erikth
New Member
- Jun 21, 2018
- 19
- Boat Info
- 1991 Sea Ray 170 BR
Twin Alpine Subs with Rockford Amp
- Engines
- Mercruiser 4.3L IO w/ Mercarb - Alpha One, 14x23 Spitfire
Hi guys.. newbie here. I picked up a 170 BR last summer and have been enjoying it greatly. Ran like a dream for the first season. Did the winterization myself with help from youtube. Starting from spring fire-up I've had nothing but problems.. At first it was hydrolocked which was puzzling because I flushed everything with RV antifreeze, and then drained the whole cooling system for the winter. Cylinders full of water (both sides), oil looked like chocolate milk, etc. Everyone I talked to said cracked block but I was optimistic it would be salvageable based on my flush and drain. Long story short I did a top end rebuild (intake and exhaust - did not do head gaskets) and a couple oil changes later I have beautiful oil and it ran.. I was thrilled.
However, the first time I put it in the water I had issues going beyond 1800 RPM. Would lose power and backfire. Re-checked timing, tried to tune the mix screw on the carb, but no improvement. I rebuilt the carb and it briefly ran better (got it to 3000 RPM once at no load). Since then the performance has steadily degraded. I first suspected fuel supply, so changed all fuel filters, flushed the fuel tank and filled with fresh gas, and even put a primer bulb in the fuel line so I could give it a bit of extra pressure with a squeeze.. nothing helped.
After ruling out fuel supply I started looking at ignition. I put in new cap, rotor, and plug wires and checked with a timing light to make sure the Thunderbolt IV module was advancing the timing. It was. I noticed that when using the timing light the flashes were not consistent. At first I thought that it was the timing light because I borrowed it from my neighbour and it was made in the 70s. (It was a non-inductive one where you clip the light on a spring that you insert right on the spark plug.. old school!) After giving myself a shock with this (literally) and being annoyed with the missing flashes I decided to get a new inductive timing light.
This is where I start narrowing in on the problem... Even with the new timing light, I would clearly see breaks in the sequence of flashes - this was plainly visible by pointing the light at the white fiberglass hull. It seemed like it was missing 3 or 4 out of every 10 flashes. I re-checked and it was the same with both the oldschool and inductive timing lights. This corresponded to the sound of the misfiring engine and so I am convinced this is the root cause of the problem. I started replacing ignition components. First the ignition sensor inside the distributor, then the Thunderbolt IV module itself, and finally the coil. None of these made any difference. Worse.. as I was doing all this, the performace was slowly deteriorating.. as measured in the idle getting rougher and rougher and missing more and more flashes as seen on the timing light. At present it's missing more than half the flashes and still barely manages to run.. but very rough... shakes the boat.
I have cleaned all the connections, tested the ignition and grounds and tested all the wires in the harness that clips to the Thunderbolt IV module. Everything checks out. The missing sparks can be seen on all cylinders, not just cylinder 1. I removed the grey wire that goes to the tach and the white/green wire that goes to the shift interrupt switch to rule those out.
I've been searching through forums on thunderbolt ignition troubleshooting, but all the problems seem to relate to no spark at all. My problem is that I have sparks sometimes, but they are not consistent.
I thought I would throw this out and see if anyone has had similar issues. I've reached the point where I've run out of ideas to try. I've replaced every component there is in the igntion system and the problem persists, and is even getting worse as time goes on.
Any ideas on what would cause inconsistent spark firing? I'm open to any musings.. thanks guys!
However, the first time I put it in the water I had issues going beyond 1800 RPM. Would lose power and backfire. Re-checked timing, tried to tune the mix screw on the carb, but no improvement. I rebuilt the carb and it briefly ran better (got it to 3000 RPM once at no load). Since then the performance has steadily degraded. I first suspected fuel supply, so changed all fuel filters, flushed the fuel tank and filled with fresh gas, and even put a primer bulb in the fuel line so I could give it a bit of extra pressure with a squeeze.. nothing helped.
After ruling out fuel supply I started looking at ignition. I put in new cap, rotor, and plug wires and checked with a timing light to make sure the Thunderbolt IV module was advancing the timing. It was. I noticed that when using the timing light the flashes were not consistent. At first I thought that it was the timing light because I borrowed it from my neighbour and it was made in the 70s. (It was a non-inductive one where you clip the light on a spring that you insert right on the spark plug.. old school!) After giving myself a shock with this (literally) and being annoyed with the missing flashes I decided to get a new inductive timing light.
This is where I start narrowing in on the problem... Even with the new timing light, I would clearly see breaks in the sequence of flashes - this was plainly visible by pointing the light at the white fiberglass hull. It seemed like it was missing 3 or 4 out of every 10 flashes. I re-checked and it was the same with both the oldschool and inductive timing lights. This corresponded to the sound of the misfiring engine and so I am convinced this is the root cause of the problem. I started replacing ignition components. First the ignition sensor inside the distributor, then the Thunderbolt IV module itself, and finally the coil. None of these made any difference. Worse.. as I was doing all this, the performace was slowly deteriorating.. as measured in the idle getting rougher and rougher and missing more and more flashes as seen on the timing light. At present it's missing more than half the flashes and still barely manages to run.. but very rough... shakes the boat.
I have cleaned all the connections, tested the ignition and grounds and tested all the wires in the harness that clips to the Thunderbolt IV module. Everything checks out. The missing sparks can be seen on all cylinders, not just cylinder 1. I removed the grey wire that goes to the tach and the white/green wire that goes to the shift interrupt switch to rule those out.
I've been searching through forums on thunderbolt ignition troubleshooting, but all the problems seem to relate to no spark at all. My problem is that I have sparks sometimes, but they are not consistent.
I thought I would throw this out and see if anyone has had similar issues. I've reached the point where I've run out of ideas to try. I've replaced every component there is in the igntion system and the problem persists, and is even getting worse as time goes on.
Any ideas on what would cause inconsistent spark firing? I'm open to any musings.. thanks guys!