Mercruiser 5.0 Thunderbolt I'v dist sensor wiring

[reptileguy]

Hello I have a mercruiser 5.0 350 cid and just replaced thuderbolt iv sensor in distributer. Old sensor had 2 posts one red/white and other had two green/white ( one going to shift switch) and the others going to ignition amp on riser . Also amp ground wire connected to bottom of dist on sensor mount screw. Here's the prob . Installed new plastic sensor comes with bullet connecters and additional ring connectors and lil bolts to connect to old wires. I hooked red/white up no prob. Hooked green/white up and also connected green/white from shift switch in that as well. Then the ground wire down to engine ground bolt on bell housing. Also amp wire I hooked back to bottom of dist again on the mount bolt for the sensor . Go to fire and nothing . It stumbles every 3 secs like it wants to fire but nope. Pump 4-5 times give 3/4 throttle crank for 15 secs it catches runs for 10 secs at 2000 rpm then dies coughs up smoke from carb and lots from outdrive. To me it seems like timing is now waay out. I'm taking my timing light tomorrow to check but is there something I hooked up wrong ?

 

[achris]

http://forums.iboats.com/forum/engin...n-systems-work

The only thing I would do differently would be to hook the Amp ground to the engine ground, not the distributor body. Now that you have the sensor ground back to the engine ground, the distributor doesn't need a ground.

And yes, check the timing.

Chris....

 

[reptileguy]

So the amp ground is only 5" long is there somewhere close I should hook it up or do I need to crimp in a longer wire

 

[reptileguy]

And why would the timing go waaay out after changing the sensor ?

 

[alldodge]

What caused you to replace the sensor?

 

[achris]

So the amp ground is only 5" long is there somewhere close I should hook it up or do I need to crimp in a longer wire

Check continuity (to engine ground) to the exhaust elbow it's mounted to, then attach it to a clean bolt hole (one of the mounting holes for the amp itself is a good place).

Chris..........

 

[reptileguy]

Carb needed a clean as it was hard to start . I popped of distributer cap as well just to look and it was coroded and the old sensor was rusted up and in poor shape and past the point of cleaning with emmery cloth so I replaced

 

[reptileguy]

Am I right with the hook up of the two white/green wires that then connect to the other white/green to the amp ?

 

[reptileguy]

Also when cranking this engine. Tach is up to 3000 rpm which I know is Wayyy out too not sure if it could be related to this prob

 

[alldodge]

When cranking the motor, it should come up to around 300, 3000 is way to much. Might be your tach is shorting out. Remove the gray tach wire off the negative side of the coil and see if your miss goes away

 

[reptileguy]

Talked to a merc tech today at our local marina. He says to leave amp ground to distributer as the is proper way to ground . Then told me just to disconnect tach and should be fine. Haven't got to test yet as we had sevear storms and 12' swells with white caps inside marina break walls lol

 

[achris]

If you leave the ground on the distributor, then make sure there is a wire from the distributor to the engine ground. I know the distributor is bolted to the engine block, but I chased a problem for 7 months that turned out to be a bad 'connection' between the distributor and the block. Single wire from engine ground post to distributor fixed it. And since then, all mercruiser engines have a grounding wire on the distributor.

Chris......

 

[Pete104]

THis is we should find out how this unit is?

 

[Pete104]

Also when cranking this engine. Tach is up to 3000 rpm which I know is Wayyy out too not sure if it could be related to this prob

This is where we should find out how old this unit is.

 

[reptileguy]

She's a 91 original to the boat the new ignition sensor I installed has a ground that goes to engine block ground in bell housing. Then there is a ground running from amp on riser that goes to bottom of distributer on the bolt that holds ignition sensor down passes through distributer body and a nut goes on end of it