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1989 K5 - Gradual Learning

First 4x4 - learning basic maintenance / upkeep and maybe some small mods.
Overview Gallery Discussion
Wes Harden said:
Did the fuel pressure ever get checked, and how old is the fuel filter ?
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Yep, pegged at 14 PSI while the truck is running. Drops fast once I shut the truck off though.

Fuel filter was replaced in August of 2019 (151,350 miles). The K5 now has 162,800 miles on it. So the fuel filter has about 11,500 miles on it.

Wes Harden said:
also thinking an adjustable fuel pressure reg might be a good investment. DO you remember the injector part number.

Also if you haven't done so yet advance the base timing 2-4° before top dead center.
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The injector part number I used was ACDELCO 2172286. I think my timing is currently set to a flat 0°. I'll play with that a little bit and report back.
 
It couldn't hurt to change the filter. I think they recommend every other oil change. I had to change the fuel filter on my C10 before it hit 10K miles. New tank and 50% of the fuel lines are new, still plugged up before 10K. Pressure was fine at idle, but dropped off under hard acceleration.
 
Yeah the fuel filter is also a water trap, if the gas stations have water in the tanks the fuel filter won't last as long. Ethanol fuels have an affinity for water.
Your injectors are correct for a 350 so that is good, 61 lb hr.
 
"Well, there's your problem"... or at least there's part of it...

I went to adjust my timing like @Wes Harden suggested. I checked it with the timing light after getting back from a long drive. The Blazer was stumbling bad, even in Park.

The timing mark was jumping all over the place, bouncing around like crazy. I called @ZooMad75 and let him know that I thought I had found the problem. I figured it was a bad EST/ESC system. He wisely told me to disconnect the EST/ESC wire (tan wire with the black stripe). I did that and the engine was still struggling bad. I was disappointed but we agreed that I should probably just move forward with advancing the timing and see whether that helps it out at all.

While looking into the engine bay, I happened to see that the #3 spark plug wire was arcing:

Then I walked around to the passenger side and I saw that #4 was arcing even worse than #3:

I am pissed because I just replaced the plugs and wires not too long ago. I must have over-tightened something, or ripped a plug wire off the wrong way, or whatever. It was always a massive PITA to get the plug wires off, I had to yank on them with all of my strength before they would come off. Then I'd slam my hand into something and bleed. I hate dealing with them.

I feel pretty stupid for not seeing it before tonight. I don't know how I missed it... but at least I have a major clue about the stumble.

It's hot as all hell right now, but I'll remove the plugs and wires for those cylinders tomorrow to look for cracks.
 
They'll need to be replaced. Yes sparkug wires can be a pain in ythe ass to remove.
Always twist the boot and pull from the boot, never the wire. I try to old the boot at the metal clip to the plug.
 
Yes had one similar in the 90s worked fantastic made out of spring steel. Unfortunately it grew legs, and I was never successful in finding another.
Still need to twist the boot with that tool
 
mrk5 said:
Damn! I didn't know such a tool existed!
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One of my techs had one and when the rest of us in the shop saw it, we each ordered one.

It’s been super handy. But like Wes said, give the boot a twist first. Then use the tool.
 
For anyone who sees this in the future and is interested in picking one of those tools up...
  • Doesn't look like Taylor 43392 is available any longer on Summit, but I found it here for $12.
  • Lisle 51250 looks to be similar and is available on RockAuto for $6.50.
 
I went through a nice little rabbit hole tonight.

I fired up the K5, and it was not arcing at all. I couldn't believe it. I even turned the lights off in the garage to be sure... it was not arcing on either side.

Next I pulled the #3 and #4 spark plug boots. They had damage on them. I pulled the plugs and could not find any damage on them at all.

Through this whole "lean stumble" saga, I've read many times on the web that my ignition coil could be related. I found a thread online about brand new spark plug wires arcing. When reading that, one user mentioned that a weak coil can actually lead to the spark jumping through the boot because it isn't able to produce high enough voltage for the spark to jump the spark plug gap.

I said okay, let me try testing my ignition coil. I found this image online and went for it.


1694740184050.png

The thread with this picture in it said that test #2 is misrepresented on the diagram, so I did it a slightly different way than shown.

Here were my results:
  • Test #1: Infinity (Expected)
  • Test #2: Infinity (Unexpected, but my ohmmeter's lowest setting was 200... I'm not sure whether it was an accurate test)
  • Test #3: 7.12 kOhms (Which is a clear failure)
So, right now my shopping list is a new (higher quality) set of spark plug wires. Would you guys also pick up a new coil if you were me? GM Genuine is $48 on RockAuto, NGK is about half that price. I am sorta thinking why not, especially since it failed one of the tests.

Here are pics of my spark plug wire boots, if anyone is interested.

#3 Cylinder:

PXL_20230915_005626319.MP.jpg

#4 Cylinder:

PXL_20230915_005651188.MP.jpg
 
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I’d do a new coil and wires. MSD used to be quality but I’ve run into a few bad parts out of the box with them in the past few years.
 
I always keep some old plug wires around. You can often swipe a boot if you need to replace one.

I also have often shortened many plug wires, and recrimped the end back on.

Martin
 
82355 said:
I always keep some old plug wires around. You can often swipe a boot if you need to replace one.

I also have often shortened many plug wires, and recrimped the end back on.

Martin
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I might have some old wires laying around somewhere... it would be a good test to put good wires on and see whether the arcing happens again after the truck is warmed up.

82355 said:
Do you still have the EGR disabled?

If so, fix it.

Martin
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I still have it disabled. That thing is a nightmare, but I feel like I have learned a lot since the last time I tried walking through the diagnostic procedure in the shop manual.
 
If A-B is open circuit, the primary winding is broken. Kind of amazing it would run at all, unless a) it broke during disassembly/handling or b) the leads weren't making contact with one of the terminals. The secondary resistance being a little low may or may not be a problem. It could be just a different wind than what was available when the manual was written. OR, some of the secondary has shorted, which will give less voltage, but possibly still run.

I know you were chasing spark earlier in this thread, but the normal symptom of a cracked plug wire is that it misfires more and more as the load increases. I guess it's possible that a partially broken ignition coil works better when there's less dwell, so the idle speed falls apart. Maybe more likely that the timing gets messed up by sparking when the dwell starts instead of finishes. If the timing gets off by too much, the rotor is not pointed at the terminal and spark gets weak/missing.
 
Blue85 said:
If A-B is open circuit, the primary winding is broken. Kind of amazing it would run at all, unless a) it broke during disassembly/handling or b) the leads weren't making contact with one of the terminals. The secondary resistance being a little low may or may not be a problem. It could be just a different wind than what was available when the manual was written. OR, some of the secondary has shorted, which will give less voltage, but possibly still run.

I know you were chasing spark earlier in this thread, but the normal symptom of a cracked plug wire is that it misfires more and more as the load increases. I guess it's possible that a partially broken ignition coil works better when there's less dwell, so the idle speed falls apart. Maybe more likely that the timing gets messed up by sparking when the dwell starts instead of finishes. If the timing gets off by too much, the rotor is not pointed at the terminal and spark gets weak/missing.
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I think I should retry test #2. I read that the correct way of doing the test was to place the leads on the upper-left slot and the bottom-right slot. My ohmmeter showed infinite resistance and I guess I would expect to see a flat "0" on the 200-ohm scale. I was having to use jumper wires because my leads were too fat to fit into the slots. Maybe those jumper wires weren't firmly contacting the terminals.

I'm inclined to replace the coil because it's not too expensive, but then again I can always just start with spark plug wires and go from there. The only risk is that my coil is weak and that's truly causing the arc under high load. If that were the case I guess I'd burn right through the new wires too.

Thanks for the detailed response Blue. I can't say I'm not learning anything through all of this.
 
shima said:
I found a thread online about brand new spark plug wires arcing. When reading that, one user mentioned that a weak coil can actually lead to the spark jumping through the boot because it isn't able to produce high enough voltage for the spark to jump the spark plug gap.
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I can't see the science in that. The plug wire and boot must have enough insulation to withstand (greater than) the maximum voltages ever seen. The arcing just means that hole in the boot is lower (or similar) resistance to the plug gap. The spark plug may be firing in parallel to the arc, but as you put more load on the engine the resistance of the plug gap increases, making this problem worse.

(There is an old saying that electricity follows the path of least resistance, but it's not really true. Electricity follows all available paths, inversely proportional to their relative resistances.)

Definitely start with the plug wires because you know that's a problem. IMO changing one thing at a time is better.
 
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