What makes these trucks destroy distributor caps/rotors?

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redfishsc

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Are the Delco 9718Q the right style? Thats the only Delco I see on Rockauto.com

If so, I will order two sets since I have two of these trucks
 

Schurkey

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Always cylinder #5...

The formation of ozone, moisture and crankcase gases all find their way inside the cap. The combination of these compounds with humidity create nitric acid. This is what's eating up cap parts.
Ozone,moisture, crankcase gasses, nitric acid...would affect EVERY terminal in the cap, not just #5.

The problem with #5 is probably not INSIDE the distributor cap, even if the damage is showing up there. The distributor cap is a symptom, not a cause.

As I told him in another thread, I'd be looking at cranking compression, spark plug, and plug wire. Wouldn't surprise me to find that the plug wire has excess resistance, maybe even open-circuit. Fifteen minutes on an ignition oscilloscope would probably tell that tale (although five minutes with an ohmmeter might be just as effective, if not as interestingly.)


Just adding ACDelco spark plug wire information. New wire wound plug wires measure 1K ohms total, while the carbon filament type wire measure 12k ohms per foot. These new one deliver 25% more voltage while keep RFA down.
RFA? Do you mean Radio Frequency Interference (RFI)?

No amount of resistance will change the voltage delivered until current starts to flow. The carbon-rope plug wires use heavy resistance to reduce current flow. The helical-wound plug wires use inductance to reduce current flow. Both types reduce current flow. The big advantage of the wire-wound style seems to be that they have a longer service life compared to the carbon-rope kind--not that they actually work better.
 

redfishsc

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Ok guys so I did several things this evening. The only thing that seemed to "fix" (or more properly, pacify) the problem was replacing the plug on #5.

I pulled the distributor cap and didn't find much corrosion and the posts looked 100% solid (not burned/consumed) . I used some 400 grit to file what little bit of white oxidation was there.

No change.

I adjusted the cmp retard to 0.5(+). It wasn't far off but still out of spec (was +4.6).

No change

Swapped the plug (NGK) out of curiosity with a new one i had spare and viola...... No misfires. Drove it about 8 miles, didn't log (or feel) a single misfire.

I always thought NGK was a good brand for Chevy but not in this truck.
 

redfishsc

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By the way, I will be ordering new Delco plugs and wires, and also cleaning the distributor vents. Just didn't have time tonight for that.
 

Schurkey

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I swapped the plug (NGK) out of curiosity with a new one i had spare and viola...... No misfires. Drove it about 8 miles, didn't log (or feel) a single misfire.

I always thought NGK was a good brand for Chevy but not in this truck.
Nothing wrong with NGK, as long as you have the correct plug for the application.

If it was a matter of "NGK is not compatible with this truck" the other seven cylinders would complain, too.

There's something wrong with THAT spark plug. Inspect it carefully, figure out what happened.
Fouled?
Cracked insulator?
Loose conductor inside the ceramic?
Worn?
Gapped wrong?
Something else?

I'd still test the plug wire and the cranking compression.
 

Gramps

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Nothing wrong with NGK, as long as you have the correct plug for the application.

If it was a matter of "NGK is not compatible with this truck" the other seven cylinders would complain, too.

There's something wrong with THAT spark plug. Inspect it carefully, figure out what happened.
Fouled?
Cracked insulator?
Loose conductor inside the ceramic?
Worn?
Gapped wrong?
Something else?

I'd still test the plug wire and the cranking compression.


Not only that but ac Delco plugs are reboxed from 3 other manufacturers. Ngk, champion, autolite depending on what plug it is. Iirc ngk makes all the ac iridium, and it’s a mix of the 3 for the copper and platinums.
 

454cid

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Not only that but ac Delco plugs are reboxed from 3 other manufacturers. Ngk, champion, autolite depending on what plug it is. Iirc ngk makes all the ac iridium, and it’s a mix of the 3 for the copper and platinums.

I didn't know about Champion and Autolite. I thought NGK make most of them. I have some regular NGKs but they're still sitting in the boxes.
 

redfishsc

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So do i want to order the 9718Q or the 718Q plug wires? Both are Delco, the 718Q is more expensive but that really doesn't mean anything.
 

98 Nitro

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The one with 9 is the cheaper made in China version. Last year I bought the Delphi set XS10241 on Amazon , it's in between in price but was US made i believe and I've had no problems.
 
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