Oil and Excess Pressure in fuel

[HAULNTX]

Good evening, I am new to the forum.

I have a 09 Kenworth Cummins ISX 871 with a little over 300K miles on it that is getting what I think is oil in the fuel. The fuel tank builds excess heat and pressure and the diesel in the tank is very dark. Truck eventually shut down on us on the side of the road which started this project about a month ago.

Mechanic stated that there was oil in the diesel which I had not noticed. He thought it was the injectors. Once at the shop pulled injectors and realized the head had a coolant leak into cylinder 6. Replaced the whole head with a new one. Put everything back with original injectors. Couldn't get it to crank. Through researching this forum narrowed it down to the gear fuel pump. Replaced that and it fired right up. Ran well for about 10 days then the oil and pressure in the fuel tank came back. Figured maybe it was the injectors and replaced all 6 of those with no change. Today was the first day on the road again since replacing injectors late into last night. Still getting excess heat, pressure, and possibly oil in the tank. It also started shuddering and had very low power at the end of today and it was throwing PID 94 (Fuel Pump Delivery Pressure below normal).

Im getting pretty worn out on spending money on this engine so any help or pointers would be very helpful thanks

[tree98]

First off you should send a sample of the fuel out to get tested so you know exactly WHAT is in the fuel instead of guessing.

What do you mean when you say the "fuel tank builds excess heat and pressure " how hot is it getting? Why would the fuel tank be building pressure? It's vented, it's impossible to build pressure unless the vent is plugged, in which case I think it would actually pull a vacuum.have you checked the vent tube?

Is this thing demandated? If so who did it? The only thing I can think of that would cause excessively hot fuel would be if your cylinder head was running much hotter than it should (how high is your coolant temp getting?) or you have an obstructed fuel return circuit.

I really hope you put a new genuine cummins head and injectors on it and not some after-market crap.

[HAULNTX]

I plan on sending the sample out to get tested. I already have the kit and will do that soon.

I will check the vent tube. I haven't measured the exact temp, but the fuel seems to get much hotter than my other trucks all with cummins engines in them so I was just comparing.

It is demandated, as of end of July, forgot to mention that. As far as the person who did it I don't think they knew what they were doing after reading up in this forum. The whole transaction seemed weird and he couldn't answer basic questions. Coolant runs at normal temps it has not over heated.

I did not purchase the head nor the injectors from Cummins. I did not realize it would make that big of a difference.

[tree98]

(09-05-2024 )HAULNTX Wrote:  I did not purchase the head nor the injectors from Cummins. I did not realize it would make that big of a difference.

Oh boy, you got a real can of worms on your hands now. Cummins engines don't do well with aftermarket parts, especially cylinder heads and injectors.

Does it still have the VGT turbo on it?

Also you can bet your ass that demandate program is really bad!! Send a copy to Rawze to have a look at

[Rawze]

(my thoughts)...
== Sounds like bad de-mandate programming as part of your issues.

== What micron filter are you running in the Davco? (fuel water seperator).... if its greater than 10 micron then your wasting your time, as ashpaltine (black fuel) will build up in the fuel tanks making it turn black.

AND WHY WOULD YOUR OIL BE SO BLACK (even if it was getting into the fuel) IF IT IS DE-ANDATED???... unless you had bad programing or you were not changing oil often enough vs. your fuel mileage?

the CM871's cannot be compared to newer common rail engines either. There is a lot of return fuel to the tanks, and they have higher asphaltine buildup especially if your dumping in B20 (bio blend) fuel into it.

- Also, unlike newer trucks.. ALL of the fuel that is not used by the system goes directly back to the tanks after running thru the head, ecm, IFSM, etc.. and this makes the tanks stay at close to the same temp as the coolant + have more ashpaltine buildup (making the fuel black) if you don't filter the fuel very well (10 micron filtration or less)!.

Newer enignes do not do this, so it cannot be a comparison.

The fuel tanks being warm (at or near the coolant temp) is 100% normal for trucks with CM570, CM870, CM871's in them.

The fuel tanks getting black is a matter of proper filtration and staying away from bio-diesel as much as you can + ensuring the injectors are not leaky .... (mentioned below) ...


SENDING FUEL SAMPLES TO A LAB WILL TELL YOU THE ACTUAL PROBLEM!!!... NOT GUESSING AT IT LIKE A FOOL!.

FOR ALL ANYONE KNOWS, IT COULD BE ALGEA OR ASHPALTINE, COULD BE OIL, WHO THE HECK KNOWS!. Wasting thousands of $$$ by throwing parts and guessing blindly is a clear sign of someone not knowing what the heck they were doing.

And if pressure is building in the fuel tanks... then the breather tubes are partially clogged. That, or your injectors are so leaky that they are back-feeding combustion thru the fuel system badly (also makes engine run poorly).

which brings me to the next statement...

- It must have been some kind of moron does not know how CM871's work to troubleshoot this ... because they should have done proper injector leak tests to ensure the injectors were not leaky / combustion gasses were not back-feeding into the fuel system etc.. instead of blind-man throwing expensive injectors and heads at it like a complete fool!. - What a waste of moneys.

CM871's will also have leaky injectors if the damn overhead valves (injector rockers) are simply out of adjustment too!. I have seen mechanics that were so da%mn dumb in the past, that they would set the injector rockers at 0-N_m (or use a gap) like the old big-cams engines of yesteryear, and then wonder why the engine has all these kinds of issues.


For all anyone knows.. it still could be doing this.. as you did not mention ANYONE doing injector tests BEFORE ... OR ... AFTER all that $$$ was replaced!.
REF: https://rawze.com/forums/showthread.php?...8#pid67948

and yeah.. after-garbage injectors and after-garbage head = nothing but problems!. Plain as that, so you wasted all that moneys for a half-arssed repairs and red-neck garbage,.. and so you end up with half-arssed engine run quality is the result.

- As well, the head likely never had to come off it to begin with. There are kits available to replace leaky injector cups to stop the coolant leak. Its worth doing this if the head and engine have a lot of miles on it vs. tearing into it, ... and then to ensure that the leak does not return, it could have been switched over to a zero-pressure coolant system to boot.

[HAULNTX]

(09-05-2024 )tree98 Wrote:  

(09-05-2024 )HAULNTX Wrote:  I did not purchase the head nor the injectors from Cummins. I did not realize it would make that big of a difference.

Oh boy, you got a real can of worms on your hands now. Cummins engines don't do well with aftermarket parts, especially cylinder heads and injectors.

Does it still have the VGT turbo on it?

Also you can bet your ass that demandate program is really bad!! Send a copy to Rawze to have a look at

Yes the VGT turbo is still on the truck.

I am not familiar with the process on how to send a copy.

I was being (helped by a so called mechanic) through this process and after getting half way through the head rebuild I started to realized he didn't know what he was doing and politely told him I could finish the truck myself.

I'm positive the demandate is crap, but I don't personally have a computer that I can connect to check it.

[Rawze]

(09-06-2024 )HAULNTX Wrote:  ...
Yes the VGT turbo is still on the truck.

I am not familiar with the process on how to send a copy.

Thank god you still have that turbo. Don't get duped by the morons on social madai who would tell you to remove it.

copying program: https://rawze.com/forums/showthread.php?...5#pid72945

[HAULNTX]

Just an update. I did an injector leak test today and no5 injector was blowing bubbles.

[HAULNTX]

Second update. Once again I'm learning all of this as I go and most of it is from this form.

On Thursday I pulled the valve cover to replace leaking injector no5. When I pulled the cover I noticed the injector cam and rollers had wear and pitting that was not there a couple weeks before. That sent me down the rabbit hole of finding out that the crankcase filter was getting clogged up way to fast. I haven't even put 10K miles on this truck but I've changed the filter 3 times. The last time I pulled the filter out I noticed the green slime and thick sludge and it had a lot of water collected in there. Going off this forum yesterday I pulled the oil pan and as soon as I did that I could already see coolant drops. Without even pressuring the system I could tell no5 cylinder was leaking from the liner. I pressurized the system last night and I let it sit over night, but at this point I don't think that was even necessary as I could see it draining down without even putting pressure to it.

At this point I'm going to go ahead and do a complete inframe, but as I go I will have some questions.

First off the head that I replaced a couple weeks ago, before I knew it made a difference, isn't a cummins head like the original one is. The original head was replaced due to no6 injector cup leaking coolant. Since I'm already pulling the head again, should I have the original head rebuilt with new injector cups or just leave the current aftermarket head? This truck has the CM871 and it only has 310K miles total on the truck. I believe around 9-10K hours. Also I currently have diesel and oil samples sent off and I'm awaiting test results. I really appreciate all the helpful posts from everyone it has made all of this process so much easier because of the info y'all put out.