M35A3 Fuel Pump/Prime Issue

fuzzytoaster

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I've read the TM's and covered the dozen or so related SS thread regarding fuel prime on these M35A3 trucks but I fear my issue has surpassed the TM troubleshooting steps and into deeper water.

This M35A3 fired up momentarily when I first cranked her. She turns over quick. She does fire on either. I've had some luck to get her to puff white smoke but it has come and gone..and remained gone at this point. Fuel is old but decent and has 3/4 tank. I've held the throttle open and cranked the living hell out of it, used a can of either gently as well, but no luck staying running.

So far I've replaced the fuel filter, which was full of fuel, and removed the check valve on the fuel tank to inspect and clean. Sure enough it was stuck closed with crud but now works well. I disconnected the fuel line after the elbow on the tank and pressurized the fuel tank with air to visually see it flow a steady stream which is clean red diesel.

I've loosened the fuel line up at the injection pump and pressurized the fuel tank to purge any air then tightened it. The IP shut off solenoid gives a sharp audible click with the power switch on and off. I've followed the TM steps in "giving it a gentle tap" and checking for power and ohms which are both fine. It felt like a solenoid issue initially but I had some smoke here and there. I was getting some pressure through to the fuel filter or so I thought since I had some smoke.

I suspect I had some pressure built up from cranking and air pressure from the fuel tank but the volume of fuel that was drained from the fuel/water separator drain valve was forceful but short lived. I suspect it was left over from the filter exchange and I used a brake clean red straw to clean out any debris but now no fuel drains out. I've cranked it more and got very little fuel but even then it too stopped. I loosened the line on the top side of the IP that goes to the fuel filter and it appears dry. Tapping the fuel filter it sounds empty.

steven stuchell mentioned in a previous thread of a check valve in the return line that can cause a 3116 to not fire up. I'm assuming this is on the output side of the head (front). My understanding is the blockage could be due to the stuck valve which is trapping air preventing it from purging or firing. In this case it explains why I have no return fuel to the tank but I should have fuel to the drain on the fuel/water seperator right after the IP.. which I don't.

Some forums have said it's possible the governor is stuck or sticking which may be true. This isn't an "all or nothing" fuel situation until recently. At this point I'm guessing it needs to be sent off for rebuild. Even with a pressurized fuel system (5 psi), confirmed fuel to the IP, assumed working solenoid (yes I know, will verify by removal), and cranking it with the throttle full open I still don't get fuel.

Thoughts?
 
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Monkeyboyarmy

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Since I haven't opened the hood on my A3 in 5 plus years, this is by memory (sometimes weak).

So the route of the fuel is from the tank, through the check valve on the tank, through a small check valve at the pump on the front of the engine, through the piston pump, through the fuel filter to the back of the head, through the head and injectors, through a pressure relief valve at the front of the engine (next to the pump), and returns to the tank. Soooooo

I found crud holding the check valve open at the piston pump therefore couldn't create any pressure in the head. I installed a primary filter at the tank to keep debris out of that check. Also make sure that the seat at the pressure relief valve is sealing properly. If you did not remove the return line at the tank before pressurizing it, the fuel will just push against itself from either line. If you remove the return line and pressurize the tank, you should get fuel flow at the return....if you exceed the pressure relief seat pressure. The fuel solenoid simply moves the rack control to a "no fuel" position on each of the injectors.

Hope that isn't too confusing because I think I confused myself.
 

fuzzytoaster

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3116 CAT fuel system - YouTube ? Then return line check valve above that on the Governor or tank check valve ? Wonder why they never added the filter / primer ball set up like on the FMTV's.
I pulled the both lines on the IP to check things out. The intake primer ball was in good shape but there is no strainer like in the video. The return/output line has the check valve and it's stiff. I've got it soaking at the moment. Unfortunately I don't have fuel that far to check it at the moment.

Since I haven't opened the hood on my A3 in 5 plus years, this is by memory (sometimes weak).

So the route of the fuel is from the tank, through the check valve on the tank, through a small check valve at the pump on the front of the engine, through the piston pump, through the fuel filter to the back of the head, through the head and injectors, through a pressure relief valve at the front of the engine (next to the pump), and returns to the tank. Soooooo

I found crud holding the check valve open at the piston pump therefore couldn't create any pressure in the head. I installed a primary filter at the tank to keep debris out of that check. Also make sure that the seat at the pressure relief valve is sealing properly. If you did not remove the return line at the tank before pressurizing it, the fuel will just push against itself from either line. If you remove the return line and pressurize the tank, you should get fuel flow at the return....if you exceed the pressure relief seat pressure. The fuel solenoid simply moves the rack control to a "no fuel" position on each of the injectors.

Hope that isn't too confusing because I think I confused myself.
It makes sense. Unfortunately, I'm getting nothing through the IP to the fuel filter and I've got about 10 psi on the fuel tank pushing fuel to it. I've got it soaking over night right in hope it may help "de-gum" it.
 
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glcaines

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Try opening the drain petcock on the bottom of the fuel filter. Normally, when open, you will find the passage will be plugged solid with dirt, so take a small piece of wire (welding rod works great) and rod out the open petcock. Then, leaving it open, crank the engine until you see a solid stream of fuel coming out of the petcock. Usually when you do this, the engine will start and I let about a pint of fuel come out of the petcock with the engine running and then close it. Every time I change the fuel filter, I have to go through this routine on mine. When everything is normal in an A3, the CAT 3116 engine won't even turn over a full revolution before starting. The easiest starting diesel I've ever owned. I've had so-called diesel experts tell me all kinds of things were wrong, especially that the pump needed to be replaced or rebuilt. The fuel filter on the A3 is mounted upside down, which I believe leads to this issue. Good luck.
 

fuzzytoaster

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Try opening the drain petcock on the bottom of the fuel filter. Normally, when open, you will find the passage will be plugged solid with dirt, so take a small piece of wire (welding rod works great) and rod out the open petcock. Then, leaving it open, crank the engine until you see a solid stream of fuel coming out of the petcock. Usually when you do this, the engine will start and I let about a pint of fuel come out of the petcock with the engine running and then close it. Every time I change the fuel filter, I have to go through this routine on mine. When everything is normal in an A3, the CAT 3116 engine won't even turn over a full revolution before starting. The easiest starting diesel I've ever owned. I've had so-called diesel experts tell me all kinds of things were wrong, especially that the pump needed to be replaced or rebuilt. The fuel filter on the A3 is mounted upside down, which I believe leads to this issue. Good luck.
I followed previous write ups and serviced the petcock when replacing the filter drain. It's a poor design choice for sure but not the issue.
 

Mullaney

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Try opening the drain petcock on the bottom of the fuel filter. Normally, when open, you will find the passage will be plugged solid with dirt, so take a small piece of wire (welding rod works great) and rod out the open petcock. Then, leaving it open, crank the engine until you see a solid stream of fuel coming out of the petcock. Usually when you do this, the engine will start and I let about a pint of fuel come out of the petcock with the engine running and then close it. Every time I change the fuel filter, I have to go through this routine on mine. When everything is normal in an A3, the CAT 3116 engine won't even turn over a full revolution before starting. The easiest starting diesel I've ever owned. I've had so-called diesel experts tell me all kinds of things were wrong, especially that the pump needed to be replaced or rebuilt. The fuel filter on the A3 is mounted upside down, which I believe leads to this issue. Good luck.
.
THANKS! Hopefully that will help me on my 3116 too.
It cranks reliably, but it always spins (way too long in my mind).

I have noticed that it takes enough rotations to see oil pressure on the gauge.
Might be completely unrelated to fuzzytoaster 's situation - but I may have learned something useful!

Thanks glcaines I will be replacing the filter and see what happens.
Did that once, but it has been a while...
 

fuzzytoaster

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Solution:

I did some deep diving on Ag forums and found some other check valves in the transfer pump/governor. I pulled the check valve off the back of the pump, this is the output side from the pump to the fuel filter. I removed the adapter plug and fished the plastic bit out which was a solid ball of algae. I pushed some penetrating oil in there to displace any air/debris then I reassembled and primed with air from the tank leaving the output hose on the governor off to watch for return fuel. It finally did. I cranked her and she fired right off.

#5
3116cutoutviewoftransferpump.jpg

2021-08-02 16.48.46.jpg

 

fuzzytoaster

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Problem #2

Now the other sister A3 I have is exhibiting the same symptoms so I repeated the same steps from the beginning and it too was clogged on the back side of the pump. I replaced the fuel filter, used a brake clean straw and cleaner to free the petcock/drain, physically inspected all check valves, and primed the system without issue.

I initially had "puff puff" but no fire, now no smoke at all. I've checked the governor linkage for movement and shut off solenoid for functionality - all are good. I'm getting a steady stream from the return check valve above the governor just from the air pressure in the fuel tank. I cracked the fuel petcock again and the stream is weak even when cranking. I removed the output line from the governor to the fuel filter and cranked and I visually see fuel moving but it's low pressure. Some Ag forums were saying 9 psi during cranking and 59 psi running. Can anyone verify?

At the moment I suspect I'm not retaining enough pressure in the head whether it's due to low pump pressure or low retaining pressure from the check valve. Ugh.. always something. Joys of the hobby. :jumpin:
 

glcaines

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I followed previous write ups and serviced the petcock when replacing the filter drain. It's a poor design choice for sure but not the issue.
I don't think I was clear. I wasn't saying that the petcock was the issue. What I'm saying is that the filter doesn't fill up with fuel because air is trapped in the filter. Opening the petcock while cranking lets the air be purged from the system.
 
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fuzzytoaster

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I don't think I was clear. I wasn't saying that the petcock was the issue. What I'm saying is that the filter doesn't fill up with fuel because air is trapped in the filter. Opening the petcock while cranking lets the air be purged from the system.
Understood. It's something I've been looking for and makes me suspicious on truck #2. I eventually got a strong stream on truck #1 once the clog was resolved. I'll retrace my steps.
 
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fuzzytoaster

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Truck #2: I continued fiddling with this truck and inspected the check valve on the return side which was fine. I removed the fuel filter and primed the system which got flow as well as a hairball equivalent of algae that popped out. It must have settled in the bottom of the pipe over time but not compacted until I started pressurizing the system. After all that was cleaned and reassembled I still had no smoke despite having good return flow from the output line at the governor.

I removed the valve cover and with the power switch on, to hold back the shut off solenoid, I gently manipulated the governor arm with a screwdriver to make sure it wasn't frozen. Great! I then ran the rack checking injectors and found #5 frozen. The injector is now out and soaking in the ultrasonic cleaner over night. Maybe she will purr tomorrow..maybe..

 

fuzzytoaster

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2021-08-06 18.21.22.jpg
Don't be fooled, the top injector is injector #5 pulled yesterday and spent 2 hours in the ultrasonic cleaner. It freed it up most of the way but it has a rough spot in at mid throttle and I opted to pull a good used injector from my donor truck (bottom) instead. Ironically injector #5 was the only free moving injector on the donor truck, all the others were frozen. Small blessings am I right?

I installed the injector, set tolerances (which weren't hard), and checked all the rockers. I noticed one push rod for cylinder 6 was off and I had to reset it. During the process I could only guess maybe it contributed to why the truck was deadlined or at least why someone took the fuel check valve assembly off it. Who knows..

I pressurized the tank and put my foot the the floor and..



Solution for truck #2: clog post transfer pump, stuck injector, and push rod for cylinder 6 was off. She runs smooth now and wants to move. The CTIS is alive and I'm sure in a panic as 4 of the tires are completely blown out lol. I'll get it up and moving next week. Overall a mechanically sound truck that needs cosmetic love.
 
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