Thursday, July 09, 2009

Cat 3116 Troubleshooting No Power

The problem with this 3116 Cat Diesel Engine was no power. The funny thing was it felt like someone stuck a banana in the tailpipe. There was no engine miss or hesitation what so ever. I checked for excessive back-pressure and that was normal.

One thing that seemed curious was the rpms in neutral went to the maximum without any problem but as soon as you put a load on the engine the rpms stayed at around 1200 rpm with no torque at all.

The Cat 3116 Governor controls the fuel rack which in turn decides how much fuel to allow to the injectors according to engine load and speed. The operator controls the throttle and the load is read off of the turbo boost pressure. The boost line goes directly to the governor air fuel ratio control. The more boost, the governor moves the rack for more fuel.

I tested the air/fuel ratio diaphragm with a regulator on the bus and it was leaking into the housing meaning the diaphragm had failed. Once I replaced the diaphragm it was a no-brainer to retest the new assembly and check for leaks. The new diaphragm was holding nicely.

NOTE: Don't test diaphragm over 20 psi

Here is a picture of the old diaphragm with a split in it. I remember the red flag that popped into my head when I called the Cat dealer for this part and they had 3 diaphragms on the shelf. Perhaps a recurring problem?

The 3 allen head screws are removed to pull the cover off to replace the diaphragm. This is an easy procedure once the governor is removed from the engine.
The governor linkage must be unhooked from the fuel rack before removing. Here you can see the pin which slides into the linkage and secured with a C clip.

The governor does not have to be timed and is fastened to the engine with 3 m8 bolts. Not much to it once all the fuel lines and piping is removed. This was a case of a smooth No Power situation. There was no white or black smoke, the engine did not miss or do anything really obvious. Testing the diaphragm with the air regulator is just another way for a diesel mechanic to troubleshoot a Cat 3116 Diesel Engine.


Rod said...

I am having a very simalar prob with a 960F frontend loader can idle all day but when you go to use it in about 10min experencing major powerloss the power is never up to full but after 10min the loader just falls on its face any ideas?

John Whelan said...

Hey Rod,
I would check the fuel lines from the tank to the primary and secondary fuel filters. The 3116 has a history of the steel lines along the governor side of the block rubbing through and creating cavitation. If the hole is small you might not really notice a difference at first. This is where I would start. Once it dogs again check the fuel filter, if it's close to empty you obviously aren't getting the fuel you need. If you have a fuel priming pump start using that when the engine starts to die off, this will also tell you that the fuel system is lacking flow. One other tip is to put the fuel line before the secondary filter (closest to the governor) into a clean bucket of diesel and see if the engine runs better. But, I would definitely start at the steel fuel lines first......

Bunedoggle said...

Hi John,

thanks so much for sharing your knowledge with us, the site is great.

I have a 1993 Thomas Saf-t-liner with a Cat 3116. As I understand it this is the 185 horsepower engine.

I converted this bus to an RV and we've taken a number of trips in it already. I have a number of questions I'm hoping you can help me with...

First, the bus is governed at 2800 RPM or so and that gives it a top speed of about 60 MPH. This would be fine with me if it could maintain 60 but even the slightest grade drops the speed. I realize 185 HP is not a lot. I'm wondering if this is to be expected or if there may be a problem.

Second, I understand this engine came in multiple horsepower ratings. What accounts for these different HP rating for the same engine, is it injector size, or more than that?

Lastly, I'm considering adding propane injection to give me a bit of extra power for hills and such. Do you have any insight/wisdom regarding such systems?

I'd like to thank you specifically for your note about the Thomas buses overheating on hills. I'll be adding the "pre-cooling" switch to my bus soon to solve our overheating problem.


John Whelan said...

185 HP is light on power but you should have a trans kickdown to help out. Are you running a 3000 allison?
I'm assuming you have serviced the fuel and air filters lately? The HP is determiined by the injectors, fuel timing & fuel setting.
I'm not at all familiar with propane injection. I believe the diesel can take the extra boost but I'm wondering about all that extra heat in the combustion chamber. You may have to weigh the expense of installing this system plus setting it up against leaving it the way it is and planning to arrive later to your destinations.

Anonymous said...

Hi i have 950F Series II Cat Wheel Loader with 3116DI engine.
I am having problem of mixing diesel with engine oil. I think there is leakage inside the governor or transfer pump. Please guide me how to solve this issue.

J. E. Whelan said...

That's a possibility that the fuel transfer pump inside the governor is at fault. This would require removing the governor (no timing required to re-install) and checking out the transfer pump for signs of leakage.

Anonymous said...

Hi, Jhon i have checked the Governor and feul transfer pump i found no leakage however i have replaced the feul transfer pump but after fixing the Governor back still there is mixing of diesel with Engine oil. As soon as we put our machine on loader after few hours engine Oil is full of diesel inside. Pls help me where is the problem what should i check now., regards, irfan ..

lajara said...

check the seals on the injectors. upper seals

Anonymous said...

My Cat 3116 DI will not start.
The fuel appears to be turned off.

Anonymous said...

I just wanted to say thanks for the great article! This helped us figure out what was wrong with one of our customer's trucks; the great write up is much appreciated!

Anonymous said...

I have a cat 1997 3116 out of a army truck with a 4 speed automatic, I wanted black smoke on full throttle and turned out the tiny set screw under the valve cover 2 turns CCW, it did nothing but incresed the idle RPM. I can hold it to the floor in 4th gear, and even though it goes great there is not one puff of any kind of smoke.

Jeff said...

I have a cat 1997 3116 out of a army truck with a 4 speed automatic, I wanted black smoke on full throttle and turned out the tiny set screw under the valve cover 2 turns CCW, it did nothing but increased the idle RPM. I can hold it to the floor in 4th gear, and even though it goes great there is not one puff of any kind of smoke.