Rough Idle on Caterpillar 3208 Suggestions?

[Yukon Cornelius]

Don't get frustrated and focus on the basics. You've got a good engine that doesn't smoke, seems to have good compression, and runs well once above idle. Don't let anybody talk you into pulling the injectors, or, even worse, the injection pump (at least not yet).

It sounds like you have bled the low-pressure side of the fuel system, but you need to also bleed it all the way to the injectors. I don't have any experience with your particular engine -hopefully someone will respond with the detailed procedure, but generally once you are past the injection pump you can no longer use the manual lift pump like you have been doing -you need to have someone turn over the engine with the starter to finish bleeding all the way to the injectors.

You seem to imply that there are no 'good' mechanics available to you. The thing that separates the good ones from the mediocre ones is their ability to provide good diagnostics. Luckily, If you decide to seek help, I think a mediocre mechanic can handle this -just be sure to insist he concentrates on these simple fuel issues first.

[a64pilot]

They run, so idle them up and loosen each injector line one at a time, let it squirt some fuel out and re-tighten them, have a rag to catch the squirt and only loosen one at a time, when you loosen one, the engine will quit running on that one cylinder as of course it's not getting fuel so don't worry when it runs rough with the line loosened.
This is real, real basic Diesel stuff, real sure someone on your dock knows how to do this, just ask around. Once you see it done, you'll think is that all there is to that?

[whatever]

Responses to previous suggestions...No glow plugs..If bleeding from high pressure side is cracking all the injector nozzle nuts, have done that before and have done 6 of the 8 on port motor just the other day, but will all 8 again. Will also inspect vent tube and try without filler cap on fuel tank. I am also going to put a pony tank to circumvent the main tank with fresh fuel. Will respond with results or subsequent psychiatric admission! Used to be a Shrink, now I understand the true feeling of conflict. Thanks to all you guys that have been trying to help us plug along thru this nightmare and provide hope and encouragement!!!

[whatever]

One other thought...it has been puzzling to both the Admiral and myself thru all this, is we have a 12.5 Westerbeke genset that runs from the same fuel supply. If the fuel is bad, or there is air in the fuel lines, wouldn't the genset run bad as well? Or is it not as sensitive as the motors? Would this somehow indicate that it is "possibly" the injectors or the fuel injector
pump(s)? That has been our thought all along, as one had mentioned previously both start acting up so close together was so hard to believe for us as well!

[DeepFrz]

I don't think both pumps and your injectors on both engines went bad at the same time. That is why I think you have an air leak in the system. Could be wrong, its difficult to diagnose a problem on the internet. However, they are great engines and should last a long time.

As for cracking the injector lines, I don't think that is necessary once the engines are running. If you can run the engines above 1,000 rpm and they are smooth and clean I don't think you have an engine problem per se. Do hook up the pony tank and let us know what happens.

Oh, about the genset. It runs at a higher rpm and at a specific rpm. It might not idle so well either.

[a64pilot]

Gen set also has a different fuel line and return line too, I bet

[whatever]

This is the Admiral here...So DeepFrez you don't think we have to crack the nuts on the injectors? We thought that was also needed to ck for bad injector. Now I am assuming the pony tank is to bypass any air leaks instead of possibility of bad fuel? And yes the Genset has different line and return line, so that would indicate maybe not the fuel? unless because of what DeepFrez said running at higher rpms and it does that from the getgo.

[Sailmonkey]

Like I said earlier in this thread, and have experienced on my own boat, you've either got dried out hoses or dried out packing on the fuel valves. These usually won't leak fuel, but will introduce air.

Just get a five gallon jig of diesel, a short length of fuel hose and run from the jug to the secondary (include the lift pump) and see if the problem disappears.

[DeepFrz]

Don't over think the problem. Just take it one step at a time. See how it runs with a pony tank and then we go from there. It could well be what sailmonkey says. Its as good a guess as any right now.

[whatever]

SailMonkey as far as we can tell, all fuel hoses except for the return lines are either copper or steel. Not sure where any packing would be either on the fuel valves. We will be hooking up a pony tank, and will report back results when that is done..DeepFrez that is my(Admiral) problem exactly and the Captain tends to run that direction as well, over analysis

[HappyMdRSailor]

Originally Posted by whatever

SailMonkey as far as we can tell, all fuel hoses except for the return lines are either copper or steel. Not sure where any packing would be either on the fuel valves. We will be hooking up a pony tank, and will report back results when that is done..DeepFrez that is my(Admiral) problem exactly and the Captain tends to run that direction as well, over analysis

Sealing the stem (for the handle) of the (any) ball valve

One air leaky in in the system = your problem symptoms...

A day (pony) tank should take about 10 min to set up max...

[DeepFrz]

I hope you do have one piece of flexible fuel line at the engine. The line from where the steel line leaves an attachment point on the hull structure to where it attaches to the engine needs to be a flexible line or the steel line will develop cracks.

Over thinking a problem is something I struggle with as well. When one is faced with something new, something way out of one's experience, it can be daunting to take that first step. What is the old saying? Oh yeah, "Get off your buts and do it".

[DeepFrz]

Here is an interesting article that may help with your problem or with future problems. Written by my mechanical guru.
The Vacuum Gauge Tool - Professional BoatBuilder Magazine

[sailorchic34]

I'm with DeepFrz. Your injectors are most likely fine. You mention that with manifold valve closed, engine ran smooth at idle. when Open the idle varied. So look at the valves and upstream between manifold and tank(s) for the vacuum leak. That's where it is.

Could easily be a valve stem leaking or a slightly loose fitting or cracked hose. It's not the tank vent if the generator runs fine.

[Stu Jackson]

Originally Posted by motion30

One of my 3208s does that , especially when cold. I can bump the throttle up a little bit and it smooths out.

+1,000

1000 rpm max for transmission issues is way too low. 1200 to 1300 for my Universal with a Hurth. Anywhere the engine "feels" comfortable is just right, either set it on the throttle adjustment stop bolts or with your hand at the binnacle. Your rpm is being reported by either the alternator or a mech sensor on the engine, and it ain't "perfect."

I think you're over complicating this a whole lot.

But then again you said you were a shrink!

Good luck.