Hi all, first time poster here. The forum has been tons of help in the past, but I've finally run into a problem that I can't figure out on my own. I'm handy with a wrench and a manual, but am no expert mechanic by any means
I just bought this boat. Engine is a 1996 4.3L Alpha with Thunderbolt IV Ignition. Engine Serial Number: 0F770091.
I took it out day one and it ran all day, although it wasn't happy at idle. It would sometimes idle fine, other times I had to continually give it a little gas to keep it from stalling. I figured I'd start by replacing some maintenance items and adjust the idle. I replaced the distributor cap and rotor, ignition wires (including the coil to distributor wire), spark plugs, and fuel filter.
Now while on muffs, I have to keep pumping the throttle to keep it the engine from stalling, I can't drop the RPMs below 1500 or so. I start checking connections, and hooking up my timing light, and here is what I find. 4 of the ignition wires are flashing like normal, and 2 are flashing at strange intervals. Even more strange is the fact that the spark intervals on cylinders 2 and 4 are consistently wacky!
[FONT=arial, sans-serif]4 normal Cylinders: ta..ta..ta..ta..ta..ta..ta[/FONT]
[FONT=arial, sans-serif]Cylinder #2 spark: ta........ta........ta.......ta[/FONT]
[FONT=arial, sans-serif]Cylinder #4 spark: ta..ta.......ta........ta..ta[/FONT]
[FONT=arial, sans-serif]Upon first discovering this, I pulled off the distributor cap and found that the arm of the rotor broke and the metal part hanging on an an angle. It must have hit one of the points a little too hard. Defective part or maybe I didn't have it seated properly? I run to my nearest marine parts store and buy a new cap/rotor combo and install them. Same cylinder spark results as before. I've re-checked the rotor several times since, and it appears to be fine. I've tried replacing the wires and spark plugs with some of the old ones I just took out and I'm getting the exact same results. I also remove the spark plugs on #2 and 4 and put them to ground, crank the engine and I've confirmed I'm getting spark from them.[/FONT]
[FONT=arial, sans-serif]I've double and triple checked that the distributor wires are in the correct order and have gone though the TB IV Ignition troubleshooting guide. It's currently guiding me to replace the ignition sensor in the distributor. I have a hard time believing it's the ignition sensor though. From what I've been reading, the sensor either craps out or it doesn't, I find it awfully strange that the ignition sensor would function fine for 4/6 wires, and intermittently work for the other 2. Before I start spending money on parts and waiting for shipping, I thought I'd reach out to the community. Is there something I'm missing here? Did something get damaged when the distributor rotor hit point and broke? Might it be a control module issues? Has anyone seen a similar ignition problem before?
Any thoughts or advice would be greatly appreciated! Thank you.[/FONT]
I just bought this boat. Engine is a 1996 4.3L Alpha with Thunderbolt IV Ignition. Engine Serial Number: 0F770091.
I took it out day one and it ran all day, although it wasn't happy at idle. It would sometimes idle fine, other times I had to continually give it a little gas to keep it from stalling. I figured I'd start by replacing some maintenance items and adjust the idle. I replaced the distributor cap and rotor, ignition wires (including the coil to distributor wire), spark plugs, and fuel filter.
Now while on muffs, I have to keep pumping the throttle to keep it the engine from stalling, I can't drop the RPMs below 1500 or so. I start checking connections, and hooking up my timing light, and here is what I find. 4 of the ignition wires are flashing like normal, and 2 are flashing at strange intervals. Even more strange is the fact that the spark intervals on cylinders 2 and 4 are consistently wacky!
[FONT=arial, sans-serif]4 normal Cylinders: ta..ta..ta..ta..ta..ta..ta[/FONT]
[FONT=arial, sans-serif]Cylinder #2 spark: ta........ta........ta.......ta[/FONT]
[FONT=arial, sans-serif]Cylinder #4 spark: ta..ta.......ta........ta..ta[/FONT]
[FONT=arial, sans-serif]Upon first discovering this, I pulled off the distributor cap and found that the arm of the rotor broke and the metal part hanging on an an angle. It must have hit one of the points a little too hard. Defective part or maybe I didn't have it seated properly? I run to my nearest marine parts store and buy a new cap/rotor combo and install them. Same cylinder spark results as before. I've re-checked the rotor several times since, and it appears to be fine. I've tried replacing the wires and spark plugs with some of the old ones I just took out and I'm getting the exact same results. I also remove the spark plugs on #2 and 4 and put them to ground, crank the engine and I've confirmed I'm getting spark from them.[/FONT]
[FONT=arial, sans-serif]I've double and triple checked that the distributor wires are in the correct order and have gone though the TB IV Ignition troubleshooting guide. It's currently guiding me to replace the ignition sensor in the distributor. I have a hard time believing it's the ignition sensor though. From what I've been reading, the sensor either craps out or it doesn't, I find it awfully strange that the ignition sensor would function fine for 4/6 wires, and intermittently work for the other 2. Before I start spending money on parts and waiting for shipping, I thought I'd reach out to the community. Is there something I'm missing here? Did something get damaged when the distributor rotor hit point and broke? Might it be a control module issues? Has anyone seen a similar ignition problem before?
Any thoughts or advice would be greatly appreciated! Thank you.[/FONT]