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8950 hard starting


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I recently purchased an 8950. This tractor is hard starting, it cranks fine but has to crank for a while until it fires. Every 8.3 Cummins I've been around cracks off on first compression hit. Not this one. It has to crank 5-6 seconds on every start. That doesn't sound long, but when you do it it seems like a long time. I can't figure out why it has to crank so long. The wierd thing is, it can be running and shut off and if you start it right back up it still has to crank that long. I changed all the fuel filters and thought I'd never get it started again. I bled the complete system and it would not start. I finally gave it shot of brake cleaner and it started. It's not the fuel solenoid. That thing is working good. If physically tied it to on position and made no difference. I'm questioning the lift pump and return check valve. But I believe I've eliminated them as being the possible cause also. I've had hose pinchers on fuel supply and return hoses to manually have a check valve. Still does not start right. The tractor has just over 10k hours on it and I was told it had engine work, but honestly who knows. It has very little blow by, not sure on power yet as I have not had it in the field yet. Also have not checked valve adjustment. Anyone ever had this problem? Is there something in injection pump that can cause this? Can the fuel rack stick even though the lever moves fully on outside? When it's running it has a very good sound to it, doesn't miss or smoke abnormally. I'll also add I replaced fuel supply hose, clamps, and the manual shut off valve to eliminate these as possible problems. Sorry this is so long I just want to make sure I explain everything as best as I could. I'd appreciate any thoughts anyone has.

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Verify that the fuel solenoid is going full on when you start cranking.  I have seen them where they are weak at going to run position. Can also be a power position not getting correct voltage, power post can be a problem

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12 minutes ago, bitty said:

Verify that the fuel solenoid is going full on when you start cranking.  I have seen them where they are weak at going to run position. Can also be a power position not getting correct voltage, power post can be a problem

The solenoid snaps in immediately, and says in. As I said I tied it to "on" position just to see how it would act and there was no change.

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Just a dumb idea that I always forget but there is a bleed screw hidden on the front of the inj pump right next to the cylinder head I always forget about. I'd try bleeding the fuel system right there and try it.

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The pumps can get weak . I have seen more issues after the mandatory ulsd was getting delivered to our area 

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Get a fuel inlet pressure gauge in between final filter an injection pump. I like to remove the banjo bolt that has bleeder screw in it and pull my tests from there. I brazed an 1/8 NPT coupling to a banjo bolt to make a test fitting. Once you get a gauge in there it will tell you your inlet pressure. Inlet should be 20+ psi and then when you shut engine off it should sloooowly drop to "0" if it drops fast you have (a) a bad check valve in manual transfer pump or (b) a bad outlet valve on injection pump, if this is the case you will likely struggle to make the correct inlet pressure also. You can isolate this using your hose clamping tool on the return. 

Check your pump - to - engine timing as they can slip timing due to no key between pump shaft and pump gear. 

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I think CIHTECH is correct. Had a 8950 this past spring with hard starting. Timing was way off. Removed the gear, reset the timing and BINGO, didn't have to crank it for 5-7 seconds anymore. I put the blue loctite on the pump tapered shaft which will break loose with a puller. Was afraid to try the red loctite which would require heat to remove.

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One thing to keep in mind, is the 8950 had P pump with an RQV-K (automotive style) governor. If the idle is set too slow, it may not be going to start fuel without moving the throttle lever to about 1/2 way up. The tapered shaft should not require loctite, but they need to be torqued to 150ft lbs when they have the 30mm shaft, 30 mm socket size. 

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No luck yet. Replaced fuel transfer pump, no change. Checked timing- dead on. Throttle lever position makes no difference. I need to make something to be able to check and monitor fuel supply pressure. I think I can drill a hole in banjo bolt and tap with 1/8 pipe. Anyone know what fuel supply pressure should be?

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8 hours ago, ThirdGenRed said:

Reread CIHTECH's post above.  His post said 20+ psi inlet fuel supply pressure. Good luck!

Yes, he said 20+. I was just asking what the actual spec. was. 25? 30?

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I got a gauge installed. 22 is the highest I could get, but, I could get it higher by pinching the return hose slightly. So the transfer pump has the ability to supply more pressure, just didn't know what the actual spec calls for. Getting back to the problem. As I said I now have a gauge installed. When I start cranking the engine it take several engine revolutions before the gauge moves. When it gets up to 15-18 the engine starts. 20-22 is where the pressure runs with engine running. When I shut engine off, the pressure drops to 0 fairly quickly. The engine can be cranked immediately after shut down and still has to make several revolutions for pressure to come up. I think return regulator valve is faulty and I'm replacing it. I have another thought/question. The return line from the injectors connects to the fuel supply line at the fuel filter base, it's all connected  with a banjo bolt setup. So basically the return fuel is circulated right back in with supply fuel and the return is also somewhat pressurized. It would be the same pressure, as supply pressure. Is there anything with an injector that can go wrong to cause this problem? I mean obviously if there was an external fuel leak on the return line it would cause this but I have no visible leaks. I've had injectors with weak/broken needle springs that allowed compression into the return but I don't think I have anything to that extreme. I don't think I have air entering the system, I think I have a problem building and holding pressure. 

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The return fittings on the 5.9 and 8.3 P pumps are a problem area. 'usually they miss at idle in gear, but the tractor idles faster so may not show up. The return fitting has been revised many times to it's current form which lasts now. It has a smaller hole in the center. (about .100")

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I replaced regulator and I think that was the problem. It doesn't start just immediately but much better. So far it has to crank 2-3 seconds, hopefully it stays that way. I have fuel pressure as soon as it starts cranking and it takes about 10-15 seconds for pressure to drop to 0 when engine is shut off. Thanks for everyones help.

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Might be normal on one with an RQV governor. 

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48 minutes ago, Injpumped said:

Might be normal on one with an RQV governor. 

You know I never thought about that, you're probably right. None of the engine's I was comparing this engine to had the RQV governor. Thanks. 

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The RSV governor has a start spring that pulls the rack to start fuel as soon as the solenoid kicks it on. The RQV governor has to have the throttle moved to about 1/2 throttle to get it to start fuel position. 

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