patinated_imperial
Member
I am experiencing erratic firing in my Imperial at cruise with a very light foot on the throttle. There are probably a million threads about this topic, but I could not find any with a precise match.
It only occurs when the engine is hot. I.e. after 10-15 min of driving.
After installing a wideband AFR gauge I realized that the misfires occurs the same time as "jolts" of lean condition. Cruising at AFR 14-15, and then jolts/spikes of AFR 16-17 lasting just long enough for the gauge to register it. It happens every few seconds.
The car accelerates fine if I step on it. I can not recreate it in neutral.
It is a stock '66, 440cui, automatic transmission, carter AFB 3856S (not exactly stock, but same CFM), new points, dwell set at 30, new coil. I have cleaned the carb and set float heights and float drop. It has a fuel pressure regulator and electric fuel pump. Last weekend I changed the gasket between carb and manifold. I have not been able to find other vacuum leaks.
A have a few more ideas of the cause, but I would really appreciate any inputs or links to old threads from this knowledgeable forum?
The suspicions I have left:
1. If the vacuum canister spring is weak and advancing too much causing a knock - but would that show as a lean spike?
2. If the step up springs are too weak - but I would think they should still be in the jets at light cruise? The carb has the 3 step - step up rods.
It only occurs when the engine is hot. I.e. after 10-15 min of driving.
After installing a wideband AFR gauge I realized that the misfires occurs the same time as "jolts" of lean condition. Cruising at AFR 14-15, and then jolts/spikes of AFR 16-17 lasting just long enough for the gauge to register it. It happens every few seconds.
The car accelerates fine if I step on it. I can not recreate it in neutral.
It is a stock '66, 440cui, automatic transmission, carter AFB 3856S (not exactly stock, but same CFM), new points, dwell set at 30, new coil. I have cleaned the carb and set float heights and float drop. It has a fuel pressure regulator and electric fuel pump. Last weekend I changed the gasket between carb and manifold. I have not been able to find other vacuum leaks.
A have a few more ideas of the cause, but I would really appreciate any inputs or links to old threads from this knowledgeable forum?
The suspicions I have left:
1. If the vacuum canister spring is weak and advancing too much causing a knock - but would that show as a lean spike?
2. If the step up springs are too weak - but I would think they should still be in the jets at light cruise? The carb has the 3 step - step up rods.