MTFCA Forum

My 26 coupe has started lurching while driving. Not huge lurches but enough to feel it. I don't think it has anything to do with the engine as it sounds fine. Any ideas?

I forgot to mention I only seemed to notice the lurching in high gear.

Does the lurching get worse,at low,speed. Does it get worse when accelerating at low speed. Does it happen at 30 mph.
It could be timer, wiring, coils, or vacuum leak.
Need more information.
Check compression etc.
Keep us inform as you investigate.

Broke tooth off either ring or pinion gear ?

Most likely a misfire. When the engine is running fast, as it is while in low, a misfire is hardly noticed, but when the engine is turning slower and more highly loaded, a miss becomes very prominent and causes the engine to "lope".

Josh, have you tried moving the spark lever when it lurches?

I would begin by making sure the mixture control is working as it has been working, then I'd remove and inspect the spark plugs. Another thing to check is the sediment bulb. At least look at the wiring around the timer, checking for frayed insulation and rubbing. Look at the plug wires and see that the terminals on the side of the coil box are snug.

What type of timer are you using? If not electronic have you cleaned it out and checked the internals for wear?

Mine was lurching for a few minutes this afternoon. When I started it, it kicked over and quit. So I opened the mixture control and it started right up. Then I started down the road and it started lurching again. I rotated the mixture control back to where I usually have it and it smoothed out and ran fine from there on. Several things could cause the problem.
1. Mixture, as I mentioned above.
2. Ignition problem. This could run fine at idle or when running at a constant speed, but start missing when you give it gas or when pulling a hill. This is usually caused by a weak spark. It takes a stronger spark as the compression increases, and the ignition does increase as you open the throttle, especially when pulling.
3. A leaking valve. This will give constant low compression in one cylinder and it is not as noticeable when going at a constant speed, but worse with pull. This can be detected by a compression test. The cylinders should all be about 45-50 psi If one is noticeably lower it is usually caused by a burnt valve or sticking valve.
4. Other things not related to the engine, would be excessive slack in the drive train. This is most noticeable when decelerating or going downhill.
Norm

The connection at the mag post was loose. It lurched only when the car was going into a heavy head wind at 25 - 30 mph. Otherwise the car ran very smooth. Check all ignition related wires.
Art Mirtes

"Uuuuuhhh... Lurch is not a problem."

Lurching and surging can be confused. Surging is like someone turning the ignition off an on at random and is caused either by a lean mixture or too much spark advance. It usually only occurs at a steady cruising speed. I'd be checking for an incorrect mix (GAV) or low fuel level if you're sure the spark is not too far advanced for the speed you are going.

Thanks for everybody's help, turns out it was just a loose wire.

Jlenon wrote: ↑

Sun Oct 31, 2021 2:35 pm

Thanks for everybody's help, turns out it was just a loose wire.

Thanks for the update.