1994 Merc 2.5L 150hp EFI Trouble/rebuild/fix thread

[matt'sdrag95]

Hi guys,
Re-powered my '87 Ranger 335V earlier this year with the aforementioned '94 2.5L 150hp XRi EFI off a newer Nitro. Serial # 0G017076. When motor was purchased compression in all cylinders was 125PSI. After rigging I installed a new impeller kit, new NGK plugs, fuel/water filter, and removed the entire oil injection system and installed the block off plate in the engine. I also removed/disassembled/cleaned the VST, and installed a new aftermarket high pressure fuel pump because the male/female spade connectors on the OEM Bosh pump had loosened up causing the pump to be too temperamental, so I installed one with ring/post connectors.

Motor has been treating me very well since installation right up until this past Sunday.

The "event"
I was taking off from the launch tournament morning when 1/4mile away the motor dropped power significantly. Backing off the throttle the motor picked up, and stumbled again when I got back on the throttle. Power loss dropped me off plane, and when I put the motor in neutral it died. I was able to start it back up, but it died again when I put it in gear. It would not start again after that.

The start of diagnosis
After a difficult (trolling motor only) tournament I came home to dig into the motor.

Spark
Installed new plugs and verified spark on all. I noticed that after cranking (attempting to start) 5 out of 6 plugs were dry (no fuel). The wet one seemed more like oily water than fuel/oil mix (lowest cylinder starboard side).

Compression Check
5 out of 6 cylinders all show 125psi just like during initial rigging.
The cylinder that I mentioned had that oily water (again lowest cylinder starboard side) checked out at 150psi! I verified this three times. More on this later.

Fuel
Testing the fuel pressure at the schrader valve I found that although the aftermarket high press fuel pump was being energized (and moving fuel) it was not building pressure (not even 10psi). Rigging the OEM pump back into place I immediately saw 39PSI at the schrader valve. Great, I found the problem and why the motor died/wouldn't run!

Run Test
Pump energized with key on, and engine fired right up, billowed out a large cloud of white smoke, and died in a few seconds. This repeated identically at least 5 more times. I witnessed the water pressure pee hole attempt to flow water out, but never produced a steady stream.

Uh Oh
Now my mind starts thinking about the "oily water" and the 150psi reading I found on that one cylinder (it would even spray fluid/vapor) out the plug hole when cranking.

What Now? Further investigation
Starting to prep to pull the starboard cylinder head to inspect. Not sure if I should expect a simple blown head gasket that I can replace and resurface head, or if this "event" on Sunday caused some permanent damage that will require a powerhead rebuild.

Anyone ever seen something like this?
I never would have expected to see cylinder compression increase with a potential blown head gasket. Very curious to hear any thoughts/advice.

Also, I'm having a hard time determining which head gasket is correct for this motor. If anyone is able to help it would be much appreciated.

Will update with photos/etc once starboard cylinder head is pulled.
Thanks in advance,
-Matt

[Blackwoodz]

Could reeds cause the issue? What about the rubber charge lines? I've got a 99 efi 150 so I'm always interested in knowledge.

[leonreno]

No fuel in the cylinders means no oil, the bad cylinder maybe filling with water cause the high compression, maybe gasket maybe cracked cylinder due it heat. Only way to find out is pull the head. Good luck, hopefully the bad cylinder didn’t hydrolock and break a rod.

[JOE54]

^^^^^ +1 would not reuse rod very likely bent

[matt'sdrag95]

Thanks for the replies guys.

First things first. As I lowered the trim to work last night a oily water stream exited the prop (first attached photo). I'm used to water from the lake running out, but not this mess.

HEADS
Pulled both heads last night. To my surprise both heads and gaskets looked just fine. Zero visible signs of blown anything. This makes sense in a way because adding an in-compressible fluid (water) to a cylinder that holds compression might increase the measured compression.

Cylinders/Pistons
All cylinders and pistons look great, and they all cycle as they should when turning the motor over. Here is an example to show all cylinders still exhibit nice crosshatching.

I spoke with the local trusted mercury marina this morning and based on this information they suggested I pull the exhaust divider and check it for damage/cracks.

Exhaust Divider
I just finished pulling this. Man is there a lot of carbon buildup on it and the whole chamber it resides in! I have a bunch more cleaning to do, but other than the strip gasket falling off I still cannot find a smoking gun for where all this water is coming from. Even the gasket looks good.

[Rip Bass]

I wonder if a spun cylinder sleeve can allow water in? While you’re in there,it looks like those red/yellow wire couplings are burnt,might want to check those out too.Im following this post,I love a good mystery.

[JOE54]

question ; when the event happened did a massive amount of water wash up on back of boat filling cowl

[JOE54]

they can leak behind sleeve, tops of pistons on water cyl should be spotless clean if leak has been present for a while

[matt'sdrag95]

Thanks for the replies guys.
What may or may not prove to be pertinent info to the "event:" I had just crossed over another boat's wake and the boat jerked violently. Almost immediately following that they boat experienced the power loss I described. Water did come over the back of the boat falling off plane so fast, but not a massive amount that came up over the motor in my opinion.
The top motor mounts were pretty worn, so we are now wondering if the exhaust adapter plate below the powerhead could have been damaged.

Currently prepping to pull the powerhead to look...and install solid motor mounts while I'm in there.

[matt'sdrag95]

Got the powerhead pulled pretty easily.
engine pull.jpg

Right away I found a bit of a water/oil mess.
20190831_133702.jpg20190831_133706.jpg
Water was also found in areas I'm not sure if it should have been.

Pulled the Exhaust adapter plate and again found water in areas I'm not sure it should have been (like in the cavity the upper motor mount lives).
20190831_134813.jpg20190831_134817.jpg

I also found the starboard motor mount really beat up (you can see the air gap around the metal bushing), so I replaced both with solid mounts from Bob's.
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A good cleaning and inspection of the adapter plate does not show signs of a crack, so I'm hoping that the worn motor mount perhaps contributed to some gasket surfaces letting go and letting water in areas it shouldn't be

This week I should have all gaskets, a new water impeller/housing/gasket kit, and new lower end fluid. I'm cleaning the carbon buildup everywhere I can, and I'm going to clean the fuel injectors and throttle plate before reassembly.

I was going to pull the trigger on some new TDR reeds but decided to see if all the new gaskets/etc solve the problem before putting more money into the motor. If this doesn't solve the problem I may be into a full powerhead teardown over the winter. Send positive thoughts!

[123trentm]

looks like base plate gasket was leaking and make sure and check/replace lower crank seal

[matt'sdrag95]

looks like base plate gasket was leaking and make sure and check/replace lower crank seal

Thanks for the recommendation. Sounds like just the place that could have been letting water into the lower cylinder(s). I'm just going to replace them regardless since I have the powerhead off.

[123trentm]

Yep, leaking crank seal is my guess. Look at driveshaft and make sure it is smooth where it meets seal

[123trentm]

P.S. Don't forget to put shift shaft in before putting powerhead back on. Ive only forgot that about 3 times over the years before finally learning.

[matt'sdrag95]

Finally wrapped up everything.
All new plate gaskets and solid motor mounts
20190912_171430.jpg20190916_173821.jpg

Powerhead got new head gaskets, new exhaust diverter plate gaskets, thermostats, and crank seals before I dropped the powerhead back on.
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Pulled apart the fuel system, gave everything a good clean (including injectors), and reassembled with all new o-rings and seals
20190917_175859.jpg20190917_175909.jpg

Lastly, I dropped the lower end to have a look down there and do a full waterpump, and replace the lower end oil (since I was there).
20190917_185312.jpg

All buttoned up!
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Took a bit to get all the air out of the fuel system, but eventually it all worked out and the motor idled great.

I lake tested it this past weekend and happy to report that everything ran like it should. Started up great, idled great, putted around well, and hopped up on plane and ran like a champ!
Didn't have the space to stretch the legs and see what she would do top speed-wise, but very happy everything worked out and my season isn't completely over!

Thx for the feedback you all provided during disassembly/diagnosis.

[leonreno]

Nice job! Great post and love all the photos. Will be helpful for other too.

[fastfiat]

Nice job! Great post and love all the photos. Will be helpful for other too.

Agreed.