On my 76 Lincoln Mark IV, when the car is coasting or accelerating, the engine seems to have a bunch of small surges, and my acceleration seems to be worse than it used to be. It seems to me (based on my limited knowledge) that it may be a misfire, but I don’t know how to diagnose this.
Thanks!
Pull the spark plugs and read their condition. They should be light tan in color, not black and wet with oil. The gaps should be in spec. If any are wide, replace the set. If any seem wet with fuel, those are likely not firing. Check the plug wires and distributor cap and rotor for burns and corrosion. If they are all a bit sooty, the carburetor may be too rich and need rebuilding. Same with very light tan (a lean condition) with some blistering or burned electrodes on all plugs.
Consider that 1976 was in the peak years for complicated, poorly executed emission controls and likely would surge when brand NEW! Considering all the vacuum lines and vacuum operated accessories and emission controls, if you haven’t replaced EVERY vacuum line with brand new, do so right now before even starting anything else!
Good luck.
I assumed you’d be working on this yourself since finding a mechanic who’d even touch it would be almost impossible.
Are you using gasoline that contains ethanol?
The fuel system on your 76 Lincoln was never designed to operate on gasoline that contains ethanol.
Ethanol is very corrosive to older fuel systems. It can damage fuel tanks/lines/pumps/and carbs.
Where I live, we can purchase gasoline that doesn’t contain ethanol for older/classic vehicles for this very reason.
http://msra.com/wp-content/uploads/2017/05/May-2017-Non-Oxy.pdf
Tester
@tester makes a great point! The ethanol in the fuel could be dissolving your rubber fuel lines as well as making the engine run too lean. They ran too lean for emissions back in the day, anyway. 10% ethanol just makes that worse. You need to increase the jet size a small amount, at the least, to compensate. And change all the rubber lines in the fuel system.
I agree. Vacuum line is dirt-cheap by the foot.
I’d suggest that if you choose to undertake this yourself, you remove and replace only one line at a time. That prevents crossing lines when reconnecting them. Sometimes newbies remove all the lines at once and then make a mistake putting the new ones in and find themselves struggling with strange new symptoms.
Change the spark plug wires because they could be frayed and arcing, creating the misses and surges you are describing. To test: start the car, spray some water on the spark plugs cable and look for any signs of arcing or sparks.The engine will misfire if there is a problem with the cables.
I’ll check the plugs and I’ll get to work on replacing all of the vacuum lines. I was planning on doing that at some point, but I guess there’s no time like the present!
@Tester I’m not running ethanol. I learned my lesson on that one after it ate through my fuel pump!
Luckily, my local favorite gas station sells ethanol-free gas, so that’s easy enough for me to do.
@rascal243 I replaced the plugs and wires when I got the car about 4,000 miles ago, so it seems unlikely that this could be the case, but I’ll try that if I still have issues.