ThirdBird

'87 454 mags. We're having trouble with ignition breakdown mostly at high RPMs and sometimes at lower RPMs under high load while planing.

We've been through the normal tune-up stuff (plugs, wires, caps, rotors). The issue was happening with the port motor only. We swapped coils from one to the other, no difference. We installed a new ingnition sensor (under the distributer), no difference. then we swapped the ingintion amplifiers (ThunderBolt boxes) from one to the other. At first, success! The starboard motor is now doing the same as the port did. Perfect! We found the problem - NOT!! A few minutes later, both engines are bogging down under load and at high RPM.

We're now stumped. What is the failure mechanism of an ingintion amplifier? Does it just stop working or can it degrade? And, why the heck are both doing it now when only the port was initially the problem?

Any help is appreciated, we've reached our knowledge limits!!

FIXX

iTrader: (2)

Bad ground,loose ignition wire at the key switch,also check the main engine plug, take them apart and spread the bullets to make better contact...Believe it or not i had a bad alternator that was throwing a/c current(over charging) that made a 454 run like chit..

ThirdBird

ThAnks for the reply MRFIXALL. Port key switch has been replaced and main connector looked good. Maybe a ground someplace.

Any other ideas? Failure symptoms of the ignition amplifier?

wtfo

If you swap the ignition modules back do you get the starboard engine back?

ThirdBird

Haven't tried that yet, frustration levels were too high for further wrenching yesterday!!!

Biggus

iTrader: (1)

I've experienced the exact same issue. It was a loose heavy black ground that is part of the ingition module harness.

BenPerfected

I had the same issue...we had to scrape the paint under the ground connector. The back of head is a good place to ground.

ThirdBird

Do you mean where the ingition module ground goes through the main engine harness plug? Or do you mean at the ignition module itself?

Biggus

iTrader: (1)

The harness that plugs into the module. It was the black ground. I bolted it directly to the back of the head, problem solved.

Good luck,

Kurt

ThirdBird

Thanks Kurt. It does all of a sudden act like a main power loss. Hard to explain that since it was only the port engine before we started swapping parts back and forth. But, we'll go after grounding issues for a while and see where that goes. With our troubleshooting luck, the gauges will stop working or the head will start backing up!!!!

Bottom line though, no one on the forum thinks it's the ignition modules themselves causing the problem. Any other suggestions are welcomed.

Dave and Mike - Stumped in Sandy Creek.