Boost pressure mercruiser 1.7d

katarina77 · 09 July 2016, 19:58

Hello guys.

My mercruiser 1.7dti has too high boost pressure under full load. The boost gauge says 1.4bar (20psi). according to manual it should be max 1.2bar (17). Is it possible to adjust the pressure with the waste gate rod? should there be a certain preload on the waste gate rod when connecting it to the waste gate valve?
Or maybe its getting too much diesel?

<thank you

matata · 09 July 2016, 20:09

Do you know the gauge is correct/ Nik

katarina77 · 09 July 2016, 20:13

Havent checked it, but it is brand new electric/mechanical. Its connectied too the inlet manifold.

matata · 09 July 2016, 20:53

not much help but i'd make a water manometer about the height of your house 46 feet exactly and check the gauge. ok only joking!!! Convince yourself the gauge is correct and take it from there. Ive got a tiny tach which was set up for me a few years ago. I have a honda set of outboard gauges / rev counter and its consistently inconsistent. i'd have thought correcting the boost pressure is prob very easy. Nik

C-NUMB · 09 July 2016, 21:46

Wastegates are known to get stuck on that engine, maybe worth checking if it operates as it should. Not sure but think that if it's not opening enough the pressure gets higher than it should.

beamishken · 09 July 2016, 23:52

Easy to check the waste gate is stuck ( it probably is as it's a common problem)
Remove the two bolts holding the presure operated waste gate actuator and see if you can push/pull the operating leaver in the middle of the turbo that's connected to the waste gate flap
Some are siezed solid and require a new turbo but you can sometimes free them off by spraying with wd40 & carefully trying to tap/ pry the operating leaver untill it moves once it's moving you can usually work it untill it's free enough to operate

beamishken · 09 July 2016, 23:56

Don't be tempted to just keep running it as you will crack a piston if the waste gate is stuck
They usually go like f-- € when the waste gate is stuck but only untill a piston let's go which is almost inevitable so it's important it's fixed

Daibheid · 10 July 2016, 13:44

Seized wastegate. If you.ve a high pitch prop on and/or operate at high revs the engine will self destruct so get it looked at and hopefully it can be freed up or you may be replacing the turbo as it's built into the housing.
It might be possible to fit an external wastegate but there's not much pipe work around that rather compact turbo
Let us know how you get on

katarina77 · 23 July 2016, 13:11

hello again, I have checked the waste gate flap, it is operating freely, so the waste gate is not stuck. I have checked the waste gate actuator with a pump too chech the opening preesure, the rod starts to push on the waste gate at 1,2bar, for the waste gate to be fully open it requires 2,3 bar. Its not the waste gate, I also belive the turbo boost pressure should be more than 1,4bar if the waste gate flap was stuck closed.

beamishken · 23 July 2016, 23:15

Sounds like it just needs adjusted there should be a threaded portion and lock nut in the rod try screwing it untill it's cracking sooner

katarina77 · 24 July 2016, 08:33

yes it has a threaded portion. Now it has zero adjustment, meaning that the actuator rod is fylly back, and it fits the waste gate flap without use of any force.

If I lenghten the rod example 3 fully rounds, then the waste gate flap needs to push a little open to fit the rod, so the waste gate will always be a little open and bypass some off the exhaust cousing lower boost pressure?

If I shorten the rod, I have to pull out the rod to make it fit the waste gate flap, meaning the waste gate flap is shut closed with some force, cousing it to increase the boost pressure?

Am I correct?, I dont know how to adjust actuator rod.

beamishken · 25 July 2016, 10:34

It needs to be adjusted so the wastegate is closed at zero pressure but opens at the required maximum boost.If you can't adjust it then I'd imagine the actuator is at fault requiring too much pressure to open the gate

katarina77 · 25 July 2016, 10:37

it starts to open at maximum required pressure 1,2bar, but needs over 2 bar to be fully open.

beamishken · 25 July 2016, 12:15

It may be that it doesn't need to fully open & or the pressure from the turbo running will assist with opening I'd adjust it and try again and see if it's still overboosting maybe with a second gauge