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+--- Thread: High exhaust pressure (/showthread.php?tid=7726)
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High exhaust pressure - lwilder27 - 09-20-2021
I have a ISX12 CM2350 that is failing the regeneration analyzer due to high exhaust back pressure. In the report its showing 165-175 Inhg.
Heres a list of what I have done so far.
The exhaust pressure sensing tube was plugged, so it was replaced at the same time I did exhaust manifold gaskets. It has a new EGR valve, IMAP sensor, EGR diff pressure sensor, EGR pressure sensor, and exhaust gas pressure sensor. The turbo was just rebuilt and I had the DOC/DPF cooked and flow tested. I checked my decomp tube, all is clear, used a mirror and checked the SCR and looks good.
Ran the analyzer again and monitored exhaust pressure at 160 inmg and took the exhaust pipe off at the inlet of the DOC and saw no pressure drop.
In the analyzer report, the EGR valve remained at zero percent for the duration, which tells me it would not be a resitriction in the EGR system. Is this good logic or am I miss understanding?
The only culprits I can think of are a bad turbo rebuild and or actuator install and EGR restrictions.
RE: High exhaust pressure - lwilder27 - 09-20-2021
I also noticed the EGR orifice pressure is -4.5 inhg with the engine off. Maybe a bad sensor right out of the box?
RE: High exhaust pressure - Rawze - 09-20-2021
You did not mention cleaning out the passageway thru the thermostat housing out in your post above.
If the crossover tube for the exhaust pressure sensor was plugged.. you can be assured that the circuit thru the thermostat housing is just as plugged up.
High exhaust pack-pressure can also be from ...
* Out of calibration turbo.
* Restrictive EGR cooler (is getting plugged up or is an aftermarket unit) or other EGR circuits/sensors.
* Can be caused by the EGR pressure sensor (or circuit) not reading correctly, forcing turbo to close harder than it should.
* CAC or other intake boost leak.
* a clogged up DPF or other exhaust unit.
RE: High exhaust pressure - Rawze - 09-20-2021
(09-20-2021 )lwilder27 Wrote: I also noticed the EGR orifice pressure is -4.5 inhg with the engine off. Maybe a bad sensor right out of the box?
could also be clogged tubes.
RE: High exhaust pressure - lwilder27 - 09-20-2021
by thermostat housing do you mean the EGR differential pressure tubes? They have been cleaned.
During the regeneration analyzer test, it never commanded the EGR valve to open, so could a plugged EGR cooler still be the issue? My thinking being it wouldnt have any flow through the EGR circuit anyways, plugged or not.
Ill pull the turbo actuator and reinstall/calibrate and leak test the charged air circuit. If the turbo is closing harder than it should, would I be able to see that percentage command out of normal on insite?
RE: High exhaust pressure - Rawze - 09-20-2021
(09-20-2021 )lwilder27 Wrote: by thermostat housing do you mean the EGR differential pressure tubes?
...
THE EXHAUST GAS PRESSURE SENSOR FOR THE EXHAUST MANIFOLD HAS A FEED TUBE (between the exhaust manifold and the thermostat housing) -> AND THEN the circuit RUNS THRU THE THERMOSTAT HOUSING UP TO THE exhaust gas pressure SENSOR ITSELF... WHICH IS MOUNTED TO THE TOP OF THE THERMOSTAT!!!
THE PASSAGE-WAY THRU THE THERMOSTAT HOUSING LIKES TO CLOG UP AND MAKE FOR BAD EXHAUST BACK-PRESSURE READINGS!
to check the entire circuit ... http://rawze.com/forums/showthread.php?tid=7421&pid=65445#pid65445
OR...
http://rawze.com/forums/showthread.php?tid=6762&pid=59765#pid59765
or...
http://rawze.com/forums/showthread.php?tid=254&pid=57885#pid57885
RE: High exhaust pressure - lwilder27 - 09-21-2021
On the ISX12 the pressure sensor tube is on the back of the manifold and runs up to the mounting for the EGR cooler. It does not go through the thermostat housing. They are similar in the fact that there is a small passageway from the tube to the sensor. I cleaned that as well and blew air through from the sensor hole out of the new tube before I put the manifold back on. All is clear there.
RE: High exhaust pressure - lwilder27 - 09-21-2021
I just took out the exhaust pressure sensor and sprayed some brake clean in the hole and turned it over and it shot it right back out. Confirmed its clear.
I took the DOC inlet temp sensor out and built a guage to check back pressure from that port and got less than 1 PSI so I do not have a restriction downstream.
Charge air cooler passed leak test.
Swapped the EGR orifice pressure sensor with the exhaust gas pressure sensor and got the same readings.
RE: High exhaust pressure - lwilder27 - 09-21-2021
Removed the turbo actuator and did the install/calibration procedure and ran the analyzer again and again failed for high exhaust pressure.
The only thing I have left is the EGR cooler. Whats the best way for checking them? remove and visually inspect?