I've been planning this fuel system refurbishment for quite some time. My old lines were broken, spliced, kinked, and rigged in about every way imaginable; and I'm a real stickler when it comes to clean and reliable setups. So before winter hit, I figured it was time to get this project underway.
The fueling system is probably the number one posted about topic in the 12 valve forums. I'd wager it’s caused the most headache to owners than any other component of these trucks. And before undertaking any kind of fuel system project, it’s important to know what you're dealing with. Luckily, this forum has a huge amount of information devoted to the fueling system. Take the time to read these and familiarize yourself with all the working pieces of the system and it will help not only to follow the rest of this thread, but also when it comes to actual troubleshooting and problem solving.
First things first…. Remove everything from the fuel supply system. Lift pump, pre filter assembly, fuel filter, fuel tank, and all factory fuel lines and fittings. It helps to go ahead and remove the intake tube, intake horn and afc housing just to make space to fish things out and room to work. Here’s my pile of parts you’ll probably have something similar.
Empty on the inside. Cover the opening in the block to keep debris from falling in.
Save the diesel out of your fuel filter for lubrication during assembly of fittings and hoses as you’ll see later on. Once you’ve got it all out, go ahead and take the bowl off the pre-filter so you can remove the stud for the fuel heater. Toss that thing in the trash, clean the pre-filter and bowl out really well, and reinstall. The threads in the lift pump are 3/8 NPT. I installed two 3/8 NPT to 3/8 Push-On hose fittings from McMaster (Detailed parts list including numbers will be posted at the end). Use only the Yellow PTFE Thread tape on any of the fuel system fittings. The regular white stuff is not rated for petroleum products and the diesel will dissolve it leaving you with leaks everywhere.
Next move to the lift pump. If you read Cowboy’s or Tony’s threads you know there is potential for flow increase in the fittings as well as high rpm performance from replacing the stock spring. If your goal is more power from the stock pump, now is the time to modify. Unless going totally custom, the two stock fittings that thread into the lift pump body have to be retained as the check valves that make the lift pump operate as designed are intrinsic. Something I haven’t seen mentioned in other threads that is worth considering is that if you remove the outlet check valve the orifice that fuel is pumped through is incredibly small. You have a 1.180 bore piston pushing fuel through a roughly ¼” diameter hole… you do the math. If you’re handy with dremel or die grinder, you can open this hole up to improve flow. CAUTION: DO NOT JUST SIMPLY DRILL THE HOLE BIGGER. If you look closely that tiny hole is already butted up against the end of the bore. Take care making sure you don’t break into it when removing material. I didn’t bother with this because my truck will never see more than 500hp. I thoroughly cleaned all the fittings and the pump body in the parts washer before reassembly. DO NOT take any kind of abrasive material to the OD of the piston, or the bore in the pump. They are lapped to each other to create the hydraulic seal necessary for pressurizing the fuel, and scuffing the surface is going to greatly reduce its efficiency. The same goes for the plunger that rides the cam. If they’re dirty use a very soft bristle brush, cotton cloth, and some clean diesel to clean it out. I re-assembled with the stock ½” barb on the inlet side, but replaced the stupid metric o-ring face seal fitting on the outlet with a M14 x 1.5 to 1/4 NPT adapter, and then a ¼ NPT to 3/8 Push-On. I also replace the short ½” hose with a new one as they have a tendency to crack and leak air into the system, its cheap insurance and easy to do with everything off the truck anyway.
Next I moved to the injection pump. Despite the struggles of others, the plug in the front port of my pump came out with just the 10mm allen wrench and a short piece of pipe stuck on the end for leverage. In that port I installed an M18 x 1.5 to 3/8 JIC adapter (I had to grind the points on the hex down slightly to clear the timing cover i.e it’s a 12 point hex now). I could only find this fitting from Discount Hydraulic Hoses. NOTE: If you decided to run ½” line instead of 3/8” like I did, this part becomes much easier as M18 x 1.5 to ½” JIC adapters are available from many online sources. Off my adapter is a 3/8 JIC to 3/8 Push-On short 90 elbow from Parker (they also have a ½” hose version of this part as well).
After that was taken care of I installed an M14 x 1.5 to 1/4 NPT adapter in the factory inlet of the injection pump with a 3” long ¼ NPT brass nipple threaded into that. People running ½” line, remove the helicoil and use an M16 x 1.5 to 3/8 NPT adapter instead. I prepared a 4 way brass T fitting with a ¼ NPT to ¼” Push-On fittings in the sides, and a .020” snubber fitting for my fuel pressure gauge in the bottom. This is something that can be adapted to work with a needle valve as well for the more common fuel pressure gauge setups. While I was here I also pulled my factory OFV and installed the adjustable version from Tork Tek. My factory worn out valve opened at 2 psi using regulated air, the Tork Tek one that is preset to 30 psi actually opened at around 25 psi. My fuel pressure gauge confirmed that as idle fuel pressure was right at 25 psi.
Thread it onto the nipple and wala
At this point you have to make a decision on retaining the stock fuel filter or creating a remote setup. If you’re using 3/8” line I think it’s reasonable to retain the stock filter and I muddled through it waiting for other parts in my down time. There are two major ways to go about doing this:
1. Install M12 x 1.5 to ¼” NPT adapters in the inlet and outlet ports of the housing, then use ¼” Hose fittings. This setup becomes pretty tall and ugly looking, but requires no drilling or tapping unless you want a custom port for bleeding air (Using a Tee with a plug in the unused port is possibility for this…but just adds to the ghetto-ness).
2. Drill the ports out and tap for 3/8 NPT. Then you can just use 3/8” hose fittings without the bulky adapter. Definitely cleaner looking of the two approaches. Can also work with ½” line if you’re dead set on keeping the stock filter. If you go this route chances are you’re more comfortable with machining as it is, so you have flexibility for adding a bleed port that isn’t rigged looking. Just be careful when drilling out the inlet and outlet not to drill all the way through or you will remove the separation between filtered and unfiltered fuel. Less costly than the other option, cleaner looking, but more time consuming and independent thinking is involved.
There’s a small caveat with both of these that pushed me to the decision of building a new filter setup, my inability to tie the injector return back into the system after modifying the filter housing. The first setup is waaaaay to tall for the banjo to tie in anywhere. The second version was promising at first with tapping the top of an elbow hose fitting, but there was not enough area to thread into, and there was not enough sealing surface for the neoprene washers to keep diesel from dribbling out everywhere. Not saying it can’t be done, because really you don’t have to tie back into the filter housing at all. You can just cut the drain tube, stick a hose on the end, and tee it into the return for the tank or anywhere post lift pump that you want. But I wanted a little better than that. This is the area where everybody does something a little different, so depending on how picky you are, it can be the easiest part of the overhaul or the most consuming.
Next time to tackle the tank. I’m not certain about access to the sending unit on 98’s that came with the short bed, but I actually found getting to all the connections on top of the tank without actually dropping it or lifting the bed isn’t too much of a bear. You can sit up beside the tank in the fenderwell and see everything you need to get to. Pop off the electrical connector and the two plastic quick connects for the fuel lines. A small screwdriver makes pushing the tabs in to release it a lot easier. Once you have those off, if you haven’t already, you need to remove the old fuel lines. There’s 3 plastic clips behind the tank that hold the fuel lines, the wiring harness, and the rear brake line all together that’s mounted to the frame with those annoying little Christmas tree style push rivets. There’s also two additional rubber insulated clips mounted with a bolt farther up along the frame rail that hold them all together, but they are easily removed by just taking the bolt out. Personal preference comes into play here, if you don’t want to drop your tank you can work them off the lines using a long narrow screwdriver and some patience. Another trick is to just cut off the Christmas tree end from the other side of the frame and pop the things out the other side. Then you can just slide all the clips up the lines until they’re up to the front of the tank where you can get at them easier. At first I wasn’t going to reuse them, but I ended up changing my mind because of how they hold the brake lines up away from the frame. Near the back of the tank there’s a spot where the frame narrows down and these clips do have a purpose in keeping the line not only from shaking, but also from rubbing a hole in itself in this area. Some may think it’s unnecessary as its likely going to take a while for the line to actually rub a hole in itself, but all it takes is the one time you need to slam on your brakes and not having any to make it clear why it IS necessary. Been there done that and nearly crashed so I don’t mess around when it comes to brakes. So if you managed to get all the lines out without dropping the tank and don’t care how they’re routed back up to the front of the truck, this will be easy for you. Slide the 3/8 hose onto the 3/8 barb on the sending unit and secure it with a hose clamp, do the same with the 5/16 return barb and hose. (If you plan on installing a sump reference Tony’s thread).
If you haven’t already picked up on it, I’m picky so I wanted to route my lines behind the tank like the factory, so I did drop it. It’s really not all that difficult especially if you have a buddy that doesn’t mind helping you out. Loosen the clamps that hold the filler neck and breather tubes to the tank and pull the hoses off. Then one bolt each holds the tank straps on, they’re on the passenger side of the tank. Put a jack underneath to support and probably your buddy on either side to keep it from tilting when you let it down, then go ahead and take the straps out. Once the bolts are out the other side of the strap has a little slot it sits in to keep it from falling out. Slide it towards the passenger side of the truck and it should fall through with a little wiggling. Slowly let the tank down and make sure you don’t get hung up on anything. With it down you have plenty of visibility and room to work to plan on how you want to route your lines. I went to Home Depot and bought 28ft of ½” wire loom and two bags of some ¾” plastic clips in the same style as the rubber ones you took off earlier to secure the new lines. Pictures for clarity.
Lines into the top of the sending unit
Picture showing the factory clips still holding the brake line and wiring harness, along with my feed and return lines mounted with the clips I bought and self-tapping screws. The other wiring harness is for my electric brakes as my truck didn’t come wired for them from the factory.
I wouldn’t reinstall the tank until you fire the truck up and make sure you don’t have any leaks.
Moving on, reinstall your lift pump. If you’ve never done this before you can make your life a whole lot easier by ditching the two factory bolts and converting to studs. It costs less than 5$ to get the hardware you need from ACE and it will save you frustration and fighting to keep all your holes in the pre-filter, lift pump, and both gaskets lined up trying to work the bolt through and get it started in the block. Just trust me, you’ll be glad you did as I’ve done it both ways. No studs took around 2 hours, with studs it takes about 5 minutes. Get two M8 x 1.25 studs or threaded rod between 50 and 60mm long (slightly longer than 2”), and two each of 8 mm lock washers and lock nuts. Thread the studs into the block, slide your first gasket on, slide the pre-filter on, slide your next gasket on, and last slide the lift pump on taking care not to drop the plunger that rides the cam down into the engine. Install washers and nuts and tighten it up. Don’t be surprised if it starts getting tight before everything is squeezed together. That’s the spring inside the lift pump being compressed. Have fun doing that and holding it all in position with the factory bolts. All installed:
Comment for this picture is I left that short little elbow hose going from the pre-filter to the lift pump off. I’d recommend installing it beforehand to make things easier, but it can be done with everything already mounted on the engine. I had to cut maybe a half inch off one end of the elbow to get it to fit up on both barbs without kinking.
Next comes the fun part. If you’ve never used Push-On hose or fittings before they are tough to install. The barb grips the hose very tight. I’ve seen many methods for making things easier. Using hot water to heat up the hose and make it more pliable, and dish soap for lube has good success. I wasn’t too crazy on introducing soap and water to my fuel system though. A heat gun to heat up the hose is also another method. Whatever you choose, you definitely need some kind of lubricant to slide these things on, and even then it’s not a quick process like it is with regular barbs and hose clamps. I experimented with diesel fuel as lube at first, but as weird as it may sound I ended up using household Crisco. People in the machining world may know of its usefulness to keep grinding wheels from loading up when working with non-ferrous metals like aluminum. I figured if it was useful in that unintended purpose maybe it will be useful in this unintended one too. And I was right. Made things much easier to assemble after putting a generous film inside the hose and on the barb. Still isn’t going to make it as easy as regular barbs, but certainly better than nothing. I was even able to pull one of the hoses off the barb with this stuff on it. It was a slow fight, but it did work. I imagine Vaseline would probably have the same effect. Crisco is also an oil, so when it gets warm and mixes into the incoming fuel it’s not going to hurt a thing. The install of this part is fairly self-explanatory: push your hose onto all your installed fittings. Measure twice and cut once here, if you are two short getting these things off is not easy and most just end up cutting the hose off. Take your time so you don’t waste hose or more time trying to pull them off and cut more. The return line is easy. Stick it on the return barb coming tucked up behind the injection pump under the intake manifold and secure with a hose clamp. Here’s a pic of my lift pump area. If you kept the stock filter you can route those too, but I have a new filter so mine aren’t shown.
In that picture near the top left you can also see what I worked up for the injector drain. It’s just a piece of scrap aluminum with an M8 x 1.25 hole tapped in the top, and a ¼” NPT hole tapped in the side with a ¼” hose barb installed. This is an area where I’ve seen everyone go about it different ways. Some make a custom pipe fitting by tapping the top of a ¼” pipe plug and screwing it into a tee that ties into the return line. The most crude and basic method would be to just cut the line off right before the banjo, clamp a piece of hose over the end, and run that into the system somewhere convenient. Come up with whatever you want just don’t forget about it…
So now for the fuel filter. There was a dual filter/water separator unit floating around on eBay that was a Donaldson brand and I did consider that. Right now there is a dual filter base being offered on eBay that accepts 2 micron filters for those who want to go that route. Cummins Diesel Remote 1 Micron Fuel Dual Filter Mount for Cat 1R 0749 SHD | eBay
I ended up going with a NAPA 4770 Filter base. It has two ½ NPT inlets and outlets which is exactly what I needed. One inlet from the lift pump, outlet to the injection pump. The other inlet tied into the injector drain, and the other outlet converted to my bleed screw. The base accepts 1”-14 thread filters. I used a Fleetguard FF5319 from Cummins, but like I said any 1”-14 filter will work. You’ll need two ½ NPT x 3/8 NPT bushings for the main inlet and outlet that your barbs will thread into, a ½ NPT x ¼ NPT bushing for the injector return, and one of the ½” plugs supplied will do for the bleed screw. Here it is all installed:
Something I may end up changing in the future is drilling that boss centered in the filter mount for 1/16 NPT and installing a plug there for a new bleed screw that is easier to get to, the highest point in the fuel system, and makes less of a mess. But for now sticking with the plug. Also I’m going make a new injector drain block that is thinner and has 1/8 NPT threads, along with a clearance hole to bolt it to my mounting bracket I’m getting ready to show you, as right now it’s just hanging from the injector drain line.
Final step in this process was creating a mounting bracket to hold my new filter base. And it wasn’t too difficult. A piece of 3” x 3” x 4.5” aluminum angle did a nice job and I used the factory fuel filter mounting holes. I milled two 3/8 slots in the one end of the angle to adjust how far in or out from the motor I wanted to hold my filter, then measured how high up I wanted the filter to sit on the other end of the angle. Tapped two ¼-20 holes at approximate location and bolted it all together. About two hours of work that was mostly consumed by trying to work around that annoying wiring harness that runs right across the top of where the old filter sat, but in the end turned out as a nice clean install that with some paint could look factory. I used two M8 x 1.25 flange head bolts in the existing holes that the old filter housing bolted to, and two stainless ¼-20 cap screws and washers to mount the filter base to the angle.
Time to fire it up. If you have one of those little 12 volt transfer pumps for changing oil in power equipment etc, now is the time to use it. If you try to hand prime the system using the plunger on the lift pump you’re gonna have some sore arms by the time you get it running. They’re like 20$ for one at Harbor Freight, rig that thing into the feed line somewhere, open your bleed screw and let it pump until you see diesel. Makes an hour job turn into a 2 minute job. Once it’s running check for leaks, monitor fuel pressure, just give it a good 5 minutes or so to make sure everything is as it should be. When you’re done, reinstall the fuel tank and whatever else you removed to give yourself working room.