Diesel Doctor

[kirkt]

Now I have a question. My uncle back east has a Cat RC60 lift truck that he uses on the farm. It has a Perkins 4 banger Diesel, naturally aspirated. It developed a misfire at idle only, and smokes gray all the time, but especially under no-load and partial throttle.

I am 2400 miles away, and he does not dare touch a computer. I told him to make sure there is no restriction on the air intake, so he took the hose off right at the intake manifold. Problem remained. I asked him about the fuel, and the filter, and he was insulted. He's not stupid. He pulled the pump and injectors (not an easy task) and had them rebuilt. Problem remained. He took the pump back off and had it bench tested then re-installed. No change, pump checked out OK. There is no way he can mess up the timing, as the pump is gear driven. He has tweeked the pump back and forth to slightly alter the timing, no effect. Hose is still off intake, valve clearance is OK, and compression is good. No oil consumption, and level is always the same. No oil in coolant, and no excessive crankcase blow-by.

Any ideas for me to tell him? I'm stumped!

kirkt

[tims87]

If this is like the 4 cylinder Perkins Cat uses in the 416 backhoe there is a brass screen under the little cover on top of the fuel transfer pump. The screen could be plugged up. Sounds like you have covered all the bases except fuel pressure. Engine should have about 5 or 10 lbs of fuel pressure. You have to make a test fitting out of a bango fitting and connect it to one of the spare out let fittings on the filter housing to check fuel pressure. The latest fuel transfer pumps have a plastic screen inside the inlet fitting on the pump. The transfer pump could be bad.

[kirkt]

Thank you for the tip. Sorry I didn't post the result of what was found. I remembered that Perkins uses a cold start aid that uses a thermocouple screwed into the inlet of the intake manifold. As you apply power to the unit it opens up the fuel return line, (that normally only returns fuel to the tank), therefore dripping fuel onto the red hot coil inside the intake manifold creating a small fire for the engine to suck in.

Somehow when my uncle replaced the ignition switch with an after-market one, he attached the wire that feeds this unit to the "run" terminal instead of the "start" terminal. It was always turned on, therefore opening the thermocouple and dripping raw fuel into the intake manifold and subsequently into the engine as it ran.

The problem was solved with a little proper re-wiring.
kirkt

[tims87]

So, you already knew the solution to the problem when you posted your request for help. I will be reluctant to help anyone in the future.

[kirkt]

Sorry for the confusion folks, but I did NOT know what the repair would be as I posted the request for help, that's why I said, "sorry" at the beginning. I didn't reply after I found out the solution was found. I did not know what the problem was, or I wouldn't have posted it in the first place. Sorry for the confusion tims87, and thanks again for the response about the lift pump, as I did have my uncle check that out before he stumbled onto the cold start aid problem.

kirkt