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Pre-ignition / starting problem. Ripping hair out.

18436572

firing order is correct? Figured you checked it more than once, had to ask.

can you record the two different starting scenarios? Maybe a third when you use the kill switch then throw power back to the distributor.
youtube it if you can
 
bradshawtech said:
18436572

firing order is correct? Figured you checked it more than once, had to ask.

can you record the two different starting scenarios? Maybe a third when you use the kill switch then throw power back to the distributor.
youtube it if you can
Click to expand...


I have not checked the firing order, due to how smoothly the engine starts (cold), runs, and drives. I will check it tomorrow though. Couldn't hurt.

For the videos of starting - ya I can do that.

I will make a cold start, hot start with slow crank, and hot start with distributor disabled.

I don't suppose there is a way to post the videos here on the free account?
 
If I am understanding, this is an intermittent condition ? That doesn't seem to care if is hot or cold, or been hot soaked ? After the last few updates I am not sure what the symptoms are. If so then put the timing at 8-12° btdc, and start looking at the cranking system electrical, cables, starter, battery.
 
Wes Harden said:
If I am understanding, this is an intermittent condition ? That doesn't seem to care if is hot or cold, or been hot soaked ? After the last few updates I am not sure what the symptoms are. If so then put the timing at 8-12° btdc, and start looking at the cranking system electrical, cables, starter, battery.
Click to expand...


The problem only happens when the engine is hot. So all of the following is when its hot: Abut 80% of the time it cranks extremely slowly and sometimes the engine just stops turning over. If it does keep turning over, it will start. Occasionally its cranks perfectly and fires right up. So you could try to start 5 times in a row, randomly 1 of those times it cranks over perfectly and starts. It mimics the sound of a almost dead battery or poor battery connection. Like the starter is not getting enough power. However, if disable the distributor, the problem vanishes and it cranks over great every time. Engine spins quickly. Then, while its spinning, if re-enable the distributor, it fires right up. Does that make sense? Why does the distributor having power cause the engine to crank slow most of the time, but only when the engine is hot? It must either be per-ignition, or could this be a power wire somewhere that is grounding out? Some wire that powers the distributor? But if that's the case, why would it not happen when cold?
 
This problem happened with the stock starter, as well as with the brand new high torque gear reduction mini starter that I just installed.
 
The starter motor needs much more amperage when hot. Since the symptoms are the same for both starters, I am leaning toward cables, connections, fuse links, and battery. The ignition switch is also suspect here, esp with rapid key cycles and it works. The switch can be adjusted on the steering column, or simply may just have badly worn arched contacts. When cranking the distributor is firing the spark plugs, and drawing current. It maybe that firing of the plugs is enough resistance to over come the current flow resistance issue. All this is just an area that needs to be tested and proved good, if it is all good then my next step would be the distributor and or the ignition control module, even the pick coil can cause random driveability.
Is the battery a side or top post? Cables are original, replacement, have had ends replaced ? Age of battery ? Voltage at battery when resting and when problem occurs ? What is the condition of the wiring at the starter, when you replaced, did anything looked melted, or have replacement terminals ?
 
78 GMC Jimmy said:
Anyone else have any ideas on what I might try in order to fix the starting issue?
Click to expand...
Yes, go check the timing manually like has already been suggested multiple times in this thread. You know, something down the spark plug hole while turning the crank. They make a tool for it, but you can use other objects, as long as they can't get lost down there or scratch something up. You can also put your finger on the spark plug hole and feel for compression, but you may need a helper. Then fine tune the position with your foreign object and see where the timing mark lines up.

th


Also, have you had a timing light on it cold (when starting fine) and hot (when cranking slow) to confirm the timing is really changing?
 
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78 GMC Jimmy said:
All else aside, it ALWAYS cranks great with the distributor kill switch turned off. So it MUST be per-ignition. It cant be the battery or battery connections. It has to be ignition related. Am I wrong?
Click to expand...
This is the logic I'm using.
 
You know, I wonder if it could be a bad pickup coil, or even bad module, such that when it's hot, the connection is bad and it interprets the zero crossings out of phase.
 
i made that tool out of an old spark plug for the engine in question, and a 2" 3/8 16 bolt. Ground the tip round, knocked the porcelain out of the thread nut, tapped for 3/8 16, thread 2" bolt. Easy
 
Does it still have the vacuum diagram underhood? Is it this?

R.8e17b2e86d52cd8157781c6307051950
 
Wes Harden said:
The starter motor needs much more amperage when hot. Since the symptoms are the same for both starters, I am leaning toward cables, connections, fuse links, and battery. The ignition switch is also suspect here, esp with rapid key cycles and it works. The switch can be adjusted on the steering column, or simply may just have badly worn arched contacts. When cranking the distributor is firing the spark plugs, and drawing current. It maybe that firing of the plugs is enough resistance to over come the current flow resistance issue. All this is just an area that needs to be tested and proved good, if it is all good then my next step would be the distributor and or the ignition control module, even the pick coil can cause random driveability.
Is the battery a side or top post? Cables are original, replacement, have had ends replaced ? Age of battery ? Voltage at battery when resting and when problem occurs ? What is the condition of the wiring at the starter, when you replaced, did anything looked melted, or have replacement terminals ?
Click to expand...
God info. I guess I could eliminate all electrical possibilities by just hooking jumper cables from a known good battery to the starter, turning the ignition on, and bumping over the starter with a screwdriver. Thoughts?
 
not sure, maybe. Depends on where the cables are connected. Jumping with a screw driver is do able, and could point to the ign switch and related wiring. The arching by the screw driver might damage the studs. If you had a jumper with a momentary push button that would be my go to. Voltage drop tests will do the same. Do you have digital volt meter ? To do a voltage drop test, place positive lead on large battery lug at starter solenoid, the other lead to battery positive, activate the ignition switch and watch the voltage reading. Okay result will be under 1 volt, less than .5 volts is ideal. Do the same for the negative cable ends. If the reading is higher than 1 volt, while the symptoms are present, there is high resistance in that circuit. This test can be done on any non solid state circuit you can get to each end of.
 
So I swapped out the coil, cap, rotor, and ignition control module. As usual, the engine fired up quickly and easily with the first bump of the key (cold) . Tomorrow I will run it around the block to get it fully warmed up, and then see what happens.

Note: I checked the old cap to see if it lost the center pin. Nope. That coil must have just died for what ever reason when I pulled the cap the other day.
 
The problem remains. Those new distributor parts did not help. Set the timing to maybe 22 when cold. Hot, it looks like its now at around 14. This happened once before, I thought that the timing somehow moved to a lower number on its own but I assumed I had made a mistake somewhere.
 
Have to verify the timing marks. Have never seen a balancer ring move willy nilly, I suppose it could happen I would expect some rpm relate vibrations to be felt.
 
Update:

Compression on #3 is 125 lbs.
Timing chains slop:

You can put an 8 inch breaker bar on the cranks and the end of the breaker handle can move back back and fourth just under an inch before it spins the rotor (excluding the play in the tools). So if there was zero play on the socket and zero play in the pivot on the breakers, then there would be almost 1 inch of play in the timing. Is that too much?

Maybe the chain heats up and expands when the engine is hot, exacerbating the problem?

Maybe I should just throw the 195 thermostat away and drop in a 160? That would probably eliminate the symptoms of the problem.
Or maybe just use the distributor kill switch to get the motor turning over and then flip the switch to activate the distributor so that it will start?

Thoughts?
 
So I ordered a 160 thermostat, and I plan to flushed the cooling system as well. Might install some electric pusher fans as well. Tired of dealing with this problem.
 
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