Auxillary braking issue

[69dave]

Hi everyone
I think I may have posted in the wrong area, so here it is

I have a 2018 model Hino FM with the A09C 350hp engine. According to what info I can find, these engines are all fitted with compression (Jake) brakes, and mine is also fitted with an exhaust brake immediately after the turbo. Previous year models were apparently fitted with a multi-stage combination switch to activate auxilliary braking. Mine only as a single stage switch. My truck has had thousands of dollars spent by the previous owner diagnosing and rebuilding the jake brakes, only for them to discover that the jakes don't work with the engine warmed up, only when cold. With a bill of over $8K, they said there is nothing they can do, as the engine has low oil pressure.
I believe the dealer to be wrong based on a couple of reasons.
1. The engine runs beautifully quiet hot or cold, starts perfectly and makes good power
2. The exhaust brake does not work either, except via the "test" button on the dash next to the steering column

The indicator light for the exhaust brake lights and exhaust brake does close when the test button is used, and the indicator light for the Jakes lights up reliably on use of the combination switch, but they do not work when hot.

I believe I will have to at some point pull the rocker cover to verify the mechanical ntegrity of the Jakes myself.

My question is, are there any common causes of what I am experiencing?
All input welcomed

Tia
Dave

 

[greasytshirt]

Sounds like an Australian truck. I have an A09 manual on my computer at home, maybe it has some insight.

 

[69dave]

Gday greasytshirt. Thanks for the reply. I have a copy of an A09C workshop manual, and an electrical manual, but the electrical manual must be wrong as none of the fuse panel aligns with what is in the truck, and I cannot find a more relevant 1 to download.
As an update, today I finished putting in an oil pressure gauge to see if it had low oil pressure, or a pressure drop when switching on the engine brake. It shows over 80psi cold, and once hot, shows 45psi at idle and goes straight to 80psi once over 1000rpm. It has 517,000km (323,000mi) on it. Next step will have to be to lift the rocker cover to see what is really going on. On the invoice from the dealer under the previous owner, they say they replaced the 2 electric solenoids, checked switched power to the solenoids and replaced all the pistons. The invoice then says "working".... until hot. They checked and reported low oil pressure
I honestly think they either don't know how to adjust the valve clearances/and subsequently the slave piston clearance and an 'O' ring has popped out, or maybe an apprentice installed the solenoids and forgot the 'O' rings.
Tia, David

Edit: Yes, It's an Australian truck