4.3 mercruiser issues

[hawkeye625]

My boat starting acting up 1st thing last spring.  It ran fine at idle, but, when trying to throttle up it struggled, then it would correct itself and run fine.  We could troll all day without issue, then when throttling up, it would hesitate again...almost like it was starving for fuel.  We figured it was water in the fuel so went through weeks of changing filters and running dry gas additives.  (4 hours for me to get to the lake-so I didn't have a chance to run it every day).  The problem seemed to be getting better as the year progressed but it would still miss when throttling up sometimes.  A friend rebuilt the carb (Rochester quadrajet) but, it still didn't fix the issue.  I dropped it off to a well known mechanic up there to clean/rebuild carb - that didn't fix it, after diagnosis - he figured it was an ignition module - so put a new one on.  Got it back last August, still ran rough but, a little better.  I towed the boat back to PA and when trying to winterize it, it would not start.  I had a local mechanic look at it, he couldn't get it to run either.  He manually winterized it and said we will look deeper into it in the spring - he thought maybe the distributor was stripped.

 

Figured someone else may have similar problems in the past so might have an idea of the problem.

 

Over the past 2 years most of the ignition components were replaced.  I think the only thing that wasn't was the distributor itself. 

 

Any ideas?

 

Jeff

 

 

[Xxx]

what about the coil, or is that a HEI ignition, what year is it, to my knowledge I've never heard of GM using a plastic gear on the distributor, sounds to me like a electrical problem meaning bad electrical advance, coil, now it wont start at all I'd pull a plug to see if theres fire at the plug, if so, look in the carb while someone works the throttle, with engine not running, see if there's fuel squirting out of the primary jets.

[hawkeye625]

1992.  Coil has been replaced.  The carb was wet, and, I shot starting fluid in.  No fire so assuming no spark.

[Xxx]

Is it a points distributor?? Could be the condenser, 

[Xxx]

From what I have info on its not a points distr. so those have a pick up modular, you say that was replaced! I had a 1990 Chevy pickup truck that used to eat those pick up mod. Like candy I carried a spare in the glove box. Finally I got sick of that nonsense I replaced the distributor with a HEI and never had a issue again. Because they are a electrical no returning them for a new one. There are all different makes of those pick up mod. I had some that didn’t get me home, the cheaper brands, I learned that the Bosh made ones lasted the longest, but this shouldn’t be a issue in your case, if there’s no fire I’d check power wires to the distributor and also make sure your grounds are good, from the battery to the block, and that the key switch isn’t giving you the griefs. Check the power wires from the ignition at the back of the switch to the distributor, and power to the coil.

[hawkeye625]

Thanks pap. It has the thunderbolt ignition.

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[Matt5512]

Depending on the year of the motor There are 3 different parts under the distributor I for got what they are called one is just a rotor , an then a pickup, an then a sensor, the sensor fails on them alot.. all 3 parts where around 90.00 bucks, after reading your post and symptoms it's definitely something in the distributor ignition wise I would just replace all three parts look them up on the internet and get them from a Mercury dealer no aftermarket...Hope this helps you been there.

[Matt5512]

Just now, Matt5512 said:

Depending on the year of the motor There are 3 different parts under the distributor I for got what they are called one is just a rotor , an then a pickup, an then a sensor, the sensor fails on them alot.. all 3 parts where around 90.00 bucks, after reading your post and symptoms it's definitely something in the distributor ignition wise I would just replace all three parts look them up on the internet and get them from a Mercury dealer no aftermarket...Hope this helps you been there.

Under distributor cap sorry..The sensor on some model might plug into or on to the distributor.

[Xxx]

Wait if you put a thunderbolt in how did you time it, I think you need to be under 800 rpm, on the account you need to time the motor without the spark advance coming Into play.

[Valinote]

You've probably already checked this, but look for carbon tracking and/or oxidation in the distributor cap. After 2 years of having the same symptoms and being convinced by others that I had water in my gas, a new distributor cap resolved all my problems. Even my idle improved. Just my experience...8-]

 

-Steve D

[Gill-T]

Check ignitions coils.

[hawkeye625]

The Rotor, cap, and sensor have all been changed in the last 1.5 years.  I pulled the cap and everything was clean and dry.  The mechanic from NY ran through the diagnostic sequence and it ended with the module.  I'd just take it back to him, but, 4 hours away, I'd rather get it fixed at home and have it running 100% in the spring.  I wonder what the next thing in the diagnostic sequence is? 

 

Fuel pump was also replaced before we got into the electrical hunt.  Also put new plugs in. 

 

Thanks for all the input guys. 

[rolmops]

I have a small question. How old is the fuel?


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[hawkeye625]

Fuel freshness varied throughout the year, but, all new now.  We also ran it on new gas from a portable can and it ran the same.

[Firechief48]

I had the same problem with my Volvo Penta. Changed filters, made it better for a bit. Cleaned and drained fuel system, made it better for a bit. Sometimes it would go good, sometimes like it was starving for fuel. Marina even changed prop, no difference just wasn't getting RPM's. For 2 years my buddy at work kept telling me he thought it was timing. He ended up taking a ride with me and he was right. He fixed it in 15 seconds. 

[Gill-T]

x2 on timing.  

[jimski2]

The carburetor has an accelerator pump that enriches the fuel mixture when you go from using the idle jet to the high speed jet. Look in the throat of the carburetor and move the throttle linkage. A squirt of gasoline must be seen when you pump the throttle. If none is seen, hesitation and stalling happens. The pump could be replaced.


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[hawkeye625]

My mechanic at home played with the timing for a while, it didn't fix the issue.  The accelerator pump was replaced in August, also did not fix the issue, but, made starting (when it ran) much easier.  One other thing I just remembered was going on when I got it back, it almost seemed like the battery was dead when I tried to start it.  Hesitated, then started to crank like normal.  The battery had full charge.

[Xxx]

That sounds to me like the timing is to far advanced a hard buck than spins but won’t start because either it was timed at above the recommended rpms to time motor or it could even be a tooth off. I don’t know why my posts keep disappearing but I’m pretty sure your electric is to far advanced!!!

[Fishnut]

That sounds to me like the timing is to far advanced a hard buck than spins but won’t start because either it was timed at above the recommended rpms to time motor or it could even be a tooth off. I don’t know why my posts keep disappearing but I’m pretty sure your electric is to far advanced!!!

I agree with You Pap. If your getting a hard turnover from start then after a couple revolutions it turns over good? Your timing is too far advanced.


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[Xxx]

1 hour ago, Fishnut said:

 

I agree with You Pap. If your getting a hard turnover from start then after a couple revolutions it turns over good? Your timing is too far advanced.


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Thank you sir  see if this post disappeares???

[Gill-T]

Get a reputable marine mechanic that knows how to tune the timing to specs recommended by the manufacturer.  

[Xxx]

The manual seloc says when I timed my motor to idle the motor to 600 rpm, as you turn the distributor towards the advance mode the motor will pick up r,pm and you need to continue to adjust the rpms back to 600 hundred until your at the desired timing mark, is says the  centrifugal force spin the weights out and advances the timing as much as 25 degrees advanced. So if you timed the motor like a car your way advanced before the centrifugal weights come into play. If I wasn’t so full from supper and lazy I’d get my book and scan the page and post it, but what I said is damn close!!

[L&M]

Thunderbolt ignition has no mechanical / centrifugal advance weights Pap, the ignition advance curves & total advance are controlled by the ignition module not to be confused with the ignition sensor that's stationary in the distributor . Initial timing set up differs depending on which type of T'Bolt system it is, but they all work on the same principle.

[Xxx]

Either way it can be timed to far ahead. So back to the thunderbolt book to see if timing is to far advanced, or how to set proper timing at an idle before the module  advances the timing at what ever rpm or call-need for more electric???