Hi GreasT
I contacted you over on the thumpertalk forum and you recommended I post here. We have a 2012 Isuzu npr cabover with 120,000 miles on it, rarely if ever sits idle (though spends some time in traffic) and is driven Monday - Thursday every week if not more. Here's the scoop:
Frequent regeneration began shortly after a PM service at our local GM / Isuzu dealer and service center. Regeneration would occur more frequently than before (3-4 or more times per week (Mon-Thu) driving in and out of Boston everyday (about 35 mi each way plus driving during the day) as opposed to once or twice AT MOST). Also, the bars on the regen scale would jump from zero, or one or two, all the way to regen required.
At this point, the regeneration cycles wouldn't happen on their own (like when it regens and the bars disappear, but you never really know it happened). Instead, you had to hit the button on the dash to activate the regeneration cycle. After a few manual regens, they came accompanied by warning level 1 lights and low power condition (derated to 55mph).
We brought the truck to the service center and they replaced the DPF filter, again. From what I understand these should last 100,000 miles and it had already been replaced.
1,000mi. later our employee checked the oil level and it was 5/8in. over the top fill line. (If you could elaborate on the severity of the over fill and what issues it can cause that would be helpful.) We then brought the truck to the service center to have the oil level lowered.
Not two weeks later, all of the same conditions came back. If you could provide any input on our series of events that would be incredibly helpful. Thank you.
Hi again. I'm much better versed in Hino than Isuzu, but they have some similar traits. It sounds like it was overfilled with oil at the service center. How much, no one knows.
On Hinos, the amount of soot in the DPF is determined by a calculation, not by constant reading of differential pressure like on American trucks. Isuzu MAY be the same way, to some degree. I don't know for sure.
What happens on Hinos is when you have bad injectors or an unaccounted-for fuel source (like engine oil) enter the DPF, the ecu doesn't realize it, and when the truck regens it gets stupid hot and melts the ceramic substrate that makes up the DPF.
So you've got a ton of extra oil and it may have been making its way into the exhaust stream, possibly through the turbo and very likely through the crankcase ventilation system. Pull the intercooler hoses off and look for puddles of liquid oil (a little oily film all over everything is considered normal. Remove the crankcase breather hoses and see if there's liquid oil in there too, and follow these hoses up to where they connect to the intake air stream. I'd just want to make sure that these areas are relatively oil free at this point. Then I'd remove the DOC and blow it out with compressed air. Wear a mask. If the face of the DOC was clogged, it may not come up to temp properly.
It's funny that you mentioned that the DPF bar graph jumps. On Hinos, this is an indication (usually) that one of the DPF temp sensors is going bad, or that there's a break in the temp sensor harness (not that unusual). Seems to me that one of these sensors may be having an issue, or possibly the differential pressure sensor has an issue. This sensor is pretty hardy, and is rarely the problem. Clogged pressure lines are possible. It's also possible that someone forgot to disconnect the hose from the sensor and whacked the sensor with 150psi of shop air while blowing out one of the pressure tubes or something. Not that I have any personal experience with doing that. Nope.
Sorry for the nebulous answer. I don't know how Isuzu calculates soot volume, and I don't know what causes their graphs to jump.
