Sudden power loss, melted EGR vacuum modulator

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EricG

EricG

10 Year 15 Year
Joined
Jul 12, 2006
Threads
171
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2,584
Location
Colorado Springs, CO
Last week, I was coming home from work, probably about 35-40 MPH on a moderate hill. Pulled out to pass a truck and tried to accelerate hard, and lost power in a pretty sudden & dramatic fashion - I think the car behind me had to hit their brakes. Could barely maintain about 25-30 mph. Got it over to the shoulder and took a look - didn't see anything obvious - nothing leaking, no smoke, no CEL, unmodded temp gauge in the normal range. It felt a little hot to me under the hood.

Shut it off and restarted fine, engine is smooth - no bucking or hesitation. Got back in and drove some more - it's not right but it's doing OK - maybe 40 mph. Then in another 3 miles it starts getting worse fast - I'm down to 10-15 mph and falling and I pull over again. The other thing I notice now is a noise near the back of the engine that sounds like a massive vacuum leak, and a brief small curl of smoke near the EGR.

I'm only about half a mile form home now, so I get my wife to come down and strap me home ... will be hearing about this from her brothers I'm sure.

I took the IR thermometer out and pointed it at various bits - water pump, block, head, etc. Everything is in the range 155-160F, so doesn't seem to be overheating.

Anyway, once it cools down, I take a closer look and find that the hose is blown off the bottom of the EGR vacuum modulator and a hole is melted into the bottom. The noise I heard is exhaust gas blowing out of the hose normally attached to the bottom of the part.
tmp_8033-IMG_20160903_160516009-449540169.webp

I now have some difficulty starting it and keeping it running. It struggles to get over 2500 RPM, but still smooth. Still no CEL.

I've found a few threads on melted EGR vacuum modulators - two that ultimately attributed it to blocked cats, one that resolved with a new ECU, and one that simply replaced the modulator and put a hose clamp on it..

Cats
near RTH: Vacuum Modulator Meltdown
Melted EGR Vacuum Modulator

ECU
Photo of EGR carnage

Replaced
It's been almost 5 years since I've had an MIL (401 EGR Code Revisited)
(Never mind - found another thread from a month later where he finds clogged cats Had a bit of a scare on the drive home (temporary overheating?))

The catalytic converter stories seem to match mine the best - loss of power, etc.

Any suggestions on how to confirm this? I've found some stuff about checking the exhaust system back pressure - what's a good number for these trucks? Is that hose off of the EGR a good place to put a gauge, rather then breaking into the exhaust pipe?

As far as replacing the EGR vacuum modulator - this is apparently an $80 part. Hate to spend that if it's a symptom rather then a cause and I melt another one. There are plenty of identical looking ones out there in the $15 price range. I know I'll catch hell from the purists, but what's the worse that can happen - an EGR code, then replace it with the right part?

https://www.amazon.com/Dorman-911-609-EGR-Vacuum-Modulator/dp/B0083H5RDM/?tag=ihco-20
https://www.amazon.com/Toyota-Replacement-Vacuum-Solenoid-Modulator/dp/B00D2XR6AE/?tag=ihco-20
 
Last edited:
One more note - cats & O2 sensors were replaced in 09. Used a dual inlet/single outlet cat.
 
Final verdict - catalytic converter failed. Not sure why it only lasted 7 years.
 
Do you remember what brand aftermarket cat you were running? I've read mixed reviews on MagnaFlows.
 
Cat replacement was done by a well regarded local shop - I hope he took the time to size it right, but guess I don't know. I believe it was a magnaflow though.

One other thing I was considering - the slider arrangement I have has a big plate under/around the cat on the bottom which likely restricts air flow around it significantly. Will they get to hot in this kind of situation, leading to premature failure?
 
EricG said:
Last week, I was coming home from work, probably about 35-40 MPH on a moderate hill. Pulled out to pass a truck and tried to accelerate hard, and lost power in a pretty sudden & dramatic fashion - I think the car behind me had to hit their brakes. Could barely maintain about 25-30 mph. Got it over to the shoulder and took a look - didn't see anything obvious - nothing leaking, no smoke, no CEL, unmodded temp gauge in the normal range. It felt a little hot to me under the hood.

Shut it off and restarted fine, engine is smooth - no bucking or hesitation. Got back in and drove some more - it's not right but it's doing OK - maybe 40 mph. Then in another 3 miles it starts getting worse fast - I'm down to 10-15 mph and falling and I pull over again. The other thing I notice now is a noise near the back of the engine that sounds like a massive vacuum leak, and a brief small curl of smoke near the EGR.

I'm only about half a mile form home now, so I get my wife to come down and strap me home ... will be hearing about this from her brothers I'm sure.

I took the IR thermometer out and pointed it at various bits - water pump, block, head, etc. Everything is in the range 155-160F, so doesn't seem to be overheating.

Anyway, once it cools down, I take a closer look and find that the hose is blown off the bottom of the EGR vacuum modulator and a hole is melted into the bottom. The noise I heard is exhaust gas blowing out of the hose normally attached to the bottom of the part.View attachment 1317798
I now have some difficulty starting it and keeping it running. It struggles to get over 2500 RPM, but still smooth. Still no CEL.

I've found a few threads on melted EGR vacuum modulators - two that ultimately attributed it to blocked cats, one that resolved with a new ECU, and one that simply replaced the modulator and put a hose clamp on it..

Cats
near RTH: Vacuum Modulator Meltdown
Melted EGR Vacuum Modulator

ECU
Photo of EGR carnage

Replaced
It's been almost 5 years since I've had an MIL (401 EGR Code Revisited)
(Never mind - found another thread from a month later where he finds clogged cats Had a bit of a scare on the drive home (temporary overheating?))

The catalytic converter stories seem to match mine the best - loss of power, etc.

Any suggestions on how to confirm this? I've found some stuff about checking the exhaust system back pressure - what's a good number for these trucks? Is that hose off of the EGR a good place to put a gauge, rather then breaking into the exhaust pipe?

As far as replacing the EGR vacuum modulator - this is apparently an $80 part. Hate to spend that if it's a symptom rather then a cause and I melt another one. There are plenty of identical looking ones out there in the $15 price range. I know I'll catch hell from the purists, but what's the worse that can happen - an EGR code, then replace it with the right part?

Amazon product ASIN B0083H5RDMAmazon product ASIN B00D2XR6AE
Click to expand...
Thanks for your writeup. I'm in the same spot after a second melted vacuum modulator. Which cat replacement did you go with? I know Magnaflow makes a direct fit part but I believe it's a single cat and 96 has two inline. Any issues with just using a single cat? Hoping for a solution that lasts though the recent reviews on the Mflow make it seem like quality has gone down.
 
jatree said:
Thanks for your writeup. I'm in the same spot after a second melted vacuum modulator. Which cat replacement did you go with? I know Magnaflow makes a direct fit part but I believe it's a single cat and 96 has two inline. Any issues with just using a single cat? Hoping for a solution that lasts though the recent reviews on the Mflow make it seem like quality has gone down.
Click to expand...

It worked fine until the head gasket went out last year. I don't remember what the replacement was.
 
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