Timing Jumping all over

[pennyduke]

305 Mercruiser. Just replaced the distributer (TB IV) and ignition Module and the Timing mark is jumping all over. I have turned the dizzy slowly and tried to get it to stop at 8 Deg before but it keeps jumping past zero. Anybody know whats wrong? Thanks

 

[franktrav]

Re: Timing Jumping all over

thunderbolt v ignition has a purple/white wire that needs to be grounded out to put in base mode
timing jumps all over the place if it is not grounded due to the idle spark control feature built into the icm
but as far as i know the t4 is not set up that way...somebody who know more will chime in shortly...
is there any excessive play in the actual distributor shaft itself?

 

[pennyduke]

Re: Timing Jumping all over

No excessive play in the shaft. This dizzy was in new condition. It did have a ground wire which my old one did not have. I grounded it to the main ground from the battery and cleaned all the wires real good.

 

[Don S]

Re: Timing Jumping all over

Is the engine idling smooth, or is it going up and down in rpm?
Where is your module mounted? If on the exhaust elbow, did you also replace the wiring harness between them? Sounds a lot like poor connection.

 

[pennyduke]

Re: Timing Jumping all over

The idle is very smooth. The dizzy came with a module mounted on it but I took it off and used the brand new one I bought last summer mounted on the exhaust elbow.

 

[Don S]

Re: Timing Jumping all over

Did you use a new harness between the distributor and module?

 

[pennyduke]

Re: Timing Jumping all over

no I did not.

 

[Jeffboats]

Re: Timing Jumping all over

I just put a Hot Spark module conversion in my '78 -305. My idle was very eradic. I know you said yours is smooth. After alot of brain storming I finally out of frustration replaced the copper core ignition wires with stainless Steel mag silicone Bosch wires from Autozone about $35 bucks and it cured the eradic idle and power loss. Then I was able to get the motor in time with a light. May not be the fix for the problem your having though...... Best wishs's!

 

[Don S]

Re: Timing Jumping all over

Check it and make sure all terminals are clean and shiny copper in color. If not, replace it. You can also try a wiggle test and see if the timing settles down while you are wiggling it.

 

[pennyduke]

Re: Timing Jumping all over

Ok, I will try wiggle test. I'm going to run it in the dark and see if there is any sparking going on too.

 

[H20wens]

Re: Timing Jumping all over

I had a similar problem with a electronic ignition conversion recently. Drove me batty. Finally discovered that the cap had some very hard to see hair line cracks. Check for (any) continuity between the electrodes with an ohm-meter. Anything other than an infinite (0) reading is bad. Replace the cap and try again.

 

[pennyduke]

Re: Timing Jumping all over

Replaced the cap and did the wiggle test with no results. The timing is still jumping around but not as much. The idle is steady at 700 rpms and the timing jumps from 8 before to about 8 after in no defined pattern. I reved it up hard and had no backfire. It really sounded good. Is it possible that the timing light is bad. I just bought it last summer from Advanced.

 

[westpennsam]

Re: Timing Jumping all over

Dont know much about the electronic conversions but do they still use the vacuum advance off of the distributor???? If they do then make sure the vac advance is disconnected and plugged when you set your initial timing.

 

[Don S]

Re: Timing Jumping all over

Is it possible that the timing light is bad. I just bought it last summer from Advanced.

Sure it's possible. Hadn't even thought about that. In the pickup you clip onto the plug wire, there is a graphite colored bar that's the actual pickup. If it's cracked, it can give you some odd readings.

 

[fat fanny]

Re: Timing Jumping all over

Just oddly enough I had almost the same issue but with some small twists. Like I run a 3.0LX and I have an est ignition I cannot get my timming to advance w/ the light (using correct procedure) I will most definately be looking @ my lights pick up here shortly but the boat ran the best ever today no misses and or issues hit 40 mph without even a hiccup. Thanx for the tip Don!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[Don S]

Re: Timing Jumping all over

Be careful, the EST distributor does jump around a lot at low rpm, unlike the Thunderbolt IV.

 

[fat fanny]

Re: Timing Jumping all over

Don starting my own thread so as not to high jack pennies. Please chime in !!

 

[pennyduke]

Re: Timing Jumping all over

Update: I got a new in the box timing light today.Hooked it up and got the same results. I then changed the Module to the one that came with the distributer and grounded it because it had a ground wire. Fired it up and got the same results. Now i'm thinking it must be the new pickup coil in the distributer or the distributer itself. Any thoughts?