Engine Timing..

[JCBoater]

Hello,

Engine type:
1994 Mercruiser 7.4 L
Ser no. 225318

My last cruise was around Christmas and both engines ran great. Also, both engines ran great all summer. I started the engines a couple of times sense with no problems.

The last time (a month ago) I started the engines it took a minute but both finally started. When the port engine started it ran smooth no problems. The starboard engine started but was backfiring at idle but would stay started.
Today I'm ready to start troubleshooting the stbd engine; I removed the air filter on the carburetor, did a visual of the engine and tried to start. It almost starts but does not start. I think if I continue to try, it will start but will continue to backfire like before. When I release the switch a little gas shoots out of the top of the carburetor.. I'm guessing that this means that the timing is off??? Not sure how the timing would be off the engine has just been sitting (maybe that's the problem ).

So what I?m looking for is some steps to take to start to troubleshooting the problem.

Thanks!!!

 

[Bondo]

Re: Engine Timing..

Ayuh,.....

When was the last time these motors had an actual Tune-Up,..??
How about a Full,+ Complete Service,..... With Filters,..??
Do the motors draw off the same tank, or seperate fuel tanks,..??
And,....
You're Right,....... The Timing rarely changes by itself.......


Btw,......
Welcome Aboard to the forums here at iboats.com.........

 

[JCBoater]

Re: Engine Timing..

Thanks for the reply!!!

Both are do for a complete tune up. I'm actually thinking about doing it myself. My mech. is sort of flacky.

The engines are currently feeding off of seperate tanks.

 

[Don S]

Re: Engine Timing..

What is the letters in front of the SN on your engine. Just the number doesn't help.

 

[JCBoater]

Re: Engine Timing..

Only one letter.. "F"

 

[Don S]

Re: Engine Timing..

You lucked out. One of the few OEM service manuals that is online is for your engine.
http://www.boatfix.com/merc/Servmanl/16/16cov2_1.pdf
Just scroll down till you get to the outline, then click on the section LETTER that you want to view/save to your computer.

Your problem sounds a lot like moisture and crossfiring in the distributor cap. Pull the cap and look.

 

[JCBoater]

Re: Engine Timing..

Thanks for the link to the service manual!!

I removed the distributor cap and did not see any moisture and not see any cracks in the cap. Wiped it out and replaced.

Sense the problem sounds like moisture and crossfiring in the distributor cap should I replace it?

 

[Wotknot]

Re: Engine Timing..

I would......couldn't hurt even if it's not your problem. I learned as a 17 yo kid that distributor caps and water don't go together. Didn't spray wash my engine anymore without covering the cap.

 

[JCBoater]

Re: Engine Timing..

Replaced cap and rotor still have the same problem. I'm guessing I should go ahead and replace plugs???? It is probably time anyways.

 

[JCBoater]

Re: Engine Timing..

Also, should i go ahead and replace the starter coil, the sensor under the distributor cap and spark plugs and wires as part of a normal tune up and hopefully this will also fix my problem too?

 

[Don S]

Re: Engine Timing..

Sure, throw money at it till you find the problem. That should cost a fortune, and probably still not start.
What's a starter coil?
Do you have spark on all plugs?
How long since the last full tuneup.
Have you done a compression test???? Why not?
Are you getting gas out of the accelerator pump nozzels in the carb when you pump the throttle?

 

[Bondo]

Re: Engine Timing..

Both are do for a complete tune up. I'm actually thinking about doing it myself. My mech. is sort of flacky. Also, should i go ahead and replace the starter coil, the sensor under the distributor cap and spark plugs and wires as part of a normal tune up and hopefully this will also fix my problem too?

Ayuh,........

Don has given you a copy of the Factory Service Manual,.......

Read it,...... It'll tell you Exactly what Needs doing...... Rather than just Throwing Part at it......

I also have No idea what you're calling the Starter Coil,.....
And,...
The "sensor under the distributor cap" has specfic test procedures stated in the Manual,... They Rarely go Bad....
Ditto the Plug Wires,.. Test them to see if they Need replacing....

 

[JCBoater]

Re: Engine Timing..

Hello,

Sorry Don and Bond-O, I did not think that replacing those items would be just throwing money at the problem because I figured they were part of a full tune up. Like I mentioned before both engines are due.

The last compression test was at the beginning of last summer all was fine. The engine will actually start and idle. When running it does a idle idle idle then "pop" ...idle idle idle then "pop" coming from the carburetor, so there is gas. The "starter coil" that I mentioned is actually the "ignition coil".

I will test to make sure that I have spark on all of the plugs and report the findings.

For sure not trying to throw money at the problem to fix.

Thanks again for all of the help.

 

[Don S]

Re: Engine Timing..

Caps and rotors and spark plugs are tuneup items. Coils, sensors, modules, etc. aren't and don't need replaced unless needed. That is the parts I was talking about throwing money at for no reason.
When the engine is running, watch the coil tower, when the engine pops, do you see a blue spark jump from the coil tower to one of the smaller terminals? If so, the coil tower may be cracked or have some carbon tracking on it. A bad plug wire or bad spark plug can cause the coil tower to crack.

 

[JCBoater]

Re: Engine Timing..

Thanks again for the quick responses!!

I will check for the spark at the coil.

Don S, on a side note the manual that you referenced. When I check for my serial number (F225286) it references an engine with EFI. I think that stands for Electronic Fuel Injection and I do not have EFI. I do see MIE 7.4L (Carburetor) OD840300 to OF820141, but the serial numbers do not match.

 

[Don S]

Re: Engine Timing..

Looks like your SN is in a lot of them.

Stern Drive Engines
MCM 7.4L Bravo OD830779 to OF800699
MCM 7.4L Bravo Three OD838819 to OF800699
MCM 7.4LX MPI OF595275 to OF801999
MCM 454 Magnum (Carburetor) OD837587 to OF801999
MCM 454 Magnum EFI, EFI/MP and MPI OF111570 to OF802349
MCM 502 Magnum (Carburetor) OD831432 to OF114528
MCM 502 Magnum EFI, EFI/MP, MPI OD840650 to OF802599
Inboard Engines
MIE 7.4L (Carburetor) OD840300 to OF820141
MIE 7.4L EFI/MP and MPI OF490697 to OF820103
MIE 8.2L (Carburetor) OD857200 to OF819619
Ski Engines
MIE 454 Magnum EFI, EFI/MP and MPI Tournament
Ski OF215800 to OF820099

 

[JCBoater]

Re: Engine Timing..

Update...

No blue spark jumped from the coil tower to one of the smaller terminals. I'm thinking about buying one of those little testers (only $10.00) to make sure I have spark at the end of the spark plug wires. Is it ok to test the spark plugs by leaving them plugged up and looking for spark? Or do I just remove the plugs and "read" the plug?

 

[Reel Poor]

Re: Engine Timing..

I would remove the plugs and see if they have water/rust on them. While they are out, DO A COMPRESSION TEST.

The pop your referring to could be water in the fuel, lean carb condition, secondary ignition system failure, valve train/cam problems.

 

[JCBoater]

Re: Engine Timing..

Update....

Replaced the spark plugs two of them (3,8) were "wetter" than the others so I replaced them all. Tried to start and the engine would not start
I did the Compression test here are the results:

1= 0
3 = 150
5 = 150
7 = 0
2 = 150
4 = 100
6 = 149
8 = 160

I also removed the valve cover on the 1,3,5,7 side and saw a little milky oil. Not sure what all of this means but I'm sure it is time to get a mech. involved???

 

[Bondo]

Re: Engine Timing..

1= 0
7 = 0

Ayuh,......... I think it's safe to say,.....
You have Serious Problems,..... That a Tune-Up, Isn't going to Cure......