troubleshooting thunderbolt V issue

[revkev6]

Hey guys, I'm helping out with a boat project my uncle has. It's a 1996 crownline that he bought with the engine pulled due to a cracked block and soft floors. He replaced the floors and bought a rebuilt 5.7l marine long block and we have swapped everything over(carbureted motor). We got everything connected and went to fire it off last weekend. it keeps acting like the distributor (thunderbolt V) is in 180 out... popping out the carb. I put the timing light on it as it was cranking over and the light comes on at the timing mark on the balancer so I can't see how it would be 180 out.... He has tested everything according to the manual and is at the point where he thinks the problem has to be the distributor/module itself.

my question is, would a distributor/module failure exhibit these type of symptoms? my understanding is you usually either get no spark at all or one spark then nothing with a bad thunderbolt system.

hopefully I will get a chance this weekend to get in and really look it over myself as I got it as far as hitting the timing mark last weekend before I had to leave.

thanks for your help

 

[Boat Doctor1]

firing order correct on plug wires???????????? The cam / crank timing chain could have been installed 180 out also when built?? a possibility. now maybe easiest -drop in an old gm dizzy & get fired!! that will tell all about the merc ignition!!

 

[Bt Doctur]

What you need to do is get #1 cylinder on TDC compression stroke, install the dist with the rotor facing #1 on the cap.
plug wires go clockwise 1,8,4,3,6,5,7,2
ONCE YOU HAVE IT RUNNING, you must put the ign system into base timing mode by installing a jumper., set the timing with a timing light, SHUT THE MOTOR OFF, remove the jumper to return to normal ign timing.

 

[revkev6]

What you need to do is get #1 cylinder on TDC compression stroke, install the dist with the rotor facing #1 on the cap.
plug wires go clockwise 1,8,4,3,6,5,7,2
ONCE YOU HAVE IT RUNNING, you must put the ign system into base timing mode by installing a jumper., set the timing with a timing light, SHUT THE MOTOR OFF, remove the jumper to return to normal ign timing.

My uncle insists all this is correct but I want to double check.

I tried checking that the distributor wasn't 180 off by turning the motor over with the timing light connected... it would show on the damper. I didn't have the manual in hand but my father had said there was a wire on the harness that you had to ground for the base timing... not a jumper??

also, he's got a vacuum advance HEI unit from a friend that he's going to try. if that works then I guess he will pick up an aftermarket distributor... I really want to double check the thunderbolt install to make sure it's correct first though.

 

[Bt Doctur]

you ground it by using the jumper. there is no port for the vac advance so that wont work., an aftermarket dist wont work with a TB V module so..........................
you cant set the timing with timing light unless the motor is running.might work for a TB IV but not a TB V

 

[alldodge]

Here is the TB-V troubleshooting guide

 

[revkev6]

you ground it by using the jumper. there is no port for the vac advance so that wont work., an aftermarket dist wont work with a TB V module so..........................
you cant set the timing with timing light unless the motor is running.might work for a TB IV but not a TB V

ok, good, that's how I did it... first without the wire grounded then double checked with it grounded. made about 5 degrees difference.

why can't you run the timing light when cranking to get an idea of the location of the timing mark?? it may not be 100% accurate but it seemed to work good enough to know we were in the ballpark??

we have run every one of the above tests and get either spark or 12v.... replaced the coil... etc... I think the firing order or distributor is setup wrong...

 

[Bt Doctur]

Again ,without the motor running you cant check the timing or the total advance.
As a mechanic you should be able to have #1 cylinder on its compression stroke and at top dead center.Install the dist with the rotor facing the #1 position in the cap.
Install the wire`s in the correct order clockwise. 1,8,4,3,6,5,7,2 Turn the key and it should fire up and stay running.

 

[revkev6]

hey guys, thanks for the tips... for future reference you are all correct, you cannot use the timing light as a reference to make sure you are on TDC when cranking.

finally got the owner of the boat to stop and double check the simple things before replacing parts... spun the distributor 180 and it ran like a top! next is to put her in the water!