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Old 12-29-2020, 08:31 PM   #1
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1995 Thomas RE Fuel Tank questions!

Hi all.
Still chasing my loss of power in my 1995 West Coast-Er.
Cat 3116 (mechanical) engine.

Just replaced all the fuel filters. Still no power , starts and idles great though...

My current train of thought is its sucking air from a bad or split pickup tube.

I found the access panel (thanks Thomas!) and took a look.

I have 4 lines and one empty port.

Two low pressure lines. I'm guessing a vent for the tank itself and then???

Then two hard plastic lines, one red and one green. I think the green is 1/2 inch and the red is 3/8. Not positive on the id of these.

I presume like a gas engine with return, the red smaller ID is the feed line and the largergreen larger ID is the fuel return. Is that correct?

I'll be checking them tomorrow for a crack/split/leak.

Thanks all!

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Old 12-29-2020, 08:38 PM   #2
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The turbo is not quite right ????
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Old 12-29-2020, 08:49 PM   #3
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Quote:
Originally Posted by Dead pirate View Post
The turbo is not quite right ????
I am 99% sure the turbo is still fine. I can hear it spoiling up most of the time. Sometimes you can hear it spool up if you hold the accelerator pedal down and let the rpm hit 2000 or so.

The other thing I'm thinking is the primer rod( not a bulb type) dribbles a tiny bit of fuel when you unlock it. Maybe that's sucking aur under a heavy load?
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Old 12-29-2020, 08:50 PM   #4
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Sounds like its sucking air from somewhere
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Old 12-29-2020, 09:20 PM   #5
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find the problem and quit guessing

okay step one..... on the turbo there should be something called a "waste gate" google it watch some videos... learn what a waste gate is.... on the waste gate there is a hose/tube that is connected to the intake side of the engine..... Put a "TEE" fitting in the waste gate hose and connect a 0-60psi gage to the waste gate hose. That will tell you how much boost you are making or are not making.... 0-30 psi or so should be "normal" If you only see 10 psi as a maximum... you have a problem if you see only 20 psi You PROBABLY have a problem.

The larger line 5/16 to 3/8 inch is usually the feed line to the fuel system, the line 1/4 inch or so should be the return to tank line. Google "fuel pressure cat 3116" and do some reading. I expect after you read and look at diagrams for a couple of hours... you will begin to get an idea of what the pressures should be. Stuff I read indicates you will need gages capable of up to 300 psi. That way you dont break the gage.

fuel pressure, intake manifold pressure are a start. Then there are possible problems with the governor and/or "rack" take one step at a time and work to eliminate guess work.

I have been doing repairs on all kinds of engines for more than 40 years. I see time and time again people spending money on parts that dont fix the problem because the problem was never pinpointed. people Guessed at the problem and guessed at the solution...

william
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Old 12-29-2020, 10:04 PM   #6
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Thanks for the info William.
I'm no slouch when it comes to playing in engine bays either! (Mostly electrical stuff, although I have rebuilt a few cars for the frame up)
.
My problems now are trying to figure out terminology and the differences in functionality between gas and diesel.
I've activly avoided diesels until recently.

The way the engine lost power , but then is able to maintain highway speed on a flat surface just screams that it is starving for fuel, at least my experience with passers says that...
Its free to check the pickup tubes and sediment filter.
I'll be ordering a fuel pressure guage in the next day or so, even if it is a bad pickup tube, I'll want that tool handy for future issues.
.
I also have no experience with turbos. Other than knowing what the parts are abd the super basics of function.
I'll get a guage to check that asap as well.

Don
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Old 12-29-2020, 10:10 PM   #7
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All diesel powered vehicles NEED to have a pyrometer and a manifold pressure gauge. These are just as important as your other gauges. No boost or low boost and low egt is lack of fuel delivery. High egt and low boost is a lack of intake air. On a RE bus you can't hear small problems. Just loud problems. Fuel pressure is another important gauge to have. These three gauges will usually help you see problems while driving before you are on the side of the road calling for a tow.
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Old 12-29-2020, 10:13 PM   #8
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this may be worth reading -
~~~~~School Bus Mechanic: Cat 3116 Troubleshooting No Power
Quote:
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
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Old 12-30-2020, 07:48 AM   #9
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Thanks for the info!
.
Still curious as to what the other low pressure hose is for. Would these tanks have two vents? If it was a gasser, it would be an evap hose. Pretty sure my engine setup does not have an evap system...
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Old 12-30-2020, 01:03 PM   #10
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You could also have a crack in your fuel line on the suction side of your fuel pump. Check out the Adept Ape on you tube. He is a Cat mechanic and has a whole video on diagnosing fuel system problems.

Ted
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Old 12-30-2020, 05:19 PM   #11
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My primer pump is definitely leaking, drip-drip-drip!

No visible rust/corrosion or cracking in the pickup tube in the tank.
.
I have ordered a fuel pressure guage set. And a new primer pump.
.
Not much else I can do till the diagnostic tools get here.
.
I have been reviewing AdeptApe videos!
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Old 12-30-2020, 05:49 PM   #12
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get to know that beast and it will treat you well.
The fuel system is a bit of f#@kery but when they're running right they run well and for a long time.
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Old 12-30-2020, 05:58 PM   #13
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I'm hearing you ECCB!

I hope I'm not wrong, this really feels like it is a simple thing. It ran so fantastically until the sudden power loss.
.
When I take it for a test drive, it acts like it wants to go, but someone stuffed a banana in the tailpipe!
.
My experience with gas engines really makes me think it's a lack of fuel ( or air in the system )...
I'll definitely update with info as soon as the pressure guages get here and I can do some better diagnostics done.
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Old 12-30-2020, 06:38 PM   #14
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Quote:
Originally Posted by KlingonFiero View Post
I'm hearing you ECCB!

I hope I'm not wrong, this really feels like it is a simple thing. It ran so fantastically until the sudden power loss.
.
When I take it for a test drive, it acts like it wants to go, but someone stuffed a banana in the tailpipe!
.
My experience with gas engines really makes me think it's a lack of fuel ( or air in the system )...
I'll definitely update with info as soon as the pressure guages get here and I can do some better diagnostics done.
The tech article I linked earlier- I think it said something about that.
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Old 12-31-2020, 09:09 AM   #15
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Quote:
Originally Posted by EastCoastCB View Post
The tech article I linked earlier- I think it said something about that.

Hahaha! Thats funny. It must have been in my head when I responded last.
.
Couldnt get the pressure guage in town without waiting a couple of days. So I ordered the same kit on Amazon for half the price.
It sucks not buying local, but I'm on a budget here!
.
Hopefully the guage kit gets here soon...
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