View Full Version : 1988 4.3 mercruiser

08-31-2010, 05:36 PM
Hello all
This is my problem if someone could help. I have a 1988 4.3v6 185hp mercruiser.Took it out at the begining of the summer and ran fine at first then rough. After a while on the lake it would die out and start back up after i sat on the lake for 20min. Then do it again. So i took it home and changed the fuel pump. Cause it seemed like it wasnt getting gas. So i took it back out and now its worse wouldnt leave idle mode without dying out.So back home checked the fuel getting fuel. Check the spark and it is very week some plugs dont spark the ones that do are very week spark.So i changed the cap, rotor, and coil.Still not starting wants to start, back fires after cranking it a while.I know its getting gas threw the carb, wont even fire up wih starting fluid. been trying to get it started for 2 weeks burnt out the starter, replaced it.Someone suggested the ignition sensor, but i wanted to get your thoughts because its costing me on guessing.

08-31-2010, 07:54 PM
What did the optic trigger under the rotor look like? If it was heavily rusted that would cause the problem. Search my posts for Thunderbolt Ignition Test. Follow the steps. By the way, did you test the spark coming out of the coil as compared to what is reaching the spark plugs?
plug wires could be shot.

09-02-2010, 12:18 AM
Thanks for answering guyjg but for the life of me i cant find your post on how to test the Thunderbolt Ignition. If you can point me into the right direction i would apprecitate it. the spark out of the coil is stong the plug spark is yellow and week.

09-02-2010, 12:26 AM
if you have good spark at the coil but weak at the plugs i would check for high resistance of the plug wires

09-02-2010, 10:11 AM
You can perform the tests but I agree w/rkent5469; it sounds like you need a set of quality marine plug wires. Yellow spark @ the end of the plug wire won't jump the plug gap; it should be bright blue/white.

Tests for Thunderbolt Ignition:


Check the kill switch first!

#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 are 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.

09-02-2010, 10:06 PM
Ok first I would like to say Thank You guys for helping me out. I replaced the wires, plugs,cap,rotor,fuel pump,starter,and still no start. I did the test guyjg said to try and this is what I got. 12 volts at read wire connected and disconnected. On the green and white wires (2) there is 4.3 volts. 12 volts at the coil. So does this mean the ignition sensor is bad in the dist? I noticed the coil spark yellow and isnt as strong as i thought it was because it was stonger than the plugs,witch trying to start it today I tested the spark on all the plugs, cranking the motor the spark isn't consitent 1 to 2 sparks each plug cranking the motor for a few sec at a time. and still weak yellow. some plugs I cant get to spark unless I hold the key for 30 sec but dont want to do that anymore because thats how I lost the first starter.

09-03-2010, 09:27 AM
What did the optic trigger under the rotor look like? If it was heavily rusted that would cause the problem.

So does this mean the ignition sensor is bad in the dist?

Same part; cheaper than the amplifier module. Intermittent spark is a good indicator of its failure.

09-03-2010, 10:29 PM
Well I hope that is it because I am broke putting parts into it. Going to put it up untill next year or until I can afford to put more into it. Unless you guys know someone or somewhere where I can get a good cheap one, real cheap.
Other then that I really appreciate all the help you guys gave me.

09-04-2010, 11:09 AM
Merc. PN 87-892150Q02 (javascript:showPicture('showSpecialPicture.asp?pn =892150Q02'))

09-06-2010, 05:44 PM
I had a similer problem with my 4.3 Run a jumper wire from the + on the battery to the+ on the coil. If this works than your wireing is breaking down and needs to be replaced or modified. Let me know and I will fill you in on how I set mine up.

09-09-2010, 06:05 PM
hords i am getting 12 volts at thr + side of the coil already but tried it and that didnt work, thanks though.guyj i changed the ignition sensor in the dist. and still wont start. but now i get 12v on both sides red/white wire side and green/white wire side should that be?

09-09-2010, 10:47 PM
Did you perform the "spark gap test"? You may be having to get a new amplifier module. Buy it on eBay in December; cheaper price.

09-10-2010, 06:30 AM
timing chain... or jumped time...check the rotor in the distributer make sure it is turning when you crank the engine.

09-18-2010, 09:31 PM
sharkin you hit it right on the head 12 degrees out of time. My question is would all the electric parts on put on it make the timming off? another ? what is the timming suppose to be at? thank you all for your support

09-18-2010, 10:25 PM
If it is the same as my 95 4.3lx the thunderbolt IV timing is 8 Degrees BTDC and thunderbolt V is 10 Degrees BTDC According to my Mercruiser shop manual. If you are looking for a tune up kit with dist cap rotor, ignition module inside the distributer and wires you can get it from this website for 35 bucks plus shipping and handling www.amarket.com (http://www.amarket.com) they have great prices on mercruiser parts and they will be more then happy to help you find out whats wrong and guide you through troubleshooting over the phone. If anyone wants a copy of my mercruiser shop manual let me know and I will email it to you its about 12 megs.

09-19-2010, 10:40 AM
wish we could clone this thread.

09-30-2010, 07:02 PM
8 btdc.... make sure the hold down clamp on the distributer is tight. If that's not it, timing gears and chain have to be replaced.:cool: