Changed nozzle and adjust cracking pressure 220kg/cm² Changed plunger of the pump NB (EP-9) type The reason, engine rebuild, komatsu engine SA6D108-1 of a PC300-5 excavator. After installing injector and pump, found the exhaust of number 5 cylinder is cold at low idle no load, just injecting when going suddenly from low to high idle. Interchange with other injector and still the same. Fuel shop guy said the delivery of the pump is correct at LI and HI but no explanation for this behavior. Is it normal or something wrong. By the way the engine smells unburnt fuel at LI no load.
Something is wrong. I would guess it is compression related. How did you run in the engine on first startup? As I recall those engines don't have liners. Were they bored out or at least honed to break the glaze? Did you check ring end gaps before installing them on the pistons? Is it possible a valve is a little too tight? How much has it been run since the rebuild? Maybe you just have to get a real heavy load on it to fully seat the rings. Those excavators don't load the engine real heavy for a good break in. I've turned the TVC pressure up to pull the engine down around 250 to 300 RPM to get the firing pressure high for a good loaded break in. I would run it a couple of hours like that and then reset to factory specs.
"YOU" replaced the plunger in the pump?? That's not an easy job!! are u SURE you got the plunger in correctly?? But if the fuel shop says its pumping.. then chances are pretty good that its pumping. I'd start looking somewhere else.??
Engine newly rebuild, liner were changed and are in specs, no taper no out of round. Don't be afraid "I DIDN'T REPLACE THE PLUNGER",fuel pump and injector were rebuild in a fuel shop and yes it is injecting around 4 cc at 360 rpm (bench rpm) Just curious to know why cylinder number 5 has cold exhaust. On load it is injecting, the rack should be almost fully pushed , and on test bench it gives the same delivery as the others
How many strokes?? because it should pump around 18-20 cc or MORE {30-40 depending on application} at 1000 strokes.. Best that I can remember, seeing I don't have the spec sheet infront of me. The more strokes you run it at, the more variation you will see.. the spec calls for 1000 strokes.. w/ a variation of no more that 8-12 for a rebuilt pump AT 1000 STROKES.. I NEVER let mine go with anything greater than 5.. {"MASTER" injection pump rebuilder} SO "IF" your pumping 4 at 360rpm.. ??? THAT MEANS {to me} that the tester ran it at 100 strokes & is hiding something.?? Lets just say, YOU NEVER run an idle check at 100 strokes. ALL THIS is purely speculation on my part with the information given.. I DONT KNOW seeing I'm not there. Disregard this IF you meant a 4cc VARIATION between cylinders. Good luck.
My question is how it is determined the injector is not injecting at low speed but IS working at high speeds. When running at low speeds and with cold exhaust on #5 is the exhaust nice and clear or is it showing white smoke from unburned fuel? You did mention the "smell of unburnt fuel" so I'm guessing the injector is in fact injecting fuel but for some reason it is not getting enough compression temperature to ignite and burn. You say the engine was rebuilt, not to ask a dumb question but why? Was the head also rebuilt? Any new valves or valve seats? Years ago we had a somewhat similar problem with a 903 Cummins engine we rebuilt. It was missing on one or more cylinders on one bank. While checking for the cause we discovered the valves on the factory rebuilt head were recessed below the surface of the head considerably more than the spec's in the manual. It took a lot of arguing with the service department but they finally exchanged the head with another one that was in spec. Guess what problem was solved, well it was still a 903 but it was firing all eight! If worst comes to worse and you end up pulling the head I would suggest making some accurate measurements of height of the pistons in the cylinders at top dead center. Just wild guessing that there could be a problem like a slightly bent rod. We had a Kubota in a Bobcat that had a miss and in that one I found one rod was a few thousands shorter than the other three. Machine shop had checked them for being straight and said they were all good. But if you put two rods together with one wrist pin through the two you could feel at the "big end" there was a difference from on to the other. As I recall that engine had a bad head gasket and I assume coolant got in the one cylinder and hydro-locked the piston tweaking the rod.
Slight white smoke can be seen from the exhaust of the 5th cylinder. Just on the transition between low idle to high idle it injects, here the rack is pushed to reach the high idle speed then it goes to some minimum position, but of course on load at high idle it works properly, rack position around 12 mm. Engine rebuild because all piston rings were broken and seized (blowby pressure), too much dirt in the intake manifold, bad maintenance. The head was rebuild, new valve and guide, I trust machining shop and we didn't have problems till now. By the way I tested compression pressure, it gives 26 kg/cm²
Is that compression of "26 kg/cm²" on just the missing cylinder or is it the exact same pressure on all 6 cylinders? Do you have a factory manual that states what the pressure should be? Well I had good luck with Cummins Recon parts for years till I go the one head that did not meet specks for valve head protrusion on recession. If this engine was in such bad condition before rebuild how close did you check the camshaft? Did you measure each and every cam lobe for lift? White smoke make me think it "IS GETTING" fuel but not firing and with most diesels that would point to poor compression from some cause.
All piston rings broken? How many hours did you get out of that motor?
More than 16000 hours, just top rings on all cylinder, some of them broken and the others seized. By the way let's say the engine is running at low idle 750RPM with no load or even at 2100RPM nol load, What should be the position of the rack, is it around 4 mm slight above the no injection rack position
I mean 8.4 mm rack stroke