Diagnosing any issue on a 12V

[ISX]

Seems a lot of people don't even know where to start or what to look for or anything, so I'm gonna make a complete list of everything to check off the list that could possibly be a problem. I encourage everyone to comment on mistakes I made or additions to be made to this list.

I am going to also put a number 1-5 between least likely (1) and most likely (5) based on what seems to always be trouble with these things. Like a dirty fuel filter is an easy culprit that people who buy a new truck can overlook if it's their first diesel, so it would be a 4 or 5.

This will be pretty general so you guys will have to google some things or start a thread on something specific if you want. I can't go into detail about each thing in full because you guys would be scrolling down what I wrote for an hour

All vehicles in the simplist form need 2 things. Air and fuel... So I will start at the beginning of each (air filter and diesel tank) and work my way up.

Fuel System

The fuel systems main enemy is air followed by fuel delivery at the proper pressure and rate. This will detail each thing that can be a suspect.

[*][3] Diesel Fuel Tank -- Does it have fuel? Is it gelled? The fuel filter holds a lot and can give the illusion that it does for a while. The tank must also not have bacteria and crap in it that makes the diesel worthless. The fuel must be good. Diesel doesn't seem to go bad over years but like I said, bacteria does form. It's like slime on the fuel filter. Fuel also gells if it drops to a temperature of 20*F and will need an antigel. Cold climates usually add this at the station so if it is a reputable station (trucker stations) then you might not worry about this at all. If you live in a considerably colder climate (-20*F), you might consider adding some or ask the station how cold their fuel gels at. Gelling is just like it sounds, it forms crystals and turns into jello. It won't flow through the fuel filter and therefore won't run. Add antigel to the tank and warm the engine with the block heater which should radiate heat into the fuel filter. Otherwise pull the fuel filter and add some of the antigel to it as well. For emergencies, they make diesel 911 which is a hard core antigel which works faster. Use this crap sparingly if you really need it as it has no lubrication properties. Regular antigel isn't much better but that stuff is pretty harsh. Luckily the P7100 is lubed by engine oil but the lift pump isn't.

[*][3] Fuel Gauge -- Does it work? This seems to be rather obvious but if you recently dropped the tank and reinstalled it, you could have put the float in wrong and it could be hitting a high spot in the tank making it seem like it has fuel. I think

[*][2] Lift Pump -- Is it supplying fuel to the fuel filter and giving good pressure? Most likely you will need a fuel pressure gauge to confirm this which is installed after the fuel filter. If the pressure is low you can slowly clamp the rubber part of the return line and see if the pressure goes up. If it goes up, then the overflow valve is bad. If it doesn't the lift pump is bad or a filter could be clogged. Sometimes the oring for the primer can go bad and become an air leak.

[*][3] Prefilter/Fuel Heater -- This is on the side of the lift pump and has a very fine metal screen filter that occasionally needs cleaned. The fuel heater itself is plastic and has a tendency to form an air leak over time. The fuel heater has a tendency to also burn up so if the connector is melted you can disconnect the wire so it doesn't light stuff on fire.

[*][5] Fuel Filter -- Is it getting fuel? Is it clogged? Does it have water in the bottom? Are there any air leaks? The water in fuel light might be on if there is and you would need to drain the water out. Water isn't exactly a fuel... Be sure to clean at the bottom of the fuel filter canister of it is dirty. The resistance of the water "connects" those 2 metal terminals and turns the water in fuel light on. The fuel filter is also another culprit for air leaks. Make sure the o ring the fuel filter seals with is good and not doubled over (did you take the old one off?, are you sure?..)

[*][3] Fuel Shutoff Solenoid -- Does it work? The solenoid is an automatic way of pulling up a manual lever that lets the injection pump "pump" fuel to the injectors. It engages when the key is in the start position and holds in place when the key is in the run position. These like to burn up or the relays go bad. You can hit the starter for a second and leave the key in the run position and walk around and see if the solenoid pulled the lever up. There are 2 relays that run this (one to engage it and one to hold it) and if one goes bad then will either go up when in the start position then drop in the run position, or it won't go up in the start position but in the run position you can push the solenoid up by hand and it will stay there. If neither works then you may very well have a burnt up solenoid. Another thing is that the solenoid sometimes gets out of adjustment and doesn't pull the lever up far enough. That is more if you messed with it though, I doubt it does this over time. However a weak solenoid might need some adjusting to compensate.

[*][5] Overflow valve -- Is it crap? The fuel pressure is regulated by the overflow valve which is basically a blow off valve that opens when the required pressure is reached. The spring inside it easily wears out so you will get low fuel pressure over time which will equate to low power. A fuel pressure gauge will tell you whether it is bad or not. Remember that a bad lift pump, fuel filter, can also cause low fuel pressure.

[*][1] AFC housing -- Is it working correctly? I have seen an AFC that is locked up and this will limit the amount the fueling arm within the pump can move, limiting power in a big way. You can take the AFC off and put 10psi on it (wouldnt go over 50psi) to see if it moves. Should go 1/4-3/8". Make sure all the lines are hooked up to it as well. One goes from the intake manifold to it and another goes over to the wastegate on the turbo. If the lines leak then it will leak the pressure out and do the same thing. The pressure of the turbo drives the AFC foot forward. Make sure the fueling arm actually hits the AFC foot as well. It can drop under it sometimes.

[*][1] Fuel Plate -- Same with the AFC foot, the fueling arm can run under it and cause full fueling issues. Make sure it's adjusted correctly if you have those symptoms.

[*][1] Idle Screw -- Is it adjusted correctly? If you recently messed with it, it might be too low. 12 valves have no computer so it if it is too low then there won't be enough fuel to start it. The do relax over time so the RPM slowly drops over the years. On a cold engine it might be too low to start so you can step on the pedal a little and it will start right up. Some trucks like to have the pedal stepped on while they start even in the summer, no clue why but they do.

[*][1] Injection Lines -- Make sure they are tight. Probably pretty rare to not notice fuel shooting out but figured I better list this. If they are bent or something then they won't be happy.

[*][3] Return Lines -- These have a tendency to leak over time because of the nature of copper sealing washers. One way to avoid this is to always use new copper washers instead of reusing old ones. They form to the surface so using an old one has an old form and you are overlapping it with a new form and it accumulates into an air leak.

[*][3] Injectors -- Make sure they are actually getting fuel when you are cranking by loosening an injection line and seeing if fuel is shooting out. This is also how you get air out of the injection lines. The injectors can be dirty and not fire right which will cause some running issues. They can stick open and cause a hot cylinder which can melt the whole piston and will be seen as excessive smoke since they are leaking fuel the whole time. Pop pressures wear down over time but they should all wear relatively equally. Having them reset every 100-200k miles will keep them properly tuned.

Intake/Exhaust

Problems with the intake/exhaust are mainly lack of boost and proper temperature of air for the conditions along with issues on the exhaust side. Here are all the things of suspicion.

[*][2] Air Filter -- Air filters get dirty over time and the filter minder lets you know when it's time to change it. If you have a dirty turbo compressor, you may check to see if your air filter is properly sealed. Crappy filters (K&N) will let that dirt straight through so make sure and get a good one. Not much else to say, pretty obvious stuff here.

[*][2] Turbo -- The turbo itself must be in good working order and it seldom isn't as long as it has had good oil pressure its entire life and hasn't been glowing red. There should be minimal side to side and in and out play in the turbo shaft. Make sure the clamps for the air filter and intercooler tube are tight. A bad clamp can cause boost leaks at high pressures that can overpower the clamp. I will cover the wastegate further on.

[*][2] Intercooler -- The intercooler may get dirty over time and cause a rise in temperature. Pretty rare since the radiator blocks any engine oil slinging around but it's a good idea to power wash through it every now and then. The clamps on the boots are the main issue here. Crappy ones can leak. The intercooler might also develop cracks though as the sides of it are made of plastic which don't take well to shrapnel of some sort.

[*][3] Grid Heater -- The grid heater can stick on from a bad relay since these things require a lot of power which means a lot of heat which the cheap relays don't like. If you notice your voltmeter is staying down, this can be a culprit. They should cycle on and off for 5 or so minutes idling after startup. They can also NOT work and this can be the cause of bad starting. This goes back to the relay or further back to another wiring issue. Checking for power at the relays would confirm which.

[*][2] IAT Sensor -- The intake temp sensor only turns the grid heaters on by seeing the temp of the intake air and serves no other purpose on a 12 valve. If it somehow goes out, the grids will not work. I think the wait to start light just stays on all the time if it goes out.

[*][3] Valves -- Valves need to be adjusted every 75,000 miles or so. They can get out of adjustment and cause efficiency issues. If they are too tight, they can stay open and cause chugging sounds as the piston blows the air back out the valves.

[*][3] Wastegate -- The wastegate sometimes gets a lot of buildup or general corrosion and seals shut. This means the boost will go as high as it wants and if the engine is turned up, you could risk blowing a head gasket. You can take the wastegate line off from the AFC and put an air hose to it (no more than 50psi ish) and you can watch it on the turbo and it should open around 20psi. It only moves 1/4" or so. The HX35 can overspool and basically blow itself up if you run it hard enough (45psi+ or so). 35psi should be the max limit you set for the HX35.. Above that it is out of its efficiency range.

I might add more about different components of an engine. Any suggestions?

[ISX]

Forgot timing I'll do it later.

[Rogan]

this should be a sticky, IMO.

[ISX]

Maybe one of the moderators can make it one :lmao2:I'm still in between how to organize everything. We have 10 stickies or something in this section...

[Rogan]

haha! that's what I was hinting at ;)