Not sure on this D6T issue

Vetech63 · Dec 3, 2018

D6T S# LAY704

At start up, this thing sounds like its running on 3 of 6 cylinders and the rpms (should be around 800) are around 300 while this is going on. The funny thing is it doesn't do this every start up. The operator is telling me that its at its worst on cold mornings, so I was thinking maybe there was water in the fuel system that was freezing overnight...…….no water found. I was suspicious of the fuel transfer pump and went ahead and replaced it since it was the original and had 7800 hours. It seems a bit better, but with the inconsistency of the issue, I'm having trouble trying to narrow this down. I would like to know how this fuel transfer pump works electrically and I have the schematic for the machine. Does this pump run fulltime from ignition on? is there a pressure switch that runs it? In the schematic its not easy to follow (which is unusual) and a bit confusing as to where exactly the wiring runs in a certain area. I need to make sure the transfer pump is working properly before I call CAT ET out. Any suggestions?

Nige · Dec 3, 2018

The Service documentation on the fuel priming pump for LAY00704 sent me to this......although I can't see D6T on it.
What Part # of priming pump does it have installed..?

Vetech63 · Dec 3, 2018

Nige said:
The Service documentation on the fuel priming pump for LAY00704 sent me to this......although I can't see D6T on it.
What Part # of priming pump does it have installed..?

1908970 is what they got me.

brianbulldozer · Dec 3, 2018

Does this engine have an intake heater?

Nige · Dec 3, 2018

Vetech63 said:
1908970 is what they got me.

That's correct according to what I can see. The Special Instruction does apply to that priming pump Part Number. It's the 2nd one on the list.
There is some info in that same document regarding how the pump is supposed to operate.

Vetech63 · Dec 3, 2018

Nige said:
That's correct according to what I can see. The Special Instruction does apply to that priming pump Part Number. It's the 2nd one on the list.
There is some info in that same document regarding how the pump is supposed to operate.

So is it my understanding that this particular pump runs continuous with ignition on? The wire schematic shows a broken dashed blue (ignition on) wire but there isn't an item in the legend for that particular color code. I have been assuming the dashed blue wire is an intermittent ignition on feed.

Vetech63 · Dec 3, 2018

brianbulldozer said:
Does this engine have an intake heater?

Not sure about that, I haven't got that far.

Nige · Dec 3, 2018

According to that doc I posted above, the pump runs all the time.
I need to have a look at the Electrical Schematic, haven’t done that yet.
We have an LAY-prefix D6T on site only 100 or so Serial Numbers from yours. If I get a chance I’ll take a look at that too.

Mobiltech · Dec 3, 2018

That serial number has a mechanical fuel transfer pump on the back of the high pressure pump. The electric pump on the primary filter should only run when the key is off and the primer switch is toggled to on position.

Vetech63 · Dec 4, 2018

Nige said:
According to that doc I posted above, the pump runs all the time.
I need to have a look at the Electrical Schematic, haven’t done that yet.
We have an LAY-prefix D6T on site only 100 or so Serial Numbers from yours. If I get a chance I’ll take a look at that too.

That would be great Nige. Thank You!

Mobiltech said:
That serial number has a mechanical fuel transfer pump on the back of the high pressure pump. The electric pump on the primary filter should only run when the key is off and the primer switch is toggled to on position.

That's not something I am aware of. What is confusing me is the Ignition on blue dash line on the wire schematic that is leading me to believe the electric pump is supposed to be coming on, at least intermittently. I was aware of the primer switch, and that operates correctly.

thepumpguysc · Dec 4, 2018

To hell with the diagram for now.. u need to get it running.. hot wire the pump to RUN for now to see weather or not that's the problem.. its GOTTA have fuel to run..
THATS what I would do for right now.. get the pressure UP TO the inj. pump & see how she runs.

Vetech63 · Dec 4, 2018

thepumpguysc said:
To hell with the diagram for now.. u need to get it running.. hot wire the pump to RUN for now to see weather or not that's the problem.. its GOTTA have fuel to run..
THATS what I would do for right now.. get the pressure UP TO the inj. pump & see how she runs.

Believe it or not, it runs......everyday! It will start, just misses like a MOFO for the 1st 2 minutes, then straightens up and runs fine. Hitting the primer for 20 seconds before the initial morning start up has seemed to help.....a bit. I'm trying to get all the correct info I need before I shut it down to troubleshoot. At this point, Im not sure its a supply issue yet but I want to eliminate that as a problem. The inconsistency of this is what's making it difficult, some mornings it starts up just fine. Where's the hair-pulling emote?

thepumpguysc · Dec 4, 2018

It def. sounds like a "bleed-back" problem..if the pump isn't coming on when u turn the key, THATS A PROBLEM.. its gotta have pressure AT THE PUMP INLET to run properly..
Have u tied in a clear line or gauges yet? A clear line will show u if its draining back AND if its going to the inj. pump when u turn the key on..
Hot wire the dam thing.. lol w/ a toggle in the cab..

Vetech63 · Dec 4, 2018

thepumpguysc said:
It def. sounds like a "bleed-back" problem..if the pump isn't coming on when u turn the key, THATS A PROBLEM.. its gotta have pressure AT THE PUMP INLET to run properly..
Have u tied in a clear line or gauges yet? A clear line will show u if its draining back AND if its going to the inj. pump when u turn the key on..
Hot wire the dam thing.. lol w/ a toggle in the cab..

Yeah, I thought bleed back also, which is why I changed the transfer pump (electric) out since the check valves are in it. I don't believe the electric pump is coming on with the key, which sent me to the wire schematic...….and now the schematic is confusing! LOL Believe me, I will hotwire that B**** once I have the info I need just in case that doesn't help. I can only shut this machine down once, or if it goes down on its own. Has no active fault codes either.

Nige · Dec 4, 2018

What schematic are you using ...?
The snip below is from KENR5131-04 (latest available dated 16/12/2014) and I don't see any wire carrying power from the ignition switch. All I see is a wire #326 Purple that is live as soon as the Master Switch is closed. If you want the complete schematic please let me know.

kshansen · Dec 4, 2018

Mobiltech said:
That serial number has a mechanical fuel transfer pump on the back of the high pressure pump. The electric pump on the primary filter should only run when the key is off and the primer switch is toggled to on position.

That is what I'm seeing, the electric pump is just to fill filters at service or if run out of fuel.

Being this is a HEUI fuel system, could the starting problem be leaking seals in one or more injectors? I know this is a different engine from the 3408 we had in the 769D haul truck but the starting hard problem sounds similar. Ours would start and run good all week but come Monday morning it would crank for ever to fire up.

After checking all kinds of things Cat Tech and I removed valve covers and when cranking engine we could see a flow of oil out the top of some of the injectors. Replaced injector and it started good no matter how long it sat.

Nige · Dec 4, 2018

Ken, if you look at post #12 I don't think it's the HEUI pump, not with symptoms like that ........ It will start, just misses like a MOFO for the 1st 2 minutes, then straightens up and runs fine. Hitting the primer for 20 seconds before the initial morning start up has seemed to help.....a bit.

Vetech63 · Dec 4, 2018

Nige said:
What schematic are you using ...?
The snip below is from KENR5131-04 (latest available dated 16/12/2014) and I don't see any wire carrying power from the ignition switch. All I see is a wire #326 Purple that is live as soon as the Master Switch is closed. If you want the complete schematic please let me know.
View attachment 188985

Yeah, my schematic doesn't look like that one, they probably got me the wrong one. Mine is publication # KENR8916-12 (Schematic pt # 331-4065) Yours look more like what I have on the machine...……….no wonder this wasn't making any sense! Yes, if you wouldn't mind, a complete schematic on the electrical would be wonderful. Im supposing the electrical transfer pump is only for filling the filters as Ken suggested? I was expecting it to be a supply pump like a lot of Deere equipment has.

Nige · Dec 4, 2018

I double-checked and KENR5131 is deffo the right one for an LAY-prefix tractor. Drop me a PM with your email address. I didn’t get chance to look at our 6T but when I questioned one of the mechanics he told me that the electric priming pump on that tractor was for filling the filters after PM.

JPV · Dec 4, 2018

We have a 325d with a C-7 acert that had a similar issue. It turned out it was the temperature sending unit that was bad and made the computer think it was warmed up when it was cold. It would then read normally as soon as it warmed up slightly, then it smoothed out and ran fine. I plugged into it one morning and noticed it was reading hot when it was cold.
Had me scratching my head for a while!

Not sure on this D6T issue

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