Contour Enthusiasts Group Archives Forums General Troubleshooting Poor Fuel Economy

Our 1996 Mystique that we have owned from new, with 103,000 km, now gets about 27 imperial MPG on the 110 km/hour highway we have here. When new, it would average 37, with the odd tank over 40. It gets oil changed every 5,000 km and fuel filter every 10,000. It had the O2 sensors replaced under warranty at about 40,000. The throttle body has been replaced twice (would stick at idle). All hoses were replaced at 80,000 (6 years of age, very sticky inside). Has Continental Touring 2000 tires, stock size on the alloys and ice radials on steel rims for our nice Canadian winters. Does not matter, fuel economy is the same winter or summer. Car gets lots of highspeed highway use as well as puttering the 3 km to work. Fuel economy does not change if I am driving or if my very conservative wife is driving.

Any ideas on what to look at next? I have checked the FAQ and searched for problems but I seem to have dealt with them all, no change. The shop that does the regular service thinks its fuel injectors that need cleaning. Any ideas would be appreciated. Thanks

Other than those typical things that you've probably looked at (PVC, IAC, air filter cleaning, Throttle body cleaning, manifold cleaning, etc.) there's not much I can think of. I'd put the typical engine cleaning liquids into the various fluids of your car. Things such as Fuel Injector Cleaner in your gas tank, Carbon remover in your oil, that kinda thing. I know that I use a product called BG44 every few months or so that really cleans out the engine well. It's a bit pricey ($15 for a little can) and I don't know if you have it in Canada, as it's hard to find even here in CO, but it's great stuff, and I'd at least do it to clean your engine, even if it doesnt yield the results you need. Try it alongside some fuel injector cleaner, maybe that will do the trick.

Welcome to CEG!

A few things to think about:


As the catalytic converters age, they tend to block exhaust flow causing increased exhaust pressure even if they still work. This reduces power and efficiency gradually over time.
Unless severe, only checking exhaust pressure will tell you if this problem exists.

The EGR passages also clog with carbon and soot over time. The missing exhaust gasses are replaced with like ammounts of fresh air and fuel. The ignition timing becomes reduced because of pre-ignition (often called pinging) and fuel economy and power suffer again. With a similar result, the DPFE sensor can go bad either reducing the EGR flow itself or lying about the ammount of clogging and keeping the CEL from lighting.

You are about due for new plug wires.

Vacuum leaks occur around the intake manifolds when the O-rings begin to crack. A 96 is due for gasket replacement.

The rubber hose from the upper intake to the PCV valve eventually goes bad and is often missed because of it's placement under the throttle body.

The MAF needs periodic cleaning, apparently unbeknownst to FORD.


Luck!