Injector Pump: How to know if its time to rebuild

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Engine is totally rebuilt with new pistons/rings, valves/guides, etc. I put new nozzles in the injectors as well. Great, even compression.
It starts and runs good, but Im trying to track down this final issue.

When cold starting it runs a bit rough with a small amount of whitish smoke. If I let it idle when cold, it marbles a little and just slighty rough running.
If I give it a little fuel when cold it misses and gives white smoke. If I push the cold start lever in, and give it fuel, it smokes way more.
There is an occasional big air bubble in the fuel line, but not the foamy little bubbles that cause rough running.
This all clears up in about a minute of running.

Once its warmed up, no smoke. But I get this strange misfire/RPM jump at a certain throttle position. I can accelerate past the missing just fine. No missing on acceleration, just when I let off the pedal slightly and hold it at about 55mph in 5th gear. Smokes a bit when missing.
Additionally, sometimes I'll be cruising on the highway at a constant speed, and without any change of the pedal, the RPMs just drop by maybe 100-200 for a second and then return.
It idles great when warm, but I get a little bit of marbles at the beginning of acceleration.

The pump has 300k miles on it, and Im suspecting its got issues. Everything else has been replaced. I suppose it could be a bad injector as well. I dont want to rebuild the pump unless I have to. I did a cold start yesterday, and opened each injector. They all did the exact same thing.
I put a stethoscope on each injector at the head and at the pump, no noticeable difference.

Any further testing I can do to determine whether or not it is the pump or an injector?
Any ideas what could cause the RPM jump and missing?

[TylerDurden]

Any air is suspect. A clear line on the IP outlet line will show if air is being sucked into the IP.

When any air gets in, the IP internal pressure can drop and timing will retard, also tiny bubbles can get sucked into the HP head and cause a miss. It's like a blender inside the IP when running, air can get whipped around like a milkshake.

I'd also pop-test the injectors.

[Quantum-man]

Forget your pump for now, chek that your new nozzles aren't leaking[dribbling] slightly. If they are new, it is not unheard of to improve [bed in] after a 1000miles or so.

[Fatmobile]

Make sure all the injection pump mounting bolts are tight,..
including the ones holding the brackets to the block.

Have you tried advancing the timing for a smoother cold start.
An idle miss during cold startup is a common sign of slightly retarded static timing.

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I pop tested the injectors before installing. None leaked before breaking pressure. The new nozzles have about 1000 miles on them.

I set the timing at 0.97 or 0.98 IIRC. Cold start lever acts like should. I was going to do some hilbilly timing but I'm hesitant to advance the timing because it sounds a bit rattly already.

The reason I suspect the pump is because it misses at a particular throttle position in all gears. On occasion the RPM will jump down and back up when cruising on the highway, like a suddden change in fuel pressure or something.
I would think a bad injector would have problems throughout the RPM range

[82vdub]

On occasion the RPM will jump down and back up when cruising on the highway, like a suddden change in fuel pressure or something.

Or it sucked a big bubble into the IP. Troubleshoot your fuel delivery system to eliminate the bubbles and then see if that changes anything.

[Fatmobile]

I set the timing at 0.97 or 0.98 IIRC. Cold start lever acts like should.
"If I push the cold start lever in, and give it fuel, it smokes way more".

These two statements say the opposite thing.

I'm not sure advancing the timing will help with surging in higher gears,
that sounds like mounting bolts (the reason my Golf acted like that) or a fuel line restriction.

But it should help quicker starts with less smoke.
If it gets too noisy and doesn't help youi can move it back.

Often too rattly after a cold startup, does the rattling quiet down after it warms up?

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These two statements say the opposite thing.

I think we may be saying the same thing... advanced = less smoke

When its cold it definitely smokes more (white smoke) when the CS lever is pushed in (not advanced).
When I say the CS lever acts as it should, I mean it advances timing and rpms go up.

Yes the rattle quiets down after warm up, but also its a bit rattly when I first start to accelerate.
I dont have a problem with quick starting, usually on 1 or 2 cranks of the starter.

Here is a video of a cold start, smoke, and the fuel line bubbles:

http://youtu.be/Z03sJ0aiLLE

[Quantum-man]

You could check the internal pressure of the pump.
You could substitute a set of injectors to see if the problem changes.
You could try swinging the pump on the fly.

Reduce the fuelling...
Try both the aneroid, then the max fuel screw out a little....

[TylerDurden]

Too much air.

You can expect some smoke when revving a cold engine, but that much air in the line is going to play small havoc with the internal IP pressure and get sucked into the HP head.

I'd get rid of that fuel filter and go to the earlier style with no tee fitting. I will bet a buck the tee is letting in air.

A clear line from the IP to the return line will also show if there is an ingress of air within the IP, like at the input shaft seal.

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Too much air.

Ive always wondered if those bubbles were enough to cause problems. The strange thing is that they have always been there. The previous engine had the same bubbles & injector pump and none of the smoke issues. I drove it like that for 50,000 miles without any problems. I dont know if you watched the whole video, but there were fewer bubbles at the end. Could be air getting in while sitting overnight.
I also realized that I had a leaking injector return line when I filmed that, which I have since replaced.
Ive also heard many say that a few bubbles is normal, in fact it says it is OK in the VW diesel training manual.

I am planning on replacing the filter O-ring to see if that helps.

Does your supply line have zero bubbles? Im just curious how "normal" this is.
What do you use for clear fuel line?

[82vdub]

The white smoke is a sign of poor combustion. This is either from low compression, timing, or possibly fuel related or one to three of those. However, if you set your timing by the dial, it probably needs to be advanced. I've done the belt on Ole 82 about 4 times now, each time setting the timing by the dial, and eventually leaving the dial gauge in the tool box and just rotating the pump until it sounds good. Next time I'm just going to wing it and leave the dial gauge to get friendly with the other tools in the box. The point is that you're not wanting to mess with the timing, when that is likely the culpret, and most easily remidied by advancing the pump. You will know when you advanced it too far. You'll definately hear it.

Plus, I'm unsure what state Jefferson is, so without knowing where you're located, it's hard to say how your car will "cold start", because cold in Florida is about summer temps in Wisconsin. These older diesels will cough, buck and snort when it's cold out. Makes a person wonder why they subject their engine to those conditions, but after a couple minutes, they run like a swiss watch.

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Its definitely not compression, its a complete rebuild with 475 PSI. Rebored, new pistons/rings, New valves, guides, seals, etc. New injector nozzles.
The only thing I have not replaced on this engine is the pump. I dont want this to run like an old diesel, I want to run like new, and the only thing that is old is the pump.

Although I said I was hesitant to move the timing, I actually bumped it forward the other day and it made no difference.
I will have more time this weekend to adjust it and Im going to try and eliminate any air bubbles.

And yes it generally runs great when warm, but I do get that RPM jumping and slight miss I mentioned, which cannot be a static timing issue. Also there is rattle when I first give it fuel in any gear.


FYI, the "State of Jefferson" was a movement in 1940's to secede and create a new state in southern Oregon/Northern California. I no longer live there though, Im now in Upstate NY. So when I say cold start, Im usually meaning below freezing at least.

[Dakotakid]

I also think Tyler is correct on that more complicated pre-heater fuel filter. Those are known to draw air if the hardware associated with it is not fresh. Additionally, does this car still have the big plastic water separator located under the passenger rear seat area under the car? They suck air here as well. You can delete the box.

[Fatmobile]

Thanks for advancing the timing so we can rule that out.
How much did you advance it? Use a dial gauge or just some paint and scratch a mark?

Air in the lines will cause white smoke.
There is no visible air in my fuel line between the filter and pump.
Having the recirculating fuel filter setup will keep any air in the loop for awhile after startup,
instead of sending it back to the tank.

Good questions about the under car water seperator and check valve.
These can cause air in the fuel.
From my experience air in the fuel is most often caused by a fuel line restriction.
It causes the dissolved air to expand and become visible as the pump pulls harder and creates a vacuum.
Vacuum gauge connected to the fuel line.
All my cars have them dash-mounted.