CAV injector pump troubleshooting

   / CAV injector pump troubleshooting #1  

adambreich

New member
Joined
Jul 24, 2025
Messages
1
Tractor
70s Ford
Hello!

I have a Ford 3-cylinder diesel tractor with a CAV injector pump and have been having issues it to run consistently. It starts up strong, runs for about 10-20 seconds, and then slows to a stop. It can start back up immediately and repeat the same performance over and over. I have double checked that all of the fuel lines are tight, and I've replaced most of the gaskets in the pump after replacing the rotor. The few folks I've spoke with suggest that air getting into the system is the likely culprit, but some of my observations make me skeptical. Here's what I'm seeing...

1) I thoroughly bleed the system at the fuel filter, as well as the main bleed valve on the pump and governor cover. I do not see any evidence of new air in the pump after several times of the stalling behavior described above. If air is getting pulled into the pump, it is not showing up in the fuel that comes out of the bleed port when I try bleeding again.
2) If I leave the bleed screw out during operation, the pump will continue running well (despite the constant stream of diesel) and does not exhibit the stalling behavior at all. I observed a similar thing before this issue started--I had initially forgotten to install the o-ring that creates a radial seal between the rotor and the main pump housing. There was fuel leakage at this interface, but the tractor ran great otherwise. Once I installed the o-ring, this issue started.
3) If I run it at full throttle, fuel can be seen weeping out of the gasket seal of the governor cover as the engine starts to slow down and stall. It is a new gasket and the fasteners are secure.

This leakage makes me think that the pressure is getting very high inside the pump cavity. Combined with the fact that the pump runs well when the cavity is not sealed (e.g. bleed screw or o-ring are not installed), this makes me think that the high pressure in the main pump cavity is somehow related to the stalling behavior. I have checked both the transfer pump regulating valve as well as the automatic advance device to make sure that the pistons in them are free-moving and all springs are in place, as I know both play a role in regulating or responding to pressure. Both look good to my inexperienced eyes, similar to videos on youtube.

Does anyone out there have any thoughts on what might be causing this problem? I'm pulling my hair out trying to get to the bottom of this! If air is a likely cause, can you help me understand why introducing more opportunity for air ingress (by removing the bleed screw / o-ring) would make the issue go away, and why I don't observe any air in the fuel when I try bleeding again?

Thank you!!
 
   / CAV injector pump troubleshooting #2  
I'm no expert at all but have you checked to return line from the pump ??

gg
 
   / CAV injector pump troubleshooting #3  
Also check fuel tank cap for venting. Your issue sounds a lot like a vacuum is being created in the tank. If not that, the tank screen may be clogged. In any case, it sounds like a fuel supply issue.
 
   / CAV injector pump troubleshooting #4  
My brother had a similar issue, his problem with the check valve on the side plate for the return, he took out the ball and spring and it runs great now.
 

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