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Paccar px-8 engine brake question

Mike L

Mike L

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So the engine brake in my service truck (paccar px-8, cummins 8.3) seems to surge when Activated. Not 100% of the time but most of the time and mostly above 1500 rpm’s. It comes on and slows me down then seems to shut off. It has plenty of power so I don’t think the turbo is bad. I’ve inspected the turbine and it’s good. I’m not extremely familiar with the vgt turbo. Other than the throttle position sensor and the switch in the dash, what tells the engine brake to come on and what could cause the surging? When it works it works good but obviously something isn’t right.
 
Truck Shop

Truck Shop

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You are taking about a exhaust brake correct? I'm not familiar with the PacCar version of the 8.3.
 
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Birken Vogt

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8.3s with VGT are also DPF units, and since the exhaust butterfly was no longer allowed, they started putting real Jake actuators on them. However, I believe the actuators were optional. The VGT will also clamp down to provide more braking force, and I believe to provide more boost for the Jakes to work on. However I think some trucks just have the VGT alone and it sort of acts like an exhaust butterfly.

That's all I know, I only rode them, I don't know what makes them work
 
Mike L

Mike L

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Birken Vogt said:
8.3s with VGT are also DPF units, and since the exhaust butterfly was no longer allowed, they started putting real Jake actuators on them. However, I believe the actuators were optional. The VGT will also clamp down to provide more braking force, and I believe to provide more boost for the Jakes to work on. However I think some trucks just have the VGT alone and it sort of acts like an exhaust butterfly.

That's all I know, I only rode them, I don't know what makes them work
Click to expand...
I’ve been under the valve covers and it doesn’t have a jake actuator. I was under the impression that it operated off the turbo and I had it in my head that the vgt retarded to act as an exhaust brake but I’m not sure
 
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Birken Vogt

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So having a VGT and being an 8.3 puts it post 2007 but pre 2010 emissions, non-DEF correct? Because I thought they went to 9-something liters when they went to the DEF system.

Either way, with no Jake actuators, it makes me wonder if the VGT nozzle position is getting hung up, like the computer is trying to place it in a certain position but it is not moving smoothly there and kind of hunting as you are trying to use it. It seemed we had those kinds of problems on the acceleration side of things, but it has been a long time and memory has faded. We always had the ones with Jake actuators under the valve cover so any VGT braking effect problems would not have been as noticeable.
 
Mike L

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Correct. It is a 2008.I have zero complaints on the acceleration it’s only when the engine brake engages.
 
Coaldust

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I’m going to concur, the VGT nozzle has carbon built up restricting nozzle movement. Try taking it apart and cleaning it.
 
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398370

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Please post picture of turbo. On Cummins isx exhaust brake position 1&2 is under valve cover position 3 kicks Vgt in also. The 6.7 in my shop truck is all vgt. On the isx if operator say exhaust brake weak will run turbo relearn / calibration. But usually means replacing turbo in a month or so.
 
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Birken Vogt

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Mike L said:
Correct. It is a 2008.I have zero complaints on the acceleration it’s only when the engine brake engages.
Click to expand...

What I meant was that it would throw codes for VGT position on the acceleration side. They always drove just fine. But occasionally you would hear a weird squeak from the turbo or could hear turbo RPM changing not in a steady manner. Or eventually DPF regen problems. But no symptoms an average driver would notice. After a long time (months) it would get to the point where it would have a check engine light or derate or be doing an active regen 2 times a day and then off to the dealer and come back as a turbo nozzle problem.

But I just can't say how it affected braking because we had the exhaust valve actuators which provide way stronger braking than the VGT anyway.
 
Truck Shop

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On the DDEC V Series 60 you knew when the VTG was a problem or the real problem was
with the VPOD. First a slight surging would start then it would start huffing/barking back
through the air cleaners. Dead giveaway the VPOD controller for VTG was bad.
 
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Mike L

Mike L

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398370 said:
Please post picture of turbo. On Cummins isx exhaust brake position 1&2 is under valve cover position 3 kicks Vgt in also. The 6.7 in my shop truck is all vgt. On the isx if operator say exhaust brake weak will run turbo relearn / calibration. But usually means replacing turbo in a month or so.
Click to expand...

ED60CC47-9186-40B9-B1BC-5461EC2980E7.jpeg FD3BF217-E321-4C4E-8131-E0FD4D716B7D.jpeg A243CEF9-2339-4573-A3B9-16FFC0A3E816.jpeg
 
Mike L

Mike L

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Coaldust said:
I’m going to concur, the VGT nozzle has carbon built up restricting nozzle movement. Try taking it apart and cleaning it.
Click to expand...
What do I have to take off to get to the nozzle. Sorry, I’m just not familiar with these turbos.
It hung up hard the other day coming down a long grade. When I stepped on the throttle I had nothing until I shut off the switch at which point the throttle immediately started working.
 
Coaldust

Coaldust

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Mike,

Remove the turbo and the turbine housing. You’ll see the nozzle ring and all the vanes. Lots of moving parts. To add insult to injury, the sticking vanes will make the vgt actuator overheat and eventually fail.

lots of videos on YouTube on how guys clean them.
 
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pushbroom

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If the vanes on the turbo started sticking it would be noticeable accelerating. It will throw engine codes as well. I wouldn't put any hopes into cleaning the turbo on this model, vanes will be worn out and not worth it to clean.
You will need insite to recal the actuator if you remove it.

Honestly fastest way is to run it with a laptop on and see if the jake shows always on or if the status comes on and off. Either its on the signal/electrical side or if jake shows on all the time, mechanical side.
 
Greatwestcam

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Try changing the exhaust pressure sensor as the VGT responds to its signal, had one that had an in range failure, no codes, once it was changed the driver said the truck performed better. also check the line to the sensor for leaks or plugging. cheap and easy fix.
 
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