Cat 3126b HEUI pump transfer drive question

If it is a Freightliner. There may be a little metal inline fuel filter ( about the size of the ones on an old school carbureted car) in the 1/2 plastic line going to the pickup pump right after the tee for the tanks. Usually buried in a hard to see and get at spot behind engine above transmission. They plug up and are not mentioned anywhere in the maintenance service regiment. We removed ours and replaced the line after they plugged the first time.

 

I had probably a dozen problems with the heui pump on my ‘99 3126B in the 17 years we ran it everyday. Seemed like every 200-250k miles there would be something going wrong with them. From minor leaks to not pumping fuel. Derating itself down to 1800 rpm and top speed of 45 mph a couple times. They mixed fuel and oil a lot too. More oil in tanks then fuel in crankcase tho luckily.
But when running good they were awesome pullers for their size.

We found one way to help them live longer was to never go more then 8k on oil changes. Clean oil was the key. They would start to idle unevenly and get a little vibration in the fuel system when close to 8k so you knew it needed fresh oil.

 

That is one thing I wouldn’t touch. I would take it to CAT and let them mess with it. It always seemed like a can of worms was opened along with it so I was to spooked to work on it myself. Always seemed like other things that I didn’t have time for has to be replaced/repaired related to the pump failure at same time. Great thing was at the time the company paid for it so it didn’t hurt me, but now I would be stuck with the payment if it goes south again.

 

I saw one once that the drive gear on the front of the heui pump had come loose. Are you building actuation pressure? If the pump isn't turning it won't run the transfer pump.

 

Pull the transfer pump , crank the engine and see if the transfer pump actuator is moving. Much easier.