Ignition Coil Fuse

[k4tmc]

Well...the old VX has left me stranded twice now in less than a month. The problem is that the ignition coil fuse blows. The first time (April 25), I did not know what happened and had it towed to the local Isuzu repair specialist. After 2 days of investigation, they were unable to determine what caused the fuse to go. They gave me a few extra fuses, just in case it happened again.

Yesterday, it did. After going through 3 fuses, I had to have it towed again. Of course, after the tow trip, they cannot find the problem again.

They suspect a wire is shorting out somewhere. But both times I was going down a smooth road with no excessive bouncing. The first time, early morning, the engine was hot after 20 miles. The second time, late afternoon, I had only driven one mile.

Anyone have any ideas?

Henry

[etlsport]

its not a terribly large circuit. 4 connectors, 6 coils and 2 grounds.

my best guess is that its grounding in the fuse box, or a wire ran close to the engine block has melted

the other thing to look at is a bad ignition coil. if one of them is bad it could just be drawing a lot of power and not actually shorting. This would cause a fuse to blow too. Or if one is not giving any resistance, you would just ground right out since the circuit literally goes from the fuse to the coils to ground with nothing in between. There is a "condenser" in the system located "top right front of engine" not sure what this does, but it also provides a ground in the system

The wire from the fuse box to each component is black/orange according to the manual, so you can keep an eye out for them

Check section 20 of the electrical troubleshooting manual in the downloads section, it outlines the system very well.

From the manual...

With the starter switch in On or START, battery voltage is applied to the Powertrain Control Module (PCM), various engine sensors, and the ignition coils. When the engine is cranked to start, the crank shaft position sensor (CKP) sends timing information directly to the PCM, which breaks the ground path in the primary of the ignition coils, thus creating a high voltage secondary impulse which fires the spark plugs, and the engine starts. The PCM receives information such as firing order and starting timing at each ignition coil from the CKP sensor. The PCM relies on information from the various engine sensors to determine correct ignition timing.

[k4tmc]

Well, almost a year later, I think I have solved this mystery. After the initial episode last May, I wound up disconnecting the condenser since it was just a single wire connection. By the way, the condenser helps remove the "ignition noise" that you sometimes hear in your AM radio when there is not a strong station close enough. Since I am only a FM-type there was no concern about the ignition noise. Anyhow, back to the problem... This seemed to help for about 6 months. Then the fuse started blowing again but very infrequently - once a month...until a few weeks ago. In a one week period, I went through about 2 dozen fuses. All of these occurred while driving down the road. Finally, one evening after going through a few fuses on the way home, I needed to go back out to the grocery store. I could not get the VX started due to fuses popping. Raised the hood and pulled all of the ignition coil wires. No fuse pop! Started replacing the coil wires one at a time. The last one caused a fuse pop. Looked around the coil area and everything looked good, except for the accumulation of dirt on top of the engine and coil wire. Then I noticed that the coil wire was actually touching the engine. So, bent the wire up a little and tried another fuse. Engine started! Went back and cleaned the engine and ignition wire, and found that the wire insulation had been removed presenting bare copper wire. I have now wedged a piece of high temperature plastic between the wire and engine as well as a plastic tywrap to hold the ignition wire away from the engine. Note that the subject ignition coil is the one nearest the air intake filter.

I suspect that over time, the combination of the accumulated dirt and the high temps had slowly rubbed the ignition wire insulation away, thus exposing the wire. When I unplugged the condenser wire last year, I must have move the wire enough to correct the problem temporarily.

So, I hope this is the end of this problem and the story will be helpful to others.

Now dealing with catalytic converter problem - see recent post.

Henry
(160K miles)