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I've got a problem that has me stumped. (which doesn't take much)

My truck was running okay until a week ago. I was driving around town all morning and went back to my house for a minute to get something. Shut the truck off, went inside for a minute, came back out and tried to start the truck and no dice. The engine cranks fine but it won't fire up.

The red "Gen" light stays on unless I disconnect the battery. Which happened once before a few weeks ago but it stopped after a day so I ignored it.

I have tried using starter fluid with no effect so I am assuming I am not getting any spark. I was already planning to do a tune up so I replaced the voltage regulator, coil, rotor, dist' cap, plug wires and 3/4 plugs. (I'm pretty sure the threads on #4 are buggered up and I don't feel like dealing with it). Hooked everything up and the red light is still on and still get no fire.

I tried hooking a multimeter between the +lead and +terminal then pulling fuses to see if voltage dropped. No luck. (As I am typing this I realize I should try pulling fuses to see if red light goes off. Tomorrow)

The local part store can't test the alternator. (As I am typing I think maybe I should disconnect the alt' and see if that turns off the red light. Good idea?)

I noticed that when I put the -lead back on the battery I hear the voltage regulator and the fuel pump relay click. Is this normal? Looking at the wiring diagram, this may be because one of the POs bypassed the clutch safety.

Any way to be certain I am not getting spark? An induction light would work but I don't have one. I am used to working on motorcycles where I just hold the start button with one hand and pull a plug wire with the other hand. If I get zapped, it has spark.

Any ideas?

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79 LUV
4x4
4sp manual
emissions removed (mostly)
stock afaik

Easy, simple way to check for spark? Take any old spark plug laying around, remove any plug wire, connect the spark plug, lay it against metal on the engine, crank it over and watch for spark at the plug gap.
Generator light should be on with key on engine stopped. Should be off with engine running. Should be no clicking when connecting battery UNLESS key was on.

You could get a remote starter button to turn truck over with ignition on to see if you have spark.Might want to also turn it over with distributor cap off to make sure the distributor is turning too.

I'm guessing stuck voltage regulator or something shorted/dead in the alternator. The gen light should be on if the key is ON but not if the key is OFF. If yours is on all the time (key off) then it has to be something going on in the charging circuit. (Alt or the reg) Because the fuel pump relay and the ignition relay run off the same circuit, that would be why it won't start. Hook a wire from the battery to the + side of the coil temporarily and see if it will fire up. DO NOT leave that wire hooked up as the stock coil is not designed to have full 12v from the battery running to it all the time. I've had one LUV coil blow its top from having full voltage running to it. If you get spark and it fires up (might not run long with no power to fuel pump) then you can figure you have a problem with the alt or regulator.

A little background on the coil power: Key turned to START engages the resistor bypass relay giving coil 12v to generate hotter spark to help starting, the fuel pump is also powered on a bypass. Once the truck starts the key is released to ON and the alternator begins to generate power, the bypass relay turns off, the charging circuit kicks on the fuel pump relay and coil relay. The coil then is getting power passed through the resistor that is mounted atop the coil, which drops the voltage.

Final idea, I did have one 79 LUV that had severely fried wiring, the main alternator wire had shorted to other wires in the harness. Bad wiring can cause all sorts of strange problems.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

Okay, I was away for a few days and finally got back at it.

I followed Egg's tip and used a spare spark plug to test for spark and got nothing. Next I checked the alternator using the tests outlined in the shop manual and found that it was bad. I got & installed a new alt and it fixed most of the problems. Red light is now off, and neither the voltage regulator or the fuel pump relay click as soon as I put the -terminal back on the battery.

So I'm getting pretty excited at this point.

I reach through the window, turn the key, engine cranks hard... nothing. Spray starter fluid in carb, crank, nothing. Still no spark!

So, assuming that all of the parts I got from Nappa are good, what is the next thing to check?

If that resistor bypass relay is fried (or the wires to it) would that prevent the coil from getting any spark or just from getting the little boost when starting?

What is the likelihood that the key switch is bad? Maybe just the lead going from ON position to... wherever it goes... is burned out. (I wish I could ask that more eloquently, but the wiring diagram that would tell me where that lead goes, is out in the garage ).

Cleaver, I removed the rotor cap again to check the points and the rotor was in a different spot so it is turning.

_________________
79 LUV
4x4
4sp manual
emissions removed (mostly)
stock afaik

I'll be doing this tomorrow:
http://www.youtube.com/watch?v=rJYJ3KvPhhY
http://www.youtube.com/watch?v=bl0Z6kbyI0c&feature=relmfu
http://www.youtube.com/watch?v=e66tA43wsNo

_________________
79 LUV
4x4
4sp manual
emissions removed (mostly)
stock afaik

So, I should be happy that my truck is running again. Except that I have NO idea why its running again.

I spent 3 hours trying to diagnose why it wasn't getting spark. Which I should add, it definitely was not sparking. When, for no reason that I can figure, It fires up like nothing was ever wrong. Which is nice except for the fact that, whatever the problem was, is still there waiting to leave me stranded...

Oh well. I guess I'll deal with it when it happens. Until then

_________________
79 LUV
4x4
4sp manual
emissions removed (mostly)
stock afaik

When mine did that, it was a connection on the bottom of the fuse block.

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Click on C.M. logo to go to my webpage


RIP R.J.B.

I'd agree with tilted, fuse block is a constant source of trouble until you clean all those connections. also worth checkingthe wiring at the battery. The smaller wire or the fusible like connection to it could be flakey.

_________________
95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good