Is my 500 efi done for the year? Got hot and now hard to start.
 

Running back to the ramp to beat the sunset time. Running about 4400 rpm and she just felt sluggish. So not sure I started to back out of it and it just didn't sound right. Than I could actually feel something wasn't right. But all gauges were fine except for 180/190 water temp on the starboard side. So idling the last 1/2 mile back the starboard side died. Port side is fine. Got it home hooked it to the hose and the starboard side is hard to crank and it wont start unless I increase the throttle than it will start but wont idle below 1000 rpm and than it runs rough. No water in the oil and no oil in the water. Pull the plugs and they are black a little wet with fuel. The threads did have a little oil on them. Put a new rotor and cap with new plugs and thermostat on. Back flushed the cooling system and got a little piece of impellor and small piece of some type of plastic ring and three small stones. The engines do have 550 hrs. on them. I was told when I bought the boat last year he had the springs done. But I don't know for sure. I guess at some point in time I will pull the valve covers. Any thoughts?

I'd pull the plugs and run compression on them real quick. Even if only by a finger over the hole. Help see if there is a major issue. Of the valve covers are easy then by all means check your valve train. Good luck and I hope it's something simple, but something was causing it to run warm...

Head gaskets are gone.

He said no water in oil so probably not head gasket imo

Seeing as 502 blocks get very hot between the cylinders because there is no water there and they are very thin I would bet money at a minimum the gaskets are gone between the cylinders. Hopefully the deck isn't burnt as well.

You could be right... Happened to me on a race motor and ran fine 10 laps then started to be sluggish

Its been so stinkin hot here, 112 degs in the polebarn. But I am going to try to do a compression check first thing in the morning.

This is almost the same thing that happened to me a couple weeks ago.
Head gaskets were gone. No water in oil on mine either.
Compression test and leak test will tell you for sure.

After a compression test, check fuel pressure had 500efi that would start the same way with two different problems. First time it was a fuel pressure regulator, second time it was the computer. Both times after starting it would run at idle but coughed a sputtered a lot.

1st cylinder 150 psi, 2nd-45 psi 3rd and 4th-0 psi, 10 psi with a couple squirts of oil. I finished welding up my second outdrive stand last night. So I am pulling the motors this weekend.

Yep! No other choice! Let us know what you find out!

Ok. The engines were pulled and everything pulled off of them. Dropped the engines off to the builder and he just told me the first engine that I was having problems with is toast. The head gasket blew and there is a very large valley worn between two cylinders and the head is burnt. I need at a minumum a block and a head. He also said there must be a computer or fuel program issue that caused this. Has anyone had the same issues and what did you do to fix it?

Here's the issue. Loss of cooling water means everything is very hot - obviously hot enough to burn the headgasket fire ring between the cylinders - and cause pre-ignition + detonation on it's own.

Once that fire ring is melted away, the adacent cylinders are open too each other and the combustion of each cylinder will 'trough' right thru to the other taking cyl head and/or block surface metal with it.

Could the fuel system cause the same headgasket and valleys in block and heads ? Sure ! But so will an overheated motor.

With the engine being rebuilt, even if this issue did not happen,it is always a smart idea to have your inectors cleaned andflowed...new filter baskets installed, and then when put back in boat, verify fuel psi from idle all the way to WOT and top rpm.

I've rebuilt/replaced many a motor for same issues you have that where ust overheated. Have rebuilt/replaced many engines for same issue you have that where from pre-ignition and/or detonation.

Oh, and also from too much nitrous and not enough fuel. LOL.

I can find replacement heads. But I can't find a block. Did they discontinue making the blocks? Would it be a good idea to rebuild the bad motor or start with a new one. Possibly sell the good motor and get two like replacements? Is replacing them with 525s an option because I don't see a whole lot of 500s out there for sale. To many questions with not alot of answers.

You need a Gen 6 GM block. Not a hard find. If you wanted to sell them as is, I would be interested.

I thought they were 7s. But no matter, I am concidering selling them both as is minus headers. Rather they are 6s or 7s will standard GM blocks work or is something like the water jackets or anything for that matter different?

Had a handful of the same failures this year. Loose a fuel injector and the motor gets toasted. For this reason I don't like fuel injection in a boat. There are no warning signs while it's running. At least with a carburetor it will snap crackle and pop through the intake. Efi doesn't let you know anything till you come back down to an idle and have a miss. Even then the fuel injection does a great job of covering up the miss in the motor.

Yeah, I've seen it on a 500 EFI. had to replace the block with a bare block, one head and 2 pistons, it ended up being a bad headgasket between 4&6, Torn down the other motor and the fire rings were distorted ready to go. had the injectors checked and flowed all ok. My point is that like BB said the injection system will compensate for this and mask the symptoms till the damage is so great it can't any longer. Crappy Merc headgaskets was the cause in this case.

was your oil temp overheating and would it start at all before you pulled them I have a very similar problem with 500 efi mine

Can the block deck be milled?

The block is ruined. It wouldn't even make a good boat anchor.

I torched the block and head on a race car engine years ago and just had them both welded up and resurfaced. I swapped sides with the heads upon reassembly and it ran fine for years. it is not a difficult fix at all for a quality machine shop

GM 502 block new from Jegs is $1800. In stock

A guy brought me a hp500 carb motor to build, block channeled and burnt, heads channeled and burnt in several places, my machinist said it could be welded and sleeved and be a good repair, customer wanted nothing to do with this block as he did not trust the reapair, i gave him a timeframe of 6 weeks to rebuild it and replace block. He chose to buy a 540 from aetco instead, they assured him they only used virgin blocks BUT needed his old long block to build his 540, i didnt understand WHY since his block was junk, crank , rods, pistons, cam, rockers, lifters, timing chain, pushrods werent going to be reused. I told him he should just send them his sheet metal, balancer and intake as rest was either junk or not needed for a 540 but they wanted all of it, kept saying they needed his block to get started. He got his 540 back , no where on his bill did they charge him for a new or used block, i highly doubt they just gave him ANOTHER "virgin" 502 block at NC. So its pretty obvious they repaired it (no one gives away a 2000$502 block on a 7500$ rebuild)
It still runs good today fwiw

Oil temps were fine. Water temp. started to rise and that is how I knew something was up. Would not rev over 4400. Once I noticed it was running it hot I shut it down and limped back to the ramp on one motor.

Ordering a block and head and everything else from Summit. If they can get the order all together at their Ohio store I may run up and pick them up myself.

I can get u a Dart Block for around $1800 and you don't have to drive to Ohio. They come out of Philly. Pm me if you need a hand.

Wow I have never seen a channel like that between cylinders .

Is it specific to injected motors?

After having a welder spend almost 5 hours welding almost an inch of new block back on in some areas of the exhaust portion of my dad's fully dressed 225 yamaha 4 stroke outboard, and me spending hours upon hours hand decking the main mating area, I gotta believe almost any block can be repaired.

Good call .

Very common on GM 502 blocks when they don't have enough fuel.

Since i started flowing and testing injectors as part of my business this year i have seen and heard of at least 5 guys burning up pistons from leaning stuff out from low flowing injectors, every set i tested so far from these instances had 1 or 2 that flowed 20+% LOW, more common than you would think. Makes sense though, hp 500efis and 502 mpis are getting to be 15/16 years old, guys are running injectors that have NEVER been checked for 15+ years, its especially prevelant in stuff guys buy that hasn't ran in a couple years, a couple cans of seafoam is wishful thinking!

So it's specific to 502 s. Do the after market blocks have the same issues ?

If one quit completely it would be a different story, boat would have dead cylinder vs a critically lean cylinder still firing which destroys piston,bore and sometimes the block!

Good info. Ty

Not as common to burn an aftermarket block because of leaning out but they will burn through as well. A block will burn through b4 a cometic gasket. I have never seen a cometic burn through.

These marvelous fuel injected motors have kept me buisy all season...

I will keep that in mind. Thanks

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Both engines are fully rebuilt. I still need to get all the attachments installed back on them and get the headers pressure tested. But what a relieve to get this far.

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Well I'm getting there. Maybe they will be ready to put back in the boat tomorrow.

wow! moving along fast!