Turbo Questions, Yanmar 4JH2-TE

[imus]

Regarding your test run and low boost - I have noticed in most turbo vehicles I have driven, the turbo does not build much boost until it is loaded - an example would be cruising along the highway - the boost gauge might read 2 or 4 psi, however, when you step on the gas, the RPMs remain the same, but the boost PSI spikes considerably because (I am guessing here) of increased exhaust flow due to increased combustion - as opposed to exhaust flow being a function of RPM only. I am guessing that's why boost spikes while rpms remain the same? If all that is correct, I wonder if your engine is actually loaded enough to require the extra fuel at speed that's needed to spin the turbo enough to build significant boost ? Seems like you might be able to turn your prop all the way to rated RPM perhaps without boost?

Anyway, just my own crackpot theory.

[CrispyCringle]

^^^^ I agree with you. Thats why I ran it up to 3500 rpm under load. I believe 3600 is the max. At least thats where all of the performance charts cut off.

[imus]

Your prop pitch may not be steep enough or your prop diameter too small to fully load the engine is what I'm getting at - like you can basically run it as non-turbo engine all the way up to max rated as is possibly. If that is the case, the only way to solve that part of the boost riddle is to adjust the prop.

[CrispyCringle]

I see. I dont think thats the case. It will go a little over about 3700 rpm if I push the ball to the wall. And thats off of the rpm gauge, which read a little high if my digital rpm device is correct. Pretty sure the prop is about perfect. Its a Variprop and the PO spent a lot of time (or money) getting it right, it seems.

In other news, I requested an exchange for the manifold gauge with Amazon and it showed up in less than 18 hours. As much as I want to hate Amazon, I cant help but be in love with that kind of service. Amazing. The human lung pressure test registered about 3 psi this time. Keeping my fingers crossed that I get different results on the boat.

[CrispyCringle]

Ive got new pressure gauge installed but still haven't tested it out. In the meantime I started thinking about possible causes of low pressure output. I shouldn't have thought about it and just tested out the gauge first. Im still hoping that a faulty gauge was the issue. But assuming the turbo is freely spinning, the one issue that stuck in my head the most was some sort of blockage in the exhaust. Reasoning being that a clogged exhaust path would hinder turbo spin-up. When I had the mixing pipe off of the turbo I only looked into the mixing pipe at one end- the the end that bolts up to the turbo. The other end was still connected to the exhaust pipe. I had to know what was going on at the other end of the pipe. So off came the mixing pipe. It was 100% free and clear. Only had a light layer of black carbon which I rinsed out. I decided to replace the rubber exhaust hose from the mixing pipe to the muffler since it was sounding a bit crunchy when I took it off. So, I was putting it all back together in anticipation of good weather this weekend and of course lost the gasket to the mix pipe/turbo down into the bilge!!! So annoying. Tried fishing it out, but its non-magnetic metal and I couldn't see it. No local part supply, so its on order. I was thinking only seconds before losing the part that I really need to stuff a towel under the work area- clink, clink, splash. Gone.

So anyway, I checked the 3" exhaust hose all the way out to the transom. No kinks or possible blockage that I can see for the exhaust. That would have been an easy fix. Next I checked the oil return off of the turbo. This can cause turbo oil leaks. Not really my issue, but while Im there... No kinks, continuous gravity feed path to the sump, and its a large pipe. I find it hard to believe it could be clogged, so I didnt take it off.

Next will be running the engine and checking manifold pressures again. I also need to pay attention to the blow-by by taking the oil fill cap off or pulling the CCV hose going to the air screen.

If the next test run still shows no to low manifold pressure Ill be pretty stumped. Its not binding, clogged, dirty, bent, leaking and spins freely at idle. What else could cause it to not work?

[Toccata]

Followup on my previous post.
Re water in fuel (added this but just to complete the storey for a future reader)
The water in my fuel tank had been there for some time I suspect, it had caused corrosion in the fuel pump. The diesel is also the lubricant in a fuel injection pump, displacing the fuel had caused damage to the fuel injection pump. Not allowing full travel of the rack. But you are obtaining full rpm so I suspect fuel flow in not the issue in this case.
At the risk of sounding like a broken record, what is your exhaust back pressure reading?

[CrispyCringle]

Toccata, I went back and read your post #10 on measuring exhaust pressure. I was about to say that I didn't know how one would measure the exhaust pressure because of where to tap into it, but you had a good explanation. It wouldn't be as simple for me. I apparently have an aftermarket mixing pipe. Its pretty much a flange and heavy SS bent tube with a Y-connection for the water. No place to tap pressure from. But to answer your question- exhaust pressure unknown. Cant see how it would be much with a 3" pipe that isnt kinked. Im curious what kind of pressures were you getting?

[Toccata]

From memory it was about 200mm of height difference (one side of the water column compared to the other side) It was well within specs, but only after rebuilding/re-routing the exhaust system following David Gerrs' rules.
For the purposes of the pressure measurement, You can readily drill a hole, tap it and connect a hose tail. After the measurement, install a blanking plug.
My suspicion, after all you have done, is that the turbo may require a professional check/overhaul. there must be gas escaping/blowby? or poor bearing performance with heat? or out of balance? or worn blades? or out of tolerance between the blades and housing?
I was told "they don't rebuild these little turbos" so I bought a new one (lots of $) then I found a small shop who rebuilt the original. Very frustrating! particularly when the problem was in the fuel injection pump all along.
Of note a local diesel mechanic followed my logic and agreed with the thought process, it was indeed an unusual fault to find the corrosion inside the fuel pump.

[CrispyCringle]

Follow up. The stars finally aligned today and I did an engine run up in the dock. Prior to this I did a few things while waiting for the new gasket:

-I cleaned the exhaust side of the turbo with carb cleaner. The light carbon layer easily cleaned off and I had shiny turbo blades.
-I changed the oil in the engine. I went to a lighter grade, still recommended by Yanmar. The idea being the thinner oil would allow the oil bearings in the turbo to spin more freely.
-I was looking through the maintenance records and receipts from the previous owner, checking for what was done during the engine rebuild 360 hours ago, because I was considering getting new injectors if they were not replaced. Come to find out the turbo unit was replaced about a year prior to the rebuild. The injectors were "serviced".

So I did the runup at the dock. I went up to 3000 rpm. I didnt feel comfortable going higher because I was doing this alone and I was getting nervous about the prop wash on the boats across from me as well as having to run down the companionway and check the manifold pressure and run back up to the cockpit to make sure I hadnt broken free.

The result is I got about 5.5 psi at 3000 rpm. I dont have any data on what the pressure should be at certain rpms but it seems low to me, unless its an exponential curve to 3600 rpm. However in the Yanmar troubleshooting grid for the turbo it mentions if you cant reach max RPM (3600) the turbo may be faulty. I can reach max RPM.

I think Im going to give the engine a good flogging the next time Im out of the slip and monitor. Of all the checking Ive done, Ive come up with zero negative findings. As you all may recall, my original issue was no turbo sound (which I used to have) and light white smoke. From all my research on these issues, one thing that Yanmar says can cause white smoke is water in the fuel. My fuel is sort of old. I have a 100 gal tank and it had about 50 gal in it when I bought the boat. I filled it up about a year and a half ago and Im still at only a half tank. I just dont need the motor very much because I generally go out on good sail days. So maybe the fuel is an issue. Although the motor runs fine, and I see no water in my Racor glass fuel bowls. I dont know. Im rambling. Ill report back if I find anything else.

[skipperpete]

It sounds like you have a fairly healthy engine, don’t be too concerned about boost pressure being a bit off, I suspect that you can’t achieve full load even with the prop stalled running against the mooring lines, in fact the load might even drop off at high rpm due to cavitation after a certain point. The turbo on your engine has a continuous rated speed of 155,000rpm with a max temp of 700°C and that’s usually what you would expect on an engine Dyno test, but that’s hard to replicate in the water unless you have a variable pitch propeller. Easy to do on gensets. Previously a poster mentioned the turbo behavior in automotive applications where the boost is visible on a panel gauge and the temp on a pyro, this is the best way to get an idea of how the turbo responds to load. Even under those circumstances it can be difficult to get a predictable pattern with the now common variable nozzle turbos, more like jet engine tech than plain old diesel mechanic stuff
An interesting snippet from the 4JH2 manual is that they consider it reasonable to do a turbo wash using their method every one or two weeks, seems ridiculously excessive but that’s what Yanmar suggests.

[CrispyCringle]

Thanks for the feedback skipperpete.