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Need Help Timing 4.3L TBI

1

1marc1

Contributing Member
Hey i just installed a brand new GM longblock. We have timing close enough to where boat runs and idles fine but need to set base timing now with timing light. Im having difficulty finding what wires i need to jump in order to do this. Its a 2003 Mercruiser TBI with a thunderbolt iv.
 
To add i had a local mechanic to help me with this........we found which wires to jump and we timed it to 8 degrees, as specified. The boat idled great and was able to pull up rpms normally on muffs. I now just came back from a drive on the lake and i am still dealing with the same issue. I will note that when i retightened my distributor up......... i unplugged my IAC and one of the harness's next to it for they were in the way of my wrench. The boat was still able to run with both of these unplugged......because i had forgot to plug them back in when i went for my test drive until later when i looked at my engine while out on the water. Now would a boat run without an IAC???? Cause mine did, and when i plugged it back in.....it didn't make much of a difference. I have a new thunderbolt iv ignition just installed as well. All plug cables, prop and everything else that is on the boat was on the boat when it was running last and it there were no issues then before i blew the old engine. Im going to take off my fuel filter for that has been on my boat for a few years, but it definitely doesn't have much for hours on it for run time. But either way i have a new one so i'm going to put the new one on. Any other ideas would be greatly appreciated!
 
Bt Doctur said:
TB-IV is a point and shoot , nothing to connect to put motor in base timing mode.
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You're 100% on this? The boat is efi, any information we went to look on it, it says that something needed to be jumped in order to put it in base timing. Even on my engine cover it says specialty timing required.
 
Also i just pulled my fuel filter and filter wasn't quite full. It was down at the 3/4 mark or maybe just under. I have a brand new cool fuel pump, but upon installing my engine one of the fuel lines from the filter to the pump got kinked and that kink didn't fully come out.
 
Bt Doctur said:
Well, TB IV is not normally used with a fuel injected motor .They have ECM`s that control the dist, and advance
Click to expand...

Im sure the parts person said thunderbolt iv. I explained to him it was TBI and also gave him my serial number. I originally just had the old 2 wire ignition in there.......the one with the exposed "green" board. I understand that they no longer make the one i had due to overheating. This one is all enclosed......and has a third wire.
 
And my fuel line that was kinked from my filter going to my pump.

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Bt Doctur said:
timing, idle mixture, and idle speed are all adjusted in base timing mode.

The purple and white wire as mentioned in your post......this is what we initially tried to do. But when we grounded that wire the boat wouldnt even attempt to fire or make any sign of life which is why we decided to look further into it. The mechanic i was working with then found that we would have to jump a black and black/white wire on the ecm plug, which in my mind seemed to be the correct way cause the boat was at least was firing this way.......but wouldn't fully run until we ran the engine normal and brought it up to operating temp first.
Click to expand...
 
do you mean the plug for the diagnostic connector? that's the only place I see black and black/white wires.
Those are not what you jumper for base timing mode
 
Well that plug doesn't look exactly like mine. My plug has quite a few more wires than that. And in the service manual it says for thunderbolt iv ignitions, on efi engines your supposed to hook up the special diagnostic tool in that plug for base timing. Well we don't have that tool, so we found that if you jump those 2 wires it will initiate base timing......and then set it to 8 degrees etc etc etc. So that's what we did, and now the boat runs fine. I no longer think my issue is timing as I mentioned before. I have a kinked fuel line.......my boat is not getting the proper amount of fuel it needs......when it needs it.
 
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