.813602/



I have since gutted both cats and have yet to throw a code, even after 15,000+ miles :cool:

Running better than ever at 382,xxx miles :grinpimp:
Click to expand...
Any problems passing state smog tests with cats hollowed out?
 
Last edited:
No smog in FL, but I hooked it up to the monitors at our shop here on the Island and it passed with ease :cool:

Not sure how it works in Jersey nowadays, but here in NY, as long as you have an OBD-2 car that doesn't throw a code, you pass :)

Next time I'm there, I'll hook up the sniffer and see what kinda numbers she puts out :hmm:

*sent from my android powered string cup*
 
98 SNAKE EATER said:
No smog in FL, but I hooked it up to the monitors at our shop here on the Island and it passed with ease :cool:

Not sure how it works in Jersey nowadays, but here in NY, as long as you have an OBD-2 car that doesn't throw a code, you pass :)

Next time I'm there, I'll hook up the sniffer and see what kinda numbers she puts out :hmm:

*sent from my android powered string cup*
Click to expand...
I'm OBD-1 so I get the sniffer, it passed in July just after getting all back together and after sitting for about a year. It took the dunces at the state facility 10 minutes to find the cats with a mirror, flashlight and one guy under the truck looking as they are under the slider, but come on, duh! I asked them if they were looking for a bomb or contraband, and that confused them more. I don't really want to spend over $1200. for two new ones again, so it seems like I have other options ;)
 
Last edited:
JerseyCruiser said:
After smelling some burning plastic I looked under the hood to find the
EGR modulator in an extremely melted condition and it even melted some of the hood insulation. All the hoses are connected none were loose. My question is can blocked, or melted cats be the cause of this? I've been lightly driving it since I replaced a dead #6 injector this summer that was causing the cats to glow cherry red. It was running fine when I first got it back together but now seems to lacking power so I'm guessing the cats are probably breaking down and getting clogged. Is there anything else that could cause this meltdown and at this point what else could I've have destroyed as well?

Thanks
Merry Christmas, Happy Holidays
Click to expand...
I have the same exact condition as you and am trying to get a plan together to attack this. Someone suggested that the EGR could be stuck open above but that seems like it would cause no start issues. Did it end up being your cats? And short-term, did you just replace the modulator and keep driving?
 
jatree said:
I have the same exact condition as you and am trying to get a plan together to attack this. Someone suggested that the EGR could be stuck open above but that seems like it would cause no start issues. Did it end up being your cats? And short-term, did you just replace the modulator and keep driving?
Click to expand...

Replace the modulator.

The exhaust blows against a diaphragm in the modulator to regulate the vacuum signal to the egr. If the ecu doesn’t want the egr it opens the vsv to vent the signal the modulator created.

If you take a good one apart you will see a tiny black dot in the filter pad. That is a controlled exhaust leak(bleed), the distance the modulator is from the exhaust pipe that feeds the egr will dissipate the heat created from that control bleed.

When that diaphragm gets old it breaks down and leaks internally, letting to much exhaust flow through the modulator thus creating enough heat to melt.
 
95BBC said:
Replace the modulator.

The exhaust blows against a diaphragm in the modulator to regulate the vacuum signal to the egr. If the ecu doesn’t want the egr it opens the vsv to vent the signal the modulator created.

If you take a good one apart you will see a tiny black dot in the filter pad. That is a controlled exhaust leak(bleed), the distance the modulator is from the exhaust pipe that feeds the egr will dissipate the heat created from that control bleed.

When that diaphragm gets old it breaks down and leaks internally, letting to much exhaust flow through the modulator thus creating enough heat to melt.
Click to expand...
Thanks for your response. I've had the truck 1.5 years and still enjoy learning every new system. I'm picking up and installing a new modulator today and hope that solves the problem.

Because I hope to own and enjoy it for another 20+ years I'll probably dig deeper soon. For the next couple weeks I just need to go 5-10 miles in the city. But I'd feel better knowing that the throttle body was cleaned and that the EGR Valve and VSV both work as they should. I'd also feel better knowing that excess exhaust pressure isn't going to cause this new $100 modulator to fail again. So gonna come up with a plan for that too.
 
Posting another data point - I replaced the modulator 11 months ago and last week I had the same thing happen again (melted like OP). I need to go back and re-learn about the EGR system because clearly something is wrong. Dealer is replacing the part under warranty but while chatting, they really don't think it's a symptom of excess exhaust pressure from failing/clogging cats (any ideas to test this would help). So I will probably go the route of opening/cleaning, replacing vac hoses, testing again, possibly changing the VSV even if it tests fine. What's the lifespan of the valve itself? When taking out the melted modulator, I thought I spied a little pinhole in the side but when I was doing the tests last fall, it worked fine and between replacing this expensive part and disabling the system, I'm definitely leaning towards the latter.
 
Just to follow up - I confirmed high backpressure (>10psi) via hole drilled between Y-pipe and first cat. I already went through and removed and cleaned the TB, put a bunch of new vac and fuel hoses, and replaced and rerouted the VSV. I've avoided melting the new Vacuum Modulator by limiting driving/rpm's but putting a plan together to replace the cat, likely with a single Magnaflow 99006HM.
 
jatree said:
Just to follow up - I confirmed high backpressure (>10psi) via hole drilled between Y-pipe and first cat. I already went through and removed and cleaned the TB, put a bunch of new vac and fuel hoses, and replaced and rerouted the VSV. I've avoided melting the new Vacuum Modulator by limiting driving/rpm's but putting a plan together to replace the cat, likely with a single Magnaflow 99006HM.
Click to expand...
@jatree any updates on this. I experienced the same.
 
Cruiser804 said:
@jatree any updates on this. I experienced the same.
Click to expand...
Hi - Yes, I found a shop that was able to replace my two original catalytic converters and with a single magnaflow. There was some blockage in both -- problem has been solved since then, though I still have the patch of melted hood insulation as a reminder!
 
Another data point for the thread - I'm currently out on the road experiencing this issue. I thought my lack of performance was due to the added aerodynamic penalty of my new roof tent, but as I observed the beginning of this power loss before then I am now ruling that out.

I've had the P0401 code for all four years of owning this rig. I replaced the VSV when I first got it, then reverted to an old habit from my VW days - keep a code reader in the door pocket and fuse panel cover removed. In hindsight, I don't recommend this.

This was a big clue at 251k miles that something else was wrong today:

1000012054.webp


Have been running it hard on a road trip for a little over a week now and I think my Vacuum Modulator has called it quits.

The line on the bottom was missing entirely when I discovered the problem.

1000012055.webp


Oddly enough, P0401 has remained off for miles and miles while I limp the rig back home. Will be picking up a replacement at a dealer on the way back and will provide updates as they happen. I already have fresh hose ready to go in. Fingers crossed a few hrsprs come back.

Thanks to everybody else who has contributed to this thread, it's been very helpful.
 
Roketdriver said:
Another data point for the thread - I'm currently out on the road experiencing this issue. I thought my lack of performance was due to the added aerodynamic penalty of my new roof tent, but as I observed the beginning of this power loss before then I am now ruling that out.

I've had the P0401 code for all four years of owning this rig. I replaced the VSV when I first got it, then reverted to an old habit from my VW days - keep a code reader in the door pocket and fuse panel cover removed. In hindsight, I don't recommend this.

This was a big clue at 251k miles that something else was wrong today:

View attachment 3620101

Have been running it hard on a road trip for a little over a week now and I think my Vacuum Modulator has called it quits.

The line on the bottom was missing entirely when I discovered the problem.

View attachment 3620108

Oddly enough, P0401 has remained off for miles and miles while I limp the rig back home. Will be picking up a replacement at a dealer on the way back and will provide updates as they happen. I already have fresh hose ready to go in. Fingers crossed a few hrsprs come back.

Thanks to everybody else who has contributed to this thread, it's been very helpful.
Click to expand...
What are you picking up a replacement of-modulator? Something else has got to be wrong, such as a bad EGR valve.
 
Having gone through a very similar loop -- check for exhaust blockage. My cats were clogged enough to melt the modulator. A backpressure test can tell you.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom