TB5 distributor

[MBAKER]

Is there any reason for this distributor to be grounded. Since its an electronic ignition without points, I dont think there is any reason it would need to be grounded.


Im fighting what i think is an ignition problem causing a backfire started out at higher rpms 4000+ but now occurs starting at 3000. Also did it off and on, but only a single backfire, maybe a handful of times over the last few seasons. Did a full tuenup at the beginning of the year and ran perfectly but timing was advanced from spec, so I backed it down and then this started happening.

 

[Tail_Gunner]

Re: TB5 distributor

TBV is a plug and play system..you cannot change the timing curves without some type of reprogramming. The timing procedure is in the pdf

http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF

Page 18 graph's the typical curve

 

[MBAKER]

Re: TB5 distributor

I know the timing procedure and Im not trying to change anything. Im simplly trying to track down a problem and rule out simple things. I just wanted to verify the electronic type do not need to be grounded like a points style setup. I dont see any reason they would need to be, but you never know.

 

[muc]

Re: TB5 distributor

Yes it needs to be grounded. Not to work but to bleed any voltages spikes off and protect the system. Stock it came with a ground wire connected (on the bottom of the distributor) to one of the two screws that hold the sensor.
The replacement sensors now come with a much bigger ground wire that is to be connected to the main engine ground.
Anytime I hear somebody say that they had to adjust their timing I always worry.
After working on thousands of engines over the years the only engines that I have had to adjust timing on (other than engines that have had the distributor disturbed for repair work) was because somebody changed it.
This was a big problem back in the days of points because people would get the dwell set wrong and that would throw the timing off.
Yes wear of the timing chain and gears will affect timing but only 1-2 degrees and that’s not enough to cause problems.
Are you sure you had the engine idle low enough when you reset the timing? It really should be below 700 rpm on a shop tach --- not the dash tach.

Would love to help with your problem but not giving a serial number and model number I have no idea what GM engine you have or even if you have carb or EFI?

You might want to use the info Tail Gunner posted and a advance equipped timing light to rule out ignition problems.

My guess is you have a fuel problem.

 

[MBAKER]

Re: TB5 distributor

So the ground wire is from the sensor to the housing itself then the only ground from the housing to the engine is through the dist clamp?

I have worked on engines for years and normal engine wear aside, I know timing will not change appreciably unless you move or change something. In this case I changed the rotor which has the trigger wheel on it, and it would be possible that it is not indexed the same as the original which could make it fire a little different. That is the only reason I changed it, and yes I used a shop tach at 650 rpm, and put the ignition in base mode.


Here is the rest of the story.....

After we got this boat a few years ago I checked it over replaced plugs (one was cracked) and checked timing at that time and it was at 12*, spec is 10* but since it had been that way likely since new I left it and we ran it 2 seasons. This spring I did an ignition tuneup, plugs, wires, cap/rotor etc. and rebuilt the carb. Took it out first time and dialed in the carb, and it ran like a top, better than ever. Same thing for the next 2 outings. Then the 4th time out I brought a timing light just to check and found the timing had jumped to 14-15*. Since I had changed the rotor with the trigger wheel on it it made sense that it was slightly different than the original and was firing a little sooner than before, so I set it back to 12* where it had always been. Took the boat out that day filled it up with gas and it ran great again, but never ran it hard, maybe 35-3800 rpm. The next morning lake is calm and smooth, open it up and as soon as it hits 4000-4200 it coughs and backfires a few times. Back it off and try again but consistently at the same rpm it continues to happen, but occasionally it will continue through to 4600 fine although lacking power. Thinking we had a fuel issue, we dumped in some fuel treatment and changed the fuel filter. Tried to run most of that tank out and refill with more treatment and thought it was better, but next day same thing. Eventually changed out the coil that week just for good measure, and still same thing. Few weeks later pulled the sending unit from tank and tried to pump out and sample some fuel, didnt find any appreciable water. Explained problem to auto mechanic in course of general conversation one day and he immediately thought it sounded like a bad plug wire or plug. So back to thinking its an ignition problem. Now the problem has gotten worse, it starts in about 3000 rpm and has noticeable reduced power. Never did go back and reset timing to before I changed it to see if that fixed it, just got busy and it all kind of got put on the back burner. The only reason I question the ground is if it does ground through the dist clamp, and when i moved it from the factory setting it might be resting on paint now not making contact with the base, but although it wouldnt need the ground to function maybe it needs the ground to keep from burning the sensor up. I dont know. Either way the ground to the distributor would be intact, only the ground to the engine would be in question.



2000 Maxum, 5.0 Alpha one, Mercarb

engine SN# 0L648620

 

[MBAKER]

Re: TB5 distributor

forgot to mention..... it only does it under load, you can rev it in neutral and its fine.

Also since it is getting worse something is obviously changing, now whether its fuel related, or electrical and something like the wires or a sensor is going south, I dont know.

Either way, as much as I hate to give up on the challenge and do it myself, I just dont have the spare time to run to the lake every other day to test it and chase it down so its prob going to the shop. I would like to get it resolved before its time to winterize so that next spring its ready to go again.

 

[muc]

Re: TB5 distributor

The ground wire comes out of the wire harness and connects to 1 of the 2 screws that is long enough to go thru the sensor and out the bottom of the dist.
Recommend that you try to take it to a shop that is on the water or has a dyno.

 

[muc]

Re: TB5 distributor

P.S. your serial number was never registered with MerCruiser so it’s possible no safety recalls have been done. Might want to talk with the dealer about that.

 

[MBAKER]

Re: TB5 distributor

Dropped it off for service last night, should have an idea by the end of the week what it needs.

Worst part about workign on a boat yourself to me is you cant just go road test like a car. Unless you are working on the lake anyway. I like doing stuff myself for the boat and car, saving some cash, but time has become more valuable lately.

thanks for help...