Hi all...
I've been reading and reading and reading, and while I have found some ideas to try based on other T5 posts, I'm going to post my issue now and hope like heck someone responds soon because I have no faith that the things I'm going to look at this afternoon are going to solve the issue. I apologize for this lengthy post, but as you read you'll understand why it's so long. It's a very strange issue and I've already done some testing and troubleshooting which I wanted to be very detailed about...
I have twin '99 Merc 5.0 MCM motors (2 bbl carbs with T5 ignition). Sorry, I don't have the serial numbers handy but I don't think we need them for this...
One motor (starboard) runs fine, the other won't make power and won't rev above 2800rpm. It also idles fairly rough, and stalls when in gear at low speed. This all started last year so I did new plugs, wires, cap and rotors in the spring, and over the winter I had my mechanic check the distributors out to make sure the sensors were working. He did NOT check the modules or whatever the built-in component on the distributors is called. (I am NOT referring to the control module and knock sensor that is mounted on the exhaust riser)
I redid the timing yesterday, with a brand new digital timing light, being fairly certain I had not done it right originally. I was right and reset the timing to 10 degrees BTDC on the first motor (the one that runs well) and everything went fine. Runs great now (although the idle mixture/speed screws are still black magic to me so I just do it by ear for smooth idle without unnecessary richness). Still not the weird part....here we go....
When I checked the port motor I COULDN'T GET A CONSISTENT SIGNAL TO THE TIMING LIGHT FOR CYLINDER 1. It kept going on and off for periods of time (5-10 seconds). The motor starts fine, and it revs fine (no load), In fact, when I rev it the signal to the timing light comes back and seems to stay steady, but as soon as it returns the idle the timing light will show all zeroes as if the engine is off, then it will come back, then it will go off, and so forth. The engine idles rough....not horrible, but not silky like the other one. So probably a weak coil giving me a weak signal, right? Not so fast....read on.
Here is what I tried last night, along with some ideas that I'm going to try today:
- Verified timing light works properly on good motor, several times throughout troubleshooting. Definitely not the light.
(Now it gets weirder)
- I put the timing light on number 8 (right beside number 1), and it's also intermittent. BUT IF I PUT IT ON A WIRE ON THE OTHER SIDE OF THE DISTRIBUTOR, IT WORKS CONSISTENTLY.
*Theory #1 - something wrong with cap. Today I'm going to try number 2 which is immediately on the other side of number 1 and see if it is inconsistent like number 8 is, and I'm going to swap caps with the good motor and see if the problem moves with the cap.
- I swapped the coil with the one from the good running motor. No change, so I returned the coils to their original motors.
- Next I swapped ignition modules and knock sensors (the ones mounted on the risers). No change, and the good motor runs fine with other module. I left modules swapped.
- Next I swapped the rotors. No change. Good motor runs fine with other rotor. I left them swapped.
- Next I swapped the #1 spark plug leads. Still no change to intermittent timing signal and good motor runs fine with wire from other motor.
So now I'm at theory #2 (and the main question I have for you guys):
The voltmeter on dash says port (the bad motor) alternator is NOT charging. It was supposedly a new alternator when the boat was bought last year (that's a whole other story about lying brokers for another day) and it LOOKS new, but it was reading low last year too. I assumed it was a bad gauge last year, but I put in all new gauges over the winter and it's still reading low. The starboard side reads as it should. I checked the wiring on the back of the alternator and it looks fine....tight and the wires are in the right places.
Could a lack of power from the alternator cause the ignition problems I'm having, even with brand new, fully charged battery?
While waiting for (hopefully) an answer to that, today I am going to swap alternators and see if the problem follows the alternator.
I read in another post from RobertD ("Found an electrical gremlin!"), who was having an ignition problem, that he ended up tracing the purple wire from the alternator all the way back to the coil (I didn't realize that's where the purple wire goes....but I'll assume he's right until I learn otherwise), and he found a weak spot in the wire before he got to the coil. He replaced the wire and his problem went away. That seems to boost my theory that the alternator issue is affecting the ignition.
I've never connected the two issues because I know on a car you can run for quite a while without a working alternator if your battery has enough juice to keep making spark. Are boats/TB5 different in that regard?
I'm hoping someone has seen this weak timing light signal issue before, because I'm quite certain that it's also indicating weak spark as well, and that's why the motor bogs and won't rev/make power. I didn't make the connection with the alternator issue until late last night...perhaps that should have been my first clue.
Any ideas/help are greatly appreciated. Thanks
Kevin
p.s. Oh, as a side note and just to make sure I'm not missing something....it's ok to have ONE starting battery/bank for both motors, right? i.e. I have two banks, one for the house and one for the engines, and both engines pull on the same battery/bank for starting. I ask because I wondered if it's ok to have two alternators charging the same battery/bank. The alternator wasn't charging long before I made that change, but just thought I'd ask anyway in case it's related somehow.
I've been reading and reading and reading, and while I have found some ideas to try based on other T5 posts, I'm going to post my issue now and hope like heck someone responds soon because I have no faith that the things I'm going to look at this afternoon are going to solve the issue. I apologize for this lengthy post, but as you read you'll understand why it's so long. It's a very strange issue and I've already done some testing and troubleshooting which I wanted to be very detailed about...
I have twin '99 Merc 5.0 MCM motors (2 bbl carbs with T5 ignition). Sorry, I don't have the serial numbers handy but I don't think we need them for this...
One motor (starboard) runs fine, the other won't make power and won't rev above 2800rpm. It also idles fairly rough, and stalls when in gear at low speed. This all started last year so I did new plugs, wires, cap and rotors in the spring, and over the winter I had my mechanic check the distributors out to make sure the sensors were working. He did NOT check the modules or whatever the built-in component on the distributors is called. (I am NOT referring to the control module and knock sensor that is mounted on the exhaust riser)
I redid the timing yesterday, with a brand new digital timing light, being fairly certain I had not done it right originally. I was right and reset the timing to 10 degrees BTDC on the first motor (the one that runs well) and everything went fine. Runs great now (although the idle mixture/speed screws are still black magic to me so I just do it by ear for smooth idle without unnecessary richness). Still not the weird part....here we go....
When I checked the port motor I COULDN'T GET A CONSISTENT SIGNAL TO THE TIMING LIGHT FOR CYLINDER 1. It kept going on and off for periods of time (5-10 seconds). The motor starts fine, and it revs fine (no load), In fact, when I rev it the signal to the timing light comes back and seems to stay steady, but as soon as it returns the idle the timing light will show all zeroes as if the engine is off, then it will come back, then it will go off, and so forth. The engine idles rough....not horrible, but not silky like the other one. So probably a weak coil giving me a weak signal, right? Not so fast....read on.
Here is what I tried last night, along with some ideas that I'm going to try today:
- Verified timing light works properly on good motor, several times throughout troubleshooting. Definitely not the light.
(Now it gets weirder)
- I put the timing light on number 8 (right beside number 1), and it's also intermittent. BUT IF I PUT IT ON A WIRE ON THE OTHER SIDE OF THE DISTRIBUTOR, IT WORKS CONSISTENTLY.
*Theory #1 - something wrong with cap. Today I'm going to try number 2 which is immediately on the other side of number 1 and see if it is inconsistent like number 8 is, and I'm going to swap caps with the good motor and see if the problem moves with the cap.
- I swapped the coil with the one from the good running motor. No change, so I returned the coils to their original motors.
- Next I swapped ignition modules and knock sensors (the ones mounted on the risers). No change, and the good motor runs fine with other module. I left modules swapped.
- Next I swapped the rotors. No change. Good motor runs fine with other rotor. I left them swapped.
- Next I swapped the #1 spark plug leads. Still no change to intermittent timing signal and good motor runs fine with wire from other motor.
So now I'm at theory #2 (and the main question I have for you guys):
The voltmeter on dash says port (the bad motor) alternator is NOT charging. It was supposedly a new alternator when the boat was bought last year (that's a whole other story about lying brokers for another day) and it LOOKS new, but it was reading low last year too. I assumed it was a bad gauge last year, but I put in all new gauges over the winter and it's still reading low. The starboard side reads as it should. I checked the wiring on the back of the alternator and it looks fine....tight and the wires are in the right places.
Could a lack of power from the alternator cause the ignition problems I'm having, even with brand new, fully charged battery?
While waiting for (hopefully) an answer to that, today I am going to swap alternators and see if the problem follows the alternator.
I read in another post from RobertD ("Found an electrical gremlin!"), who was having an ignition problem, that he ended up tracing the purple wire from the alternator all the way back to the coil (I didn't realize that's where the purple wire goes....but I'll assume he's right until I learn otherwise), and he found a weak spot in the wire before he got to the coil. He replaced the wire and his problem went away. That seems to boost my theory that the alternator issue is affecting the ignition.
I've never connected the two issues because I know on a car you can run for quite a while without a working alternator if your battery has enough juice to keep making spark. Are boats/TB5 different in that regard?
I'm hoping someone has seen this weak timing light signal issue before, because I'm quite certain that it's also indicating weak spark as well, and that's why the motor bogs and won't rev/make power. I didn't make the connection with the alternator issue until late last night...perhaps that should have been my first clue.
Any ideas/help are greatly appreciated. Thanks
Kevin
p.s. Oh, as a side note and just to make sure I'm not missing something....it's ok to have ONE starting battery/bank for both motors, right? i.e. I have two banks, one for the house and one for the engines, and both engines pull on the same battery/bank for starting. I ask because I wondered if it's ok to have two alternators charging the same battery/bank. The alternator wasn't charging long before I made that change, but just thought I'd ask anyway in case it's related somehow.
