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fuel mileage drop

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  #1  
Old 07-18-2015, 06:43 PM
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Default fuel mileage drop

Hi I have a 2009 town country with the 3.3 engine with about 110.000 miles on it. My gas mileage was around 19 or so it has just dropped abruptly down to about 15. I just put new plugs and wires on it new air filter, new brakes and tires. What else do I need to look at or do to figure this out. Any help would be greatly appreciated thanks David.
 
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Old 07-19-2015, 01:20 PM
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If you've done "the usual" with poor mpg. (routine maintenance, check tyre pressures, binding brakes, esp. the handbrake on these cars etc. etc.), you then need to read any errorcodes that may be available. I need not go into that one as there are a number of experienced contributors here, just check their postings.
E.g., you may have a duff lambda sensor feeding wrong fuel/air ratio data into the fuel control micro., and similar.
Diagnostic readings can have their merits, esp. in this kind of area, so long as you interpret them properly.
Wierdly, poor mpg can even be caused by air leaks in the induction system causing a wrong manifold pressure to be sent as data to the fuel control micro. Sometimes the problem could be as simple as a dirty mass airflow device, usually the hot-wire type. This item is just another sensor feeding data to the fuel micro. On petrols, there is the throttle body device which is a known fault item. (This one has been on UK tv).
Generally speaking, suspect any sensors first before condemning a micro.
Good luck!

Leedsman.
 

Last edited by Leedsman; 07-19-2015 at 01:26 PM.
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Old 07-19-2015, 08:30 PM
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Thanks for the advice. Would a product like seafoam in the gas tank help? Thanks David
 
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Old 07-20-2015, 04:29 AM
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My experience with putting additives in the gas/petrol tank is not good, it CAN work with petrols if injectors are gummy with deposits, (not likely with your fault description as a sudden onset of poor mpg.). With diesels almost never any good as the usual problem is hard carbon crud on the injector altering the modern complex spray pattern.
You need to get in your head all available data before coming to a diagnostic decision as to fault. The slowest and most expensive is to pre-judge the issue and replace components *****-nilly as do many incompetent so-called pro mechanics.
1) Always go for the simple things first.
2) Always try the cheapest things first.
3) Always consult someone trusted and above all, COMPETENT!
Being on this website means you are already trying (2) and (3).

Leedsman.
 
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Old 07-23-2015, 11:10 AM
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It's time I got my brains in gear-- I forgot to mention:

A common cause of poor mpg. is also a jammed-open coolant thermostat. This happens maybe on its own or due to other causes, but results in the engine running cool all the time. The control micro reads the engine is not up to temp. and therefore keeps the running fuel mixture a little rich. Hence poor mpg.
FYI., engines are less efficient when under temp. They need to be above 70*C before they get better. This affects diesel engines worse.
Reason?
70% of engine friction is beween piston/ring assy and cylinder wall. This drops dramatically when engine is up to temp. The rest of friction is mainly valve-gear.
No-one so far in automotive history has come up with a way round this cold-friction problem except by heating up the engine by other means (such as electricity from the grid) first before setting out on a journey. All the oil additives that might work have fallen foul of the oil filter which rapidly clogs up with added material, esp. PTFE. If anything in the oil works it will already have been included by the oil manuf.
Racing car engines are ALWAYS pre-heated, otherwise total seizure almost at once.

Leedsman.
 
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Old 11-17-2018, 07:04 AM
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I am having the same problems here, did you find the answer to your problem? My vehicle is a Chrysler Voyager 2004 same as Chrysler Town and Country in the U.S. Base model mini van. Petrol 3.3L.


I have checked for binding brakes with brake expert - no problems. The engine achieves normal temperature,is not running cool. I have checked wheel alignment at suspension experts even purchasing and fitting a camber adjustment kit and had it installed. I have checked exhaust/muffler at exhaust experts, repaired and now all good. Both upstream and downstream O2 sensors have been replaced. Air intake temp. sensor was faulty and replaced. Engine coolant sensor was replaced. None of these replacements/repairs has made any difference to the fuel consumption. Fuel consumption is calculated at the pump. Kilometres divided by litres. converting to 20 litres per hundred or in US galons: 12 MPG.
 
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