Thunderbolt IV timing advance...

[90stingray]

Previous post, if you want to get more up to speed: http://forums.iboats.com/showthread.php?t=447155&highlight=4.3+surge+backfire

Working on 1990 4.3 V6.

Anywho, I still am fighting my surge and backfire around 4000 rpm's. I took her out last weekend and was able to get 4400 rpm before the surge and backfire. Only thing i changed was the gimbal bearing. I guess it was really draggin down on the engine

Opened sending unit up to inspect fuel tank... all is nice and clean. Checked antisiphon valve... all is free. Opened carb back up checked float level and float drop... all is well. So i am running out of ideas.

I checked the timing again... she was still at 8 all warmed up at idle on the muffs. But if i give her some throttle to say 3000... the advance only goes a little ways. Off the timing tab, but i can still see it. Prolly no more than 16 btdc. That seems low to me. Figured these would be in the 26-30 range. Just wondering what exactly controls the advance? Why would it only advance a little? What do i need to check out? Help me out guys. Thanks.

 

[dubs283]

Re: Thunderbolt IV timing advance...

the timing advance is controlled by the ignition module which gets its signal from the ignition sensor in the dist

did you replace the ignition sensor in the dist?? - probably not the cause of your problem but if its not the latest style i would highly recommend replacing it, it WILL fail eventually - and i have seen some wierd issues go away with replacing them too

the only way you are going to know exactly what the timing is advancing to is with an advance timing light, you may be able to rent/borrow one from an auto parts store (they're kinda spendy, $350 for a good one)

 

[ussoldier_1984]

Re: Thunderbolt IV timing advance...

If I remember correctly the tb IV on the 4.3 advances 14 degrees, initial timing is 8 degrees for a total advance of 22 degrees wot.

 

[wca_tim]

Re: Thunderbolt IV timing advance...

at one point I had a somewhat similar problem and finally traced it to poor connections in the ignition wiring, It completely went away once I cleaned all the connections and plugs and connectors - In particular I thin that the receptical that plugs into the ignition module and the corresponding ignition module prongs were the major culprit... it didn't look like that woyuld cause such a problem, but itsure fixed it when I cleaned everything carefully. Also check the sensor in the distributor, it could easily be the problem...

 

[90stingray]

Re: Thunderbolt IV timing advance...

Just went and pulled the cap off to have a look. Everything in there but the cap and rotor is for sure original. Wires and connections are coated in black paint and have never been broke loose! I will have a look at those connections. Is there a spec on the gap where the rotor/ trigger goes thru?

 

[dubs283]

Re: Thunderbolt IV timing advance...

Is there a spec on the gap where the rotor/ trigger goes thru?

replace with a new sensor, no spec it is non-ajustable

 

[90stingray]

Re: Thunderbolt IV timing advance...

All i can find are the all plastic sensors... mine is metal on top. Also, what is that loose wire zip tied to itself with the ring terminal? I think its white with blue stripe. (you can see it if you use scroll bar at bottom) Sorry about that... didn't have time to resize pic before work Thanks.

 

[wca_tim]

Re: Thunderbolt IV timing advance...

If you haven't, go through the diagram Don posted in this thread... it'll address the ignition issues.

http://forums.iboats.com/showthread.php?t=214939

and if you're running a worn out cap and rotor, etc... things covered in paint, etc.. might be time for a full tuneup as well, eh? Always strikes me that sometimes a seemingly difficult problem is simply a number of "little things" that individually would not create a noticable problem, but that together have more significant consequences...

 

[90stingray]

Re: Thunderbolt IV timing advance...

That flow chart is more for no spark issues. I have done a full tuneup except for the sensor. And apparantly I have the old style one. Maybe its not sensing correctly above 2000rpms so its not advancing the timing any more? I dunno... that's why I posted this thread. I guess its only $60 for a new one. I can get one on order and see what happens.

 

[90stingray]

Re: Thunderbolt IV timing advance...

Don S... what are your thoughts on this??? I always feel better once you have given you thoughts and input. Thanks

 

[dubs283]

Re: Thunderbolt IV timing advance...

the black full plastic sensor is the latest style and best one available

it is fully potted to avoid the corrosion issues that the old exposed ones had

again...replace the sensor and test run - its the last part of the ignition system you haven't replaced and those old style ones are prone to issues

i can't tell which wire you refer to in the pic but not sure bout WHT/BLU - TAN/BLU would be warning horn system for oil press, temp, and gear lube

 

[Don S]

Re: Thunderbolt IV timing advance...

Don S... what are your thoughts on this??? I always feel better once you have given you thoughts and input. Thanks

I think you was given the answer back on reply #3.

Here is from the manual you should have.

 

[90stingray]

Re: Thunderbolt IV timing advance...

Don, umm yeah... i dont have a manual. i did just buy a seloc but that thing is garbage. i am returning it Thanks for the timing curve page. Dubs, I have a fully plastic, quicksilver sensor coming. And thanks for the heads up on the loose wire.

 

[Don S]

Re: Thunderbolt IV timing advance...

Don, umm yeah... i dont have a manual.

Did you look up in the Adults only sticky under Merc information?

 

[90stingray]

Re: Thunderbolt IV timing advance...

Dang! I've been in that adults only section a ton of times but prolly have never hit the merc section. Truly a great wealth of information in there. Heck prolly don't need the forums just refer everyone there