12v Cummins FAQ

[ISX]

I will be editing this continually as I think of more..

Thinking of buying 12v, what do I need to check?

Has the Killer Dowel Pin (KDP) been fixed?

How is the front end play?

When did they last change the bearings?

Auto trans -- Does it go into gear well?

Is there a lot of slippage in the torque converter?

Check and see if the fluid is burnt.

Make sure it goes into all gears and locks the torque converter when warm.

Manual trans -- Feel for clutch slippage and how well it goes into gears while driving.

Ask how many times the 5th gear nut came loose and how they fixed it, be weary if they say they welded it as you wont be able to remove the nut if needed if they did..

Check the dash as long periods in direct sunlight will make them hard and crack.

There are 4 bolts holding the AFC housing, one of which should be rounded over (tamper proof) looking the same as the top of a rivet, if they are all regular bolts then you know they have got the tamper-proof one out and messed with the fuel plate (turned it up) and if its an automatic truck, they might be selling it because the more power they got out of it is making the trans very weak.

Lastly, encourage them to let you start the truck "cold", as in having not been warmed up prior to your arrival. Any hard starting issue might mean your getting into a money pit, especially if its over 32*F out.

What is all the Killer Dowel Pin commotion!?

The Killer Dowel Pin (KDP) as its been nicknamed, is an alignment pin behind the timing cover on the front of the engine. It works its way out of position and falls out wrecking havoc. Click here for a writeup on it.

I lost 5th gear!

This is a common problem on the NV4500. There is a nut on the tail shaft which "holds" 5th gear in place. When the nut works it's way loose, 5th gear slides down the shaft until it loses contact with the splines. It is a very simple fix, though to permanently fix it there are a number of solutions. To get to the nut, you must drain the fluid out, remove the driveshaft, and take the tailshaft housing off. That is all that must come off, only the very end.. Then you will see the nut unscrewed from the threads just flopping on the shaft. Screw it back on and get it as tight as possible. There are updated nuts at the dodge dealership that contain set screws to tighten the nut down even further. People have tack welded them but that does not seem to work, if you don't care about ever taking the shaft out or disassembling the trans, then you can Tig weld it all the way around and that is said to cure it for good. There are also fully splined shafts available that allow 5th gear to slide wherever and always be in contact with the splines (the stock shaft is not fully splined which many believe is the root of the problem). If you put the nut back on and just tightened it there are ways in which you can prevent it from working loose. Avoid lugging the engine in 5th, basically keep the engine above 1500RPM, when you lug it, the nut feels each piston stroke and it hammers the nut off. The second thing is to avoid jerky driving in 5th, as in letting off then stepping on it in a jerking fashion.. this torques the nut off..

Cruise Control and/or Vents only blowing out defrost?

This is a very common problem concerning vacuum lines. They will pop out of their rubber connectors or crack causing leaks and then your vents have nothing to run them so they default to defrost and since the cruise works off the vacuum too, it stops working. You will see the little black lines that stem from the vacuum pump that is located behind the power steering pump. They run to the the cruise control unit located under the driver side battery and they also run along the firewall right below where the back of the hood would shut.

If only your cruise control is not working, the unit for the control under the battery may have issues and need to be tested.

ABS/Brake Light is on?

Check the connector on top of the rear differential, check vacuum (94-96'), check the brake switch, also check the ABS sensors.

My dome lights and radio don't work!

This is something most people overlook because of the labeling on the fuse panel. The "I.O.D." fuse is the one that controls the lights and radio, even though the radio has a separate fuse, this one still kills the radio. This fuse is also the one that has a yellow fuse puller on it, the puller only pulls the fuse out a little ways so that the contacts are not holding the fuse tightly allowing you to get the fuse out with ease, so don't try and rip the fuse puller out of the fuse panel as it is only going to go back maybe 3/16".

Why does my temperature gauge fluctuate?

Dodge came up with the idea that to be king of the pulling trucks it needed a big radiator.. Without a load, the radiator is way too big for the engine's heat output, causing every opening of the thermostat to drastically cool the engine because of the inrush of cool water. When the thermostat closes, the engine heats back up and then the thermostat opens and cools it off again. This cycle continues until the engine and radiator come to an agreement with temperature and then the range between opening and closing of the thermostat is only about 10-20*F. When pulling a heavy trailer, the radiator is now sized to perfection and the engine temp should stay around 190-205*F.

Why does my voltage gauge fluctuate on cold starts?

When it is below 60*F ambient temp, you now have to wait for the "wait to start (WTS)" light to go off. This is because the grid heater is heating the intake so that the air is warm enough to start the truck with ease. After the truck starts, it goes into the post-start cycle and will turn the grid heaters on and off to maintain a warmer temperature, this is why your voltage gauge goes up and down since the grid heater draws a lot of power. This post-start cycle will last a while depending on how cold it is. I have seen mine continuing to run up to 5 min past startup, but the longer it runs, the shorter it lets the grid stay on, eventually getting to the point of 1 sec or less then finally just staying off. The other way it shuts off is by going over 20mph. Click here for more info.

Is the oil pressure really 40psi all the time?

No. The factory oil pressure gauge is merely an indicator showing you have pressure. It is either on or off.. If you hook a real gauge up to it, you will see the pressure go up and down with RPMs.

What gauges do I need for a 12V?

There is one main/major gauge all diesels need, and that's a Pyrometer/EGT (Exhuast Gas Temperature) gauge. This measures the temperature of your exhaust and gives you an idea of how hard your engine is working and when you need to let off a little.

The next gauge most have is a boost gauge, which gives you a measurement of the output of your turbo in psi. This is not as critical gauge as a pyrometer but it does serve some good purposes.

Now it is a tossup of whatever other gauges you want. The next level from boost would probably be fuel pressure. It is not that big of problem on 12V trucks but if you want to monitor it and ensure it is running in tip top shape you can get one of them. Not to mention you can tell when your fuel filter is getting clogged.

What is the EGT temperature limit?

This is a debated topic but the rule of thumb is to not exceed 1050*F. After that is where it gets debatable.. This is what I will say and you can use your own judgement. Aluminum melts at 1220*F, however pistons have oil nozzles under them to constantly keep the piston from getting too hot, but that doesn't mean the piston crown gets cooled that well.. So if you can help it, keep the 1050*F as your limit. If your going up a hill, 1100-1200 might be considered "OK", I would make sure it is followed by a downhill and let off though. The range between 1050* and 1200* is pretty foggy and nobody really knows exactly when the piston will start to melt. However, one thing is for certain, never exceed 1200*F. Your risking everything if you do.

What is the normal boost pressure?

On a stock truck the turbo is an HX35 or WH1C (94') and the pressure should be between 17-23psi. The 160HP engines will have 17 or so with the 215HP engines having 23. The turbo is only good to 35psi, past that it generates too much heat to be efficient.

How much boost pressure will the stock head gasket hold?

In stock form it will hold about 40-45psi with some people not having issues up to 50psi. Advancing your timing will lower these limits..

Should I advance my timing and how far can I go?

Advancing the timing puts the power curve higher up in the RPM's, so you will have more power in the higher RPM's and less down low. You will gain some mileage too. Keep in mind the more you advance it, the worse it will start.

The had gasket is said to be safe up to 16* of timing. Stock is between 12.5 and 13.5. The advanced timing puts more stress on the head gasket so if you are running high boost you may want to reconsider, or do something about the head gasket.

How often do I...?

Click here for the entire maintenance schedule.

Edited December 12, 2009 by ISX

[ISX]

How much power does the block heater use?

According to my meter, I get exactly 6.25amps/120volt/19.2ohm/750watts. So to figure how much it would cost you, take 3/4 (750watts/1000watts) and multiply by the amount of time in hours. So 5 hours x 3/4 equals 3.75. That is how many kWh you used.. So just take 3.75 x price of a kWh. If it's 7 cents/kWh, 5 hours would cost you 3.75 x 0.07 = $0.26.

If you have any other questions, I would prefer you post to the forum. You can also PM me but it is nice to have other members jump in on threads and have them fill in gaps that I might not have seen..