Wednesday, June 11, 2008

Cat 3116 Fuel System Schematic


The Cat 3116 fuel system has 3 check valves, a fuel priming pump [if equipped], transfer pump and fuel regulating orifice [#7] on the return side diesel fuel circuit that exits out the back of the cylinder head.
The fuel regulating orifice provides adequate fuel gallery fuel flow for low idle fuel flow.





Check valve #8 prevents bleed off of fuel from the head during engine shutdown. This could cause a hard start after engine shutdown overnight [depending on how bad the bleed off is].

{click on photo to enlarge}

I hope you find this Mechanic Information helpful...

26 comments:

John said...

I have a Coachmen Cross country with a Cummins 300 ISB engine. My problem is that after an hour of highway driving I experience bucking and hesitation with a loss in power and speed. I have had to a mechanic with limited test equipment and his test unit indicated a fuel pressure problem. After cleaning the fuel lines both the feed in and the return line I still have the problem after an hour of travel. However once the problem starts, turning th eengine off and on with short periods of cool down does NOT eliminate the problem. BUt after an overnight shutdown the next morning I could drive for an hour before the problem re occurs. Any thoughts?
John

John Whelan said...

Check with your local Cummins engine dealer for any fuel pump related recalls. There was a recall around 2003 which matches your problem. If you give them the engine serial number they can tell you, along with service bulletins.

Anonymous said...

check the lift pump, maybe stick.

John said...

I will be getting the rig up to Horwith Freightliner for service. Hopefully the problem gets resolved and I will post the results when it is corrected. John, I did check into any recalls on our coach and nothing has been listed. All you readers of this blog will be the second to know what the solution is. Thanks for the input and anyone else out there, don't hesitate to comment on my problem.
John

John said...

Well it turns out that it was the fuel pump, however, there is also a hidden filter, Cummins terms it a strainer on the freightliner chassis. It is well hidden tucked up against the inside of the frame. Most mechanics do not realize its there because it is clamped to the inside channel of the frame typically concealed by a cluster of lines over it.

John Whelan said...

That's not surprising, probably effected the life span of your fuel pump.

I'm Glad you got it fixed!

Cat 3116 log loader said...

Hello, I have a cat 3116 which has become very frustrating for me at this point in time, it constantly looses its prime in the main filter during start up, it also has a minor spit/sputter in the mid-range. I had the lift pump and injector pump completely rebuilt, i replaced the lines from the tank to the hard lines along the motor, i pressurized the lines to check for leaks, i changed filters. Also when i do start it the only way to keep it from loosing the prime is to pretty much keep the pedal to the floor until it warms up. Any suggestions. I am replacing the check valve on the return line out of the head tomorrow, but i dont think it was messed up. thanks for any input Joshua Miesch JM Lawn and Tree

John Whelan said...

It sounds like a typical air in the fuel problem. I would check the steel lines running along the block. They are a regular problem with our engines and have to be inspected very closely to find the defect. Usually a crack or rubbed through area.

Anonymous said...

Well we continued to have the problem. The last communication was not the answer to our problem but now we have narrowed it down to the Turbo Actuator, being replaced at this moment. An update as to it's success will follow

nking said...

hi john

i have a 3116 with similar problems. the fule filter leaks down to about 1/3 full when truck is off for an hour or so. i can not locate the #8 valve that is on the schematic though. if there was a crack or hole in one of the lines shouldn't it leak fuel when running? i see no fuel leaking.

thanks, this is really frustrating!

PERRY said...

i have a straight truck with a 1997 3116 cat.it has primary fuel/water separator filter and secondary filter after injection pump. right now i have to take off secondary and fill with fuel. stays going for 5 min at any rpm but then stalls.primary filter stays full but secondary is half empty.what should i look at?

Cat 3116 log loader said...

Although i still havent cured my problem yet i can tell you that there is a suction line that goes from the tank to the primary filter and another one which can either go from the primary filter to hard lines that run along the block or possibly straight to the lift pump, if a suction line has a hole or rubbed through area than the fuel wont leak through the hole, it will just suck air through it, and when the truck is off the air will seep into the line and allow it to gravity feed back to the tank. The lines on my truck are a quick disconnect plastic type, they have three o-rings in each fitting and thouse can leak if they are old and worn out, it was a relatively cheap fix to replace all the lines, probably about 150 dollars or so. It is hard to find someone to make the new lines up, although you can order them right from the dealer, if you find a car shop that replaces old steel fuel lines with the new plastic ones with the quick disconnects they should have to tools needed to make these lines, i looked into the kit to do this and it was approx 800 dolllars with a selection of fittings. Not saying this will cure your problem, it didnt cure mine, also once the suction line goes to the lift pump, which is a very small piston style pump, it comes out under pressure and than goes to the secondary filter on the motor. so if your problem is after the lift pump than you should be leaking fuel, and if it is before the lift pump you should suck air. There are a lot of check valves in this system to keep the fuel in place when the truck is shut off. the number 8 one is very easy to replace, if you look at the engine there is a line that comes out of the head and goes into a rectangular section. that is all one line, the check valve is in the end of this rectangular section, you have to remove the steel line from the driver side of it so to speak, whis is the only side which has a removable line, the other side is all one piece , anyways when you remove the steel line it will have a fitting that has a o ring on it, you have to remove this fitting out of the end of the rectangular section and the check valve is underneath that fitting held down by a small spring, the check valve itself has a small o ring on it, i doubt the actually valve is but but the o ring might be. Again to help you identify the rectangular section it is actually held down by a bracket which slides down right next to the lift pump and is held in my 2 bolts with approx 15 mm heads, You do not have to remove these bolts to remove the check valve, just the steel return line and the fitting underneath. Make sure that when you go to remove the line that you dont spin the fitting at the same time, These lines are similar to regular brake lines on a car, the flared fitting on the line must be loose to allow it to swivel on the line, if you dont have a wrench on both the flard nut fitting and the fitting which goes into the end of the rectangular section you might loosen that fitting as opposed to the flare nut fitting on the line, so just watch for that, Sorry for the lengthy reply but i try to be as detailed as possible. My number is at the bottom so if you have any questions feel free to call. Good luck,

If you have any questions feel free to give me a call. Thank You, Joshua Miesch JM Lawn and Tree (585)509-4939

Mike said...

Put a sight glass on your fuel return and look for air bubbles. I have a 3116 that had a hard time starting but ran fine. Cat found a bad injector that was essentially allowing air from the cylinder to push into the fuel system. Now she fires right up without any hesitation.

valve replacement said...

Complex control systems using valves requires an automatic control based input of an actuator. The actuator strokes the valve allowing the valve to be positioned accurately and allowing control over a variety of requirements.

Scott Grasmick bayshorelandscapinginc@yahoo.com said...

John, I am so thrilled that you specifically posted a part about fuel check valve #8 and being a culprit of hard starts after sitting. My truck in the last few weeks only after a fuel water separator change has now become near impossible to change. I just purchased this truck, had a rough running issue, changed 1 filter at a time, first the fuel filter, second the water separator. after the water sep. was changed the truck ran great but started worse than ever (It's never started the greatest since I've owned it) My thoughts were that the water sep. was clogged enough to make the engine run bad but also clogged just enough to keep a prime on the fuel system. Should I look at #2 check valve or # 8 check valve. Where exactly are both of these check valves located? I don't think its a cold start problem because after the truck sits for 4 hours (engine still warm to the touch) the problem begins but not nearly as bad if the truck sits as you referred to as "over night". May I note that I am getting A LOT of White smoke during the cranking but am thinking there is some fuel delivery but A LOT of air along with it. THANKS FOR THE CONTINUED HELP....CAT MECHANICS ARE HARD TO COME BY!!!

John said...

The #8 check valve is the last one before the tank and should be located at the back of the head(this one would cause a bleed down after shutdown).

What I would check first is air getting into the fuel system.

The steel lines running along the driver's side of the engine are notorious for rubbing through and will cause a hard start and white smoke.

Even a crack in the line will cause this.If you can install a clear hose into the return line and check for air, you will get a good idea if this is the problem.

Good Luck

Anonymous said...

John is the fuel return line check valve on the top front of the head? Iam having fuel starvation problems on my 3116 Cat.I changed the filters and my vacume gage reads 0 on the intake side of the fuel pump between the racor and the pump.Runs great to about 1700 to 1800 rpmthen starts droping rpm.Tha harder you turn the engine up the larger drop in rpm and black smoke.It also is hard to start if you let it sit for a while.Thanks Shaw

John Whelan said...

Hi Shaw,
Yes it's at the top of the head in front. I would also check out the steel fuel lines. I've had several problems with them from vibration causing perforations.

Usually when their is a very small amount of air getting into the fuel system the engine will run great for a while then it starts to peeter out from eventual fuel starvation.

Anonymous said...

HAVE A 3161 CAT IN A 95 THOMAS PUSHER.IT WILL CRANK AND RUN FINE DURING THE WEEK, BUT WHEN IT SITS OVER THE WEEK END IT STARTS FINE BUT THEN RUNS 2ND FILTER OUT OF FUEL.U TAKE FILTER OFF AND FILL WITH FUEL ,PRIME IT WILL START AND RUN FOR THE REST OF WEEK.PUT CK VALVE IN RACOOR,RESEALED GOVNER,O-RINGS IN PUMP ON GOVNER,CLEANED VENT VALVE ON FUEL TANK,CK STEL LINES ON SIDE OF ENGINE.ANY SUGGESTIONS

John Whelan said...

If you installed a check valve at the racor filter try looking at the line between the racor and the secondary filter. It may be bleeding off slightly over the weekend, lightly enough that you don't notice. this line will go to the transfer pump and then out to the secondary filter.

Bus 139 said...

I have a 1998 Chevy School Bus with a 3116 Cat engine. Several months ago I had a problem with my bus loosing power and leaving me on the side of the road with special needs kids on bus. I am a contract driver so I pay for all of my own repairs. With the price of diesel and the low pay my husband tries to fix what he can. I brought it to a mechanic shop and they charged me over $3000 to change the fuel injector pump and it helped but now when it sit for the weekend I have a little trouble starting it in the morning and when it is around 40 degrees it is also a little hard to start again. Also, when it gets pass 2nd, around 30 mph, it hesitates or surges for a second and when it catches I get some white smoke. It doesn't hesitate every time but it is getting more frequent and taking a little longer to catch. Should I take your advice to Scott Grasmick? It kinda sounds like we have the same problem and start by having my husband check the steel lines running along the driver's side of the engine for air leaks. I really appreciate all of your help and thanks for sharing your knowledge!
Bus 139

Shadetree25 said...

After checking every line, fitting and check valve I still had the problem with the secondary filter losing prime while the engine was running. After 4 days of this, I installed an electric fuel pump ahead of the primary filter. Ran a new fuel line from the fuel tank pickup tube to the pump and then to the filter.
I actually have been able to drive the truck for 40 miles without it stalling and having to refill secondary filter. The truck had been having this problem off and on for two years with the previous mechanic giving up and taking it to a Cat dealer and an independent shop. The truck has been only used around the yard for the last months.
When I started here, the first thing they told me to do was to cure this problem. Looks like I have found a cure!

Steve said...

I have a 97 gmc 3116 having similar issues. Overnight the primary filter would run around half empty and would have a hard start until fuel got to the engine. I have done several tests with clear fuel lines. Also I put my own check valve from the tank to the first filter so fuel cannot return to the tank. I only see air bubbles coming from the last check valve #8, so all my lines are good, it must be drawing air from inside the engine. Probably the fuel injector o rings. Either way by adding another check valve helps keep the fuel where it belongs, in the filters.

Steve said...

I have the similar issue with my 97 GMC Topkick. I've used clear fuel lines to trace down the air bubble issue. In finding out that I'm only getting air bubbles coming from the return line that goes back into the tank. Check Valve #8 in his diagrahm. I installed my own check valve from the tank to the first Fuel filter near the tank. It has helped to keep fuel into the filters, I find it odd if I park on an encline it seems better then parking on a decline. The fact is air bubbles are only coming from the engine and not to the engine. I may believe that the fuel injectors might have bad O-rings????? It is a 1997 CAT 3116 Does it have O- rings that can be replaced?

Steve said...

I have the similar issue with my 97 GMC Topkick. I've used clear fuel lines to trace down the air bubble issue. In finding out that I'm only getting air bubbles coming from the return line that goes back into the tank. Check Valve #8 in his diagrahm. I installed my own check valve from the tank to the first Fuel filter near the tank. It has helped to keep fuel into the filters, I find it odd if I park on an encline it seems better then parking on a decline. The fact is air bubbles are only coming from the engine and not to the engine. I may believe that the fuel injectors might have bad O-rings????? It is a 1997 CAT 3116 Does it have O- rings that can be replaced?

texasgeezer said...

Hopefully I haven't entered this twice. Had to sign up to google+ after commenting.

Where do I put my fuel pressure gauge to check my fuel pump pressure on my cat 3116? Which plug on second filter housing? I plan to sell my 1991 Topkick & would like to know this is in spec.