4.3L Merc no fire when cold...ever heard of this?

[anymanusa]

I've read the sticky on trouble shooting the ignition, and so far I've found this:

Engine starts fine in the middle of the afternoon when it's hot outside, but will not start early in the morning or when cooled off at night. I have yet to see any spark coming from the spark plugs, the used old ones, or new ones either. The old spark plugs look a little oil fouled too. I hooked a plug directly to the coil and couldn't see any spark at all when I turned over the ignition either.

I checked under the distributor cap for water or condensation and found none. I'm gonna get my dads timing light and check for spark signal by induction as well. My coil reads 2-4 ohms on the primary, and 10,5k on the secondary...

I haven't had time to do much more troubleshooting, but this is where I'm at right now. I just thought I'd ask if anyone has seen this before. It's a '92 Sea Ray fyi.

Thanks.

 

[anymanusa]

Re: 4.3L Merc no fire when cold...ever heard of this?

fyi, the tachometer sometimes does crazy stuff when the engine is just idling too. I guess this is a clue to me where to start...

also, my test light illuminates on both sides of the coil primary-not good.

I just found this manual from another post on this forum:


http://www.4shared.com/document/IqpH...anual_7_GM.htm
__________________

this should help.

page 48-18 has what I need to diagnose this.

 

[CharlieB]

Re: 4.3L Merc no fire when cold...ever heard of this?

That year may still be a 'points' ignition.

Pop the Distributor cap and rotor, take a look at the points surface and gap.

Burnt, pitted surfaces will not make a good electrical contact and your test light will show 12 on both sides of the coil.

Replace the points, set the gap to .020



If NOT a points system then you will need the correct service manual to follow the diagnostic testing required to determine of the problem is the distributor pick-up or the ignition module.

 

[anymanusa]

Re: 4.3L Merc no fire when cold...ever heard of this?

No points. Thanks. Im leaning towards the igniion module...

 

[bruceb58]

Re: 4.3L Merc no fire when cold...ever heard of this?

also, my test light illuminates on both sides of the coil primary-not good.

So...why do you think this is not good?

Just as a test, disconnect the tach. Won't be the first time a tach has affected an ignition system.

 

[anymanusa]

Re: 4.3L Merc no fire when cold...ever heard of this?

So...why do you think this is not good?

Just as a test, disconnect the tach. Won't be the first time a tach has affected an ignition system.

I thought one side needed to read+ 12v and the other change with the coil firing the cylinder. I.e. grounded unless firing.

 

[bruceb58]

Re: 4.3L Merc no fire when cold...ever heard of this?

I thought one side needed to read+ 12v and the other change with the coil firing the cylinder. I.e. grounded unless firing.

Agree...how do you know what state the sensor is in?

 

[Don S]

Re: 4.3L Merc no fire when cold...ever heard of this?

I thought one side needed to read+ 12v and the other change with the coil firing the cylinder. I.e. grounded unless firing.

Not sure I follow that at all.

What you need to do is disconnect the GRAY tach wire from either the tach or the coil. Either one will tell you if the tach is the problem. With it disconnected, if it starts ok cold, then hook it back up, if it then won't start cold. You have a bad tack.

 

[anymanusa]

Re: 4.3L Merc no fire when cold...ever heard of this?

thanks.. I didn't even know that a bad tach could be the problem.

 

[crewscontrol]

Re: 4.3L Merc no fire when cold...ever heard of this?

A bad tach WILL cause this problem. Just ask me how I know.

 

[anymanusa]

Re: 4.3L Merc no fire when cold...ever heard of this?

thanks for all the replies, the problem turned out to be the safety kill switch. When it got a certain temperature, it didn't make contact. I found this by first checking for +12v at the + terminal of the coil. It didn't have it so the next step in the algorithm was to check ignition switch and wiring. I jumped to the coil from the ignition switch to eliminate the switch, and from there, my continuity tester told me the rest of the story.

Hope this helps someone else in the future.