Goofy Air Intrusion on Occasion

[jhenegh]

Haven't had to do much work on the truck in the past year, which is a very good thing! But recently I have been getting some air intrusion that I can't figure out or reason with. Truck starts fine (I have an electric fuel pump) and idles fine for a few minutes once started. Now the goofy part: About 25% of the time, once I pull out of my driveway onto the road, I get the MAJOR POWER BOOST of air intrusion advancing the timing as I accelerate. Luckily I live on an open road so it's not a safety issue to be shooting out of the driveway like it does, but it isn't right and needs fixed.

Where is this air bubble hiding or where is it being sucked in as I accelerate for the first time of the day? I can't find any wet spots anywhere yet on the fuel system.

Thanks

 

[no mufflers]

Could It be the pickup in the tank? Do you ever smell any fuel inside the truck?

 

[jhenegh]

I suppose it could be the pickup but it does it regardless of fuel level and will suck the tank dry. It did it today with a full tank.

Never smell fuel in the truck

 

[Macrobb]

Before pulling out, disconnect the cold advance wire(or hook it up to a switch). Chances are, that will fix it.

I've had several pumps which are very 'sensitive' with the cold advance on. I'm not sure why, it just is. And it's not air, either.
Remember that the cold advance drops the housing pressure from 5 PSI to near zero. The IP is a whole lot of hydraulic circuits. My guess is that the pressure differential being different screws with things.

I've also recently noticed that it becomes more sensitive with a lengthened governor assembly, as shown here:

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[jhenegh]

Every time it does it it is warmed up past the high idle and cold advance. I can 100% hear the difference when it advances again sporadically with the air.

I don't like driving it with the cold advance on at all because it's so rattly

 

[Macrobb]

Every time it does it it is warmed up past the high idle and cold advance. I can 100% hear the difference when it advances again sporadically with the air.

I don't like driving it with the cold advance on at all because it's so rattly

No, I wouldn't drive it with the cold advance on either... but you may be a little advanced timing wise.
I meant making sure the cold advance is /off/.

Did you delete the return line on the fuel filter housing?
I'm thinking with the E-pump, you might well want to /keep/ that line, test it out. That's the highest point in the system, and air /could/ be trapped there.

 

[icanfixall]

How many miles are on the injection pump? Might be loosing some pieces of the plastic advance mechanics in the pump.

 

[Macrobb]

How many miles are on the injection pump? Might be loosing some pieces of the plastic advance mechanics in the pump.

Plastic advance mechanics?

I thought the only plastic piece in our IP was that larger piece that's part of the governor assembly and transmits the flyweights force to the steel plate that then actuates the springs above.

That has no affect on advance, but would definitely cause issues(like either not running or runaway engine) if it broke...

The advance piston, as far as I recall, is all steel parts with a spring or two.

 

[icanfixall]

What I posted about is what Mel explained years ago. Something that spins is plastic and it has an effect on timing. When it breaks up pieces end up on the top governor area and the timing changes enough so that you can't get a set timing degree. It moves around so bad.that tells you time for a rebuild. Somewhere on this forum I posted a vid from Utube showing every internal piece of our injection pump. I will see if I can find it and repost it.

 

[icanfixall]

Here you go. Enjoy

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[Macrobb]

Yeah, I've watched that video a few times before. It's a good video, lots of good info in it.

...But I still don't see any plastic piece beyond the one shown at 9:47 - the governor linkage. Which has nothing to do with timing.

The only annoying part about that video is that our pumps seemingly run backwards compared to the one in the video(check the 'advance' piston direction), and the light-load governor isn't used on that pump either.