P-Pump Cummins Shutoff Solenoid Swap

Help! My Truck Won’t Start!

So there we were hundreds of miles from home, pulling a trailer, with a truck that wouldn’t start. Geez…aren’t 12-valves supposed to be reliable!? As it turns out, it was no big deal, but a non-starting truck can definitely give you that sinking feeling. We’ll explain how this can happen, what you can do about it, and what solenoid can do for you.

We could tell by the blue wiring cover that our factory shutoff solenoid had already been replaced at some point. Still, it was hit-and-miss on working, so it needed replacing.

One of the more common problems on virtually all ‘94-’98 Dodges, as well as some generators and tractors, revolves around the P7100 injection pump. While the pumps themselves are extremely reliable and hardly ever fail, the shutoff solenoid that is mounted to the pump fails often. Our ‘95 project truck, dubbed the Green Monster, already had its solenoid replaced somewhere down the line, but it still failed yet again (probably because it was a Chinese-made knockoff version). The shutoff solenoid activates a governor lever that allows fuel to flow into the pump. This allows the engine to start, but also to stop because cutting off the fuel is how virtually all diesels are stopped from running.

Our new shutoff solenoid and brackets (in case anything was missing) came from LarryB. Larry makes all sorts of electrical parts for diesels, including a shutoff solenoid kit. There’s even a more advanced version, with a fusible link and 70-amp relay.

Our buddy Rex Gully helped us out with the solenoid install so we could take some photos. Gully’s first step was to take off the intake horn because it makes it easier to gain access to the shutoff.

No Pain, No Gain

So our solenoid was bad, but fortunately, we weren’t dead in the water. Thankfully, even if your solenoid is weak, you can still almost always start the truck by turning the key on, walking around underneath the hood, and then manually moving the governor lever back towards the firewall of the truck. It’s a pain (and something that would be horrible in traffic) but at least that will get your truck going down the road again.

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There’s a small vertical lever down on the injection pump where the shutoff solenoid connects. This is the lever you have to turn back towards the truck (with the key on) if you get stranded.

Still, we weren’t excited about the prospect of hopping out and opening the hood every time we needed to start the truck. We knew we should contact our buddy Rex Gully who owns Allied Diesel in Windsor, California. Like us, Rex is another 12-valve aficionado and owns a fleet of them, including a 10-second race truck. Gully recommended using one of the shutoff solenoids from LarryB’s Diesel Parts. Larry has been in the business for decades and has all sorts of electrical parts for worn-out Cummins engines, including starters, relays, cables, and yes…shutoff solenoids.

A couple of bolts and a cotter pin were the only things that needed to be removed to take off the factory (or in our case previously replaced) shutoff solenoid.

Here’s the new LarryB solenoid compared to the old one. As you can see they’re virtually identical, except Larry’s hasn’t seen the ravages of time.

Simple Shutoff Solenoid Installation

With Rex manning the wrenches, we were walked through the fairly straightforward process of replacing the shutoff solenoid. It’s a task your average shadetree mechanic can perform, as only basic hand tools are required. There are still, but only, a couple of steps where things can go wrong. After around a half-hour of installation and adjustment, we were back on the road again. Now we could truck happily down the road without worrying about the next time we turned off our Cummins engine.