2800 SCR 4.3 V6 ignition problem

[marcucho]

Brian,

Thank you for the feedback . My port side engine is standard rotation just like my starboard side. Believe it or not .. season is over and my engine still no running. TDC was taken way too many times .. checking valves like you mentioned, using cameras to make sure that piston was up there on Cylinder 1 , using compression tool.. etc etc.. Timing chain did not jump since all the time the rotor came back to 1 when TDC .. swapped rotor, pick up sensor inside the distributor, sparplugs brand new and nothing.

Talked to 3 marine mechanics and I got all of them scratching their head ... at least the were honest to say .. .you had safe a lot of money telling all the test that I had performed on the engine .. I even disconnected the main cable bundle to run the engine bypassing any sensors.. same result :-( . Spark , fuel (even with stating fluid) and compression... I was told by my brother and a car mechanic who actually know very well the 4.3 chevy engine to replace the distributor... because it may be shortened.. I do not see how this could happen because only electric part on the distributor is the pick up sensor as ar as I know everything else is mechanic on the distributor, I remember that kid of situation that distributor shortened mess sup the old ignition system with condenser .. but the new ones? Module is good because I moved to the starboard side and worked fine. Spark cables are connected right and all o them have 1K ohm resistance.. good cables. (new). Looking for dsitributor now...

[mmwjr]

Instead of buying a new distributor why not swap it with the other engines? Especially since this is a low chance of success as you said you have spark. The cap and rotor will play a bigger part to deliver the spark to each plug than the distributor housing itself.

[jrsick]

I was wondering how you were coming along with this. Sorry to hear it's not running, these problems are frustrating and tiring. The oddest part is that the engine starts on the trailer but not in the water.
Did you ever try taking fuel from an external gas tank?
Good luck, and keep us posted with progress.

[BrianC72]

OK, a couple of thoughts. First off, do you have a timing light? Cheapo is fine with the inductive clamp to go over the #1 plug wire?

Step one is trusting indicated TDC really is TDC.
With the plugs out, turn the crank by hand with dipstick inside the spark plug hole touching the top of the piston, (holding the dipstick blade between thumb and forefinger just outside the hole) you should be able to feel the peak at indicated TDC and drop down on either side of it. A breaker bar is handy for this because you will change directions going just forward and backward over TDC.

Go all Yoda on it. Close your eyes, rock it back and forward by just a few degrees with one hand while feeling the piston crest at TDC using the other set of fingers on the dipstick. If what you feel from Dipstick TDC and your harmonic damper timing marks do not jive, then either the harmonic damper rubber has let go or the Crank cog keyway is sheared and the cog is slipping to the retarded side. I doubt either of these scenarios actually happened, but feel for TDC and see that it corresponds to the timing marks on the crank. Good? Check that off the list.

Next, I would pop the 1,3,5 valve cover off and confirm I'm at TDC #1 on the Compression/power stroke. I swapped in a new 4.3 long block on a new-to-me LOW hour boat with a cracked block. Here is a link to a short bad video I made showing how to find TDC and wiring plug wires to the cap. I need to go back and show the whole process, but this might help.

https://youtu.be/Mr4O64HUEr8

Once you are sure about TDC on #1 compression/power stroke, rotate around to 10 degrees Before TDC mark, remove the cap and see that the rotor, when viewed from overhead is pointing at or just clockwise of the #1 spark plug contact. Spark doesn't happen when the rotor is pointing at the #1 contact, but JUST after, at the point where the rotor breaks "contact" or just passes #1 pick up. Also you have to eyeball it using 10 degrees BTDC, NOT actual TDC. Actual TDC would be too late. The spark has to happen early so the flame has enough time to propagate. The faster the RPM, the sooner the spark has to happen. That's why ignition timing advances as the rpms rise.

If you are all good to this point, check that the plug wires are right..clockwise ..1,6,5,4,3,2
1 is cylinder closest to front on the right, 6 is close to the transom on the left. Right side 1,3,5. Left side 2,4,6.

I got to 10 BTDC, eyballed the cap, and rotated the distributor base, so the #1pickup on the cap would be JUST a blonde one counterclockwise of the rotor. Then I put on the plug wires in order, starting with 1, then 6,5,4,3,2. Primed it a little and ..started on the first shot.

Throw a timing light on #1 and crank it. You are shooting for 10 degrees BTDC while cranking on the starter with the test plug wires jumpered.



Confirm TDC between the piston and pulley first (I'm guessing it is fine), then loose rocker arms on TDC 1, then eyeball the rotor is JUST past cap contact #1.

The original no start condition suddenly found the timing out of whack. Don't ignore it. Focus on WHY did that happen? A stiff oil pump and slightly lose distributor base clamp might cause the distributor to rotate retarded. or is the cog on the distributor shaft press fit and slipping? My guess is that the driven gear on your distributor shaft is slipping. Did it shear a roll pin or something?

I skipped a step: confirm the EXACT position of the camshaft when at TDC, because that requires removal of the front cover. Mine is plastic and is supposed to be replaced every time you remove it. That didn't happen. So if all of the above fails, that's the next thing to check.

[marcucho]

Originally Posted by jrsick

I was wondering how you were coming along with this. Sorry to hear it's not running, these problems are frustrating and tiring. The oddest part is that the engine starts on the trailer but not in the water.
Did you ever try taking fuel from an external gas tank?
Good luck, and keep us posted with progress.

I did check on the fuel .. for water , no water on the fuel actually the same tank for both engines... I replaced the water/fuel filter just because ... I do not know what else to do :-) .. may be painting the engine Pink hehe..who knows... and by the way starting fluid did not make a difference.

[marcucho]

Originally Posted by BrianC72

OK, a couple of thoughts. First off, do you have a timing light? Cheapo is fine with the inductive clamp to go over the #1 plug wire?

Step one is trusting indicated TDC really is TDC.
With the plugs out, turn the crank by hand with dipstick inside the spark plug hole touching the top of the piston, (holding the dipstick blade between thumb and forefinger just outside the hole) you should be able to feel the peak at indicated TDC and drop down on either side of it. A breaker bar is handy for this because you will change directions going just forward and backward over TDC.

Go all Yoda on it. Close your eyes, rock it back and forward by just a few degrees with one hand while feeling the piston crest at TDC using the other set of fingers on the dipstick. If what you feel from Dipstick TDC and your harmonic damper timing marks do not jive, then either the harmonic damper rubber has let go or the Crank cog keyway is sheared and the cog is slipping to the retarded side. I doubt either of these scenarios actually happened, but feel for TDC and see that it corresponds to the timing marks on the crank. Good? Check that off the list.

Next, I would pop the 1,3,5 valve cover off and confirm I'm at TDC #1 on the Compression/power stroke. I swapped in a new 4.3 long block on a new-to-me LOW hour boat with a cracked block. Here is a link to a short bad video I made showing how to find TDC and wiring plug wires to the cap. I need to go back and show the whole process, but this might help.

https://youtu.be/Mr4O64HUEr8

Once you are sure about TDC on #1 compression/power stroke, rotate around to 10 degrees Before TDC mark, remove the cap and see that the rotor, when viewed from overhead is pointing at or just clockwise of the #1 spark plug contact. Spark doesn't happen when the rotor is pointing at the #1 contact, but JUST after, at the point where the rotor breaks "contact" or just passes #1 pick up. Also you have to eyeball it using 10 degrees BTDC, NOT actual TDC. Actual TDC would be too late. The spark has to happen early so the flame has enough time to propagate. The faster the RPM, the sooner the spark has to happen. That's why ignition timing advances as the rpms rise.

If you are all good to this point, check that the plug wires are right..clockwise ..1,6,5,4,3,2
1 is cylinder closest to front on the right, 6 is close to the transom on the left. Right side 1,3,5. Left side 2,4,6.

I got to 10 BTDC, eyballed the cap, and rotated the distributor base, so the #1pickup on the cap would be JUST a blonde one counterclockwise of the rotor. Then I put on the plug wires in order, starting with 1, then 6,5,4,3,2. Primed it a little and ..started on the first shot.

Throw a timing light on #1 and crank it. You are shooting for 10 degrees BTDC while cranking on the starter with the test plug wires jumpered.



Confirm TDC between the piston and pulley first (I'm guessing it is fine), then loose rocker arms on TDC 1, then eyeball the rotor is JUST past cap contact #1.

The original no start condition suddenly found the timing out of whack. Don't ignore it. Focus on WHY did that happen? A stiff oil pump and slightly lose distributor base clamp might cause the distributor to rotate retarded. or is the cog on the distributor shaft press fit and slipping? My guess is that the driven gear on your distributor shaft is slipping. Did it shear a roll pin or something?

I skipped a step: confirm the EXACT position of the camshaft when at TDC, because that requires removal of the front cover. Mine is plastic and is supposed to be replaced every time you remove it. That didn't happen. So if all of the above fails, that's the next thing to check.

Brian thank you for the write up .. I did all the steps you mentioned on the video .. the only question I have .. I noticed on your video when you showed the rotor location after TDC was found , I saw the rotor pointing to almost 8:30 to 9:00 on the clock.. and I know that #1 terminal on the terminal is around 11:00 to 11:30 (thinking of the distributor cap as a clock for location references). So did you install the cable for piston #1 on the #1 location of the distributor cap ? even that the rotor is pointing to a diferent location on the distributor cap or did you actually installed the cable from piston#1 on the closest terminal to where the rotor is pointing at TDC .. ? and then just install the rest of the cable on the following firing order.. like you mentioned 1,6, etc...

In my case rotor is pointed to to exact #1 location on the distributor cap at TDC .. and we made sure that the valves are loose as you mentioned on the video.. also we double checked that the piston is at the top position with a camera that we got into the spark plug hole.

Let me know about the rotor location while on tdc

I just rechecked the video and the rotor is pointing to pin #5 on the distributor cap when you are TDC with 10 degrees

Thank you guys ...for all the help

[marcucho]

Originally Posted by mmwjr

Instead of buying a new distributor why not swap it with the other engines? Especially since this is a low chance of success as you said you have spark. The cap and rotor will play a bigger part to deliver the spark to each plug than the distributor housing itself.

Mike, I do understand what you said . but to tell you the true I am afraid to mess with the working engine... I already found cheap working distributor for the test .. which by any chance is not the failing part .. I would keep as spare.. believe me I want it to be the failing part .. even-though that there is relation or reason to it... but hey I this point .. I just ant the engine to be fixed

Thanks

Jose

[mmwjr]

Jose you may have already tried this but I’ve lost track. Have you verified spark of each plug? This will tell you spark is getting from the coil to each cylinder than it’s just a matter of timing since you verified fuel is not the issue.

[marcucho]

Originally Posted by mmwjr

Jose you may have already tried this but I’ve lost track. Have you verified spark of each plug? This will tell you spark is getting from the coil to each cylinder than it’s just a matter of timing since you verified fuel is not the issue.

Mike.. I did check from coil to distributor cap., then @ each terminal of the dsitributor cap.. and then at each sparkplug.. . I also checked the resistance on each sparkplug cable.. 1k all of them.. good cables. .. spark is strong all over the place...

[mmwjr]

Not sure what else to suggest without being there in person to see what you are seeing.

[BrianC72]

Jose,

In that video, I had not yet rotated the distributor base so I could put the cap on where the rotor would be at or just a smidge clockwise of the #1 contact inside the cap. That's the beauty of this ignition system, It doesn't matter what direction the rotor is pointing when you are at 10 degrees BTDC. Just loosen the distributor base and rotate it so the cap will have the #1 contact just a smidge counter clockwise of rotor contact. If you aim to be right on the contact at 10 degrees BTDC, that should be close enough to get the engine started. Then you install plug wires one at a time 1,6,5,4,3,2.

Try cranking it with a timing gun on #1 and you should see the strobe light flashing on the number tape on your harmonic damper. If it is hitting 10 degrees BTDC, you should be good to go. To set timing when the engine is running at (what rpm is it? 850 or 1300?... the rpm should be on the carb flash arrester label with all of the info on it) you have to put a jumper in the timing plug coming from your ignition controller box. With the jumper in place, the box will not advance timing, so you want to keep the engine at idle speed. It makes it easier to set timing that way without the advance causing the timing to dance all around. When running at idle, set it to 10 BTDC with a timing gun, tighten the distributor, double check that it hasn't moved with the timing light, then shut it off, remove the jumper and you are done.

Also, you mentioned the rotor is pointing at #1 contact at TDC. I think the rotor should be just clockwise of the cap contact at TDC, because you are really trying to set the timing to 10 BTDC, not TDC. Lining up to TDC would make your spark timing too late, too retarded to start. If the spark didn't start until the piston was already on its down stroke then your spark is firing too late. To advance your timing, rotate the Distributor base counterclockwise. To retard it, turn the base clockwise.

A timing gun is your friend. Do you have one? Also, did you happen to confirm TDC with the dipstick method? I'm not sure if I explained that clearly enough.

[marcucho]

Guys..thank you for all the help... today just installed a new to me dsitributor..and the engine started right up. Do not ask me how come.. ut the dsitributor was shorted..how.. do not know. Got the TDC like many times we did before and installed the new distributor... started right up.like it used to.. got the timing and engine is running like always... 6 months.. now i am a believer that dsitributors go bad. Here a short video from the sea trail.. btw sunset was amazing

https://youtu.be/xWlj6KGgq1w

Thank you all and happy Thanksgiving..

Jose

Sent from my SM-N950U using Tapatalk

[jrsick]

Glad that you got it fixed. I guess the spark you were getting was either very weak or way out of timing.
Nothing like a sea trial while wearing winter coats.

[mmwjr]

Did you install another Mercruiser distributor or aftermarket? Glad you got her running.

[marcucho]

Mike , another mercruiser ..just like the old one. Used, but new to me. .. I still trying to understand why the old distributor was shorted, but to be honest... I expended 6 months thinking on what was wrong with the engine that I am just glad that it is working.. 3 mechanics told me about the distributor and I did not listening because did not sound logical.. oh well..they were right.. now let get ready for... who knows I just know that I own a boat and we are always working on something..

[jrsick]

Rec you change your oil before taking your boat out again. You've had a lot of fuel leak down from the cylinder heads while trying to start the motor.

[BrianC72]

Happy to hear you got it running again. I'm not sure your old distributor was shorting or slipping internally because you were able to confirm spark on each cylinder, so it must have been turning and triggering. How was the drive gear on the old distributor?

Way to stick with it. When all else fails, throw parts at it

Regards,

Brian

[marcucho]

Brian, The gear on the old distributor was just fine... as good as the new to me distributor (working one ). I really would like to know how to test the nonworking distributor if it was shorting... Do not know where to put the ohmmeter pin ends to check ... just curiosity.

Thank you for the help

Jose

[mmwjr]

I forgot, is this a Thunderbolt V ignition system? There should be a troubleshooting guide in the Mercruiser manual.