2001 0x66 250 TURZ Multiple Blown Head Gaskets

[Bonafishark]

Need some direction if possible. Never had any issues until couple weeks ago. Temp alarm and overheat at low RPM's after running for 15 minutes down the canal and right before throttling up. Block looked like it got hotter than should have before the alarm sounded, some melted wires, browning of the block, etc. Tested thermo switches and they functioned fine. This overheat caused (Im guessing) the head gasket to rupture on the left bank between 2 cylinders. Replaced the head and cover gaskets-no sign of warpage/pitting or scoring- water pump/impeller-old one looked fine, new plugs-PRV and Tstats. Did find one Tstat that was stuck open, maybe it could also have been stuck closed. Engine ran fine for couple outings than she started having slight surge issues through the RPM range and eventually full power loss. Head gasket in similar spot on right bank blew. Replaced the gaskets, no visible sign of damage to cylinder, did not get any heat alarms this time. Also replaced the low pressure fuel pumps and all the fuel lines. Same scenario-she would run fine at first, than start surging up and down the RPM's and than eventually power loss. One quick overheat for couple seconds but instead of the temp gauge blinking it was the oil bars blinking. The head gasket in the same spot on the left bank blew again. Need some help in the right direction. One thing I have noticed is excessive oil consumption for month or two prior to the issues, maybe 30:1 if Im lucky. Checked and readjusted the Oil Pump Linkage. I feel like Im still battling the same issue that caused the original overheat, although half the time it feels like fuel starvation issues. I dont think this would cause multiple ruptured head gaskets but I could be wrong. I did run Ring Free for couple of fill ups. The new plugs do get dirtied pretty quickly and seem to be carboning up fast. VST screen cleaned and checked and all ok.
Any thoughts appreciated. Any additional info will be supplied quickly. Thanks

 

[rodbolt]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

running lean will blow head gaskets as well as overheat.
how did you check the head and deck for warpage?

 

[Bonafishark]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

Thanks Rodbolt. I checked with straight edge and feeler gauge but am also bringing in the heads to a machine shop to double check. The heads did seem a little warped is some spots but not horrible. I did notice when this all happened that one of the screws holding the TPS was loose and retightened it and now realize that I must check the voltage readings. Do you think an improperly aligned TPS would cause the engine to run too lean?

 

[rodbolt]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

wont
however the heads are LOOOOOOONG.
maximum warpage from one end to the other,,,,,,.004". average human hair is .003".
kinda thin actually.

 

[Bonafishark]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

I appreciate your help thus far.
Regarding the TPS- I switched one out with a borrowered one from Yamaha shop, used but working, and get the same readings of 4.5 volts, throttle closed. When I open the throttles, I get the same results and a ZZZZZ sound. If I 'm reading the manual correctly it should be .48-.53 closed and 5 open.

Regarding the heads-I had a local machine shop cut them, as there was some warpage. I thoroughly checked the deck and did not see any warpage evidence, .004, so I reassembled everything, ran it for 10 minutes and checked compression and all were at 118-120. I did have some excessive smoke for a little bit, reading that it is normal, just never had it before. I brought the engine up to 1500 RPM and there was some stuturring and wanted to choke out but she kept going. Looked like a small amount of fuel/oil in the exhaust on top of the water. I did make sure all throttle valves open and close in synch and also checked the oil pump link rod and it appeared to be at the correct setting. I did pull off the O2 sensor and I was heavily caked up-worse I have seen it.
Not sure if I mentioned prior but after the first failed gasket, I did find one of the LP fuel pumps was leaking, after replacing all three, I ran for a while with a crack in one of the hoses, which I have since replaced.
I guess my question is what are the major causes of running lean-can it be due to air in the fuel lines?
Where should I continue to look.
Thanks again.

 

[rodbolt]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

your checking the wrong wires on the TPS, at least we know the TPS reference voltage is ok.
the BZZZZZ your hearing is the injectors reacting to TPS motion.
however I dont recall TPS voltages in this post.

 

[Bonafishark]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

Thanks. I was testing the orange and pink but will see where I went wrong.

 

[Bonafishark]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

Duh-was testing the wires on the wrong side of the harness-didnt notice they switched. Set it at .48 volts. Took the boat out for the day and all seemed ok, everything back to normal, but was not too suprised conisdering it is usually the 2nd or 3rd time when the issues start. Will post back after couple more trips or issue repeats, whichever comes first. Thanks again.

 

[Bonafishark]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

Ok, so the heads seem to be holding up. I had some debris in the remote oil tank filter and thanks to your Precision Blend posts I was ablt to isolate and rectify.
The new problem I am having is after running the boat for a couple miles and slowing down, due to 5 MPH zone and than getting her back on plane can be hard sometimes. Seems like she is running about 200-300 RPMs higher for normal speed at times, no struggling to get up in power, but slowly maxing out at 4100 RPMS. At times I can open the throttle fully around 3800-4000 RPMs and nothing will happen, other times she will run fine and continue to accelerate. Definately a different sound when she is having an issue, almost like one cylinder is not firing or not enough fuel getting to one cylinder. Swear I can hear a light, rapid thumping sound. Very faint but noticable. Sounds like a high strung chainsaw. Spark checks out. Plugs look good, no carbon, slight oily residue but not wet, or dripping, good light tan color. New fuel filters (2), VSt screens (2) still clean since last checked, new fuel pumps (3), TPS set correctly, I use the boat 2-4 times a week so no stale gas. Warm up and idle is fine. An occasional slight sneeze. Fuel/oil consumption seems normal. I also check the heads from time to time while running and doesnt seem to be any cooling issues.
Where do you think I should look next? Are the fuel injector screens easy to identify and examine for debris?
Thanks again for your help.

 

[rodbolt]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

check fuel rail pressure at the problem RPM and load,check O2 sensor output voltage, the injector screens are easily removed on the OX66 and mercruiser makes replacement screens,

 

[Bonafishark]

Re: 2001 0x66 250 TURZ Multiple Blown Head Gaskets

Thanks for the quick response.
This is what I have done/found: Double checked compression and spark and all looks good. Did the resistence test on the injectors and all checked out. Took out the injector screens and they all had a good amount of debris with one very clogged. Cleaned them all and put back. I had taken the O2 sensor apart 2 weeks ago and cleaned up, it was heavily carboned up. I also did the resistence test and flame test 2x and it checked out. Based on your hunch, I took it apart again and found the small insert tube was completely blocked. No where else really just the opening. Cleaned it out and put back together. Also pulled the low pressure fuel pumps from the block and found one was leaking. Being new the parts guy replaced for free.
Took the boat out and she ran exactly like she was supposed to...until I had to slow down at the bridge 4 miles in. Trying to get her up on plane was a little troubled, not alot, but that very faint slight thumping sound was back. All happnes in the 2800-3900 Rom range. Seems she than contiued to run fine after that, with the same issue happening in the same RPM range. Very occsionalsmall cough or sneeze low RPM range. I dont think I will be able to do the pressure test at load and RPM problem range because it is just me out there. Im think I still have a small air leak somewhere. Dont know if it's relevant but I do try to squeeze the bulb when this is happening for no response. Ball doesnt get exactly hard nor does it go flat. Doesnt do much of anything.
I will double check the VST filter but Im pretty sure it's clean. Engine fuel filter always 3/4 full. I guess my next step is to pressure check all the fuel lines? Anywhere else I can search?
Thanks for your help.