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Thuderbolt IV 4.3 mercruiser wont start.

R

rl65028

Contributing Member
Hi everybody. Can anyone help me salvage my short striped bass delaware bay season? Made one trip came back on a rope:mad:. Wouldnt start finally figured no fire. Went through troubleshooting procedure and found no voltage @ amplifier white red stripe wire. Bought new amplifier ( this one was only 1 yr old). New part # new harness. Installed. Now seems to have spark but still no start. Only curiious thing white w red stripe only lights test lamp dimly like very low voltage. defective unit? dunno. Stumped, engine very low time and was running great. Any thoughts?
 
I verified spark at plugs but saw spark arcing from pos coil stud to center electrode base. my theory is weak spark. New coil comeing. Anyone agree?
 
Could be bad spark plug wires creating to much resistance, ~ 5000 Ohms per foot.
What spark plugs are you using, just for curiosity sake.

Also the new sensor installed into base of distributor should have been a three wire two fo which are bullet connectors and one ground, correct?

The original sensor was two studs with ring terminal connections. Did you convert your connections?

Did you ground the black wire?



Tests for Thunderbolt Ignition:


Tests for Thunderbolt Ignition:
W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced.
 
New sensor in dist. Replaced bullets w soldred connections. AC r42 plugs. initially had no voltage to red white. rpl amplifier. now red white lights test lamp dimly dont think there is 12v. new amplifier, dist,grounded to mount bold on exhaust manifold that houses amplifier also have a ground from engine block to same mount bolt. Thanks kghost.
 
Try using a volt meter to seeif your dim test light results are equal to the 12 volts as described...

The sensor in the dist may be dead..... not much else

Oh,

disconnect the grey wire (tach) lead from - side of coil and recheck

Also confirm shift interuptor switch is not bad, disconnect the ground wire from the switch, the two leads from switch go to a terminal block. One is ground, remove switch lead from ground side of terminal block. If switch is bad it will short ignition to ground.
 
ok wilco. every time I manually moved shift interupter I saw a arc from coil pos lead to base of center electrode. Also when I cranked engine I saw same arc. With the test lamp on red white so dim I expect 6 volts or less .
 
Ok Finally got it running. Im pretty sure IGN amplifier was bad as I had no voltage @ red & white. Replaced it. wouldnt start. Then went to coil and replaced it. Nothing. Might want to note test you do with coil ground disconnected and you touch it to ground and arc is supposed to jump out center electrode didnt even work on a factory new coil. Then I replaced sensor and rotor in distributer still nothing. Finally replaced all spark plugs and it lit right off. Still dont think spark is very strong especially if it cant overcome fuel fouled plugs. Now the two week starter is not engageing all the way and just grinding flywheel without spinning it. Going to pull it off again and try to file any steps off flywheel teeth. This engine has less than 10 hours on it from US engines inc and I, m ready to throw in the towel. Nice 1992 celebrity fishawk Anyone want to buy it? Im an aircraft turbine engine mechanic by trade and if aircraft were as dependable as boats it wouldnt even be safe to go outside. Going to change name of boat to One Way Only. as you always come back on a rope.
 
When you say the ignition amplifier you are refering to the "pick up sensor" in the distributor?

The instructions clearly say what to do and what results you should get.

green/white to ground and you get a spark with key on, replace sensor inside dist.

with red/white disconnected and key on if 12 volts is there pick up sensor needs replacement

If no 12 volts amplifier is bad. (amplifier controls timing both idle and advance)

Please clarify.......
 
Amplifier: as in module bolted to riser. Red white no power amplifier. Thats the first thing i did. In the end changed the entire system with new. Coil, sensor, rotor, and amplifier. wouldnt start until after new plugs. To me thats a weak spark. A good system should light fuel fouled plugs. May try mallory 29701 coil.
 
Somethings a miss here!!

HAve you removed the tach lead from the coil?

Have you made sure the iterruptor switch is not shorted or partially shorted to ground?

Have you actually measured the voltage at the white/red and if so what was it..exactly.

We say 12 votls but it should be battery voltage and with engine running at ~ 1500 rpms should be 14 + a bit......with engine off it should be 12.4 ish

You could unplug the main harness connector and make a remote starter rig.

two switches, one momentary and one on/off.
Both powered by the same 12 volt feed from battery + and the momentary going to the starter solenoid and the on/off going to the coil +

This will allow you to start the engine from the engine compartment. also it will allow for another voltage check on the white /red wire again...with no dash connection.

if spark plugs and wires and all ignition components are new and still a weak spark then you need to isolate possible voltage losses.

Start with the dash by disconnecting the main harness connector.
 
I had disconnected gray tach lead and green and white over to interrupter. wouldn"t start then either. I now measure 10.5 volts @ red white with everything connected and 12 @ coil. originally I had zero @ red white.
 
I believe it should read same at red/white as at coil.....


What is your ignition, TBIV or TBV?

also at the main harness connector the pins get collasped over time and it is reccomended to put a hose clamp around the connector and tighten, not to tight but just tight to assure good contact between pins and sockets.....



Again if you try a remote rig and seperate dash from engine and recheck volatge.

remember the ignition on (purple) comes from the ignition switch in dash all the way back to engine. it splits to choke and coil and altenator.
 
I would ****t-can that distributor and buy an aftermarket one, it plugs right into the coil and you get rid of the modual

I have been down this road many times, those things need a very good ground and a loose battery cable will fry them, seen that more than once
 
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