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Old 02-07-2006, 01:46 PM
Mailguy Mailguy is offline
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1994 Chevy Blazer won't start

I have a 1994 Blazer with the Vortec engine which ran fine all day Saturday on the mail route and right up until I shut it down. I got in to drive it on Sunday and it turned over fine, the electric fuel pump is working, but it won't fire (no spark at the coil or plugs). It seems to me that the cause is more likely the module than the coil, but is there any way I can tell for sure without any testing equipment?
I understand I can take the module in and have it tested by an Auto Parts place, but I'm not sure where it's located on the motor.
Any help would be great! I've had to drive my stand-by vehicle and really would like to get this back on the road soon.
Thanks.
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Old 02-07-2006, 03:39 PM
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The coil usually goes bad before the ignition module.
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Old 02-07-2006, 03:55 PM
FieroSpeeder FieroSpeeder is offline
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i found more ignition modules go bad then coils.
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Old 02-07-2006, 04:15 PM
DRIVERIDERNGINE DRIVERIDERNGINE is offline
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If I were you I would take off the distributor cap and see if shaft is turning before you did anything else. You could also check if there are 12v at coil terminal. You said you don't want to test anything, so I would check the distributor first. It is a very easy thing to do, and will pinpoint the problem.
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Old 02-07-2006, 04:30 PM
DRIVERIDERNGINE DRIVERIDERNGINE is offline
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This should solve the problem...The most common tip-off to coil deterioration is difficult, unreliable starting. To test the coil, remove the ignition cable that connects the coil to the distributor at the distributor terminal. Hold the end of the cable about 3/16 in. away from a grounded component and crank over the engine. A bright blue spark should jump the gap. If the spark is weak and yellow (and the points, condenser and battery are in good shape), the coil is producing weak spark voltage. First, do this one morning when your engine is cold. Then recheck the coil the same way when the engine (coil) is very hot, like after a hard trip. Remember, a coil, like any other metal component, expands with heat and the windings may be making contact when the coil is expanded but not when cold, or vice versa. If there is no spark at all, but the headlights go on and the motor cranks over, then the problem must be either: (a) key switch not making contact to ignition wire; (b) ballast resistor or wires to and from key have opencircuited; (c) coil is now history; or (d) the switching mechanism (points or amplifier) malfunctioned.

To determine which part is defective, look at "The Basic Wiring Diagram of Virtually All OEM Ignitions."

Step 1: Put a test light between point A (+ coil terminal) and ground. The light should go on and off when the key goes on and off. If it does go on, proceed to Step 2. If it doesn't, try this. Take a jumper wire from the + battery to the + coil terminal. Now have a friend crank the engine over while you hold the high voltage coil wire (point C) about 3/16 in. from ground. If you get a spark with the jumper wire on, then plug the high voltage coil wire back into the distributor and the motor probably will start. If it does, the problem is probably, first: (a) burned-out ballast resistor; (b) bad or broken connection (usually as the wire passes through the firewall); (c) bad contact at the key; or (d) broken or cut wire (in the middle of the wire, as opposed to (b), which is a bad connection at the end).

Step 2: Move the test light to voltage point B; that is, negative coil terminal, and ground. Have a friend crank the motor over. The light should blink on and off, or at least waiver as the points or amplifier open and close.

1. If the light does not go on at all, either the coil primary is open-circuited (remember, there was voltage on the (+) coil terminal), or there is a short circuit in the points/ amplifier or the wires going from the (-) coil terminal to the points/amplifier.

To determine which, if the light did not go on, disconnect the wires on the negative coil terminal and reconnect the test light to this negative terminal. If the light goes on, there was a short in the points/amplifier or wires to the amplifier/points, and the coil is probably okay.

2. if, on the other hand, the light stays on, without blinking on and off, then the problem is probably not in the coil but rather there is an open circuit in the points/amplifier or the wires leading from the negative coil terminal to the points/amplifier.

3. If the light does blink on and off, but you only get a little wimpy spark, or no spark at all, then the problem is in the coil secondary. If you have an ohmmeter, put it between the coil high voltage output and the negative coil terminal. You would expect to see between 1,000 and 15,000 ohms. The higher the quality coil, the lower the resistance.

However, if the test light blinks and you only have a weak or no spark, change the coil and see if the engine runs better. Never forget that coils have many modes of failure, not all of which are easy to spot.

Oh, and the ignition module is off of a terminal on the coil. It should be between the distributor and coil in simple terms.
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Old 02-07-2006, 05:16 PM
Mailguy Mailguy is offline
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One More Possibility???

I appreciate the answers so far. While I was waiting for a reply, I looked at the coil in my spare mail vehicle and it was the same, so I swapped the coil from the '94 into it and it fired right up (I did it that way because the braket in my older truck was harder to remove). Therefore, I take it the coil is at least good enough that it is not waht is preventing start-up.
I also went ahead and took the ignition module to two different auto parts stores and they each tested it three times to get it hot and see if it would fail then (though I didn't think that would prevent initial start-up cold). It passed all 6 tests.
I am wondering now if the likely source of trouble is the 'pick-up coil' (which I didn't know existed)?
It seems I need to pull the ditributor to replace it and I was told ther is no way most auto parts stores can test these.
Also, where is the ballast resister. This might be an easy replace??
What say you all?
Thanks again

Last edited by Mailguy; 02-07-2006 at 05:19 PM. Reason: Additional info
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Old 02-07-2006, 05:36 PM
DRIVERIDERNGINE DRIVERIDERNGINE is offline
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The ballast resistor is off of the positive coil terminal.
As I said before...I would check the distributor yourself just by and looking at it.
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Old 02-07-2006, 06:37 PM
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One thing you should try and this will be easy being you have another truck, swap the coil wire that runs from the coil to the distributor cap. Otherwise, yeah your going have to replace the other parts mentioned earlier.
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Old 02-09-2006, 12:49 AM
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One thing I did have had trouble with one of my s-10's was on the firewall there's a little power strip with two bolts that usually has two to three red wires. That run to it. It's above the passenger side valve cover. The problem was there was no power to this spot. I knew it was always live there even without the key was off, it was live because there's a direct connection from that to the alternator, which you can also trace back to the battery. So one day I did test it. And found out there was no power. So what I had to do was run a new wire from the alternator to the firewall power strip and bolt it on. The truck would turn over. But it wouldn't start and there was no spark like what you have. And after adding that wire it ran fine after that. So test to see you have power at them two bolts on that tiny power strip.
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Last edited by justen; 02-09-2006 at 12:50 AM.
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