Caterpillar 955L No start

[Nathan Garner]

After 6 months of trouble shooting, I am finally coming here to ask..

I bought a 955L 85J6408 with a 3304 78P874 engine this past spring. It has the Scroll type fuel injection pump. It was not running when I bought it, but looked to be in decent condition. Was told that it ran when it was parked 3 years before, but had a steering issue. The steering issue isn't my main concern right now. I believe to have that taken care of. The biggest problem I have right now is I can not get it started. I have replaced all fuel filters, blown the lines out, replaced a section of the fuel line because it was kinked, removed and inspected the plunger groups, replaced hand primer, taken the transfer pump apart to inspect (didn't see anything alarming, but also didn't take measurements to verify clearances), cleaned the pressure relief in the fuel pump. I double and triple check to make sure all air is bled out before trying to start. I am very much against using either on diesels, but I have tried it on this. If I spray a tiny bit in the intake, it'll hit off of that, but will die right afterwards. The fuel gauge is reading pretty low while cranking but I'm not sure if thats normal or not. If I crank for about 30 seconds, the fuel pressure will be about halfway up the "yellow" on the gauge. I'm getting fuel to the cylinders, but my thought is that it isn't enough pressure. I am getting white smoke out of the exhaust while cranking. Any ideas on what I can look for next?

FYI, pretty sure I have some glow plugs that are shot, because I'm only showing about a 10 amp draw while trying to heat them. I will replace them soon but I know that won't cause it to not start.

 

[sawmilleng]

Did you do a compression test?
Did you bleed the lines to the injectors? Do the injectors work and spray diesel?

I wouldn't be so stingy with the ether--just dont be a bull with it and cause heavy pre ignition which is damaging. It helps you spin the motor faster than the starter can and the faster running may just be enough to start an injector working or get a tiny air bubble out of an injector line.

Jon

 

[DB2]

Glow plugs should draw 10 amps each and the old PC engines rely heavily on them to start. Like the previous poster said you may need to bleed the injector lines. Do you have a healthy flow from the the line from the tank?

 

[Nathan Garner]

Sawmilleng: No compression test yet. I'm guessing there is an adapter to put in the pre-combustion chamber in order to hook a gauge up?
Yes, the lines have been bled and if I remove the injectors after cranking it is wet in the pre-combustion chamber with diesel.

DB2: I was reading a forum earlier that said 5-6 amps each. Either way, I'm only getting 10 amps total when heating them. And yes, I'm getting white smoke while cranking.

 

[DB2]

You could be right about the amps. How does it turn over? Can you hook up an injector to a line to see what kind of spray pattern it has? If you try this keep out of the spray path as it can easily penetrate your skin if things are working correctly. I believe the compression adapter goes in place of a glow plug.

 

[grandpa]

You probably already have, but im going to ask anyway.... have you removed and check both air filters?

 

[tctractors]

The heater plugs will draw 5 Amps per plug so you should see a 20 amp total drop on the amp gauge as you apply heat, if you push the throttle to the shut off position and undo the fuel lines at the injector tops then pump the hand primer you will see fuel coming through, if it fails to start after you have tried your best I can tell you of a few other tricks. tctractors

 

[Nathan Garner]

DB2: Turns over good. I bought 2 new 4D3 batteries for it. I'll try the injector test. Haven't thought of that, thanks!

Grandpa: The filters and the air box are removed currently. Its pulling air in from the turbo intake. (New turbo, exhaust manifold, exhaust elbow)

Tctractors: Push the throttle to the off position? I have done that before, and when the throttle lever is in the "Run" position it will pump fuel through the lines, but when I turn it to the "Off" position, the fuel will not flow when pumping the hand primer. I thought that was how it was supposed to work, but am I mistaken?

 

[Nathan Garner]

Quick update, just tried what DB2 suggested. Pulled all 4 injectors and turned all fuel lines 180* and bolted the injectors back up. Bled the lines and tried to crank it. Fuel only dripped out of the injectors. Thought maybe it was air in the lines so I removed the injectors and tried it and it squirted fuel out, put injectors back on and only drips. Would that be the injector nozzles? Or something else? I’m stumped.

 

[DB2]

Seems like a lack of supply pressure as your gauge indicated. Need TCTractors to come to the rescue here

 

[Nathan Garner]

Is there another screen in the lines somewhere that could be getting clogged? I noticed that I can pump the primer and feel it building pressure, then try to start it and come back to check the primer, and it seems to have no pressure behind it and I have to pump it back up to re-pressurize it. I have good fuel flow into the injection pump, but it "seems" to bleed off while cranking.

 

[petepilot]

sounds to me like stuck injector plungers. the fuel thats dribbling by is supposed to pop the inj`s have them pop tested

 

[kshansen]

Might not be scientific but if I had a set of direct injection injectors off another engine I would stick them on the lines and see what happens. I used to keep some old American Bosch injectors from an old Mack END711 just for that purpose.

If you have a dealer or injection shop near by having them "pop test" them should only take a few minutes and if you are buying replacements from them they should do it for free!

I have not checked what the fuel system is like on this 3304 but if it is like the pumps on the 3306 in the old 966C loaders the injection pump does not have "delivery valves" like say a Robert Bosch pump. So with lines off the top of the pump while cranking I would expect a good flow of fuel also if memory serves me when in the shut down position the priming pump should easily flow fuel out the ports the lines hook to on top of the pump.

 

[grandpa]

Have you unscrew the injector nozzles off the stem to see if you had pressure then? I can't imagine all four nozzles being plugged but I guess it would be possible.

 

[tctractors]

Heater Plugs = P.C. type engine not direct injection, so it's fitted with a low injection pressure system, with all the lines open with the throttle shut off fuel only comes out steady, but as the fastest flowing lines are done up fuel will exit all pipes. tctractors

 

[Mobiltech]

Have you tried moving the throttle from shutoff to run while cranking to see if the smoke comes and goes. You have pretty much verified you have good fuel supply so I wonder if the rack in the pump is sticking and not opening up to run.

 

[Bluox]

Quick update, just tried what DB2 suggested. Pulled all 4 injectors and turned all fuel lines 180* and bolted the injectors back up. Bled the lines and tried to crank it. Fuel only dripped out of the injectors. Thought maybe it was air in the lines so I removed the injectors and tried it and it squirted fuel out, put injectors back on and only drips. Would that be the injector nozzles? Or something else? I’m stumped.

You can't check capsule nozzles this way, they don't seal on the threads so they leak there and appear to drip.
there is an adapter that holds the nozzle that allows one to tighten nozzle to holder and pressure check them.
How far did you take pump apart?
Bob

 

[kshansen]

Have you tried moving the throttle from shutoff to run while cranking to see if the smoke comes and goes. You have pretty much verified you have good fuel supply so I wonder if the rack in the pump is sticking and not opening up to run.

Good point on the smoke while cranking. If system is bleed out of air it should puff a bit of white smoke while cranking if it is actually injecting some fuel into cylinders.

I recall one 3306 that was not running right after a dealer rebuild on the injection pump. I used a few old Mack American Bosch injectors to measure the out put form a couple cylinders to prove the problem was one cylinder not getting anywhere near the same amount of fuel. Rather crude test bench but the difference in the fuel delivery from one to the other was beyond question.

 

[Nathan Garner]

Sorry for the long wait for a response. Got caught up with life.

After reading what everyone said here, I decided to take the nozzles off and have them pop tested. After a few trips to my local CAT dealer (they couldn't find the correct fittings to test them the first time), we determined that they were all bad. They are supposed to pop between 550-750 PSI and 3 of them took 850 PSI to pop, and one took 750 PSI, but once they all opened, they wouldn't re-close. It was just pouring out what fuel was left in the line. Which would explain why I was getting white smoke, but no start and no pressure in the fuel lines. There was no spray pattern to them, either.
I ordered new nozzles from CAT and installed them. After a few minutes of on-and-off cranking, and recharging the batteries a few times, I finally got it started!
I noticed while working on it that the throttle lever would never pull all the way back to the "RUN" position. It always stayed about 2" from it, and felt like it hit a hard stop and wouldn't go any further. While I was cranking it after installing the new nozzles, I noticed that it would try to start more if I moved the throttle lever back and forth, and without noticing I pulled it all the way back to the "RUN" position. Once I realized it was back that far, I paid close attention to it when I pushed it forward and heard a clicking noise when it passed that 2" spot. After I let the batteries charge one last time, I tried it again and tried to pull the handle back while it was cranking. After about 3-4 seconds of cranking, something inside the injection pump assembly "released" and it let me pull it all the way back to the run position, and it started. I'm guessing this is maybe a oil pressure switch? I've heard that if it runs low on oil pressure, it won't let you idle up. Is that the mechanism that does that?

I started it again today, about 1.5 weeks after the first start, and played with the loader (first time its been moved under its own power in around 5 years). They seemed to work great after the cylinders filled with fluid again. I tried the same "procedure" this time while starting it as I did the last. I started cranking, and kept feeling for it to release it all the way to run. After it did, it cranked for about another 4-5 seconds before starting (in 45 degree weather).

After playing with the loader controls, I attempted to move it. When I tried to put it in drive or reverse, it didn't budge. 1st, 2nd, 3rd, it didn't matter. I didn't hear the engine bog or anything. I acted like I didn't touch it. Any ideas on what to look at next? I'm going to start pulling off covers tomorrow to see if I can figure out how it works and if something might be stopped up. It did look a little low on oil according to the transmission dipstick and after running for a few minutes. I'll replace the transmission fluid shortly. Any one have any ideas on where to start looking? Filter? Bypass valve stuck open somewhere?

 

[Welder Dave]

Can you block it up to get the tracks off the ground? Then it would be easier to see if it's at least trying to move.