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Hate to say it, but another problem, SBC only starts sometimes

I hate to say this, because you are so frustrated, but you actually have a reasonably simple to find problem.

One that fails to crank for many minutes or even hours, is much easier to figure out than one that only does it for a few minutes at a time over a period of days.

When it fails to start, that is a good thing, not a bad thing. Then you have a shot at finding out what is wrong.
Remember the basics.

Compression.
Spark at the correct time.
Correct fuel/air mixture.

If you have all three, the engine will run.
Its unlikely that you are losing compression, since once it goes, it does not usually come back.
So, if it won't start at night, first open the hood with the lights out, and crank it while watching the engine for sparks.
Look especially around the coil and dizzy. You should not see any. If you do, then you need to correct that first thing.
New cap, new coil, new wires, whatever.

If you see no sparks, and it still does not crank, pull a plug wire, put a screwdriver in the cover, and put the metal part next to something grounded.
Crank it and watch for a nice blue spark.
A thin, weak, yellow spark is probably your problem.

If you have a good spark, pull the plug and check for wetness. Either gas or oil.
If its wet, you need to pull all the plugs, being careful not to mix up the wires.
Crank it over a few times to clear out any gas in the cylinders.
I can revive most any sparkplug with a propane torch. Hold them with pliers, get the firing part red hot. If there is some carbon fouling, you should see it burn off.
When they are clean, put them back in.

After it starts running good, it would not hurt to replace them.

If they were wet, after cleaning them, take off the air cleaner and tie your choke open.
It will start just fine hot as it is without the choke.

Then, try cranking it.

If the plugs were dry, and you had good spark, take the air cleaner top off, dribble a small amount of gas in the top of the carb (NOT starter fluid) and put the cleaner top back on.
If it tries to start, then you have a delivery problem with the carb.

Just because the carb has gas going to it, does not mean its going into the engine.

All this is assuming that it cranks nice and fast and does not try to start at all.If it cranks slow, charge the battery or jump it off.
If it backfires, sputters, seems to kick back and partially stall the starter motor every so often, then we need to check other things.

I know you have already checked some of these, but remember you are trying to diagnose an intermittent problem which means, you have to find it when its not working.
So, if you had spark before, you may not now.
 
I know that, I am just far too short tempered for my own good.

I hadn't thought of the screwdriver in the dark thing before.

I checked the plugs on cylinders 1,3,2 and 4, and they didn't seem wet, but when I wiped them on a white rag they left quite alot of some kind of dark residue.

It won't be very easy to reach the rear-most 4 plugs, due to my strange manifolds. (how many people have the manifolds that go up and over the sparkplugs? They collect between cylinders 5 and 7, and cylinders 2 and 4.)

I put the battery on the charger last night and it is cranking plenty fast, but isnt catching at all. It is just spinning.


Well, just tried the screwdriver thing, and we don't have spark. It must be the connections on the ICM, because yesterday I just wiggled them and we had spark again.
 
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With the way it is acting I'd say to change the pickup coil and ignition module. I always Change them both because if one is going out the other is probably on the way.
 
big reaper said:
With the way it is acting I'd say to change the pickup coil and ignition module. I always Change them both because if one is going out the other is probably on the way.
Click to expand...

My '88 ate ICM's like freakin candy. :doah:
I actually carried a spare. :haha:

I bet yer overheating the ICM.
 
My 88 camaro would kill a module just about every 3 months I got real good at changing them on the side of the road. I had it to the point I could change it in about 20 minutes. I finally added a heat sink grease for computers called arctic silver and never had to change it again. Now I use that on every module I install.
 
Well, No progress was made over the last few days due to my dog running off. I spent the last few days looking for her.

Until today, I decided it wasn't doing any good to keep looking, so I jumped head first into the K5. I picked up another dizzy, pulled out the ICM, then pulled out the one from the truck, and discovered that they will not interchange. The ICM I got from the new distributor has 2 prongs on one side, and 3 on the other. Whereas the one I pulled from the truck has 2 on each side.

Well I decided to take the old one to town to have O'riellys check it, and out of three times, it passed twice and failed once.

I won't be able to get a new one until Tuesday, so I will update this again then.


(how much of that white grease is there supposed to be? On the one I took out of the truck the entire bottom side was coated, except for the holes the screws go through and the the terminals.)
 
The new one should come with a packet of the grease just use it everywhere except where the bolts go just like the one you took out.
 
I take it your truck doesn't have the stock distributor, as my '86 (and AFAIK, ALL '86 SBC trucks) used the 5-pin (3 on one side, 2 on the other) module. That module is intended to loop back through a crude computer of sorts... trying to remember what it was called. EST or something. Either way, it could retard spark as I recall.

I hacked mine by jumping 2 of the 3 pins together to bypass the EST system under the dash.

Don't know that it's relevant, but your last post jogged my memory.
 
Ok, well the new ICM is in, and we got a lot of nothing. I bet the plugs are still fouled. I pulled all of them, and they were all pretty nasty. They smelled gassy.

I burned off what I could, but still they wouldn't spark.
Guess i'm waiting another week.

Being poor sucks.
 
You need to slow down. Start fresh in your mind. Stop thinking that swapping/throwing parts at the problem will make it go away. Other than a $10-20 multimeter (if you don't already have this necessary tool), I see nothing to indicate more money should be spent at this point. I know how the anger thing works, it clouds your ability to reason a problem out. I'm not preaching, I just know that stepping away and thinking about things for a bit helps.

As mentioned already, when it won't start, the problem being consistent/persistent is a good thing. You know it's an ignition problem, because you lose spark. The thing isn't going to start until you get spark. Lack of spark has nothing to do with the condition of the engine. Until you get spark worrying about any other suspected problem is pointless and distracting you from the known problem. Always fix what you KNOW is a problem first.

Probably better writeups out there, but this is pretty simple: http://forums.carcraft.com/70/661769/general-car-craft-discussion/gm-hei-ignition-module-testing/

Print it out, write it out, whatever, and take your multimeter with you at all times. When it won't start, get to work!
 
I probably have one, but heres the thing. After I got the new ICM in, and before I pulled the plugs out of it, I tried to start it, and it fired a couple of times, it tried. but I couldn't get anything else out of it.

I will look for/buy a multimeter.
 
Not sure if you have harbor freights around, but I got one of their $18 cheapies a few years back, and it's still going. I prefer the digitals. Since you can use them on house or automotive projects, they come in handy quite often.

Electrical problems are a real bear, especially intermittents. Trust me, I've had my share. But throw everything out that you've already done and/or replaced, and start over. It's not like it costs you money to diagnose, other than the multimeter.
 
Well, another little bump. I couldn't find any dead wires going to the dizzy, although I only had a test light.

So I pulled all the sparkplugs, cleaned them, spun the engine over to shove out all the old nasty-ness (the spark plugs did smell quite gassy) then put all the plugs back in, tried it, and got nothing.

I know I do need to actually get new sparkplugs, but I am really on such a tight budget, I'm trying to avoid that.

In other news, the hood spring gave me an un-intentional sleeveless shirt.
 
Well everyone, it is bump time. I got pissed at the Blazer, started messing with my Cummins, got it running after sitting since 09, Realized I need more money to keep messing with it, so back to the Blazer.

I know for a fact now that there is power going to the distributor, but it is not getting to the plugs. All I can guess now is a bad pickup coil? What else?
 
The Griff said:
Well everyone, it is bump time. I got pissed at the Blazer, started messing with my Cummins, got it running after sitting since 09, Realized I need more money to keep messing with it, so back to the Blazer.

I know for a fact now that there is power going to the distributor, but it is not getting to the plugs. All I can guess now is a bad pickup coil? What else?
Click to expand...

Go from there. You've replaced the ignition module, if you still have no spark, and you know for a fact you're getting power in to the dist, coil is what remains.

So as a refresher, before it had the starting problems, it ran fine?
 
Sometimes it would start, sometimes it wouldn't. If it did start, it would run great. Just when you shut it off, there is no way to know if it would start up again.

This time it never started up again.
 
I would go to a junkyard and pull a complete hei distributor that doesn't have the extra plug for a computer and put it in to see if it runs. That will help verify the problem is the dis. Then save up for a new set of plugs.

One tip when looking in a junkyard for good engine parts is to look at vehicles that are wrecked because thats a good sign they were running.
 
big reaper said:
I would go to a junkyard and pull a complete hei distributor that doesn't have the extra plug for a computer and put it in to see if it runs. That will help verify the problem is the dis. Then save up for a new set of plugs.

One tip when looking in a junkyard for good engine parts is to look at vehicles that are wrecked because thats a good sign they were running.
Click to expand...
This is what you need to do.
 
Ok, well I decided I am just going to get a new distributor, I went down to the junkyard today to see what all was there, and I found a 85 K10 that look like it was rolled, and it looks like it has a very clean HEI distributor (it has a red cap, did someone sell them in red?) and there is a 77-85? Impala or caprice. and it has a decent looking HEI distributor in it.

I took the caps of both and they both looked very clean, especially the truck's red capped one.
 
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