This article originally published in Issue 56 of the Turbo Diesel Register.

The Way We Were

I HATE TO DO THIS - FUEL TRANSFER PUMPS REVISITED

FROM ISSUE 40: ’94 to ’98 12-VALVE
FUEL TRANSFER PUMP REPLACEMENT

I did not think fuel transfer pumps on 12-valve engines were a problem. I recall reading the “Backfire” column in Issue 39, where the editor states, “The old 12-valve engines used a mechanical fuel pump (the type driven off the engine’s camshaft) which is essentially problem free.” Nevertheless, as I started to read more about the transfer pump for 12-valve engines on the TDR website, it became obvious that there are many instances of pump failure. Is this something that we 12-valve owners should be watching out for?

Warning Signs

The first sign suggesting that my pump might be failing was very hard startups in the morning. Then I noticed that the idle rpm was slowly getting lower and when driving the truck it had lost its pep. Finally, the truck just wouldn’t start. After running a fuel pressure test to determine the problem, I concluded that it was the fuel lift pump. You can purchase a new lift pump from a Cummins distributor for around $170.00 (part number 3936316; gaskets, 3939258 at $1.68).

Replacement

Following the procedure in the Service Manual, the first step is to disconnect the battery terminals. The instructions read to remove the starter motor (Remove the starter . . . there has to be a better way.), place a drain pan below the pump, remove the fuel line fittings at the top of the fuel pump, and fuel heater housing. Next, remove the fuel hose clamps and rubber fuel hose. (You can leave them connected and remove after you have removed the fuel pump and fuel heater.) Remove the two mounting bolts. Remove the fuel pump and fuel heater as one unit. Be careful not to allow the plunger to catch on the edge of the hole in the cylinder block and drop into the engine. As intimidating as this sounds, you would have to try to do this, as the plunger has to be pulled from its bore. Simple enough?

Carter lift pump with plunger removed.

Helpful Hints

Instead of removing the starter motor, I decided to get really acquainted with my engine and come in from the top of the engine compartment. This appeared easier than trying to work around the front differential to remove the heavy, bulky and greasy starter. The only problem is that when you try to reinstall your fuel pump and fuel heater unit you cannot push the pump back into place because your arms are not long enough to get any leverage to push the plunger against the camshaft. This is the voice of experience (and about an hour of labor and an evening in the easy-chair thinking about the problem) speaking to my fellow TDR members. Learn from my situation that there is a simple solution, thus making the top-removal a practical service technique.

Carter lift pump with regular mounting bolt and longer temporary bolt.

Here is the secret: When you remove the fuel lift pump, take one of the two mounting bolts and find a replacement that is the same metric thread size but about ¾” longer. You probably have one in your parts box or you can borrow one from elsewhere on the engine. When reinstalling your lift pump use the longer bolt as your starter bolt. Once you get the lift pump and fuel heater partially tightened down, install one of the original bolts in the other hole. Once it is partially tightened, remove the longer bolt and replace it with the other original bolt. Tighten the two bolts to 18 ft-lbs torque. (Tighten the two bolts alternately to prevent damage to the fuel pump housing.) I thought this was the easier and less time consuming way than removing the starter and trying to be a contortionist by working my way around the front differential.

Next step, bleed air from the fuel system. Begin by loosening either (doesn’t matter which) of the two 10mm bolts on top of the fuel filter housing. This will allow the air to escape as you prime the system. When priming the fuel system, begin by pushing the primer button a few hundred times and when you finally feel like your thumb is about to fall off, do it a few hundred more times. Seriously, don’t use your finger to push the primer button. My favorite tool for this job is a jack handle (from one of those cheap automotive two-ton jacks) that has a slot in the center of the open-ended pipe. Another method that’s been used at Geno’s Garage is using an old broom handle to push the primer button. I decided to make my broom handle a little easier to use by taking a ¾” PVC coupling and sliding it on the end of the broom handle and drilling a hole about a 1/8” below the top ridge and installing a bolt in it. This is to help prevent the rubber boot from tearing. This will always come in handy when you have to prime the fuel system. When you hear the fuel hit the pump, try starting your truck.

Broom handle, 3/4” coupling with hole drilled and bolt.

Broom handle assembled.

Overall, it was a fairly easy installation. Skill level: give it a five on the 1 to 10 scale—make that a three, you know the shortcuts. Using the longer bolt and the broom handle made it much easier.

Brandon Parks
Geno’s Garage