[kelaog]

Hello,



Things of note-
EGT at idle seem a lot higher than my 7.3.
In drive with ac on egts on the cummins are between 550-660
in drive at idle I have a bit of black smoke out the exhaust
fan seems to be pushing air OUT the sides of the shroud - I have already trimmed more shroud to let more air out the back (towards engine) but it still throws air out the small gap between shroud and radiator

Couple things stood out to me in this list.
1. EGT's are way too high at idle. I think you have a timing or injector issue to be honest. This is evident by the black smoke at idle, high EGT's, and high jacket water temps.
2. Fan should be a pull type. It is somewhat normal for a fan blade to throw air radially away from the fan blade. This is how centrifugal pumps work.
3. Are your electric fans mounted in front actually causing a significant restriction on the air flow? Are they moving air the same way as the mechanical?

To be honest, spend most of your time on #1. I'm betting it resolves your overheating issue.

I've had a similar issue before and the coolant temps dropped way down when the timing was corrected.

 

[kelaog]

Could that cause high idle EGT as well?

Yep. It's an U shaped curve.

Too little timing and the fuel is still burning as the exhaust valve is open and also, if it's injected too late then the piston is already on its way down so less of the fuel energy is converted into work (ie: converted into heat). The combustion quality is poor for a number of reasons but in a diesel engine it would be because of poor atomization and because a good chunk of the fuel is chasing the flame front while it's being injected.

Too much timing and you have combustion trying to force the piston down when it's got a long ways to come back up. The result is that you get incredibly high force on the crank due to excessive piston pressures and that excessive pressure generates a tremendous amount of heat.

Probably some better explanations out there but that's my understanding of it.

 

[kelaog]

Are we talking enough adjustment in the slotted holes to make timing far off enough to cause something like this? It is a major pain to get to that back pump bolt but I will gladly retard/advance the pump with the adjustment slots if it could be off that much. Pump was locked when I got it back from being rebuilt, lined up to "E" on cam gear. I did have to pull the pump after cam break in to fix tappet cover leak but I did not remove the front cover, just locked the pump, removed, and slid back into gear/keyway.

If the pop test is free, start there...If those are good then there may be something off with your injection pump (despite it being rebuilt).

I think the timing gear is set correctly to stock.
Timing marks on pump drive gear. | Dodge Cummins Diesel Forum (cumminsforum.com)
Timing Question | Dodge Cummins Diesel Forum (cumminsforum.com)

 

[kelaog]

Ok. Cool. One other thing I was wondering. If by some chance the injectors were much larger than what I ordered (5x12) it seem like that might also cause similar problems. The flow specs for my pump are below. When I first got everything together the smoke/egts were nuts. I had to back off the smoke screw 5 full turns and rotate the fuel pin from where they had it when it was built (most aggressive setting) to almost the least aggressive setting. I talked to the pump builder and he said it should not have smoked crazy with only 5X12 with the way he set it up. I gave him all the build info before he rebuilt the pump. Injection shop in town said they could pop test injectors and test for leakage, but he said he would try to retard the pump and see what effect it has.


stock fuel pin and screw, 366 gov spring

1000 rpm/ 0 psi boost- 70cc
1500 rpm/ 0 psi boost- 100cc

1500 rpm/ 20 psi boost- 160cc
2000 rpm/ 20 psi boost- 160cc
2500 rpm/ 20 psi boost- 160cc
3000 rpm/ 20 psi boost- 150cc
3200+ rpm defuel

I suspect your issue would get worse with timing more retarded than not but that would probably prove out the theory. I think you're in a very retarded condition (the engine, not you personally).

Other thing that could cause your issue is air in the lines/pump. Diesel fuel is basically incompressible, air is not. If you're not developing the right injection pressure then your atomization is poor and the injectors may not be popping at the right time either.