1984 toyota missfires at 45mph, then ok above


#1

I just had a new timing belt put on my 84 corolla, now it sputters around 45, need to pump accelerator to get above.


#2

If the problem occurred immediately after the timing belt change then obviously one would suspect that someone needs to recheck their work since the timing marks could be off.

If the marks are correct then it sounds like either the distributor ignition timing is not correct or the car has a carburetor problem.


#3

It might be misalignment of the timing belt, but this sounds like it might be another problem. The problem with even cars of the 1980s is that they have lots of very complex technology which tends to fail. In any event, if pumping the accelerator gets you above this speed it’s possible you have a fuel problem. It could even be a clogged fuel filter. Most reputable repair shops will guarantee their work, but you have to consider that this problem may be unrelated. It could be something like a bad spark plug wire. My advice would be to throw an oscilloscope on the plug wires and also run an exhaust emissions check. That might sound strange but it can often point out an engine problem. You also need to consider vacuum hoses and things like the EGR valve. Sometimes this will stick open and cause exactly this kind of problem. You are right in assuming that the most obvious cause of a problem is probably the last thing you changed. On the other hand, sometimes it’s not. A really good engine analyzer with exhaust emissions and ignition testing may help, but I have actually seen cases where the engine computer malfunctions, so even downloading data from it may be junk. If I had to bet on a cause I’d look at the ignition including the plug wires first, then the fuel system including the fuel filter which is often neglected. Also look at the spark plugs. They reveal a lot about combustion in the engine. The most revealing test, however, is exhaust emissions. If you really know how to read an emissions analysis you can usually narrow down the problem. Then you have to just go looking for things like bad spark plug wires, cracked or missing vacuum hoses, and clogged filters. A friend of mine once tossed a bucket of water on the engine of a Honda to diagnose a cracked distributor cap. The fact is however that if you put a car on a dynamometer and watch the ignition system on a scope while also measuring the exhaust emissions, you can diagnose the majority of engine problems. I used to do that about 1980 and I could usually fix cars that people had repeatedly brought in for repair. Oddly enough, you may also need to check out the transmission because if it is an automatic it is tied to the engine and in some cases there are even sensors on manual transmissions to alter the fuel mixture or ignition timing depending on the gear. Vacuum hoses tend to rot over time, sensors fail, etc. It is concerning to me that with the obsession with technology in modern cars we’re ending up with a lot of points of failure that are very costly to maintain, so people will tend to drive these cars in an unsafe condition. This is of particular concern with all these wild brake systems we have now. I am concerned that modern cars have become so complex that they are unsustainable. If NASCAR teams can’t figure out how to set up a race car, that should tell you something. It makes you long for the days of Smokey Yunick. Cars were complex enough then. Now they’re nearly insane.