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Old 10-09-2021, 09:33 PM   #1
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Exclamation C9 8.8L Cat 2006 , Is this a good engine??

If you can let me-know how you like the C9 I'd appreciate the feedback .. Im a first time buyer and really paranoid about the cost of maint / ownership of this unit? Any feedback you can give me would really help .... this unit has 126K but Im thinking if the seller has maint records, it could be a ok purchase??
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Old 10-10-2021, 06:39 AM   #2
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The C9 is a very good engine. There is also a C9S (came out in 2007) you want to avoid this engine at all cost.

The main problem with the C7 and C9 (and not really a problem) is the HEUI fuel system. It uses engine oil to create high pressures to actuate the fuel injectors. Dirty oil (lack of oil changes) can cause problems and if the HEUI pump fails it takes out the injectors too (so $3K - $4K).

If you maintain the engine and change the oil as recommended, this is a great engine. Maintenance costs on diesel are higher than gas - they hold more oil and have more/bigger and expensive filters, but they are more fuel efficient, have more torque per engine size, and are built better than gas engines, so generally last longer.

For some peace of mind, there is an aftermarket filter system that gets installed between the HEUI pump and cylinder head that is designed to catch any debris if the HEUI pump fails and thereby saving the injectors. It's a good investment IMO.
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Old 10-10-2021, 01:29 PM   #3
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2X what Mike says. I had the same question when considering my rig with the smaller 3126. Same HEUI caution. Our transportation department ran a bunch of them and the head bus mechanic ate lunch in our shop with us. I asked if he had any particular problems with the smaller CATs. He's said: "Nope, not really" That was good enough for me.

I just change my oil and filter a little more frequently. Cheap insurance with a HEUI. Others add the high pressure filter to protect the injectors should the pump fail. One thing to note: There's an oil pressure sensor - an iap sensor - that monitors oil pressure for the fuel system. It can get plugged with sludge which can cause a rough idle or low RPM, or no-start condition. This is the FIRST place to look if you get those symptoms. Test by unplugging the sensor from the wiring harness. If the engine starts, sensor is plugged or failed. There's been stories of mechanics diagnosing these systems as a failing HEUI pump costing the owner $$$ when the issue was really a $150 sensor. It can frequently be cleaned out with carburetor cleaner and reinstalled as an on the road repair in a pinch. If the C9 has this, make a mental note of this condition. It could save you a tow and a costly repair should it happen to you.
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Old 10-10-2021, 07:55 PM   #4
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Quote:
Originally Posted by CountryB View Post
The C9 is a very good engine. There is also a C9S (came out in 2007) you want to avoid this engine at all cost.

The main problem with the C7 and C9 (and not really a problem) is the HEUI fuel system. It uses engine oil to create high pressures to actuate the fuel injectors. Dirty oil (lack of oil changes) can cause problems and if the HEUI pump fails it takes out the injectors too (so $3K - $4K).

If you maintain the engine and change the oil as recommended, this is a great engine. Maintenance costs on diesel are higher than gas - they hold more oil and have more/bigger and expensive filters, but they are more fuel efficient, have more torque per engine size, and are built better than gas engines, so generally last longer.

For some peace of mind, there is an aftermarket filter system that gets installed between the HEUI pump and cylinder head that is designed to catch any debris if the HEUI pump fails and thereby saving the injectors. It's a good investment IMO.
Never heard of C9S designation. And what problems did they have ? Safe Travels.
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Old 10-11-2021, 12:14 AM   #5
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wow, thanks thats great info and tips guys ... appreciate the feedback
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Old 10-11-2021, 05:39 AM   #6
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Never heard of C9S designation. And what problems did they have ? Safe Travels.
C9S (2007-2010) ACERT “Regen engine”, with Common Rail Fuel System, VGT, ARD head, CGI, and DPF.

The video below is about the C7S but same components on the C9S...

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Old 10-11-2021, 11:03 AM   #7
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The 3126/C7 and C9 have a lot of similarities in their control systems, as noted above. That's most of what you'll deal with. My 3126B has 103k miles on it and has overall been good. I don't know what sort of maintenance previous owners did to it before we bought it (at 84k). Overall, the engine has been trouble-free. Preventative maintenance I've done on it:

- Oil/filter and fuel filter changes on or ahead of schedule, using the proper (factory Cat) filters and Cat oil. There's a lot of debate on filters and oils, but what does it for me is that the HEUI system is something that's known to be problematic on these engines if not cared for, and supposedly the Cat filters and oil are designed to handle the demands of the HEUI
- Replaced the stock HEUI hose with the Cat service bulletin hard line. Really there's nothing wrong with the idea of a hose, but after 20 years it needed replacing anyway and Cat thinks the hard line is better. I've had no issues with it
- This engine has had oil pressure that in some cases was below factory spec. I Initially replaced the oil pressure sensor (not it) and then replaced the oil pump and rolled in new bearings. Despite having a hair under 100k miles when I did that, there were bearings that had the top coating flaking off and it was clear that this was worth doing. My oil pressure is way better now. Some people argued I didn't need to do this work, and maybe they were right, but I am certainly more comfortable now. Also, the oil pump is a new style (I am assuming this was the C7/C9 style) and so that would indicate Cat figured there was an oil pump issue, or at least room for improvement.

Otherwise, the engine does great. When I had the oil pump off all 6 cylinders had great cross-hatching in them. It starts easily, runs strong. My 40' RV would be happier with a bigger engine (I've thought about swapping in a C9) but it handles things fine. I wouldn't shy away from a 2006 C9, although agreed the C9S/Acert engines aren't very popular and I'd probably be less inclined to go for those.

As far as the filter in between the HEUI pump and the injectors, as someone who's extensively modified my bus and various engine aspects (and am doing more...), that's just not something I think is worth it. It's an expensive kit and while injectors are expensive, my view is that the overall risk/benefit doesn't favor adding that kit.
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Old 10-11-2021, 03:20 PM   #8
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Again, such great feedback and makes me so much more comfortable with this engine ... thanks greatly !
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Old 10-22-2021, 06:13 AM   #9
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My Revolution has a 2006 C-9 which I purchased new. I have always changed oil and all filters yearly and had no troubles. Except alternator went out no problem. As with anything they need to be maintained.
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Old 11-07-2021, 06:33 PM   #10
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I have twin 2005 C9's in my boat 510hp with 2,030 hours. The C9 is a sleeved engine were the 3126 and C7's are not. That's a huge benefit. The early HEUI pumps had flaky bearings which was corrected early on with a newer style. I have replaced 1 HEUI pump in 5 years based on the IAP sensor warning going off 40 times. I had 4 trips I had to get in. Actual pressure wasn't meeting desired and a 100 psi diff is all it takes. Very sensitive sensor. Reman pump is $1400, simple job if you access. New HEUI pump from D&W Diesel fixed the issue. Change oil at 5,000 miles or every 200 hours max. Injectors should last to 7,000 hours but that's pushing it. Injector O rings should be replaced at some point. I am also considering replacing an oil pump at hot idle I'm at 12 psi, 6 psi or below is cutoff. Since I have twin engines I can swamp sensors and compare stats while running. Idk probably a bad thing if you have OCD. Good luck.
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