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1995 350MAG Alpha Engine Miss

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  • 1995 350MAG Alpha Engine Miss

    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




  • #2
    Your saying TB4 so the module is on the exhust

    Replaced ignition sensor, was it a 3 wire or 2 wire module?

    The Tach reads the ON/OFF of the ignition module grounding and then ungrounding the negative side of the coil.

    Disconnect the tach at the coil, its a gray wire and see how it runs
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 Seadoo GTX
    Merc Adults Only VP Adults Only
    G-Dad always said "First Liar doesn't stand a chance"

    Comment


    • #3
      Hi Alldodge - thanks for the reply. My TB4 is on the back of the distributor though to be perfectly honest i have not pulled it off and verifed the exact model. I assumed TB4 because of this page: https://forums.iboats.com/forum/engi...n-systems-work

      The ignition sensor was a 2-wire as shown in the attached pic. The replacement was a Quicksilver 3-wire

      I will certainly try to disconnect the tach at the coil, which I have not done and will report back asap.

      By the way, this motor is in a 95 Rinker 232 that seems was off the assembly line not too much earlier than yours.

      Thanks again for the tip.


      Comment


      • #4
        I do have one more question- if the actual tach gauge is driven by the output of the ignition module, then an incorrect tach reading could point to a malfunctioning module correct? I would think that it could be hazardous if the module is advancing the timing too much for a given RPM. Jumping ahead here - if the module is faulty, what do you all recommend for replacement?

        Comment


        • #5
          Think of the tach reading coming oa light switch. The distributor ignition module flips on/off as the rotor turns. These on/off (ground/not grounded) cycles are counted. If the module messes up the tach will react. If the tach starts to short out, it will also make on/off cycles which cause the coil to fire more or less.

          The TB4 controls advance

          If the module is bad I would recommend Delco EST
          94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
          95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
          07 Seadoo GTX
          Merc Adults Only VP Adults Only
          G-Dad always said "First Liar doesn't stand a chance"

          Comment


          • #6
            Alldodge - thanks again for the insight. I was just curious if the tachometer gauge was driven from the 0-5V signal from the ignition sensor (just replaced) which is an input to the ignition module, or if it was driven from the output of the ignition module. What you stated indicates the output of the module drives the tach gauge and matches this basic diagram as well. I will disconnect the 'tacho feed' and see what I get.

            Comment


            • #7
              I'm trying to keep ot simple and guess I shouldn't have.
              The dizzy sensor turns on/off the transistor inside the module. When the transistor turns off it does the same as like a light switch opening a circuit which allows power to flow to the secondary winding of the coil. When transistor is turned back ON it grounds the secondary side of the coil and with the collapse of the field the coil spark is generated

              Same thing happens if the tach shorts out and causes more on/off cycles
              94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
              95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
              07 Seadoo GTX
              Merc Adults Only VP Adults Only
              G-Dad always said "First Liar doesn't stand a chance"

              Comment


              • #8
                Well I am a bit embarrassed. Went to the boat today to try some things that Alldodge suggested, and decided to really dig in and identify components and check grounds/etc. To my surprise I have a Thunderbolt V module and knock sensory and not the IV. Based on serial number and year, this should not have come on my motor and therefore was updated somewhere along the way. That means I timed it like a IV and didnt put it into 'base timing' mode properly. Ran out of time tonight but will do that later this week. Should improve vibration/performance, but probably doesn't explain the miss. Here is what I have - didnt realize the module wouldnt have Thunderbolt V on it anywhere. Thanks again for explanation and suggestion Alldodge.

                Forgot to mention I didnt seen any remnants of thermal paste on the back of the ICM. I read in some other threads that this module heating up can cause some problems. Good idea to add some thermal paste?

                Comment


                • #9
                  Good idea to add some thermal paste?
                  Not sue its needed but sure will not hurt
                  94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                  95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                  07 Seadoo GTX
                  Merc Adults Only VP Adults Only
                  G-Dad always said "First Liar doesn't stand a chance"

                  Comment


                  • #10
                    Well I am absolutely stumped. Timed it again, this time doing it correctly by following the procedure to the letter of the law for a thunderbolt 5. Carefully rerouted some wiring from harness and knock sensor since i read in manual that secondary ignition wires can affect knock sensor. Even put thermal compound on.icm

                    Started and idled perfectly after. First time out of the hole and just falls flat at 3000rpm. Motor is at normal running temp of 130. More throttle gets fewer rpms. Eventually will get on plane and get to cruise and higher rpm. Then the dreaded miss starts after about 5 or 10 mins of cruising. Ran very.smooth for those 10mins at 3100rpm. I got some video but not sure how to share.

                    The most obvious thing I see is the volt gauge dips from 14.5 to something like 8 when this miss happens and then comes right back. Corresponding to loss.of rpm and luching forward in my seat

                    Upon return to marina it got a bit worse and idle was rough at dock. The volt gauge was also dipping this time at idle and bouncing a lot. Manually trigger kill switch, and the behavior.of that is different than the miss. Voltage is unaffected by kill switch and wiggling wires to that switch shows no effect. Also tried removing tacho from coil as suggested but no effect.

                    I am definitely frustrated. If module.is possibly bad, do the symptoms support that? Thanks guys for the insight. I am fearful of paying a mechanic to chase this, but I'm out if ideas and skill. That being said I'm willing to keep trying if someone has ideas. Thanks

                    Comment


                    • #11
                      Since my mechanic isnt available until September I guess I am on my own. Sure would hate to lose the rest of the season. Here are a few videos I uploaded to YouTube that show what I am battling. Any help would be greatly appreciated!

                      Volt meter blips at idle speeds
                      https://youtu.be/LWtsduvVn3g
                      https://youtu.be/LAANQ4GD79s

                      Engine Miss
                      https://youtu.be/35DrYfUpOPs

                      Lack of power getting on plane (maybe separate issue?)
                      https://youtu.be/0l_K1prH2rU

                      Thanks in advance for taking any time to have a look and offer suggestions. Video descriptions show time in the video of the event they are describing

                      Comment


                      • #12
                        The 'blip' in the engine sure makes you think ignition. That's the only reason the engine power dips lead me to think ignition first there. That seems more fuel related.

                        Before I'd replace the Thunderbolt ignition module I'd swap to EST. Cheaper than a mechanic, too. I actually did exactly that when my T-IV module was screwing up. It wasn't worth the cost to get another when for less I could replace the whole thing. When they work, Thunderbolt ignition is the best. When they don't, it sure is lonely place to be since they work invisibly by magic.
                        17 Foot '90 Bluewater
                        Alpha 1 3.0 Merc - repowered in 2016
                        now - 4.3L Vortec - Alpha 1 GenII
                        Honda BF100L kicker
                        Engine custom - Transom 0D65328 - Drive 0D648864
                        If you ain't fishin, then yer working too much.

                        Comment


                        • #13
                          Thanks Rick. I agree on the engine power issue - I initially thought fuel since it would cough/backfire out the carb at times getting on plane, which lead me to think a lean condition was happening. Changing the fuel/water separator didn't really affect anything, though it needed to be done. I think that's my only fuel filter in the system. I have the Weber 9770sa-2074 carb.

                          I assume this is the part for the EST swap? https://www.michiganmotorz.com/delco...tor-p-119.html

                          I don't mind spending the money if I'm confident it'll fix the issue of course, but this intermittent stuff is brutal.

                          Any chance a bad alternator could do this given the voltages I am seeing? I suppose I could run for a bit without it connected.

                          Thanks again for any help.

                          Comment


                          • #14
                            You know, a Weber is so easy to rebuild that you should spend the half hour and do it. Get a rebuild kit for it at NAPA. Same kit as the Edelbrock 1409. GO through and make sure you don't have a cruded up carb adding to the woes.

                            And yeah, that's the EST you want. I do remember there was one place cheaper than all the rest. Thought it was Michigan, but wow, the price went up.
                            17 Foot '90 Bluewater
                            Alpha 1 3.0 Merc - repowered in 2016
                            now - 4.3L Vortec - Alpha 1 GenII
                            Honda BF100L kicker
                            Engine custom - Transom 0D65328 - Drive 0D648864
                            If you ain't fishin, then yer working too much.

                            Comment


                            • #15
                              Sign up today
                              I'm thinking a bad connection but check advance

                              Can do this in neutral
                              Mark the damper to make it easier to see, then bring the rpm up and see how much you get
                              94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                              95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                              07 Seadoo GTX
                              Merc Adults Only VP Adults Only
                              G-Dad always said "First Liar doesn't stand a chance"

                              Comment

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