Inconsistent power from 1HDT (1 Viewer)

Joined
Aug 4, 2019
Messages
17
Location
Victoria, Australia
Hi all..
I’m getting inconsistent power out of my manual 1hdt, non intercooled whilst towing a caravan through central Australia.
Engine, pump and injectors have done 20k since rebuild.

When we left, I struggled to maintain 90kph on flat roads.
As we went on, after two days it was comfortably managing 100kph up moderate hills.
Then it was back down to about 90kph max on flat roads, then down to 4th up the slightest of inclines/headwind.

The daily temps were all around 24deg C.
Engine water temps have stayed at approx 83deg C and Egts have been consistently around 350deg C under at 100kph many
Weight/load has been approx the same(no massive change there)

Obviously if it was a petrol engine then octane would play a part - but diesel is diesel right ?

My main thought is perhaps fuel quality ?
Or water/dirty in fuel ?

I will change the fuel filter when I get back. It’s just strange that it would get better and then crap again.

I didn’t notice a specific point where it changed. Usually the next day.

Any thoughts on what could cause this?

cheers,
Rob
 
Joined
Aug 4, 2019
Messages
17
Location
Victoria, Australia
I’ve been wanting to fit an after market fuel filter with a sight bowl for that reason-just haven’t got there yet. Seems like now would be a good time.
I figured that would be the main response, but wanted to ask anyway in case someone else had another theory.
 
Joined
Sep 30, 2014
Messages
536
Being a 1HDT it would have had the earlier/smaller size fuel lines compared to the later 1HD-FT. They are susceptible to getting blocked, limiting the amount of the fuel the engine can suck through. When you change the fuel filter it may be worth blowing some compressed air back into the tank to hopefully clear out any blockages. You don't need much pressure (10-20psi) is more than enough...

Note you will need to spend some time with the primer pump to suck the fuel back through. At some point it may be worth pulling the inspection cover off and checking how clean the tank actually is. You might have a build up of algea in the tank, alternatively Algea treatment chemicals isn't expensive, so might be worth putting some through just for the sake of it.

Alternatively it could also be the primer leaking air into the lines which can result in inconsistent power.

Finally, after driving for a while open the fuel cap and see how much air gets sucked in. The fuel caps have a one way valve which can get blocked over time, preventing air getting back into the tank. In this case it gets harder and harder for the engine to suck fuel through, resulting in lower power. If the engine starts strong but performance gets worse during each trip (even over a 5 minute period) this could be the problem.
 
Joined
Aug 4, 2019
Messages
17
Location
Victoria, Australia
Being a 1HDT it would have had the earlier/smaller size fuel lines compared to the later 1HD-FT. They are susceptible to getting blocked, limiting the amount of the fuel the engine can suck through. When you change the fuel filter it may be worth blowing some compressed air back into the tank to hopefully clear out any blockages. You don't need much pressure (10-20psi) is more than enough...

Note you will need to spend some time with the primer pump to suck the fuel back through. At some point it may be worth pulling the inspection cover off and checking how clean the tank actually is. You might have a build up of algea in the tank, alternatively Algea treatment chemicals isn't expensive, so might be worth putting some through just for the sake of it.

Alternatively it could also be the primer leaking air into the lines which can result in inconsistent power.

Finally, after driving for a while open the fuel cap and see how much air gets sucked in. The fuel caps have a one way valve which can get blocked over time, preventing air getting back into the tank. In this case it gets harder and harder for the engine to suck fuel through, resulting in lower power. If the engine starts strong but performance gets worse during each trip (even over a 5 minute period) this could be the problem.
Thanks for that info.. all worth looking at-especially the fuel lines.
I have checked the tank, which was clean as a whistle.
The cap has that suction issue, but doesn’t seem to make a difference after it’s been opened to let the air in..

actually, another thing that I noticed, was that the idle dropped from 750rpm to around 400-450rpm (with Ac off).
will look into those ideas though.
Thanks !
 
Joined
Feb 11, 2009
Messages
21
Location
Mono,Ontario , Canada
Hi all..
I’m getting inconsistent power out of my manual 1hdt, non intercooled whilst towing a caravan through central Australia.
Engine, pump and injectors have done 20k since rebuild.

When we left, I struggled to maintain 90kph on flat roads.
As we went on, after two days it was comfortably managing 100kph up moderate hills.
Then it was back down to about 90kph max on flat roads, then down to 4th up the slightest of inclines/headwind.

The daily temps were all around 24deg C.
Engine water temps have stayed at approx 83deg C and Egts have been consistently around 350deg C under at 100kph many
Weight/load has been approx the same(no massive change there)

Obviously if it was a petrol engine then octane would play a part - but diesel is diesel right ?

My main thought is perhaps fuel quality ?
Or water/dirty in fuel ?

I will change the fuel filter when I get back. It’s just strange that it would get better and then crap again.

I didn’t notice a specific point where it changed. Usually the next day.

Any thoughts on what could cause this?

cheers,
Rob
Hi All
1HDT autobox or manual? Which gear did you do the towing with and how heavy was the caravan? Any strong head winds ?
 
Joined
Aug 4, 2019
Messages
17
Location
Victoria, Australia
No head winds. Manual. Caravan weight around 1200kgs loaded.
I’ve changed the fuel filter, whilst there was a little bit of debris in there, it wasn’t by means “full” or built up.
no change after the fuel filter was changed.

I’ll try to look at the primer this weekend.
 

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