Strange turbo behaviour

[dunmoven]

Hello all! I am not very clued up on mechanical diesel systems. I understand the basics and have done some simple repairs in the past.
, but can't imagine why my turbo / injector pump is not working correctly.


Firstly some info: The turbo is the standard OEM and I believe it is the original unit. and thus has done 450,000 k/m with no problems.
The previous owner had the injector pump overhauled at 256,000 k/m. It cost of some $2600. This was done through a dealership to solve an over- fueling issue during warm up.
Soon after the pump overhaul, I bought the vehicle and replaced the glow plugs, water pump, harmonic balancer and removed the sticky dump valve completely. This vehicle has always been well cared for with oil changes at 10k intervals without fail.



At around 390,00 km I went searching for the cause of a power loss and checked valve clearances and replaced the timing chain and injectors. There was a noticeable improvement in performance. The fuel economy has always been steady at around 9.7 to 10 LPH. Even with over a ton of camping gear on board I was amazed that it was 8.9 LPH over a round trip of 8,600 k/m.
For the last 10,000 k/m or so, I have noticed a power loss again, and suspected the turbo so I fitted a Redarc boost + EGT gauge. Now I see that when climbing a moderate hill (with very little weight on board) the boost does not reach more than 5 - 6 lbs, even at 3500 rpm unless I put my foot to the floor, and then the boost shoots immediately to 9.5 lbs. Of course this sends the EGT sky-rocketing and there is no power increase ( I suspect because the engine is then over-fueling).
Compression test revealed nothing of any concern, and I have no oil consumption issues. I have tested the waste-gate operation and its normal. I have replaced the muffler, fuel filter (and cleaned out the fuel lines) and checked for air leaks. and found nothing.
There is a pipe connecting the turbo output chamber to the injector pump and I presume this is for enrichment and or injection timing shift in certain conditions.
I 'm wondering if this could be malfunctioning somehow. and whether I can do any checks or inspections in that area without any major pump dismantling.
I have not given up on this and i won't because I just love this old thing and it is rust free and seems to be fine in every other way.
Sorry for the very long story, but I wanted to give all the details in the hope that someone has seen this before or can suggest something I have overlooked.
I do have 40+ years of auto electrical and electronic management systems experience, and hope that I can be of help to many members here in that area.

[Mcreight911]

The small hose from the turbo to the top of the pump is a boost hose . Inside the top of the pump is a diaphragm, boost compensator . The diaphragm may have a hole in it .
If you take out the 4 bolts the top cap comes of and the diaphragm and pin will pull up and out . You may need to turn it and pull up. The pin is tapered an essentric so mark it's orientation befor pulling it out . If no holes are visible in the diaphragm colour the pin with black permanent marker and refit it , either take it for a drive or put regulated compressed air (10psi or whatever boost your turbo is set to deliver) into the compensator line . Remove the diaphragm again and you should see a mark where follower pin has rubbed the marker off. Should be over half he length of the pin . If not there's an air leak.
You can use compressed air to test the psi required to open the turbo wastegate actuator too .

It's also possible that the relief valve (the big nut thing) in the intake manifold is leaking . I replace them with a pipe blank as there not needed . The standard engine handles 30psi no problem.

My guess is the wastegate actuator is opening too soon or the diaphragm in the compensator has a Leak .

I would set the boost to at least 12psi and not more than 15 with the standard td04 or tf035 turbo

[dunmoven]

Thanks for that advice Mcreight


I will do the things you suggested and see how it goes. Won't be able to do it for another week due to other commitments though. Do you think it's okay to run 12 psi on an older engine that has done 468,000 k/m? Just checking because I have been tempted before, but don't want to push the old thing into a quick death.

I removed the pressure relief valve from the intake a long time ago because I was suspicious of it. I had the hole welded up at the local engineers. Had to tow the caravan 300 k/m yesterday and it was a pretty painful run, so I really want to get it back to it's old state soon.

[Mcreight911]

Thanks for that advice Mcreight


I will do the things you suggested and see how it goes. Won't be able to do it for another week due to other commitments though. Do you think it's okay to run 12 psi on an older engine that has done 468,000 k/m? Just checking because I have been tempted before, but don't want to push the old thing into a quick death.

I removed the pressure relief valve from the intake a long time ago because I was suspicious of it. I had the hole welded up at the local engineers. Had to tow the caravan 300 k/m yesterday and it was a pretty painful run, so I really want to get it back to it's old state soon.

12psi won't even come close to stressing the 4m40t . Over advanced timing will create a bigger combustion pressure spike than that . I clocked up 150000 at 26-28psi and around 20000km at 32psi during turbo testing . Fuel system condition and setup is critical though . That's what will kill your engine quick . Only drama I had was a head gaskit due to running silly fueling (massive egt's )
At 12 psi the turbo will be pretty happy too, if it were me I'd run 14psi .