Ignition and backfire

BDL123

Cadet
Joined
Oct 28, 2012
Messages
29
Eng SN: 1A071822
4.3l v6

Ok. Where do I begin. I have one issue that led to another problem. To start I pulled time boat out of the garage yesterday to de-winterize for the upcoming season. Did all my stern work last fall, engine oil, gear oil, lube job, fogging, etc...
One item I did not accomplish was to replace dist cap which I did yesterday. Well, fired her off and after blowing all the fogging oil out she cranked and idled fine. Waited a few minutes to warm her up before advancing the throttle and gradually increased to 1200 rpm. Once I went pass 1200 rpm it started to backfire. Lowered back to idle, no problem. Increase rpm and once it hit 1200 rpm it began to backfire. So today I pulled the fuel/water separator filter and saw no obvious junk or water. Traced the wires to make sure I hadn't crossed a plug when changing the distributor cap but all is in order. I pulled each plug to check fouling and no issues there...I think. When pulling no. 2 plug I had troubles getting to the wire boot to re-seat it because the wire harness leading from the alternator was in the way. Disconnected the wire harness and re-routed so I could get to plug. As I was pulling the alt wire harness back in place the black lead touched the red lead and a brief spark ensued. "Great!" I thought to myself as I knew that would lead to another issue....which it has.
After getting her all buttoned up, muffs on and water flowing, I turned the ignition key and nothing, except that loud obnoxious beep when you switch on the ignition.

So here I am not knowing what to do next which is why I'm turning to you knowledgeable folks. I need to get the engine to crank so I can see if my tinkering around had any affect on my backfire problem. Any thoughts?
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: Ignition and backfire

Check the fuses and the circuit breaker.
 

BDL123

Cadet
Joined
Oct 28, 2012
Messages
29
Re: Ignition and backfire

Thumper. Thanks for the quick reply. I should have stated I already checked the 50 amp fuse and the 20 amp on the main positive lead. Both ok. Are there more you know of?
 

Fun Times

Moderator
Staff member
Joined
May 16, 2009
Messages
8,776
Re: Ignition and backfire

Eng SN: 1A071822 4.3l v6. As I was pulling the alt wire harness back in place the black lead touched the red lead and a brief spark ensued. "Great!" I thought to myself as I knew that would lead to another issue....which it has.
I turned the ignition key and nothing, except that loud obnoxious beep when you switch on the ignition.

So here I am not knowing what to do next which is why I'm turning to you knowledgeable folks. I need to get the engine to crank so I can see if my tinkering around had any affect on my backfire problem. Any thoughts?

I should have stated I already checked the 50 amp fuse and the 20 amp on the main positive lead. Both ok. Are there more you know of?
There may be one fuse that will be hard to find unless you follow the pictures on post number 65. The thread is a long read but the problem was finally found on post number 61 while post 65 shows you where to look. You may or may not have this fuse. If you do and you use the 12v accessories plug for things like small air compressors for float tubes, etc. then you will want to carry spares as the limit is 15 amp's and you could easily blow this fuse.

Post 65,
http://forums.iboats.com/mercruiser...ahoe-q4-please-help-554420-3.html#post3816678
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Ignition and backfire

One thing has occurred to me while reading your initial post.... Running at idle on flushers... This is a BIG no-no with the V6s. In the owners handbook it's quite clear and definite about this. You MUST run at 1300 +/- 100 rpm on flushers. Or you run the very real risk of pulling water back into the engine. This is only on flushers, not while the boat is in the water. The reason is with no back-pressure in the exhaust system water can be sucked back into the cylinders at low engine speeds....

On to your problem/s. Did you check for presence of voltage on the red lead after the 'splat'?

Chris.....
 

BDL123

Cadet
Joined
Oct 28, 2012
Messages
29
Re: Ignition and backfire

Fun Times....I'll review and report back. Thanks for the post.
 

BDL123

Cadet
Joined
Oct 28, 2012
Messages
29
Re: Ignition and backfire

Chris - That is news to me...seems odd but I am too new to the boating scene to question. So anytime I run on muffs I need to ensure I rev up to at least 1300 rpm and maintain that "speed" while the engine warms.

I'm fairly certain I checked for voltage on the "RED" lead which is actually ORANGE(error in my original post) but at the moment it will have to wait till I get back to town to double check.

Once I flag down the ignition problem, any ideas on the backfire problem?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Ignition and backfire

Found it in my Owners Handbook (page 91) and also on a service bulletin, which I have attached...

View attachment 99_09.pdf

As for the backfire problem, first thing I'd look at is what's happening with spark. Is it advancing?, Is it becoming intermittent? A quality timing light will be your friend here.

Chris.....
 
Last edited:

Bayou Dave

Lieutenant Commander
Joined
Dec 13, 2012
Messages
1,780
Re: Ignition and backfire

Found it in my Owners Handbook (page 91) and also on a service bulletin, which I have attached...

View attachment 226640

When I read your comment about keeping rpm's at 1300 it surprised me. My book says to keep it at idle on the muffs. The bulletin you posted is for serial #'s 803000 and above. My serial # is below 803000 and this is what my book says:
 

Attachments

  • Flushing on Muffs.jpg
    Flushing on Muffs.jpg
    155.7 KB · Views: 0

Bayou Dave

Lieutenant Commander
Joined
Dec 13, 2012
Messages
1,780
Re: Ignition and backfire

That didn't work too well.... looks like it is too small to even read. But, it says to keep it at idle speed.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Ignition and backfire

When I read your comment about keeping rpm's at 1300 it surprised me. My book says to keep it at idle on the muffs. The bulletin you posted is for serial #'s 803000 and above. My serial # is below 803000 and this is what my book says:

That didn't work too well.... looks like it is too small to even read. But, it says to keep it at idle speed.

Yes, keeping the revs up is only for the Gen + and later engines (1996 and up).... With the different heads and valve timing, they WILL pull water on the flushers.
 
Last edited:

BDL123

Cadet
Joined
Oct 28, 2012
Messages
29
Re: Ignition and backfire

Fun times. Found this fuse but it too is ok. Thanks for trying.
 

dingdongs

Chief Petty Officer
Joined
May 29, 2009
Messages
649
Re: Ignition and backfire

90 amp fuse piggy backed onto starter.square looking and not cheap when leads are sparked off
change plugs and try putting old cap back on as new one may be faulty
 

BDL123

Cadet
Joined
Oct 28, 2012
Messages
29
Re: Ignition and backfire

So I found the culprit, 90 amp fuse is blown. Will replace and report back. Also, purchased the new dist cap from Iboats...don't suppose there is a return policy??
 

BDL123

Cadet
Joined
Oct 28, 2012
Messages
29
Re: Ignition and backfire

So I found the culprit, 90 amp fuse is blown. Will replace and report back. Also, purchased the new dist cap from Iboats...don't suppose there is a return policy??

PS - thanks to all that have helped out. Can't be said enough.
 
Top