engine miss or electrical

[netting one]

So I have a 1996 merc 5.7 chevy with thunderbolt ignition. I have replaced many of all the items on the engine along with the engine. I put a module and knock sensor in a few years back also. This year new plugs wires cap rotor. When i went out yesterday just cruising about 10mph, it felt and sounded like some one shut the power off for a quick second? It did it about 3 times in a hour so I'm a little concerned. Does anyone have a suggestion?

 

[frantically relaxing]

lots of things it could be:
Does it have a lanyard switch? It might be going
I've had several ignition switches go bad over the years--
Neutral safety switch
ground wire to the distributor
either wire to the coil
Check the air gap in the distributor, between the trigger and the hall effect switch
If the coil uses a ballast, could be that
Merc's use a switch that temporarily shuts down the motor as you shift gears, if the switch or the cable is out of adjustment, that could do it..
Is it injected? The fuel pump stopping for whatever reason will cause it (loose wire?)

My first thought, BECAUSE I've had many go bad, is to replace the ignition switch. They're cheap, even if that isn't the problem....

 

[alldodge]

I'm thinking a bad electrical connection, suggest starting with the battery and work your way around, paying close attention to grounds. If it continues, remove the tach wire off the coil (gray wire negative side)

 

[netting one]

great stuff, i thought i thought of every thing but no way! i will start weeding my way through all suggestions. i like the coil one and the ingtion switch, to me not fuel it happens to quick.

 

[netting one]

So far ive checked,no lanyard cord,no neutral saftey switch,no ballast on coil,and no shifter kill switch for shifting (bravo ll ) i thing im going to switch to battery #2 and see if that makes a difference then start looking around. boat sits inside for the winter in a 70 degrees building also.going check the main big plug also.

 

[alldodge]

Sounds good, look forward to your investigation results

 

[netting one]

The more i keep checking im not finding any thing. I hope it isnt the module in the distributer again. Now has any one ever changed out the dist for one of the new electronic ones of today? I did read once that the thunder bolt changes timming when needed. For the cost of that module i could buy a hei system and be farther ahead. Going to try to work on it this weekend again.

 

[alldodge]

The TB-V is a good system and very reliable. The TB does advance the timing based on engine type, this is why there are so many model numbers for the TB. Many have shifted over the Petronix and it works, but they have one timing curve for all types of engines. The best change over IMO is the AC Delco EST, but it does cost more.

The only reason to change over is when the TB is not working. I'm still leaning toward a ground issue, and it could be the distributer on inside the distributer it self. You could connect up another and not have any issues or it could be the same. Finding something that is intermittent is a pain.

 

[netting one]

IM going keep trying i just have a bad feeling about the little black box. Last one after replacing every thing it was easier because it just quit (no spark at all) i did take it apart and it was full of water and jelly stuff. thanks again for the help i will keep you posted.

 

[netting one]

Well no luck yet, im going to try 2 new batterys this weekend. I still have to disconect the tach wire also.

 

[netting one]

Well put 2 new batteys in and thought i had it but on the way in again it stumbled. Im thinking of changing the thunderbolt ingtion out all together? Any one ever do this?

 

[alldodge]

Most recommend the Delco EST system to replace the TB. You can find some cheaper, but the timing curves are different, they do work, just different and can loose some performance

 

[netting one]

Thats my biggest worry.I heard from a old timmer once you can really hurt performance and power not with the thunderbolt system. I just dont want to keep buying those modules.

 

[lkbum]

Check your ground connection from the battery to your engine. I've seen a loose ground wire at the engine black cause this.

 

[ksmauck]

It sounds like I have this identical problem with my 1998 5.7 liter with the Thunderbolt V ignition system. When I am cruising it will momentarily cut out, usually for just a fraction of a second like it just completely loses spark and then it comes back. Occasionally if it cuts out for more than a split second it will backfire. It is very intermittent. Last year it started happening after I had the heads rebuilt because I had destroyed the valves because a buddy cracked a ceramic on one of my spark plugs and the wrong plugs had been installed. So far I have replaced the distributor cap, ignition coil, ignition sending unit, plugs, plug wires, and have disabled the lanyard on/off switch. I thought the lanyard had solved the problem as I then had two trips on the water with zero issues but low and behold the last time I went out it started happening again. While underway I have unplugged the neutral safety switch from the harness but it still happens. I am going to try to remove the gray tach wire and I'm replacing the ignition switch today as well. I'm not sure but I've also heard that the alternator can cause these problems (i'm not sure how) and that the starter solenoid can cause problems like this as well. It should not be a knock sensor because that doesn't kill ignition just retards timing. I've also heard oil pressure sensor can affect this? I'm pulling my hair out so I will follow your thread very closely and if you find the issue I'd love to know what it was for you! I'll reciprocate and let you know if I solve the issue as well. GOOD LUCK!!! P.S. I've also done as good of a visual search as I possibly could of my wiring and harness. I can't seem to find anything that's loose or chaffed. I cannot make this thing cut out when it's sitting in the driveway. It never does it at idle...and it seems like it happens most frequently when I am between 1500-3200 rpm on the water.

 

[netting one]

It does sound the same. I havent taken the tach wire off yet nor the ingition switch but i went out the other night with no problems? I still serching though.

 

[NHGuy]

OP did you try wiggling the wires under the dash? What about the ones in the engine bay? My 97 350 carb mag will intermittently hiccup when I hit a good bump, but that's the only time it does.
I'd just start cleaning each contact too.

 

[ksmauck]

Going to try to launch my boat this week. I took off the main engine ground so I replaced that. It was a little corroded with rust. I also found a crack in the 50 Amp main circuit breaker housing and I replaced that and went ahead and bought another new coil. I determined the one I had on their was not an HEI coil and the mercruiser dealer gave me the wrong coil the last time (still should have worked probably just wouldn't have lasted as long). I checked for a short on the gray tach wire and found that it had appropriate resistance and was not shorted. I also replaced the tach with a new one.. Didn't trust the old one anyway and the glass on it was looking pretty bad anyway. If what I've done does not work I am going to go ahead and change ignition systems to the Delco EST.

 

[NHGuy]

If you get a new ignition take a look a Davis Unified Ignition. DUI. They will curve the timing for your engine and use. It's not a one size fits all. I've seen good things. Plus I think it's a one wire design.

 

[ksmauck]

Tested today after having replaced the ignition switch, coil, coil wire, replacing the main ground wire, replacing the tach and replacing the main circuit breaker (I found that it had been cracked). Operated the boat for about 1 hour and thought I had it fixed but then it did it again. About 3,000 RPM and boom it cuts out for a split second. Couldn't get it to do it again after that but only stayed out about 15 more minutes.

The other issue I've been having is I can get no more than 4400 RPM (barely 4400). I have a 21 Reinell that only had me on it today with about 70 gallons of fuel and a 17 pitch prop on my alpha 1. I used to get 4800 with a 19p prop.