Ground reference

Is anyone here familiar with Ground Reference? My son was teasing a coil on my old '92, as a possible reason why his '93 wouldn't start. He left the coil on the '92, and merely unplugged the two feed wires, and the high tension lead, and plugged them into the other coil. He proceeded to crank the engine, and of course, it wouldn't start. He then returned the wires to the original coil, still on the block. It refused to start. I asked a retired mechanic near me about all this, and he said that it had lost its ground reference, and told me a few steps to get it back. Well, it didn't work, so he said to install a new crank sensor. We'll be doing that soon, but, I guess my question is, Has anyone else had to deal with this, and just how did you go about regaining the Ground Reference? Thanks...

What lost "ground reference" ? I have never heard of such a thing.

The ignition coil is tested with volts/ohms multi-meter, as is the Crankshaft Position Sensor.

The problem arose because he tried to start the engine with a coil that was not grounded to the engine by itd mounting bracket, but merely hanging on the wires. I had out the wires back on the original, installed coil, but, apparently, ehr damage was done. Yes, I got mu timing light to confirm that there was indeed a spark, but I had no way to determine that the spark was occuring at anywhere near the right time. Once he gets the CPS installed, I'll go through the steps again.

In fifty years of wrenching, I'd never heard of this either. The way the mechanic explained it, it made perfect sense. It has to do with the coil seeking a ground through various other sources, most notably through the next device in the series, the crank sensor, usually with bad results.

There is no electrical connection between the body of the coil and any of it's wire connections.

A faulty coil can damage the PCM, but the body of the coil does not need to be grounded.

Electrons will take every single path to ground possible. I mean "EVERY" single path to ground. They will flow as much as possible through the links of least resistance but they can literally spread across the entire car. For example, It is a well understood fact that cars with an MSD electronic ignition system (aftermarket system used on race cars) MUST be disconnected before welding anywhere on the vehicle. Even if the user is welding on the rear of the vehicle and places the ground 6 inches away, everything that touches ground is going to get a surge of electrons going through it. On an MSD ignition, this surge can destroy the system.


Any coil is a high amperage device and must be properly grounded. There are two ground planes for a coil. The first is the connection between the feed line (+) and ground (primary side). This is what charges the coil. The second is the end of the sparkplug which acts as the ground for the secondary side. This is what discharges the coil. The current flow on the primary side is significant but shouldn't be enough to blow a sensor. The current flow on the secondary side is more than enough to blow any sensor.


Are you sure that wire between the coil and the distributor didn't discharge anywhere while he was testing? I have seen people trying to check for spark using the main coil wire. They often ground it to the frame. This isn't a good idea. By checking a spark plug against the block at least you are using the proper path. On most cars, the negative post of the battery is directly connected to the block first and then tied into the frame. By checking for spark on the block you are following the path it was designed for.

heyhar said:

The problem arose because he tried to start the engine with a coil that was not grounded to the engine by itd mounting bracket, but merely hanging on the wires. I had out the wires back on the original, installed coil, but, apparently, ehr damage was done. Yes, I got mu timing light to confirm that there was indeed a spark, but I had no way to determine that the spark was occuring at anywhere near the right time. Once he gets the CPS installed, I'll go through the steps again.

In fifty years of wrenching, I'd never heard of this either. The way the mechanic explained it, it made perfect sense. It has to do with the coil seeking a ground through various other sources, most notably through the next device in the series, the crank sensor, usually with bad results.

Click to expand...

When I first attempted the procedure, I removed the two-conductor plug from the original, still-installed coil. I found which one was the ground, and which one has 12V. I was told to supply an extra ground, so we stripped a tiny bit of insulation from the ground wire, and using an alligator clip jumper, connected ti to the negative post on the battery. We then removed the #1 spark plug lead, and jumpered it to the ground post. Next move is to crank the engine, which we did. Then, remove the grounds, and put the lead back on the plug. Simple, right? Well, it didn't start. Not only that, I ascertained that there was no spark, using my timing light. As soon as my son gets the CPS installed, we're going to attemp to see if there's a spark. Maybe it'll start! Anyway, failing that, we'll have it towed to the mechanic's home shop, where, hopefully, he'll spend five minutes, and make us both look like fools...
He explained that, although not common, a ground reference problen may show up in various Ford and Jeep models. I don't see the connection between two very different makes and OBD systems, but at this stage (it began in February), I'd be willing to try anyyhing...

Did you happen to do a primary vs secondary coil resistance check? I wonder if the one you plugged in was shorted? Could have fried the computer if it was.

I believe it was brand new. I will see my son tomorrow, and ask him.

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