Skeester45
Cadet
- Joined
- Feb 13, 2009
- Messages
- 15
First I want to say thank you for all of the fantastic information on these forums. It has been a great help, but I am currently stuck.
The specifics - 1995 350MAG Alpha - carbureted - Thunderbolt IV ignition - Serial# 0F421712. Previous owner replaced long block in 2013 due to bad winterization. Not sure how many parts were reused, but am fairly sure all ignition parts were stock.
Issue at hand - intermittent engine miss at nearly all RPMs, but most noticeable at cruise - 3000 - 3200. Feels almost like engine is being cut off since it will cause you to lurch forward in your seat. Engine does not die and comes right back nearly instantly. Fairly harsh vibration (this is new - details below) starting at 3000RPM. Engine starts and idles well cold or hot, and shift in and out of gear just fine.
What Ive done - new plugs/wires, dist cap, rotor, batteries, battery cable, swapped coil with known good one, new fuel water seperator, new ignition sensor, set base timing at temp at 750RPM to 10 deg BTDC (was found to be approx 3 deg BTDC before adjustment).
Before all changes above, the motor really struggled to get on plane, and would cough/backfire out the carb at about 2500RPM and nearly die with any more throttle. Eventually it would recover and go once throttle was pulled back and finessed. The engine miss was present, but not frequent. The above updates really improved the power at plane, but the miss has persisted and worsened. The vibration I believe has come about after the timing was set as this was done last. This is worrying me the most as I fear I could be damaging the motor.
It should also be noted that the tachometer gauge will often drift up or down without noticing anything changing audibly in engine RPM. At least once I have seen it climb from 3200 to nearly 4000 without touching the throttle or hearing any real change.
I have also noticed that engine RPM can be adversely affected by pressing the trim up or down. The electrical load seems to have a larger affect on the engine RPM than I would think, but cant be sure. The tach and the volt gauge often 'blip' together when it misses.
Question? - does the ignition module actually produce the tach signal to the gauge? If so,does that mean the TBIV module thinks RPM is changing when it isnt? The diagrams I have found seem to indicate the tach comes from that module and not from the ignition sensor. If that is so, then is my TBIV going bad? Electronics dont typically 'wear out'. Bad ground somewhere?
Up to this point, all replacement parts have been a 'good idea', but going any further will get expensive. Thanks in advance
The specifics - 1995 350MAG Alpha - carbureted - Thunderbolt IV ignition - Serial# 0F421712. Previous owner replaced long block in 2013 due to bad winterization. Not sure how many parts were reused, but am fairly sure all ignition parts were stock.
Issue at hand - intermittent engine miss at nearly all RPMs, but most noticeable at cruise - 3000 - 3200. Feels almost like engine is being cut off since it will cause you to lurch forward in your seat. Engine does not die and comes right back nearly instantly. Fairly harsh vibration (this is new - details below) starting at 3000RPM. Engine starts and idles well cold or hot, and shift in and out of gear just fine.
What Ive done - new plugs/wires, dist cap, rotor, batteries, battery cable, swapped coil with known good one, new fuel water seperator, new ignition sensor, set base timing at temp at 750RPM to 10 deg BTDC (was found to be approx 3 deg BTDC before adjustment).
Before all changes above, the motor really struggled to get on plane, and would cough/backfire out the carb at about 2500RPM and nearly die with any more throttle. Eventually it would recover and go once throttle was pulled back and finessed. The engine miss was present, but not frequent. The above updates really improved the power at plane, but the miss has persisted and worsened. The vibration I believe has come about after the timing was set as this was done last. This is worrying me the most as I fear I could be damaging the motor.
It should also be noted that the tachometer gauge will often drift up or down without noticing anything changing audibly in engine RPM. At least once I have seen it climb from 3200 to nearly 4000 without touching the throttle or hearing any real change.
I have also noticed that engine RPM can be adversely affected by pressing the trim up or down. The electrical load seems to have a larger affect on the engine RPM than I would think, but cant be sure. The tach and the volt gauge often 'blip' together when it misses.
Question? - does the ignition module actually produce the tach signal to the gauge? If so,does that mean the TBIV module thinks RPM is changing when it isnt? The diagrams I have found seem to indicate the tach comes from that module and not from the ignition sensor. If that is so, then is my TBIV going bad? Electronics dont typically 'wear out'. Bad ground somewhere?
Up to this point, all replacement parts have been a 'good idea', but going any further will get expensive. Thanks in advance
