Getting up to speed with the 94'-98.5' 12V engine

[ISX]

To help those who are new 12V owners, this will give you a rough, possibly detailed idea of how this engine is set up. I made this so people won't have to read for months trying to understand each part and understand the engine, or other brand diesel owners wanting to know how these work so they can help someone else. First we have the specs from the factory of the 1994-1998.5 12 Valve Cummins. There is already a good/complete set of specs for these trucks. 1994-1995/1996-1998 There were hardly any changes from the 1995 to 1996 power differences, mainly just different fueling to provide more power and a slight change in pistons. Year to Year changes can be found here. Here is the part layout of the engine to get familiar with. There is no ECM (Engine Control Module) on the 12V Cummins. The chip on the firewall is a PCM (Powertrain Control Module) and serves only to provide sensory information, it controls nothing about the engine except some timers for the grid heaters and such, the engine does not rely on it at all otherwise. Any error codes from it will concern pointless sensory things which might help but it will tell you nothing about any engine issues. I think there are only 17 possible codes that can be thrown if that gives you an idea.. That list is a full list, most won't apply. If you haven't figured it out thus far, the cummins is an inline 6. The pistons are set to where they have running mates, which are pistons that move together, though on different strokes (one is on compression while the other is on exhaust). Running mates consist of 1/6, 2/5, 3/4. Knowing this will help you understand when adjusting valves since you watch running mates a lot to find TDC. The 12V uses an inline injection pump called the Bosch P7100. It uses 12mm plungers to push fuel much like a "mini" inline 6 engine. Each plunger (piston) is for each individual piston. The plungers are forced upwards by a cam that pushes the plungers up individually based on firing order (153624). Above the plunger is fuel which gets there by means of a little hole (spill port) on the side of the barrel (cylinder wall). As the plunger comes up, fuel is initially pushed back out that hole. The plunger itself eventually covers that hole and because it is sealed, fuel is compressed and after reaching a predetermined pressure, shoots out of the injection pump's delivery valve (high pressure check valve really) and into the injection lines. As line pressure exceeds injector pop pressure, they pop and fuel is injected into the engine. There is a lot more to how it works and how fuel is metered which can be seen here. The injection pump is "turned up" by means of adjusting a fuel plate and AFC settings which allow you several means of fine tuning the power and smoke output. I have articles on this since it is always asked about. Fuel Plate/AFC~Starwheel/Smoke Screw. Fuel is returned from the injectors straight back to the fuel filter, keeping them at lift pump pressures. The only fuel that gets returned is the fuel from the overflow valve in the front of the injection pump. The injection pump's internal pressure (not injection pressure) is regulated at 25-36psi, though up to 45psi is fine. Pressure is regulated with a overflow valve which is just a spring that seats a ball until pressure overcomes the spring and pops the ball out of it's seat, relieving pressure until the ball reseats, thus regulating pressure. The injection pump is driven off the cam gear in the front timing case. The injection pump itself has a tapered shaft that goes into the gear that drives it with just a nut holding the gear on the shaft. The most common way of of timing it is to take the #1 delivery valve out (which takes a special socket, or mess up the teeth with channel locks), and sticking a dial indicator into the hole so you can measure plunger lift. Here is a table showing what lift should be based on CPL number and timing desired. The engine is barred over until proper lift is seen on the dial indicator. The nut holding the gear onto the injection pump is then taken off and the gear is popped off the tapered shaft with a gear puller. The engine is then barred over to absolute TDC since that is what the plunger lifted is based on. The gear will turn but since it is not bolted to the injection pump, the injection pump will remain at the same lift as before. You then tighten the nut on the timing gear back up and confirm you are at TDC and at the lift desired (timing desired). Here is a more detailed writeup of this procedure, remember to refer to the aforementioned table to get lift specs. Fuel is delivered to the injection pump with a mechanical lift pump. It uses the engine cam to push a lobe on the pump which "pumps" fuel into the engine. This is seen as a pulsation of fuel and the pulses get faster with engine RPM since the cam is pumping it faster. It has a manual primer button for bleeding air out of the fuel filter. A fuel heater is right next to the lift pump and consists of a fine mesh filter (bug screen) and the actual heater element. The heater is typically trashed since it never seems to provide any benefit. There are 2 types of fuel filters. The first few years (94'-95' I think) used a spin on fuel filter. The later years (96'-98.5') used an element type fuel filter that goes into a canister. To change the canister version, you look at the yellow lever on the front part of the filter housing, this lever is a valve. Under that valve is a long shaft going to a hose (should be a hose there anyways), put a bucket under that hose as the entire contents of the fuel filter will drain out of that hose. Move the lever towards the engine and it will open the valve and all the fuel will dump. Loosen the nut centered above the fuel filter canister which will lower the canister as it it loosened. The nut will not come out/off, it just spins and is kept in place by some means of connection. At the bottom of the aforementioned valve and maybe off to the side a little is a sensor wire which can be tracked to a connection and disconnected, that is the water in fuel light sensor. Now you can loosen the nut completely and the canister drops down and out. The element pulls right out and a new fuel filter can be installed which should have had 3 new o rings, 1 for the outside lip of the filter (squared edged o ring), 1 for the inside of the filter, and 1 for the inner ring of the canister. Get clean oil on all of these so they will seal correctly. Reinstall and prime the filter using the lift pump primer and by loosening the bleed screw which is a small screw on the top of the filter housing that screws into a larger screw (banjo bolt). Bleed until the air bubbles stop and the fuel is continuous. Loosen slightly injection lines 1, 2, and 3 and crank until it tries to start or fuel comes out of those injection lines, then tighten them back up and start the truck. It will run rough until the air bubbles completely purge out of the system. The fuel shutoff solenoid is the only thing that lets the engine run or stop. It is the only thing controlling it since the engine is entirely mechanical. Aside from the usual glow plugs, the cummins' use grid heaters. This is a coil in the intake manifold that gets hot so all air getting sucked in is heated. How long the grid heaters run and cycle is determined by the IAT (intake air temperature) sensor in the intake manifold. These trucks use a wastegated turbo called the HX35 (WH1C on 94's). They are wastegated in the range of 15-23psi depending on the model of engine. These turbos should not be used for anything over 35psi. They all use 12cm exhaust housings. The wastegate line runs over the top of the engine and tees into the AFC. Being a 12 valve, there are 2 valves per cylinder. They are not hydraulic or anything thus they must be adjusted every 25-50k miles. 15k is better of course. Intake lash is set to 0.01" and the exhaust lash is set at 0.02". Here is a writeup on how to adjust them. The power steering pump is below the injection pump and is driven by the vacuum pump in front of it. The vacuum pump has a gear on the front to mesh with timing gears as it's means of getting powered. The vacuum pump runs a number of things like the HVAC, cruise control and 4wd axle engagement. Leaks will cause the HVAC to default on defrost vents only. The cruise control unit is under the drivers side battery. It works off of vacuum pressure and is a pain to fix once they have gone bad, though cleaning the actuators does help or even fix the issues. RPM sensor is on the front of the engine above the damper. It is a PNP type proximity sensor I believe. The engine itself is direct injected with the injectors off to the side a little. They did not put the injectors directly centered in the bore until the later 1998.5+ 24V's. This means the pistons have a cone that is to one side of it to accommodate the offset injector. That's it for now, let me know if you think something else should be here. I might get some pictures in here.

[fishslayer]

thank you for your post,being the new proud owner of a 96 ram 2500 4x4 i found it very informative.my truck is bone stock with 260k on the odometer.the only issue i have had is the t.c. lock/unlock at crusing speed.after considerable research and checking grounds,checking charging system for a.c. current(thanks moparman!)cleaning and adjusting t.p.s. voltage cleared up the problem.voltage was .58 at idle adjusted to .90 this raised 3rd to 4th shift points slightly and improved trans. operation thanks again guys for the info.i will keep you posted as i make upgrades and share any useful information i find along the way.

[ISX]

thank you for your post,being the new proud owner of a 96 ram 2500 4x4 i found it very informative.my truck is bone stock with 260k on the odometer.the only issue i have had is the t.c. lock/unlock at crusing speed.after considerable research and checking grounds,checking charging system for a.c. current(thanks moparman!)cleaning and adjusting t.p.s. voltage cleared up the problem.voltage was .58 at idle adjusted to .90 this raised 3rd to 4th shift points slightly and improved trans. operation thanks again guys for the info.i will keep you posted as i make upgrades and share any useful information i find along the way.

I'm glad it helped someone. I wish I could be more help with auto's but they are a mystery to me.

[YabbaDoo]

thank you for your post,being the new proud owner of a 96 ram 2500 4x4 i found it very informative.my truck is bone stock with 260k on the odometer.the only issue i have had is the t.c. lock/unlock at crusing speed.after considerable research and checking grounds,checking charging system for a.c. current(thanks moparman!)cleaning and adjusting t.p.s. voltage cleared up the problem.voltage was .58 at idle adjusted to .90 this raised 3rd to 4th shift points slightly and improved trans. operation thanks again guys for the info.i will keep you posted as i make upgrades and share any useful information i find along the way.

ok.. What is the "t.c. lock/unlock" I think for the t.p.s. you mean throttle position sensor??? and how do you adjust the voltage... Being new and trying to learn the abbreviations...

[Rogan]

Torque Converter lock/unlock.