1995 3/4 Ton 454 No Spark

[bigj-dog]

Got a truck that has no spark. The problem has been plaguing the owner for a few months. Some days won't start, wait a day or less and it goes, now it's been down for a week. Replaced distributor, had coil tested out at parts store, replaced plugs and wires, still no spark. Fuel sprays from injectors, all lights seem to be coming and going as they're supposed to in dash. Leaning toward ign. switch, anyone know how to check for sure before I plug in the $150 new one and lose all my money for good? Checked all fuses and also removed and cleaned computer grounds on thermostat housing. Ground straps from frame to cab and cab to rear of engine are corroded, will replace tomorrow. BYW this is a 5 speed 4wd truck. Thanks for your input.

[GMMerlin]

Do you have 12 volts going to the coil.
Have you tried a known good coil

[bigj-dog]

I do have power from the red wire to the coil, not sure if its the full 12V or not, because I was just using a test light. I did try a new coil, plugged it in and held it against the original that was still mounted on the intake for a ground, but to no avail. I didn't have my led test light, so I couldn't test the wires to the dist. and from the dist. to the coil, but does anyone know which ones and how much power any of them should show?

[mechhound]

Ignition module?

[bigj-dog]

The new distributor came with a new module in it, of course that doesn't guarantee that it works. I did notice when I had the cap off of it yesterday that there was a sticker on the module that said removing it would void the warranty, so taking it out to have tested is out of the question. I do have another distributor that I know works, guess that wouldn't be hard to switch.

[GMMerlin]

Originally Posted by bigj-dog

I do have power from the red wire to the coil, not sure if its the full 12V or not, because I was just using a test light. I did try a new coil, plugged it in and held it against the original that was still mounted on the intake for a ground, but to no avail. I didn't have my led test light, so I couldn't test the wires to the dist. and from the dist. to the coil, but does anyone know which ones and how much power any of them should show?

First mistake was a testlight.
Always use a DMM and perform a volt drop test to insure you have the proper voltage at the coil.
test lamp just tells you voltage is present (enough to light the test light depending on the impedance)

[bigj-dog]

I didn't have my multimeter with me at the owner's house. Last night I installed new ground straps from the cab to the chassis and from the cab to the block. After that I checked the ign. fuses in the box, no power to any of them with the key on. Engine still cranks, but now the dash lights have disappeared, so I'm replacing the ign. switch after work. Hopefully I'll be able to finish off the thread later tonight. Thanks for all the input so far.

[bigj-dog]

Got column all apart, wiggled ign. switch and dash lights flickered and would come on and off with wiggles. Replaced with new one and lights are all on, ign. fuses in box all have power. Turned engine to TDC, checked dist./rotor and was pointing to No. 1 plug wire. Attempted to start, no dice. Hooked spark tester back up, no spark. Checked voltage at red wire on coil, 12V. Tested coil according to Chilton's Manual, appears to be junk. Will get a new one tomorrow and check that before I put it in to see if I get the correct results. Wondering if anyone thinks that the weak ign. switch was not sending enough voltage to coil and that caused premature failure??

[bigj-dog]

Retested coil with better test leads and it's fine. Turns out that the owner had put the new dist. in 180 off and the spark tester I was using had a blown out bulb so it wouldn't light. Once I got someone to turn the key and I could watch the plug lying against the intake I saw nice blue spark. Flipped the dist. and it fired right up. The moral of the thread is, take the lower cover off your steering column if you have mysterious non-start condition and wiggle and jiggle the ign. switch and see if it starts. Hopefully it'll take you less time than it took me. Thanks for the ideas everyone.