My car has been behaving oddly since an emissions test. Any ideas what caused worse performance than normal, and a one-off failure of the car to start? The car is a 1988 Chevrolet Nova with engine 4A-LC, 1.6L, carbureted, single overhead cam.
Sequence of events:
Car ran fine with normal performance for a long time.
3/22/2025. Oil change.
3/26/2025. Drove 110 miles. Normal performance
3/28/2025. Emissions test. Passed. Drove home, 8 miles. Performance was reduced: less power, lugging.
Did not drive until:
4/4/2025. Car would not start after having been parked for one week. Roadside assistance technician’s battery test indicated battery was functioning okay. He added some gas. Car started.
Did not drive until:
4/10/2025. Gas station, less than one mile away. Filled gas tank, topping it off. Based on the gas tank capacity and the amount purchased, there had been around 4 gallons in the tank before filling up. The roadside assistance technician probably added less than 3 gallons. So when the car would not start there had probably been more than one gallon in the tank.
Since that time, the car has not failed to start again. However, performance is still noticeably worse than usual.
I topped off the tank one time only to ensure that the tank actually was full, after having had a one-off failure of the car to start, apparently related to low fuel in the tank. Normally I do not top off the tank. My calculation of how much gas was in the tank when it did not start after ensuring that the tank really was full (by topping it off) indicates that it had more than a gallon in the tank when it did not start. Usually it will start when that low.
Refueling with gas available at gas stations is a routine thing experienced by this car for 38 years. Why would the formulation of gas used suddenly become an issue? The change in behavior was right after the emissions test.
Both the oxygenated fuel and the emissions test may be red herrings.
I’m not saying oxygenated gas won’t cause problems with an old carb’ed car, but where I am E10 has been the standard since 2006. So it’s not likely that the car has a problem caused by the gas it’s been using for the last 19 years.
Likewise the emissions test may be just a coincidence. The car is 37+ years old. Anything can go wrong at any time. Just approach it as any other engine performance problem.
If you live in Southern California, you have been using E10 ethanol/gasoline for 30 years.
Inspect the fuel hoses at the fuel tank and fuel pump. If there is a small leak, air can be drawn into the fuel line causing hard starting and loss of power.
Also, there appears to be two fuel pumps: a mechanical pump on the engine and an electric pump inside the fuel tank. If one of these pumps fails, there will be a loss of power.
I’m in Northern California. Non-oxy gas is not sold anywhere that i have been in California for 30 years. 1988 cars are still running.
Next thought. Emissions tests do not include any sort of contact with the systems involved. All they are interested in is if the system works to their standard. They do not adjust things at a testing station. YMMV. It’s hard to imagine how a test site could affect the running.
If you are a home mechanic then it’s time for a tune-up and a filter, maybe spark plug cables, and how about an additive in the gas tank to try cleaning the fuel system? I’ve used SeaFoam from time to time. Or it’s possible you have developed condensation in the gas tank from such infrequent use. In that case a treament with “Dry Gas”?
If you are in California, the emissions testers WILL mess with your car if it is pre OBDII and it has a carburetor. But what they do is minimal, they may remove the vacuum line from your distributor to disable the vacuum advance in order to see if some control or device is working. They may adjust the idle mix on your carb IF the limiting caps have been removed and they might adjust the timing if it is not at what is on the emission placard.
BUT, failure to start when low on fuel is a sign of a failing fuel pump. Adding gas increases the head pressure of the fuel to the input of the fuel pump allowing it to work, but is will still cause issues with drivability at higher loads, like going up hill. Fortunately the fuel pump is cheap and easy to replace on a 4A-LC. I bought one from AutoZone with the lifetime warranty, AutoZone bought me two more over the 300k+ miles of its life.
That would not be the fault of the emissions test, but I would check that vacuum hose to the distributor.
That reminds me, you could also have an issue with the shaft bushing in the distributor. Pull the cap, turn the engine until one of the vanes lines up with the ignitor. Then move the top of the shaft and see if the gap changes between the vane and the ignitor. You need to have these lined up because otherwise you cannot see the movement.
