Wiring: Engine and Starter
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You may have noticed that I hop around talking about all the different aspects of the Diesel Suburban conversion, and there's no attempt to put anything into order. I take an engineering project manager's approach, and like to break the effort down by subsystems. Eventually, I intend to cover them all, but that will take some time.
Current Status: Based on recent posts, you are probably aware that I've started the engine and pulled the Suburban in and out of the barn under its own power -- a huge milestone for this effort! I expect to get this machine "finished" and into use hauling my family around on weekend adventures -- whether we are on trips to the hardware store for home improvement projects, or driving halfway across the country.
Wires are likely to wind up strewn everywhere during this stage. Be methodical, and all will be OK.
This post: engine and starter wiring. Before this system could be started, I spent a three-day weekend working my way through the wiring harness. Most all of the hardware components had been installed, and I figured I could work my way around the installed components. With a soldering iron and some heat shrink wrap, it's not too hard to lengthen or shorten some wires to put them where they ought to be. Things can be messy, but keep thinking about where things can go, how to avoid hot areas, and ensure that you can access things for maintenance. Wrapping bundles of wires in electrical tape, convoluted tubing, and clamping them does a lot to keep things neat, but you can't panic when things are messy meanwhile. Just work your way through it methodically. I didn't take many pictures, because strands of wire are not terribly exciting to look at.
Because this is a mechanically-injected diesel engine, there are only two wires that are absolutely required for operation. Both of these are connected to the starter. To shut it down, I've installed a "pull to stop" cable in the dash, which cuts the fuel supply to the engine. When the engine is running, however, it would be nice to know what's going on. So, I adapted the GM oil and temperature sensors to be used with the 4BD1T--allowing the instrument gauges to work properly. Because none of the ignition-related components were needed, a large number of connectors were simply removed from the wiring harness -- but this was done carefully to avoid getting rid of anything that might be needed later (for instance, I kept the connector that picks up the signal for the tach).
The temperature sensor was a no-brainer. The GM unit used a 1/4 NPT thread and was simply screwed into the coolant neck above the thermostat. There are four places where Isuzu mounted sensors and switches here, so I picked one whose wires were gone anyway, removed it, and installed my sensor. I had marked this connector when I pulled the harness away from the 5.7 V-8, so I was able to readily identify it and run it to the right location.
This metric allowed the installation of NPT components.
Like the temperature sensor, I wanted to simply plug the GM sensor into the Isuzu engine. I found a tap to an oil passage on the right side of the engine by the bell housing that had been used by Isuzu for this same purpose. I removed the Isuzu sensor and the port appeared to be 1/8 NPT. Wrong! 1/8 NPT adapters wouldn't fit. 4BTSwaps.com came in handy, again, and I found out that this port uses a metric thread. With that knowledge in hand, I hunted around and found AutoMeter part #2269 -- a component designed for exactly this problem. With this in-hand, I was able to install the oil pressure sensor.
With the adapter above, the GM oil pressure sensor was installed on the Isuzu 4BD1T.
I also had to do a couple other tricks to make things work, like bypassing the neutral switch so that I can start the engine. I also had to open the fuse/relay center to get the fuel pump to function whenever the ignition switch is turned on. Otherwise, the ECU doesn't see a running engine's tachometer signal, and shuts off that circuit. I have the components in-hand to allow a functioning tachometer, and I may reverse this process later.
When most of the wiring harness was complete, I looked at the wires coming from the battery and decided that I needed to make some changes. First, I don't like the GM-style battery connectors. They don't look like they have as much contact surface area as top-post terminal connectors. So, I chose a large maintenance-free AGM battery (Duracell's 775 CCA answer to Optima's "red top" AGMs, but at half the price) that had posts, and built up new wires using old-fashioned post clamps.
Homemade battery cables, using #2 welding cable for the starter conductors.
I used the #2 welding wire that I had purchased to do a cold compression check last year. The wires are color-coded in black and red--which might avoid confusion in jump-starting situations. I not only crimped the copper connectors and battery clamps--I coated the wire ends in flux, hit them with a torch, and fed solder into the remaining gaps, making nice, hot joints. I taped the ends for neatness and pushed them into convoluted tubing for abrasion protection.
When I installed them, I was pretty happy with the weight of the cables. There's a lot of copper in them, but I feel confident that there will be no issues starting the engine -- which I've read could require the battery's full current capacity when cold (I might add second battery, but will see how it goes with one, first). However, when I hooked up the positive cable to the starter, I got a little worried. In order to fit this engine into the Suburban without running into the front differential, the geared starter had been modified to mount inverted--putting the cylinder containing the electric motor on top instead of the bottom. Mechanically, this works well, but it points the positive terminal back toward the engine block.
For safety, this boot was placed over the positive starter terminal. It is close to the engine block.
There's enough room for clearance, but I thought about what might happen if I'm working under the hood and drop a tool or metal part down there. A small metal object could wedge itself between this post and the engine block, making for a horrendous short (considering the current-delivering capability in the wires and battery combination) and a very dangerous situation. A visit to O'Reilly didn't turn up a nice little terminal boot, but I found a pair of clamp boots and put one over that wire to keep things safer.
Other electrical circuits will be covered in other posts. I've already mentioned the tachometer, and will cover that when I get around to making it work. I also have a pair of electric fans on the radiator and a the vacuum system that's necessary for my power brakes. I've actually worked on the latter two, but want to know that everything is working properly before I report on them.
-My recipe for success: free markets, more diesel, and less government!