Looking for help on my 502
 

So last weekend the engine was idling high and surging, jumped online found that I should probably check IAC. Went ahead and installed a new one along with a TPS and Map sensor since I was there. Problem fixed. Took it out last Sunday and it seemed to run good for most of the day then it seemed to not fire on all cylinders a couple times but would snap out of it. So since I forgot to check timing last weekend I went ahead and checked it yesterday. It was not at 8 degrees BTDC so I set it and seemed to run good again. Took it out yesterday and about half hour in, the engine started only running on 6 cylinders. I shut it down and checked wiring connections. Nothing seemed to be out of place so I fired it up and attempted to head for the dock which was a couple miles away. I slowly got it up on plane and it would only rev to 3900 rpm's since it was not firing on all 8. About a mile from the dock the whole boat died as if someone shut the battery disconnect off. I had nothing. I checked everything and couldn't figure it out so I got towed to the dock. Today I started tracing wires and found I blew the 90amp fuse link on the starter so the Mefi 1 and everything else lost power. Replaced it today along with spark plugs, cap, rotor, & fuel filter. Boat starts and runs but not good. Cylinders 1,3,5,& 7 fire great and the exhaust water is warm. Unfortunetly the other exhaust is cold and the water smells like gas when it is running. When changing the plugs I put the camera down each cylinder and cylinders 4 & 6 are clean/washed. Not to mention both of those plugs are covered in gas. I plan on pulling the injectors to have them cleaned and tested. I am not positive that will fix the problem so I am asking if anyone has some suggestions? Why would it drop cylinders? Is it possible the injectors could flood those cylinders to the point they won't fire?

The mefi is very sensitive to voltage , check your batteries and all connections. Also you need to find what caused the 90 amp fuse to blow. If you have a rinda scan tool, or can borrow one might point in the right direction. Throwing darts in the dark will get expensive!

Thanks, I do have the scan tool and it has no codes.
Do you know what voltage the Mefi prefers? When the engine is not running the scan tool shows 12.4 volts. When engine is running it is showing 14.4 volts. I was wondering if the alternator is over charging or something. The fuse that blew is the one coming off the starter with the orange wire going to the alternator.

Yes I just changed one for a friend due to reversed polarity, you may well be over charging and its posible effed up the mefi .post up serial numbers and when bup comes back on he may be of help.

So I went out and checked compression today.
Cylinders 1,3,5,7 = 139-145 psi
Cylinders 2, 4, 6, 8 = 45 psi

I'd say the pistons on that side are dead.

What would make the whole side dead like that.? I can see wash down lowering compression, but wiping it out , how and why? Still the question is why is that bank not firing.

I guess I could pickup a used harness and re-ring it. The thing has ran fine all season and it only has 185 hours on it. It is weird that it is that side only with the lower compression. I watched all the valves open and close in each of the cylinders on that side as well with the camera. How long would it take to wipe the rings out if I ran it without firing trying to get back to the dock?

Split the head gasket between both cylinders have scene that before, they used aweful head gaskets.
Good luck

I would be stoked if it is a head gasket. What do you think the chances are? I will start pulling the head off in the boat tomorrow night. Probably should do both huh?

Just pull 6 spark plug out, put air in the cylinder , if it comes out number 8 or number 4 you got the problem

Will do that tomorrow before I tear into anything.

Well tonight I did a leak test and confirmed the problem when air started coming out the adjacent cylinders.
Head gasket was blown between each cylinder. Good thing I ordered Fel-Pro gaskets and ARP bolts today just in case.

Cool glad you found the problem

i reccomend checking the block&head with a straight edge for warpage.

Most definitely. May even want to take that head in to see if it needs to be resurfaced. Kinda unusual it would blow between ALL the cylinders on that side. Need to get that head off and confirm your problem. I had one blow last year between 3-5. In my opinion I doubt you have any ring problems or damage from returning to the dock..

i have seen them get hot enough to blow the head gasket and put water in enough to milk the oil but nothing warped but it still needs to be checked.

A guy brought me a hp 500 carb motor that blew the head gasket between all the cylinders on one side last year and block and heads were both channeled so you might be pulling it out once you get the head off, fwiw, Smitty

So pulled both heads off and the right side was blown between every cylinder. The left was starting to go between every cylinder. I am sure the previous owner knew it had got hot at some point (just guessing) since it recently had a new sea pump and water pump installed before the sale. Lesson learned and it is used so it is what it is. Long block will be here tomorrow, mine was a good core. Will be putting it in first of next week :).

Was that a MARINE long block. IT NEED"S TO BE.....
If not the cam will be too small and the clearances are too tight.

Yeah, Marine Block (MPI Mercruiser).
I got lucky finding one within 500 miles. LoL