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Decreased fuel consumption

  #1  
Old 07-17-2009, 02:36 PM
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Default Decreased fuel consumption

I recently changed my timing belt, water pump, spark plugs, cam seal, valve cover gasket, oil and filter, coolant flush, timing belt tensioner, alternator belt, power steering belt, spark plug o-rings.

The car runs great and is running just the way it should. However, I went from 36 MPG down to 28 MPG.

This is only the first tank of gas, but I did do anything really related to fuel. I did use iridium spark plugs instead of platinum, but I was told this would INCREASE fuel effieceny, not decrease it.

What could possibly account for such a substantial lose in MPG?
 
  #2  
Old 07-17-2009, 07:46 PM
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You mean "increased fuel consumption"...


But anyway, has your driving style changed? Are you driving city more?

Was everything done properly? (timing set properly, etc.)
 
  #3  
Old 07-17-2009, 08:52 PM
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Yes everything was installed properly. I had originally installed the alternator belt to loose, then later had to go back and tighten it. But other than that, everything thing is O.K.

I can not really think of anything that would cause this, except maybe the iridium spark plugs, but like I said, I was told the iridium is better than platinum. Someone on another forum mentioned that it could just take some time to break the new parts in???

Does that sound right?
 
  #4  
Old 07-17-2009, 08:54 PM
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Iridiums won't help. I'm not sure if they'll make it worse though. What year civic do you have?
 
  #5  
Old 07-18-2009, 08:31 AM
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A plug is a plug with regards to igniting the air/fuel mixture.
You either have a weak or strong spark.
Possibly the new plugs need more voltage but that's it.
I would suspect your engine's timing.
Remove cover and verify that the timing is correct.
 
  #6  
Old 07-18-2009, 09:14 AM
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You overpaid for spark plugs. Basic NGK or Denso plugs work just fine.

Regarding your poor gas mileage, did you properly gap the new spark plugs? If not done recently, you also should replace the plug wires, distributor cap, and rotor. Whenever you replace the timing belt, you should likewise check the ignition timing with a timing gun. In summary, having worn ignition components and improperly set ignition timing are among the most common causes for reduced gas mileage.
 
  #7  
Old 07-18-2009, 10:31 PM
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Interesting.....i honestly did not gap the new spark plugs because I was told I did not need to with the ones I had bought. I have the gauge, but have honestly never had to adjust the spacing.

also, I do not have access to a timing gun so, i dont know how else to verify that. IF the timing WAS off like one tooth....what would I notice? When the vehicle is at idle and parked, there is nothing that would lead me to believe the timing is off; everything is smooth and quiet. Even when I punch the accelerator, the car runs great through all of the gears.

I just assumed that something more major would be noticeable with the timing being off. I have not noticed anything. The plug wires, distributor cap, and rotor have NOT recently been replaced. But like I said, the car was getting 36MPG before the service, and now is getting 28MPG.

To verify timing, would i need to rip everything apart again and check that everything is still at TDC? Even if I rip everything off and it LOOKS good, how am I supposed to realistically know that it is?

If it runs good now, and was installed at TDC, if I take it apart its still going to look at TDC. If I move it over a tooth, I would think it would only make matters worse. What kind of impact is one tooth going to make? I am not getting any of that "bogging down" that people talk about when they are not at TDC.
 
  #8  
Old 07-18-2009, 10:33 PM
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You don't necessarily need to gap the plugs. It's possible that they came pre-gapped. The plugs I buy come pre-gapped at .044 and OEM spec range is .039-.043, so that .001 isn't really a big enough difference to constitute gapping them.
 
  #9  
Old 07-19-2009, 06:10 AM
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It's pretty easy to pull the plugs and check the gaps.

Because you just replaced the timing belt, the ignition timing is the first obvious thing to check. Can you borrow and inductive timing gun from someone? Call local auto parts stores. Some will rent you timing gun. Otherwise, they cost about $30. If the mechanical timing were off by a tooth, you would be unable to set the ignition timing to spec (pointer aligned with middle red mark in group of three marks on the crank pulley).
 
  #10  
Old 07-19-2009, 09:09 AM
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O.K. I will definately pull the spark plugs and see where they are at. Unfortunately, we have friends and family in town and will not be able to get to it until Tuesday or Wensday (both of our cars are constinantly being used). Do you know of a good source to find the steps required to complete a mechanical timing? Thanks in advance!
 

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