Is it the fuel filter or fuel pump?

My 1996 Toyota Corolla has started sputtering (choking?) out when I accelerate quickly (like getting on the highway) or when I get up to about 70 mph. Is this a symptom of a clogged fuel filter or a bad fuel pump? If so, is there a way to tell which it is before taking it to the mechanic? Or could it be something else?

Is the check engine light on? Is all the routine engine maintenance suggested in the owner’s manual up to date? If not, you’ll by money ahead probably by addressing those first, as these symptoms could be caused by a host of different things. During heavy acceleration the engine must move the maximum amount of air and gas through and out the exhaust pipe. So any obstruction in the fuel supply, the air supply, or the exhaust system could be a cause of this symptom. Fuel pump, fuel filter, fuel pressure regulator, air filter, and cat should be considered. Spark plug gaps too wide and cracking and crazing in high voltage insulation should also be eliminated as a potential cause by visual inspection.

If this were my car I’d start with the easy stuff: whatever can be determined above by simple visual inspection, then an intake manifold vacuum test, compression test, and a fuel pressure test.

The filter is about $20 and can be replaced in less than half an hour with basic tools. If the filter is restricted it will eventually, if not sooner, ruin the fuel pump. Putting off dealing with a problem often increases the cost significantly.

Change the fuel filter.

A dirty fuel filter won’t effect the fuel pressure. But it will effect the volume of fuel to the engine. And if that volume falls off, the engine will stumble under acceleration.


So I took my car to Ken Towery Auto (my first mistake?) and they said it’s not the fuel pump or the fuel filter (but I don’t know whether they even really checked.) Instead they said it was the plugs and distributor and fuel system (injectors?) so they put new plugs and wires and cleaned the fuel system. $470 later, that did not fix the problem. So they said they were stumped. They said it might be “ignition related” but I don’t know what they meant by that. Any other ideas? O suggestions for a competent mechanic in the Louisville, KY area?

Have you had the following tests done yet? Intake manifold vacuum test, compression test, and a fuel pressure test?


I strongly suggest you go back to Ken Towery Auto with your invoice and ask for some, if not all, of your money back

Unfortunately, it sounds as if they misdiagnosed your car

It sounds as if they were essentially making an educated guess . . . and they guessed wrong

A policy of insisting on bringing some high profit maintenance up to date before attempting to diagnose a problem ensures profits despite the lack of diagnostic skills. The shop manager must have graduated from one of the McMechanix chain store schools.

Thanks, all. I’m taking it to a local mechanic on Monday. He has good reviews here on Cartalk and everyone I’ve spoken to says he knows his stuff and is honest. GeorgeSanJose, I will talk with him when I drop my car off and see what his diagnostic plan is.

If you can’t remember when you last changed the fuel filter, do that first…A restricted fuel filter will cause the symptoms you describe…So will a bad coil…

That was my original thought, Caddyman. Shouldn’t have let Ken Towery’s talk me out of it. Is an ignition coil relatively cheap and easy (for the mechanic) to replace?


An ignition coil is relatively inexpensive and should take the mechanic no more than a few minutes to replace. It is located under the cap, by the way. If you go for the coil, I recommend a high quality Japanese part.

The filter might take a little longer to replace, because it’s on the firewall, and pretty far down.
Make sure to soak the threads with penetrant ahead of time. And make sure to use a crowsfoot or a line wrench to loosen the lines. An open end wrench will quite possibly round off the fittings.

I believe your fuel filter is due every 60K . . . how many miles on your current filter?