'87 R30 died at highway speed - will not restart

[bake315]

Did you check all of the fusible links and all of your fuses? What is it doing? Crank no start?

Hey Vile.  By the time I got the wire repaired between the link and the terminal block, it was getting dark, so I just tried it again (crank, no start), and gave up for the evening.  I'm going to go back in and just replace that link completely - even though it seems to be good the wire going into it got cooked pretty badly.  Going to check the others when I get home, while I still have sunlight.  Fuses have all been checked twice, and are all good.  Fuel delivery to the injectors is good.  I'm going to focus on checking fire tonight, as I'll have someone there to crank while I watch.

If need be, I learned about the trick to check for trouble codes using the check engine light and a paper clip also.

[bd]

You do realize that the melted wire was the fusible link, correct?  The cylindrical swell in the wire at the end of the fusible link ~6" from the junction block is just a molded splice connecting the original link to the factory harness.  Replace the melted 6" link and splice with new fusible wire; see How to make a Fusible Link for details.  DO NOT use regular primary wire to replace the link!

Once a new link is installed, switch the ignition on and listen for the fuel pump to cycle on for about 2 seconds before shutting off automatically.  If the key warning buzzer makes too much noise, close the door before switching the ignition on.

[ehjorten]

For background...a fusible link is a short section of wire that is smaller than the circuit it is protecting.  Typically it is 4 AWG sizes smaller than the circuit it is protecting.  So if you have 14 AWG wire, the fusible link protecting it is usually about 18 AWG.  Now in newer years of these vehicles they switched to square millimeters (mm²) of cross section for wire size.  You can find converters online, but don't get confused with wire diameter in mm.  The wire size that stated in wiring diagrams is cross sectional area or mm².

A fusible link is just normal stranded copper wire, but it is covered by a non-flammable insulation.  Fusible links are there to protect high-current demand items on your truck, like electric fans, starters, etc.  A normal fuse can't handle the high in-rush current that these devices usually demand at startup and over time will weaken the fuse and it will fail.  The modern version of fusible links today are called Maxi-fuses.  That is what new cars use now.

It can be hard to find fusible link in the right gauge at auto parts stores now, but you can get it easily online.

[bake315]

OK, here's where I am.  I made up a new 6" link using fusible wire (looks almost exactly like Vile's tutorial).  It may be slightly heavy  (14 ga.), but at this point I'm simply trying to get the truck to start and run, if only for a moment.  Checked the link at the alternator, actually replaced the plug going into the alternator itself.  Noted the distributor cap was pretty well worn and was contaminated with oil, so replaced it with a new one plus rotor. Reconnected the battery and tried to start. I am definitely getting fuel to the injectors to the point of flooding it. I have no spark.  I have no idea why.  I'm a troubleshooter by nature and by profession (not automotive), and this is really starting to get me down.  Truck was amazing, now all of a sudden it's lawn art.

[bake315]

Could it be the distributor itself?  I'm desperately trying to avoid throwing a bunch of money and parts with a "hang them all to get the guilty" approach.  Just don't have any solid leads. I need to know:

• which components would prevent spark in the event of their failure
• if it really was an overload on that particular circuit, what all resides on that circuit that could have failed
• whether or not those particular components are field testable by me, and what the procedure for doing so would be
  

If there is anything, no matter how remote the possibility, that you guys can think of, I would be very appreciative.

Thanks for all the input so far.  Digging that V3500 crew, Erik!

bake315

[VileZambonie]

If you are getting oil inside the cap, replace the distributor. The pickup coil and ignition control module are inside the distributor. Your module is probably toast from the sounds of it. You can verify, start by checking for spark from the ignition coil while cranking

[bake315]

If you are getting oil inside the cap, replace the distributor. The pickup coil and ignition control module are inside the distributor. Your module is probably toast from the sounds of it. You can verify, start by checking for spark from the ignition coil while cranking

Thanks, Vile.  I'll let everyone know how it turns out.

[bake315]

Okay.  Running once again.  I thought a lot about Vile's suggestion, but then I figured since the pickup coil is outside and in front of the distributor, and I'd already sprung for the new cap and rotor, that pretty much left the ICM. So, in this case, I gambled and bought/installed just an ICM, and she fired up quickly.  So apparently, when the fusible link wire chafed through on the metal edge, it also fried what appeared to be the original ICM.

Now that I'm running again, I can spend time chasing my oil leaks.

Thanks again to everyone for their assistance!

bake315

[VileZambonie]

Glad you got it running. For clarification, the pickup coil is inside the distributor. This generates a pulse signal to the ignition control module which in turn controls the primary side of the ignition coil. The ignition coil is the device bolted to the intake manifold in front of the distributor.

[bake315]

Glad you got it running. For clarification, the pickup coil is inside the distributor. This generates a pulse signal to the ignition control module which in turn controls the primary side of the ignition coil. The ignition coil is the device bolted to the intake manifold in front of the distributor.

Thanks for this.  My apologies for the incorrect coil identification!  Clearly, I continue to not always know what the heck I'm talking about.