CK5
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84 K20 "Ethel" Not an Sbc/NV4500/241C

Semi restoration of a 1984 K20 pickup. 5.3 LS, nv4500, np241c.
No.. Just got derailed. But I have the inconsistent idle again. It makes me uneasy. I'm wondering if I have a clogged fuel filter.
 
No.. Just got derailed. But I have the inconsistent idle again. It makes me uneasy. I'm wondering if I have a clogged fuel filter.

Surging at idle is most likely a pinhole on the suction side of the fuel system. As air gets in the line, the engine stumbles. Being a governed engine, the governor advances the throttle to compensate. Then when the air bubble passes the speed momentarily rises while the governor reigns it back in. When enough air gets in the line the engine will completely stall.

A clogged fuel filter will restrict power at full throttle. Since you don't have a surplus of power, you'll feel it when it happens. Should be really obvious.
 
That's a huge help. I haven't checked the tanks at all nor the lines. I know my tank valve works but I'm still to much of a wuss to fill that side and use it in fear it won't switch back.
 
That's a huge help. I haven't checked the tanks at all nor the lines. I know my tank valve works but I'm still to much of a wuss to fill that side and use it in fear it won't switch back.

Don't be a wuss. If the tank valve doesn't switch back, just start using that tank. :wink1: :haha:

Actually, if it doesn't switch back, then by definition it doesn't work and you should fix it. The switch is particularly helpful for diagnosing this kind of air leak. If the problem goes away when you switch tanks, your problem is behind the tank valve. If it doesn't, than it's either in front of the valve or you have leaks in both sets of lines.

It's easy enough to replace the lines that you might just replace them preemptively if you don't see any obvious leaks.
 
I actually turned the idle up a tad. Mine doesn't smoke... Weird.
Yeah mine is weird it will have a random stumble and white smoke at odd times but not always and if it warms up usually it goes bye bye. But when I turned up the idle a little it runs perfect.
 
Yes mine was way out of adjustment. I turned it up a lot to get my rpm in a good place when cold.

But it is both engaging and disengaging? So there's no problem in the activation circuitry?

I ask because the stumbling only when cold makes me wonder if the timing advance isn't functioning. It's fed from the same wire as the idle advance solenoid, so if one isn't getting power, the other one probably isn't either.
 
Don't be a wuss. If the tank valve doesn't switch back, just start using that tank. :wink1: :haha:

Actually, if it doesn't switch back, then by definition it doesn't work and you should fix it. The switch is particularly helpful for diagnosing this kind of air leak. If the problem goes away when you switch tanks, your problem is behind the tank valve. If it doesn't, than it's either in front of the valve or you have leaks in both sets of lines.

It's easy enough to replace the lines that you might just replace them preemptively if you don't see any obvious leaks.
It sat for so long I am worried about what lurks in the tank? I have been using this one steady and know it's clean, the other I dumped some diesel additive in .. I just don't know and I'm skeeeered! Lol I'll just have to put 10 gallons in and see..
 
But it is both engaging and disengaging? So there's no problem in the activation circuitry?

I ask because the stumbling only when cold makes me wonder if the timing advance isn't functioning. It's fed from the same wire as the idle advance solenoid, so if one isn't getting power, the other one probably isn't either.
Yes it gets power and works only when cold.
 
It sat for so long I am worried about what lurks in the tank? I have been using this one steady and know it's clean, the other I dumped some diesel additive in .. I just don't know and I'm skeeeered! Lol I'll just have to put 10 gallons in and see..
Drop the tank and pressure wash it out if you that skeered! Should be easy on that rust free California stuff you guys got.
 
Do the diesel pickups run a 3 port selector valve? I've never looked at them.

As in 3 lines running to each tank? No. The valve switches sending and return lines, the third line on a diesel tank is a water siphoning port that goes to a valve on the frame rail. Each tank has one, but they aren't centrally connected.
 

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