Not happy with 3940 starting

[Jerry/MT]

Out of town for the long weekend...

I don't think there are any check valves between the injectors and the IP. What check valve are you referring to?

I started the darn thing last night after being away for four days and it cranked for 6 - 8 seconds with "hit and miss" on the last few turns. I am not happy with this.

I firmly believe that it's a fuel problem; maybe I will install a check valve in the supply line to the IP. I called the dealer today and they are not sure what to do; they suggested that this is the way Mitsubishi's start!

I don't know whether your fuel suppy is checked or not because I don't know the details of the fuel system. I'm merely suggesting that your fuel supply maybe draining back and the 4 sec crank time maybe caused by repriming the injector fuel delivery. Make sure that your fuel fittings are all tight so that you don't suck air into the fuel lines. Open the bleeder screw(s) on the filter(s) and make sure there is no air in the filter(s).

The only other possibility is improper starting procedure where you don't wait long eneough for the glow plugs to preheat the combustion chamber. As sensitive as you are to this problem, I doubt the latter is the case. It's possible the glow plug timer or the plugs themselves are faulty. Have you checked that? Just because they changed the timer doen't mean it is OK or that the glow plugs are OK. Has this been a problem since day one or has it just started?

What was the ambient temperature at the tractor whe you tried the start that went 6-8 seconds? If it was relatively cold, it reminds me of my Ford 4610 when the block heater is off in cool weather.

 

[mwb]

Same problem starting it last night and it was cold - about 5 deg C - and it cranked for seven seconds to start after a full cycle of the GP.

I measured the GP resistance, supply voltage and voltage rise as the GP heated - everything looks good. The dealer checked the same and they said that the timer was "slightly out of spec" and changed it.

I had also checked for leaks, pressure tested the supply line, flow test and everything is good. Dealer confirmed the same.

The temp for the 6-8 second crank was near 10 deg C; GP shouldn't even be required at that temperature (well even my F250, 7.3 requires GP at any temp). The supply pump is electric so even if the lines emptied back to the tank it would have time to refill - unless there is an air lock between the supply loop and the IP. I will change the supply line to a clear Tygon to test for a while.

This problem has been getting increasingly worse, sometimes (now rarely) it fires up very fast like nothing is wrong. I am baffled because I am familiar with diesels and I am well aware of the problems that air leaks can cause (my ford with the DB2 pump is very sensitive to this).

 

[Jerry/MT]

Same problem starting it last night and it was cold - about 5 deg C - and it cranked for seven seconds to start after a full cycle of the GP.

I measured the GP resistance, supply voltage and voltage rise as the GP heated - everything looks good. The dealer checked the same and they said that the timer was "slightly out of spec" and changed it.

I had also checked for leaks, pressure tested the supply line, flow test and everything is good. Dealer confirmed the same.

The temp for the 6-8 second crank was near 10 deg C; GP shouldn't even be required at that temperature (well even my F250, 7.3 requires GP at any temp). The supply pump is electric so even if the lines emptied back to the tank it would have time to refill - unless there is an air lock between the supply loop and the IP. I will change the supply line to a clear Tygon to test for a while.

This problem has been getting increasingly worse, sometimes (now rarely) it fires up very fast like nothing is wrong. I am baffled because I am familiar with diesels and I am well aware of the problems that air leaks can cause (my ford with the DB2 pump is very sensitive to this).

The only thing I can think to do is to crack an injector line prior to a starting attempt and watch for fuel while someone cranks the tractor over. There should be fuel available at the injector right away. If there's not, something is causing the fuel to drain back. (I'd have to suspect the pump at this point because it's udownstream of the injectors but with this new a machine, the pump does not have a high probablility for problems.) Check all the lines, one at a time. You'll have to wait for some time to allow any potential drain back to occur before testing the other injectors.

How do you use your tractor? Have you followed the manufacturer's recommendations regarding air filters, fuel filters etc? Are you working it in a dirty/dusty environment? Is your airfilter relatively clean and is there a delta P sensor on it to tell you if it's getting clogged? You say that sometmes it fires right up. Anything different about the ambient conditions , or the length of time between uses, etc, that will give you a clue as to why that might be? Is your fuel control via hydromechanical controller or is it a digital electronic controller like your Ford 7.3l?

This is a pretty baffling situation because diesels in reasonable mechanical condition are pretty reliable starters except at low ambient temps and even then, with starting aids, they start well as long as they have fuel and they turn over.

 

[alltoys]

Just a dumb question but are you cycling the glow plugs long enough?

On mine I have to cycle the plugs for at least two cycles at 20 seconds and it starts immediately. My temps get down to -40 and with plugging it in I still have to cycle the plugs.

You can cycle the glow plugs by engaging the pto, depressing the clutch and turning the key to the crank position. The safety switch will not allow the tractor to crank with the PTO engaged.

 

[mwb]

Well, it's back at the dealer now (actually it has been there for five days now). I told them that I am not in a rush for it - I just want it fixed. They have confirmed that there is a problem - the last time they changed the GP controller, tried it once and said it was fixed.

They are replacing lines and fittings on the fuel supply side. I have a suspicion that it's the high pressure side that's the problem though!

 

[uphere]

Just out of curiosity, your dealer - is that the fella south of Ottawa ... in Halville (McLoughlin?) ... if so, how have they worked out so far?

 

[shakin]

is that a common rail motor or does it have an injection pump.

 

[mwb]

Dealer is in Hallville. I am very happy with their customer service and I would recommend them.

This machine has an injector pump. My fear is that the IP is the problem (under warranty though).

 

[tractorbarry]

tell them to pull the glow plug rail of and remover all the paint around the the holes. there is no contact from the wire to the plug's

 

[Tul01]

good to see ya back Tractorbarry.