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Mercruiser 3.0 timing off by 24 degrees and runs ok

R

Rocketp

New member
Hi guys. Newby in boat world. Picked up a SeaPro fishing boat with a 2003 mercruiser 3.0 stern drive . The seller said the engine might have about 100 hours on it. The engine was not running great at idle, difficult to start cold and had a pretty big bog transitioning through 1/4 throttle, so i decided to try and solve that issue and go through a few things to learn about this engine before heading out in the Ocean. once getting through the bog, the engine ran smooth and reacted with good acceleration up into the higher rpm's. No detonation, on muffs or in the Ocean under load. 1st thing I did was remove and rebuild the carb to establish a baseline. Was a little dirty, but not terrible. Retest, basically the same results. Next replaced water seperator filter, 2nd canister filter and fuel filter at inlet to carb. No water build up in seperator, but sediment present. Still no change. Replaced fuel pump filter, this looked like crap, lots of sediment built up. Retest, engine running much smoother, bog much more managable. This was for sure a problem. Next up, new plugs wires and distributor and check timing. Timing mark was way far advanced off the measuring plate. switched to base timing, idle at about 750 780rpm. I adjusted the distributor clockwise as far as it would turn until smacking into the fuel line and it still only gets to about 12 degrees BTDC in base mode. Returned distributor position back to where it was when I received it, adjusted the offset on my timing light to bring the timing mark on the balancer to where it should be for this model. 2 degrees ATDC. The gun indicated I am 24 degrees off. Tried a 2nd timing light, same thing. Whats wierd is that its actually running pretty good for this condition. opened distributor removed plugs and located TDC with a whistle plug on cylinder 1. Timing mark on Balancer lined up very close to zero mark on the plate. I suspected the distributor pickup coil may have an issue, so replaced the coil , same results. Next replaced Elecronic Control module at base of distributor. same results. Boat starts good cold now...5 pumps on the throttle and it fires right up. runs a little rough for a couple minutes until warm, but then runs smooth. but still staring at a 24 degree offset from the original timing . Note: compression tested cylinders, all about 150 pounds +- 10 . All my testing has been in the driveway with muffs, although I have made a few runs out in the Ocean. I am lost for ideas. Was really wanting to solve this one on my own, but may have to resign to the pros. Unless somebody has seen such a wierd problem before? Thanks for any ideas! R
 
The good ol EST distributor...

I hope the ignition module was a Delco...aftermarket items can be troublesome.

if the module provides a nominal advance function, I prefer to set the timing at full advance (2800 RPM) and then live with the initial timing, as long as it starts ok when hot...the advance function has as pretty steep curve so hitting the initial timing value can be difficult...
 
Hey Mark, thanks for your tips. Good to know its not that easy to get initial base timing perfect. It is not a delco unit, purchased the Sierra Marine equivilent, but it is exhibiting same results as original. I can try setting timing from full advance and see if it reacts okay to it. Seems like a good idea if I cant find the true source of the problem. At least it will be timed accuratly at one end.
 
could always do it "old school" pull #1 plug, get to TDC compression and see where the rotor points. If you cant correct by just turning the dist,rotate the plug wires clockwise 1 post and readjust the dist
 
Bt Doctur said:
could always do it "old school" pull #1 plug, get to TDC compression and see where the rotor points. If you cant correct by just turning the dist,rotate the plug wires clockwise 1 post and readjust the dist
Click to expand...

Thanks for the reply, sounds like a pretty smart and simple idea to try. when you say... see where the rotor points. Do you mean to check if its pointing in the right spot? I have heard it should be pointed to 4 o'clock. Just don't know what part of the engine is being used for 12 o'clock reference. Still trying to figure out how to attach an image onto this.
 
fastjeff said:
I have a feeling the damper pulley has shifted.

Jeff
Click to expand...

Hi Jeff, thanks for the idea that somehow makes a lot of sense, But I did check cylinder 1 @ tdc and the balancer / damper mark landed at zero degrees on the advance marker plate . Could it still be shifted, that I don't understand?
Appreciate your great ideas guys! So valuable to me you share your experience.
 
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