Diagnose my diesel.

[jr438234606]

Ok, I've been fighting this problem for over two years now. I've gotten some good advice here, but after all this time, I still have a problem with my Perkins 4.108 diesel.

Symptoms:

Diesel runs fine for about 3 hours. After 3 hours, engine will start to surge slightly, but RPMs will return to normal each time. After about 4 hours, engine will surge ever upwards and will not return to normal. I am forced to pull back on the throttle more and more. After 15 minutes of this, the RPMs will drop to near idle-- even if I throttle all the way up. If I kill the engine for about 2 minutes and restart, everything is back to normal- for about 15 minutes, at which point the whole cycle starts again. If I kill the engine overnight, I'm back to three hours of running time again. It's almost as if there is some sort of heat or suction build up going on.


What I've done.

1.) Changed filters- primary and secondary. (They have never really been dirty)

2.) Switched from 2 Micron to 10 Micron.

3.) Installed a fuel polisher and polished the hell out of my fuel. It's crystal clear.

4.) Inspected and cleaned fuel tank. No dirt or obstructions.

5.) Suctioned off the tank sump to make sure no sludge/water.

6.) Replaced all fuel hoses and clamps.

7.) Installed a vacuum gauge inline after Racor filter, but before engine fuel lift pump. This tells me when my filter is dirty. It works well, but I get no reading when the engine is experiencing the problem. There is no resistance or blockage, or else the gauge would read it.

8.) Checked for blockage in the fuel vent line. None there; gauge would indicate is this was the problem.


I focused all of my attention on the fuel supply and filters. But this doesn't seem to be the problem. The engine seems to be running with more and more air and less and less fuel (which would account for the surge) until finally it is running almost entirely on air (which would account for the decline).

The only thing else I can think of is

a.) Bad fuel lift pump?
b.) Dirty fuel injectors?
c.) Some other device that controls fuel/air mixture ratio that is susceptible to heat build up?
d.) I'm holding my mouth wrong.

It may be time to call in the diesel technician!

[sailingdog]

Is the engine turbocharged??

[Freesail99]

Dirty fuel injectors would be the first thing I would look into. BTW, how did you clean your fuel tank, as it is something I need to do ?

[Pamlicotraveler]

Originally Posted by jr438234606

It may be time to call in the diesel technician!

Problem is you'll have to pay him for 3 hours to wait for the problem to start

It sure sounds like a fuel supply issue - if it was fuel quality it would be an issue from the start.

Going to the 10 micron filter was a move in the right direction, but if you are talking about the primary filter wouldn't it make sense to try a 30 micron (Racor red)? I have used red (30) and blue (10), but I have heard people say a 10 could cause vacuum problems which would be what you are experiencing.

[speciald]

Check the exhaust elbow. Sometimes blockage secondary to corrosion in the elbow can cause the systems you are talking about. Had it happen to a 10 yr old Yanmar and after the mechanic changed the high pressure pump, cleaned the injectors, etc. and spent lots of my money, he called Fort Laudrdale and they told him to pull the exhaust elbow; it was nearly completely clogged with rust.

[capngregg]

Although I haven't worked on diesels for years it sure sounds like the injector pump. More precisely the governing section of the pump which is what should keep the engine on speed under load and prevent the surging that you're experiencing. Removing the injectors and having them serviced is also good advice.

There are several shops that can service these units and will give you technical advice over the phone.

Good Luck!

[Rockter]

My own motor used to draw air, but the revs would drop, and never rise.
I took a risk, and fitted a Walbro 2403-1 fuel pump, and kept the fuel lines permanently pressurised. End of problem. The modern equivalent (eaxct!) is the Stewart Warner fuerl pump... the 235A-D.... and available.... perhaps $70, and runs at 12V, and gives about 5 psi.

Pressurised fuel lines keep air out, and any leak can be seen readily. There is a fire risk I accept, but so is a slowing engie, into a headwind, entering a harbour, and I have been there.

It would be worth a try there JR, and would definitely eliminate any thought of vacuum. You can always switch the pump off after diagnosis.

As for the revs rising, I would have suspected the governor, but it would not have such a time lag, methinks. Over-delivery sounds unusual.

That's a tough one JR.

[jr438234606]

Originally Posted by sailingdog

Is the engine turbocharged??

No, it is not turbocharged.

[jr438234606]

Originally Posted by Freesail99

Dirty fuel injectors would be the first thing I would look into. BTW, how did you clean your fuel tank, as it is something I need to do ?

I pumped out 99% of the fuel into numerous jugs and left just what was in the sump. Then, I inserted my polishing system's uptake fuel line into the sump, drew it though the polishing system's pump and back out of its discharge line straight back into the tank at high pressure. Basically just hosed down the inside of the tank with high-pressure diesel fuel. (I also cheated a little with a rag on a stick. ;-) )

After it was clean, I drew off the sump until empty and discarded the mess.

[jr438234606]

Originally Posted by speciald

Check the exhaust elbow. Sometimes blockage secondary to corrosion in the elbow can cause the systems you are talking about. Had it happen to a 10 yr old Yanmar and after the mechanic changed the high pressure pump, cleaned the injectors, etc. and spent lots of my money, he called Fort Laudrdale and they told him to pull the exhaust elbow; it was nearly completely clogged with rust.

If this were the case, wouldn't I notice a lessening of the discharge of water from the wet exhaust? Or, heat build-up... or both?