98MazdaAC

Problems With Chugging

4 posts in this topic

I have a manual 1998 Mazda 626 I4. Does anyone have problems where when they are stopped, the RPMS drop a bit and the car chugs. I dont know why. It constantly has a small chug but sometimes it like to drop down and chug even harder.

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Have your fuel pressure tested.  Chugging is a symptom of low fuel pressure or low fuel in the tank.  The fuel pump cannot keep up with the demand of the fuel injectors and it will chug.  That's just one possibility.  Whenever I hear the word chug I think of low fuel pressure.

 

I show an example of what a fuel stream looks like with low fuel pressure AND the car is almost out of fuel.  It's pretty easy to see how and why a car would chug with these symptoms.  It's towards the end of the video at about 9:17.

 

http://youtu.be/gNJT83wiTEo?t=9m12s

 

These symptoms can be exacerbated by a dying fuel pump, split in the fuel pump hose within the tank, or clogged fuel filter.  Low fuel pressure can most certainly be a contributing factor but the culprit is the usually the fuel pump.  

 

Also something to keep in mind is an incorrectly measuring fuel level sending unit.  If your fuel gauge is incorrectly reporting the fuel level it might seem like you have a lot of fuel left in the tank but in reality you are almost out of gas.  A car that is almost out of gas will chug in the same manner even with a perfectly good fuel pump and fuel system.

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Watch my entire Mazda 626 Fuel Series.  From start to finish I show how to diagnose and fix fuel related issues including the fuel pump relay, fuel filter, fuel pressure regulator and finally the fuel pump.  The testing methods are for a 1993-1997 Mazda 626 however 1998-2002 owners can still get a lot out of it for general testing procedures.  All fuel specs are identical from 1993-2002.  It's the same fuel system but electronics are a bit different.  You'll still get a lot out of watching how it was done prior to the invention of OBD-II.

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