need opinions on why my car is surging

[80convertible]

Car just started surging the other day while driving. I can feel it most when driving down the highway. I can also hear a very faint backfire sound in the exhaust. I have not done any work on the engine lately, so I can't figure out why this just started. Plugs, plug wires, air filter and gas filter are all low mileage. Changed the rotor and cap last year. The coil, module and vacuum advance are all pretty old. Could one of these items be starting to fail causing the surge? I don't hear a vacuum leak in the engine bay. Could use some advice on what to check.

Regards,

Jim

 

[Stingray6974]

Jim,
This could become a long list:
Carbon on a spark plug
Loose spark plug
Plug wire open
Plug wire shorting to exhaust etc.
Dist cap carbon tracking
Rotor starting to burn thru
Worn out dist shaft and/or bushings
Mechanical advance weights stuck in full advance
Too much initial advance
Weak spring on EGR valve
Partially clogged jet in carb
Partially clogged air bleed in carb
Weak or broken valve spring
Cam lobe going flat
The majority of these will not show up at idle. Next time you feel it surging, hit the gas and see what happens. Bog, black smoke out exhaust, etc.

Mike

 

[SwaveDave]

It could be the fuel pump has just started not providing enough fuel. That would make it surge and backfire due to a lean condition.

ALso,, if your battery neg. to the frame ground strap is not making good connection...the electrical system will be affected. Also, the frame to engine block ground strap. Make sure these are very clean and use star washers.

Dave

 

[78SilvAnniv]

Yow! What a problem...

Is the tach showing any difference?
Is this an engine problem or could it be a tranny problem?...and how would you tell the difference?
Heidi

 

[80convertible]

Funny you should ask about the tach as I noticed it is bouncing a little. Normally my tach is dead on with no bounce. This is not a tranny problem. I can tell the engine is missing and the backfire sound is a sure fire way to know it is engine related... I think it is somewhere in the ignition system.

 

[mvftw]

Are you running Platinum plugs? If so, replace them with standard ones.

 

[pax]

Jim,
Go to the thread titled " HEI Ignition question " page 3 and read the post by GerryLP near the bottom...could be helpfull.
john

 

[vette-dude]

I can only offer advice from my experience with my Monte Carlo SS similiar problem. The car would hunt at an idle and surge on the road. I replace numerous things and finally someone said it was the EGR valve. To test, disconnect vacuum line and blow smoke through it. If it comes out around the bottom of the bellows area it means you have a hole in the diaphram. (this also works for vacuum advance cans but that is another story) I replaced it and it cured the problem. Hope this helps.

Randy

 

[pmwild]

There are many factors that can cause this condition. The first thing I would do in troubleshooting this is read spark plug color. Get a magnifing glass and take a good look. This will probably be a good indication of which cylinder is having a problem. Generally backfiring in the exhaust would indicate a rich condition. Hope this helps.