2002 Mercrusier 6.2L running problems

[Jseiler]

2002 Mercruiser 6.2L Serial # - 0L678630

Been fighting this issue trying to figure out what is going on and now at a loss and need some help or advise. Motor starts really easy and sounds well idling, you cant tell anything is wrong until you put a load to it and open the throttle up. Upon full throttle I am only seeing 2100 RPM 10MPH max speed and backfiring, I should be seeing 4200 RPM at full throttle. I had a boat mechanic down and he thought it may just need a tune up, replaced all spark plugs and wires, distributer cap and rotor as well as the sensor that's under the cap, motor stayed the same and still running like crap. Did a fuel pressure test and have 43PSI even under a load. While out on the water the mechanic had his scan tool hooked to the ECM and noticed it was not advancing at idle it was running around 30 degrees and when you give it the throttle it would be somewhere in the 20's. He did make it advance and RPMs started to climb and boat started to run great but we received a really bad spark knock in return. Once we got back to the dock I had him do a compression test and didn't find anything there either
Cylinders
1 - 205
2 - 195
3- 195
4 - 195
5 - 195
6 - 185
7 - 200
8 - 195
Pulled the distributer out to check the gear and to see if the roll pin was intact and everything looked fine there as well

Injectors seem to be working as we pulled them off one by one as the engine was running and you can hear a change. They were also all gone through just last year. I am planning on pulling them all out Tomorrow and taking them in to have them looked at again and see if there is one or two that's not opening up all the way.

we are thinking it is possibly the ECM module which is a MEFI 3 that they don't make anymore and from what I am finding to be extremely hard to find one to just try out.

My question is are we missing something?
What are my options?
and where do I go from here?

Motor is in a 2002 Sport-craft 272 sportfish if that helps at all

I am really needing so options here as I am at a loss, Thanks in advance

 

[Jseiler]

we also checked the fuel and it was clean and no signs of any water

 

[searay3]

Most folks will tell you a coil rarely fails. This is correct, but it does happen. I have an 87 4.3. Same symptoms you are experiencing. I also was told it was 'probably' the module. Checked every thing three ways to Sunday and could not get it up on plane. Friend suggested the coil. Couldnt perform under load. Gave him the same answer. Probably not the coil. No real definitive way to check 'em. So I figured 30 or so bucks way cheaper than the 400 or so for the module, if it could be found. Wa la...fired up as usual, idled fine and when I opened the throttle she pulled all the way up to 4400 rpm. Its cheap...replace the coil if you can't find any fuel issues.

 

[Jseiler]

Ok, thanks

 

[Scott Danforth]

Your compression readings are way way to high .Get a different gauge and retest. Should be around 150 psi

Check to make sure you have only fuel in your filter. Water in fuel would cause it to knock and retard ignition

 

[porscheguy]

I know squat about diagnosing fuel injected boat engines as I have no experience with them. What I can tell you is that your “normal” operating rpm of 4200 says you’re overpropped. The normal range on that engine as specified by mercruiser is 4800-5200rpm. It doesn’t matter if the builder put the prop on, or dealer, or if others with the same model, engine, and prop are turning 4200. What matters is what mercruiser says.

with that said, your current issue goes beyond being overpropped. I’d say ignition/engine management. But once that is resolved you need to look into the right prop.

 

[porscheguy]

Your compression readings are way way to high .Get a different gauge and retest. Should be around 150 psi

Check to make sure you have only fuel in your filter. Water in fuel would cause it to knock and retard ignition

I thought his compression numbers seemed a bit high but I wasn’t certain. Could that be the result of excess carbon build up from lugging the engine?

 

[alldodge]

Upon full throttle I am only seeing 2100 RPM 10MPH max speed and backfiring

For the motor to backfire then the timing has not been set correctly, or may be an issue with a sensor like the crankshaft.

By not advancing the timing fully the ECM is retarding the timing to protect itself from an issue.

How is the timing being set?
What scanner is being used and what version of software?

 

[Jseiler]

I'm not much of a gear head, the mechanic was just using a timing light. This past Sunday we put a different coil on it and it did run a bit better but it was a hotter coil out of my dads 73 vette. When out on the water and at full throttle dad pulled the plug on each individual injector one at a time. Cylinder number 2 had a slight change but not much. when 3 - 6 where pulled there was a huge difference of loss in RPM and the engine bogged down a lot. As for the the number 7 injector when it was pulled there was not change at all. We don't think the number 7 injector is opening up and the number 2 injector may not be opening up all the way. We pulled the injectors out on Sunday and they are being checked this week.

I don't think the pop is an issue, it ran great all of last year when I bought the boat and earlier this spring before all this started.

As for the timing, I'm not much of a gear head but he was just using a timing light

 

[Jseiler]

Fuel was already checked, Fuel is clean. When we pulled the injectors a few of them where dirty though

 

[Jseiler]

Also what would cause me to have more compression then the normal range?

 

[alldodge]

A timing light is not set using a light on these motors, it is done by positioning the distributor.



Remove the injectors and have them cleaned and flow tested, cost is about $20 each round trip

Also what would cause me to have more compression then the normal range?

Either the gauge is off, or there is some kind of liquid in the cylinders (water, gas, oil)

 

[Jseiler]

Ok thanks, I appreciate all that info, injectors were dropped off today to get looked at supposed to get them back Tuesday.

Well that would make since as when I pulled the flame resistor off there was oil inside the plenum, looked like it was sucking oil from the crank case through the PVC valve. we just figured that was due to the engine not creating enough vacuum to hold the valve closed.

 

[alldodge]

What kind of place did you drop them off at?
Marine injectors need to be flow tested to at least 6000 rpm, and if its an auto one then your not going to get the same testing

Oil in the plenum means you have some bad valve seals or rings.

 

[Jseiler]

Well apparently injectors are all working, they still got to do a cleaning and do a flow test yet though

 

[Jseiler]

honestly I don't really know, a buddies of mine cousin works in a shop that works on them. They know it is for a marine engine and I just told them the info you gave to me to have them tested at least 6000 RPM