85 chevy blazer full size 305 4x4 ingnition problem

I recently have been having this problem where my truck will drive for a while and die at the worst time like an intersection or miles from anyone. I thought it was the power cables hooked to the battery for the MSD ignition
when this first started happening I replaced the connections and it didn't happen for a while. Then I was driving along and at a intersection the truck died and I tried to start it, it would just turn over until the battery was dead. I checked the spark plug wire for a spark and there was nothing. I got it to start again after a while and then it just stalled out once again this time I was still in the parking lot of a store so that was good. I removed the after market ignition stuff and plugged the old HEI stuff into the distributor and it still didn't have a spark so since its been a while since tuned it up I did a full tune up that included; spark plugs, cap, rotor, wires, coil, oil, oil filter and air filter. After I did all this I tried to take it out for a test drive and it only ran for about ten minutes in the yard before I took it out. It got across the street before it died out again with no spark. I thought it might be a the HEI ignition module so I took that off and went to auto zone and they tested it. There was a row of red lights on the top that went to green as it was tested. When since my truck wasn't doing the stalling out thing right then I ask them to test it a couple of time until it got warm. It kept working after ten try's like it should and then one light (the dwell light) stayed red. Then he tested it a couple more times and it worked again like it was meant to. I decided to change that as well just to be sure. I thought that after all this I would have it working properly again so I took it out and it stalled just like its been doing. There is no spark going to the spark plugs. There is gas and it does turn over. I am out of ideas though. I need alittle help to track this problem down. And some diagnosing help also.
Thanks in advance, D.L. Man
P.S. Sorry for talking you ear off.
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DL,
When you get a no-start, check the postive lead from the IGN switch to the ignition coil/HEI module (fat red wire). It should have +12V with key to run and while cranking. If it don't, you either have a shorted wire or a bad IGN switch.
Doc

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anyone.
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Doesn't the ignition lead go through the starter before it goes to the coil? Is that the one that I should check? I have been having some trouble with the starter not starting like it should. I have turned the key on and it just clicked. I would try it again and sometimes it would work. It hasn't been that annoying to get me down there to look though. The problem with the starter has been going on long before the engine stalls.
I will check that ASAP. Thanks. If you have any more suggestions after I fix that would be helpful. The magnetic pickup is something I haven't looked at could that be a problem?
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Not through the starter, but there is a lead from the IGN switch to the starter solenoid. The IGN switch has a lead to the solenoid and a seperate lead for the coil.
You want to check the lead to the coil that runs from the IGN switch. The starter solenoid lead obviously works fine as it will crank but won't start. If this is the stock distributor cap and stock plug on the end of the coil positive, pay close attention to the connection between the lead wire and the plug it terminates into. It (the plug) has a tendency to loosen and while it might test fine, as soon as you plug er' in it wiggles loose and no juice to the coil.

Bad or dirty batter connections most likely.

If you are talking about the inductive pickup coil, yes it could be the problem. Test for voltage to the coil first, check the coil next, and if both check ok it might be the pickup coil.
Doc

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I was just about ready to mention the p/u coil and i see D.L. is already on it.. Good deal, i bet that is the problem. Too bad they are sucha bastard to change.
--
Mad-Dog
'79 Chevy K-10
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seperate
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If this stuff doesn't work could it be a computer problem? I haven't tried the truck yet but if it dies again could there be a computer in there that is doing it?
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Yer' truck don't have one bud.
Doc

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that
I didn't think it does but where does those wires go that plug into the distributor?
And what is that plug that goes into the carburetor? One wire goes to the thermostat and into the carb and then into the wires near the distributor. Aren't those computer controlled or am I wrong. Do you know what those wires job is?
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What wires? There are several and I don't feel like describing them all. What color, where do they attach to the distributor?

Again, location of wire? Where does it "go in" to the carb?

The sensor sticking out of the t-stat housing just regulates voltage based on heat. Anything hooked up to it has some function related to temp, such as EGR on/off, spark timing, etc.
Doc
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There is a harness that comes out from the firewall(I think) and then it goes into dist. It has 4 or five wires on it and they all go into a plug. the only other wire that plugs into the dist is the battery wire but that is on the other side of the dist.

Its a 2 prong plug that is located on top the carb near to where the gas line comes in.
I think this was just a "what does that do and why can't I put a holly carb in its place, because of it question"

Thanks Doc.
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On another note, the test I suggested in my first reply almost a week ago takes 10 seconds to do. Just do it and take it from there instead of futzing around on here with what it "could" be!
Doc

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the
distributor.
I have tried that and it did have voltage to it. I haven't been able to test it when the car dies because I was out away from the tester. I think that was the problem too. However, the first night that this happened to me I still had the MSD ignition hooked up and my friend was helping me crank the car over. They left the ignition on in the car and I crossed the battery plug with the ground (at the distributor) and fried the battery line going the MSD ignition. Meanwhile the car still wouldn't start even though at that time there was power to that wire at least. After I hooked up the old plug into the dist. I did set up a switch with 12 volt power in case it does die again I can flip the switch and add 12 volts to that line. If it does start up after that I know that the power to that wire is stopping.
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An 85 Blazer would have ESC, so yes, there is a computer of sorts.
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"Of sorts" being the key term. I'd hardly consider it a computer as it doesn't control anything but spark..............
Would you consider an MSD or Mallory ignition system "computerized?" Not hardly...............................................
M
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that
What does the ESC do? Where is that located? Someone told me that the computer would heat up and stop sparking. But once it cooled down the car would start again. that is similar to is happening with me. If there is a computer "of sorts" that connects to dist then that is the last thing that I haven't checked. I did like doc said and I followed the switched wire from the dist down to a wire harness that was on the firewall. And from there I followed it into the cab. As far up as the switch attached to the column. But the wire seemed fine and there was power to it into the switch. If it goes out later I will test that wire again to see for sure.
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It controls the ignition timing based upon signals received from the knock sensor. IOWs it's a spark retard control.

Above the glove box. Silver box, slightly smaller than a cigar box.

More or less true... The ESC module intercepts the signal from the pole piece in the distributor, the signal is sent to a buffer and outputted back to the ignition control module to fire the coil.

From your other posts you've found the 4 wire connector coming out of the distributor to the firewall (goes from there to the ESC module) disconnect the 4 wire connector and on the side of that 4 wire connector that is attached to the distributor, jumper the green wire to the black wire, this will by-pass the ESC module, if the engine now runs, you've found the problem. If this fixes it, you'll want to make a more permanent repair by cutting and soldering the green wire to the black, you can do this either at the 4 wire connector or, plug the 4 wire back together and cut and solder the green to black right at the ESC module harness under the dash. The ESC module does not need to be plugged in once this is done.
There is/was actually a TSB on this procedure back in the mid 80s authorizing it, reset the ignition timing to zero degrees from the OE spec of 6 degrees.
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wrote:

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Thanks for your help. It hasn't died since I checked the wiring to the ECS and to the ignition switch. There was a power wire that was spliced into the bat line of the dist. I simply spread the insulation apart more and spread the wires apart and threaded the other wire through it like a needle and rapped in around its self. I guess that was the problem. The wire to the ECS was loosing contact and dyeing. I am curious what you meant by resetting the timing to 0 and the OE spec of 6 degrees?
Thanks goes out to Doc too. You helped allot with me tracking this little problem down.
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I did like was suggested and removed the ecs module from the dist. Its weird now but I seem to have more power. I think that the module was retarding my ignition to much and to often. It seems to have a new lease on life(my truck). Since it wasn't the MSD ignition that was going out and affecting my truck I was wonder if I should hook it back up? The truck died on my when I had the regular ignition hooked up. And it died after I traced a wire that was loose. Both times the MSD ignition module wasn't hooked up. I think that it would be safe to reinstall it. I did notice that while it was hooked up it kept my spark plugs cleaner. The old ignition wasn't that great at sending a full spark because the spark plugs were always covered in carbon.
I can't wait to see what it does now that the dist doesn't retard the ignition to much.
D.L. Man
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