Nanni RPM/power problem

[benjaminpe]

My question is about a motorboat with a Nanni inboard engine. Nanni has marinized the Toyota 1KZ engine, which is also found in the Toyota Hilux, Prado, ...

The story begins like this:
We experienced engine trouble at sea, where the engine lost power, as if you were driving into a net. We immediately shut off the engine, and upon opening the engine compartment, a cloud of steam greeted us, and we saw coolant in the bilge. According to the dashboard, the temperature did not exceed 90°. The boat was then towed to the harbor, and there we began to search for the cause of the problem.

The following tests were performed in our search for the coolant issue:

- Tested the coolant cap, which was in perfect condition.
- Pressurized the cooling system, and there was no leak; the pressure remained stable.
- Disassembled and checked the water pump, which looked like new.
- Tested the thermostat, and it opened at the correct temperature.
- Conducted a CO2 test above the expansion tank, which came back positive, indicating exhaust gases in the coolant.
- Performed a compression test, which was fine.
- Removed and sent the cylinder head to a specialist, who pressure-tested and resurfaced it, confirming its integrity.
- While the turbo was off, we had it overhauled, and it was in good condition; new seals and bearings were installed.
- Cleaned the coolant cooler.
- Installed a new head gasket and reassembled all the components.
During the test run, we encountered the same issue again. Air bubbles entered the cooling system at 2000 rpm, and coolant was pushed out. The CO2 test was positive once more. As a result, we removed the cylinder head again and pressure-tested it ourselves at 7.5 bar with hot water, first on the coolant side and then on the exhaust gas side. Nothing was detected. Ultimately, we decided to install a new cylinder head because we were sure about all the components and could find no other cause. The cylinder head we purchased was not from Nanni but based on the motor code, which is a 1KZ engine. We observed that both the 125hp and 140hp versions of the Toyota engine use the same cylinder head. Our engine has a power of 200hp, but all the inputs, outputs, and mounting holes are the same. The cooling water problem was resolved during the test run, so it must have been a hairline crack after all.

However, we now have a new problem. We cannot get the engine to rev above 2600 rpm. In our quest to find the cause, we performed the following checks:

- Pressurized the exhaust manifold, both on the exhaust and coolant sides, but found nothing.
- Had the injectors retested, and they open at the correct pressure.
- Disconnected the 4 injector lines at the injector and collected diesel during startup; all provided an equal amount of diesel.
- Verified the clearance, camshaft length, valve diameter, intake and exhaust port size, and valve length on the new cylinder head with pre-mounted valves and camshaft. These measurements matched those of the old cylinder head and the specifications in the workshop manual.
- Checked the timing of the timing belt.
- Cleaned and pressure-tested the intercooler.
- Set the wastegate turbo to 1.16 bar, and it opens at the correct pressure.
- Adding extra diesel while sailing made no difference, only more smoke.
- Pressurized the bypass of the small filter located between the intake and the injection pump with an external pump set at 1.3 bar while sailing. We observed that the injection pump is fully compressed by turbo pressure, and the turbo pressure is at the correct level.
- Adjusted the injection pump timing, resulting in more smoke but no increase in RPM.
While searching for a solution, we also performed maintenance and found very fine, shiny particles in both the pre-filter and the fuel filter. This led us to suspect the injection pump. It is a mechanical rotary injection pump from DENSO. We disassembled it and had it checked by a specialist who was puzzled why we brought it in, as he had never received a pump in such good condition. All tests were fine.
To be sure there was no blockage in the fuel system, after installing the tested injection pump, we connected both the supply and return lines directly to a jerrycan placed on the injection pump. This resulted in an additional 50 RPM due to the elimination of filter backpressure.
Finally, we inspected the hull and, in particular, the propeller with a camera. There was minimal fouling, and nothing was found in the propeller.
The propeller shaft is easily turned by hand.
During the test run, we observed that the engine revs up to 2600 rpm. Beyond that point, there is still 1/4 of the throttle lever left, but pushing it further does not increase the RPM, and the engine sound remains the same, with a little extra smoke. The engine starts very well, and up to 2600 rpm, it sounds and responds as if nothing is wrong.

Can anyone help us in our search? We have exhausted all our ideas.

[skipperpete]

Well, you seemed to have covered all the bases with your trouble shooting. After a suspected overheat it’s usual to inspect the condition of the cylinders for scoring (and the head for warping..... but you did a regrind) and help me out here, 90°C barely qualifies as an overheat and you don’t mention any numbers for any of your tests, no actual readings for the compression test, no numbers for the turbo boost, no pressure cap detail, no injector pump report card? No hi idle rpm number, no exhaust back pressure info.
The service manual for this engine is incredibly detailed and it might be that you built in the loss of rpm with the replacement cylinder head either by using the wrong head gasket,( 5 different thicknesses) the wrong camshaft timing or even the wrong head for your year engine.
You had a normally performing engine prior to a minor overheat, spent a ton of money and time replacing a “not leaking” cylinder head but somehow along the way managed to build in a substantial loss of power. These Toyota engines are reliable automotive powerplants, I had one in a previous 4WD here in Australia, ran like a charm despite the outback heat.

[kmacdonald]

Clean the prop and boat bottom and retest.

[benjaminpe]

@skipperpete:
thank you for your response. We did indeed check the cylinders for scoring too. We also used a penetration paint to check for cracks. The 90 degrees doesn't qualify for overheating, but I didn't want to rule out something happened because of high temperature because we lost a lot of coolant and the temperature sensor is located in the retour line at a high point.
The numbers that I have are:
- the compression test was for each cylinder with the new head 30 bar.
- For this boat is the rpm under load 3600 rpm and in idle 4000 rpm. The engine gets under load only to 2600 rpm and in idle it actually goes to 4000 rpm.
- I didn't measure the turbo pressure direct, but I deduced it from the pressure I applied externally to the injection pump that normally is provided by the turbo, so it would be 1.1-1.3 bar, which is what the workshop manual prescribed.
- The coolant cap opened at the correct pressure that was prescribed by the workshop manual.
- We did not get a report card for the injection pump. They said everything was fine for this type of pump.


Is it possible to lose that much power by using the wrong thickness in head gasket, even if the compression test is perfect?
The cylinder head was indeed not leaking in the tests we and the specialist did, but replacing it showed there was a small crack that probably only opened under high temperature.
The timing is checked and is absolutely correct.

I'm not sure if we built the power loss during the search and replacement of the head, because we experienced a power loss while driving (like hitting a net). That was the reason for shutting down the engine immediately. So is it possible something happened because of the heat or steam build up?



@kmacdonald:
thank you for your response, we are planning on doing that. Only the weather doesn't allow us to do that at the moment.

[Tin Tin]

Maybe I missed it, did you replace the exhaust elbow?


Exhaust muffler etc all in good order? No muskrats living in there? - (don't laugh it happened on our neighbor's power boat)



Is it electric or mechanical primary fuel pump? Maybe restricted fuel supply?



New air cleaner?

[benjaminpe]

I don't think I mentioned it, but we indeed replaced the exhaust elbow, because there was some damage to it. The aluminum was crumbling at the end.

The exhaust muffler is one giant closed rvs box. We checked with our hand, but not much more than that. We could check it better.

It's a mechanical fuel rotary pump. I put an external fuel tank direct on the pump to eliminate the whole fuel circuit (tank, filters, hoses).

The air filter is absolutely nothing on this engine. It's a small cloth wrapped around the inlet of the turbo. We already tried without it. The intercooler was also already steamed and cleaned.

[skipperpete]

Originally Posted by benjaminpe

I don't think I mentioned it, but we indeed replaced the exhaust elbow, because there was some damage to it. The aluminum was crumbling at the end.

The exhaust muffler is one giant closed rvs box. We checked with our hand, but not much more than that. We could check it better.

It's a mechanical fuel rotary pump. I put an external fuel tank direct on the pump to eliminate the whole fuel circuit (tank, filters, hoses).

The air filter is absolutely nothing on this engine. It's a small cloth wrapped around the inlet of the turbo. We already tried without it. The intercooler was also already steamed and cleaned.

Thanks for providing the detailed information, you’ve done all the right things with your troubleshooting and I still can’t come up with a logical reason for the power loss. With the worst possible combination of piston protrusion and gasket thickness I don’t thing it would cause such a loss of power but I suspect there’s a possibility of the pistons hitting the head if you went too low with the thickness. Did you do the valve clearances on the new head before installing it ?
I don’t know if Nanni dumbed down this engine when they marinised it but the original fuel system had a plain ol mechanical injector pump, a throttle body and an ECU that controlled the injector pump and if all that electronic stuff is still in place you might be looking at a fault that’s creating a “ limp mode” response but as mentioned previously, your Nanni engine might be very different to my 4WD even though they came out of the same factory..... my hi idle was 4600 and the compression was up around 430 psi.

[skipperpete]

And of course there’s the most logical proposition..... your propeller picked up a plastic bag, get out the go pro again and take a closer look.

[kmacdonald]

If the hull and prop being fouled isn't the problem then its the turbo. Buy a new one, they aren't crazy expensive if you buy aftermarket.

[HeywoodJ]

Originally Posted by benjaminpe

...Beyond that point, there is still 1/4 of the throttle lever left, but pushing it further does not increase the RPM, and the engine sound remains the same, with a little extra smoke....

1/4 of the throttle lever at the helm? Or on the engine? If at the helm, have you disconnected the throttle cable and operated the throttle by hand at the engine?

While cable/connection are not related to the initial symptoms, with all the work that was done it could be that they got disconnected/connected, or just banged around.

[skipperpete]

Originally Posted by kmacdonald

If the hull and prop being fouled isn't the problem then its the turbo. Buy a new one, they aren't crazy expensive if you buy aftermarket.

Turbo was overhauled, new seals and bearings. Could be a blocked exhaust but no back pressure test result so far. If the lining of the exhaust hose opened up, that could rapidly block the exit. The OP is in the hole for a lot of money so far, cylinder head testing and grind, 2 gaskets, injector pump testing ( that’s not free) and another cylinder head , testing of what I think is the heat exchanger, water pump rebuild, compression tests...... and we still don’t even know what part of the world it’s in or if the Nanni is an electronically controlled mechanical injector pump model or plain vanilla mechanical injection. A lot depends on knowing this information.
I’m out of ideas, too many questionable unknowns.

[kmacdonald]

If it came up to the proper RPM before all that work and doesn't now, something was done wrong. The turbo rebuild is the most probable cause IMHO.

[Wotname]

Originally Posted by benjaminpe

.............
The story begins like this:
We experienced engine trouble at sea, where the engine lost power, as if you were driving into a net. We immediately shut off the engine, ...........

What was the rpm immediately before the fault occurred?
What was the rpm immediately after the fault occurred (before shutting down)?

Originally Posted by benjaminpe

...................
- the compression test was for each cylinder with the new head 30 bar.
- For this boat is the rpm under load 3600 rpm and in idle 4000 rpm. The engine gets under load only to 2600 rpm and in idle it actually goes to 4000 rpm...................

Prior to the fault, I assume you could achieve 3600 at WOT underway but after the rebuild you can only achieve 2600 at WOT underway.

Going back to basics, if you can't achieve the rated 3600 underway then there can only be 4 culprits.
1. Excess load (fouled bottom, prop, transmission fault etc)
2. Reduced Air
3. Reduced Fuel
4. Reduced Compression

Going by the above posts, it sounds like 3 & 4 have been fully checked and eliminated which leaves 1 & 2 but both have been partially checked.

I would now concentrate my efforts on continuing investigation of 1 & 2. Note that 2 includes the flow of air from the intake right through to the exhaust exit.

If fault remains after 'proving' 1 to 4 are OK then it is time to recheck all assumptions and start again because the fault must lie with one or more of these possibilities.

EDIT - The above is assuming a purely mechanical injection system; if there is an ECU, then I dunno about 3.

[benjaminpe]

@skipperpete:

- This engine has no ECU, the injection pump has a fuel delivery switch that is activated by a signal from the alternator.
- If the gasket thickness is wrong it is most certainly too thick, we used 5 holes.
The valve clearance was checked. The compression is also around 430 psi.
- The boat is located in Belgium, so extreme weather conditions.
- We checked the propeller thoroughly, but didn't find anything special. As soon the weather is ok, we are planning to lift the boat and give the hull a new antifouling.

@kmacdoanald:

- the next we will do is measure the actual boost pressure and if it's possible the exhaust back pressure. This turbo is changed by Nanni and is not the original turbo, but one that is coolant cooled. That makes it a bit more expensive than the ones that normally on a 1KZ. The boost pressure will give us a better understanding if the turbo is doing its job.
We still think that the power loss did not occur during the rebuild, but when we experienced the power loss during driving and saw the coolant everywhere around and on the engine.

@HeywoodJ:
- we checked the gas cable at the helm and at the throttle body. I even calibrated them a bit better. The response is the same, so 3/4 at the helm is also 3/4 at the throttle body.

@Wotname
- I can't answer the first question completely. We were driving around 3100 rpm, but we don't know the rpm after we experienced the power loss. The motor was shut down immediately.
- Number 1 will partially be checked if we lift the boat. About the transmission. We can still move the shaft pretty easy, the boat accelerates very good, the oil level is ok, so I don't know what more we can do to check the transmission. It works on hydraulic pressure.
- For number 2: I will check the boost pressure and think to disconnect the exhaust elbow and mount a plate on it. So the water will go through the big tube to the outside and the exhaust fumes can come directly out of the turbo. I don't see any possibility at the moment to measure exhaust back pressure.

[benjaminpe]

Is it possible to know what back pressure is acceptable?