2002 Mercury Sable engine pulsates.

My wife has a 2002 Mercury Sable. This morning she woke me up to tell me her car won't start. i was a little rough to start but it started. But if kind of felt like the engine was pulsating. When I step on the gas it felt fine but when I let off the gas is pulsates again.
She took it around that block and everything was fine. I read online that I should replace the fuel filter and spark plug wires. Would that be a good idea or could it be something else.
My blazer did the same thing and I replaced the fuel filter and Catalytic converter.

Also you could hear the sputtering from the exhaust, like puff puff puff instead of normal stream. I did notice exhaust exiting closer to the rear wheel so I think the sputtering in the exhaust might be a hole somewhere. Any advice would be great thanks

My wife has a 2002 Mercury Sable. This morning she woke me up to tell me her car won't start. i was a little rough to start but it started. But if kind of felt like the engine was pulsating. When I step on the gas it felt fine but when I let off the gas is pulsates again.
She took it around that block and everything was fine. I read online that I should replace the fuel filter and spark plug wires. Would that be a good idea or could it be something else.
My blazer did the same thing and I replaced the fuel filter and Catalytic converter.

Also you could hear the sputtering from the exhaust, like puff puff puff instead of normal stream. I did notice exhaust exiting closer to the rear wheel so I think the sputtering in the exhaust might be a hole somewhere. Any advice would be great thanks

The sputtering exhaust is not due to a hole in the pipe, but rather something afoul up front. And by 'pulsating' I take that as the engine is loping or surging at idle. Replacing the fuel filter and wires is always good maintenance to do yearly. Being that this behicle is a 2002, you need to go to an Advance Auto or Autozone where they scan the codes for free. That will point you in the right direction, because otherwise, you will be grasping at straws. Today's cars are all computer controlled and the first order of business, is to scan it.

I brought it to get looked at and it came up as an O2 sensor

I brought it to get looked at and it came up as an O2 sensor


Ok, the O2 sensor is upstream. After replacing, let us know if it did the trick. Otherwise, I have some more ideas for you.

Well had O2 replaced but the mechanic called and told me that is not the problem. the problem is I need a new plenum gasket. I have never heard of that.

Well had O2 replaced but the mechanic called and told me that is not the problem. the problem is I need a new plenum gasket. I have never heard of that.

Which engine?? Does it have a vaccum leak? The plenium is the upper part of the intake manifold of which the air cleaner tube attacks too. THe tube actually connects at the throttle body portion of the plenium.

hope this helps

Plenum gasket = vacuum leak

That will do the surging/loping.

One way to check a leaking plenum gasket is to run the engine and spray carb cleaner or something like that around the seam of the upper plenim. If the engine steadies, you found the leak.

Well they put a new pluem gasket on, still didn't fix it, then they put a new injector in the car. then they replaced an O2 sensor. And now they tell me my car has a bad Check Valve in the fuel pump. They said my car has a rough time starting because of it Well my car started up just fine before.

Is there a way to replace the check valve or do I have to replace the whole fuel pump.

Well they put a new pluem gasket on, still didn't fix it, then they put a new injector in the car. then they replaced an O2 sensor. And now they tell me my car has a bad Check Valve in the fuel pump. They said my car has a rough time starting because of it Well my car started up just fine before.

Is there a way to replace the check valve or do I have to replace the whole fuel pump.


You would need to replace complete pump, I would take the car home, sounds to me like they don't have a clue, and are just parts replacing.
Get yourself a fuel pressure gauge and hook it up to the fuel system and turn the key on, letting the fuel pump presurrize. Turn off Key and watch the fuel pressure gauge to determine how fast the pressure drops in 5 minutes. That will tell you if the check valve is leaking or not. Autozone or Oreily's should have a tester in their rent a tool program or harbor freight has them I beieve for about 15 bucks. A leaking check valve will not have anything to do with irregular idling. Have they cleared the codes and checked again for any codes after engine being run for a while??

I would take the car home, sounds to me like they don't have a clue, and are just parts replacing.

This is EXACTLY what I was thinking after reading your last post Worm. Obviously they aren't diagnosing, they're just throwing parts at it. And while it may be great having new parts, sounds like they'll drive you broke in the process. You can get all the free advice/help you need to fix it, here. And are they even sure the check valve really is bad? Aside from the plenim gasket, I'd make them put your old O2 sensor and injector back in. But that might be more work than it's worth.

Has it been tuned up lately, like the plugs and wires, cap and rotor? You could easily pull the plugs and clean them.

I know I put new plugs in not to long ago. I had a code come up about a misfire in cylinder 5. I that was a broken spark plug. Maybe I'll buy the tool and check my fuel line pressure. I don't know where to hook it up but I rather not keep spending the money. Thanks to everyone who had input. I appreciate it alot.

Maybe I'll buy the tool and check my fuel line pressure. I don't know where to hook it up ...

It's under the hood below the upper intake on the fuel rail. It will be a capped schrader valve, just like a tire valve. Follow each fuel injector on the rail and you will find it, most likely where the two lines come together, in that vicinity.

The instructions for the pressure gauge will be on the back. Easy to use and do.