Hello again everyone! I've ran across a very odd problem which I hope someone here can shed some insight. I have a customer with a 1986 OMC 4.3L V-6 GM block which came to me with the task of giving him a spring tune up and a few other small odds and ends maintenance. He told me that the engine doesn't seem to get up and go like it used to, and felt that a tune up would do the trick since he has not had one done in a few years. I changed out the cap, rotor, condenser, points, wires, and plugs and the trusty 4.3 fired up instantly but ran with a slight hiccup . I specifically made sure to gap the plugs properly, set the points, and check dwell, and timing. With a few minor tweaks and adjustments, everything came out to spec. He took the boat out on the lake and found that it was still acting funny when trying to achieve WOT, so I went with him on a lake test. The boat seems to misfire around 3000 rpm and will only reach around 3500 and feels like a chugging, poor run condition. It has the feeling as if the engine was not timed correctly, so of course I verified timing on the lake. Still no resolve. I took the boat back to my shop where I did the normal series of tests, fuel, compression, spark, etc. I found while the boat is at idle, spark is intermittent on cylinder #3 and #4. The worse of the two is #3. I threw a timing light on #3 and noticed that the engine picked up a little when spark was present which was one hit to every 4 rotations or so.
I tore down the ignition system again checking all of its components. This time I examined the distributor cam, verified my points to be set at .018 and my dwell was at 40* which spec for dwell is 38*-41*. I used a bump switch to watch #3 and #4 cam lobes to make sure that the points opened and they opened perfectly with .018 between each cam. Put it all together, and BAM.. still a huge fail. I installed all of the above mentioned ignition parts all over with NEW and verified everything when done.. Still no change.
At this point I am lost. I again did another compression check where each cylinder, (all 6) scored a 180 to 185 rating. I've learned that if I remove the #3 or #4 wire from the distributor and hold it about an inch away from the contact, that they both fire perfectly every time. Once I push the wire end back down into the distributor, no more spark.. Well, intermittent spark. I've even tried to use electric grease inside all of the contact points just as a hail marry but nothing... Asked a few old timer mechanics around town and they said they had no clue. Any insight would be awesome, Thanks...
P.S. Almost forgot, we tossed in a new ignition coil just for safe measures, and chased down all the grounds we could find. All wires seem to have good clean connections.
I tore down the ignition system again checking all of its components. This time I examined the distributor cam, verified my points to be set at .018 and my dwell was at 40* which spec for dwell is 38*-41*. I used a bump switch to watch #3 and #4 cam lobes to make sure that the points opened and they opened perfectly with .018 between each cam. Put it all together, and BAM.. still a huge fail. I installed all of the above mentioned ignition parts all over with NEW and verified everything when done.. Still no change.
At this point I am lost. I again did another compression check where each cylinder, (all 6) scored a 180 to 185 rating. I've learned that if I remove the #3 or #4 wire from the distributor and hold it about an inch away from the contact, that they both fire perfectly every time. Once I push the wire end back down into the distributor, no more spark.. Well, intermittent spark. I've even tried to use electric grease inside all of the contact points just as a hail marry but nothing... Asked a few old timer mechanics around town and they said they had no clue. Any insight would be awesome, Thanks...
P.S. Almost forgot, we tossed in a new ignition coil just for safe measures, and chased down all the grounds we could find. All wires seem to have good clean connections.
