2003 Z150TXRB Exhaust Tuner Help

[J-absher]

Hey guys, thanks for the add. Sorry for the long post but I could use some help. New to the forum and Yamaha but long-time boater. I purchased a 2003 HPDI 150 Z150TXRB a few months ago. I knew it had some issues but the compression tested okay at 110-120 across the board. So, I figured from searching these engines it was probably the usual suspects, vst filter, mystery filters, fuel/water filter etc. When I first mounted it to the boat I changed every filter on it including the 2 screens in high pressure pump and 6 in the injectors, spark plugs, low pressure diaphragm pumps, electric pump and screen filter. I learned quickly that the previous owner or mechanic’s work was suspect to say the least. The electric pump in the vst wasn’t even the correct one, it didn’t fit but was forced together. Finally water tested and ran terrible. Had a bad TPS sensor. Replaced that and idles perfect, jumps on plane but has no top end. Tops out and 4100 rpms and surges at wot. Back the throttle some and gets smoother but will not gain rpm. Seems happy up to 3800. Dropped from 21p prop to 19p and no change. YDS shows no current codes and mechanical fuel pressure gauge reads 50 while rail pressure is around 730. I read another post describing this exactly and it was a burnt exhaust tuner. My lower unit is off so can you help please? What would I be looking for? I’ll pull the power head if necessary but don’t want to if it’s avoidable.

[J-absher]

Well I can’t find any obvious damage in the midsection. At least no visual signs from below. No sign of metal cracked or melted. I guess my search continues. I’m gonna check the low pressure pumps again. It certainly acts like either exhaust restriction or fuel starvation. I’ve found engraving on the high pressure pump showing it was serviced August of 2017. Injections are also engraved. I don’t know how many hours ago but they have been serviced also.

[TownsendsFJR1300]

Can't help ya but just curious what / where the exhaust would burn (fail?).

[99yam40]

some motors had exhaust stack erosion.
from what I think I read if you can see the gaskets( not covered by the casting) you should have a look.probably need to look with a bore scope camera

but then I have no idea if your motor is one that would have that problem.

I thought that caused an over heat, not sure

[zenoahphobic]

They look bad to me in those pictures... or are my eyes failing?..

[J-absher]

I have never had one fail so I’m not sure what I was supposed to be looking for. I read another post here that described my issues exactly that turned out to be a melted tuner that restricted the exhaust flow. It made sense so I thought I’d take a look. However, I can’t see anything blocking the exhaust ports. They’re dirty, but open. So, I’m back to chasing fuel issues....

[J-absher]

Any suggestions are greatly appreciated.... I cannot get more than 4100 rpms out of this motor. 100% all new filters, plugs, fuel lines, tank drained/flushed, electric pump, diaphragm pumps, coils tested with yds and timing light, injectors checked with yds, o2 sensor cleaned (new one ordered to try), new tps. No current codes??? I’m at a loss, any help is appreciated.

[panasonic]

What other post describing this problem are you referring to? Was it on this forum or another one?

[panasonic]

Perhaps you can spray some engine degreaser up there and give it scrub. Take some more pics with good lighting. Hard to see from the pictures you posted what condition the exhaust is in.

[J-absher]

I’ll try to get some better pics. The post that really describes my issues exactly was one I read on another site. I’ve read dozens of threads on surging or bogging issues. Not the same block as mine but his fit the bill perfect. It was titled, 2003 Yamaha 250 HPDI bogs out at 4000 rpm HELP!!!!!!. He chased it for months, tried everything I have and finally found it to be caused by blocked exhaust ports.

[pstephens46]

They look bad to me in those pictures... or are my eyes failing?..

The pictures suck. Plain and simple. Damn well most likely a fuel related problem.

thought I was looking down a throat....

[J-absher]

I can’t find any cracks or metal shavings in the midsection or lower unit so I’m also back to chasing fuel . I just tested the injectors again with yds and ran another compression check. Compression is 110-120. I pulled the plugs and used a flashlight to look inside the cylinders while firing each injector with yds. They all fire but #5 doesn’t cloud the cylinder nearly as much as the rest. Anyone know of a better way to more thoroughly test this?

[zenoahphobic]

The pictures suck. Plain and simple. Damn well most likely a fuel related problem.

thought I was looking down a throat....

Yes need better pictures.
What I see in the second picture (right), that the right chamber at the bottom, has a massive chunk missing! Apart from this gap the rest of the top mating surface is quite pitted.

The thing is you are not considering a blocked pipe, no amount of carbon or deposits or corrosion was ever going to do that. What you would be looking for is exhaust escaping where it shouldn't, sufficient enough to alter the tuning (or back pressure) affecting the higher rev range; if indeed this is the cause of your problem.

[J-absher]

It’s hard to get clear pictures up there. I may have to get a camera scope. Hopefully these are a little more helpful. Thanks for the replies. Hope to find the issue soon. I can’t see any obvious restrictions.

[J-absher]