Sudden drop off in mpg

[95_tracker]

My '95, 8 valve, automatic used to get 27-28 mpg on a consistant basis. Recently it dropped off to 20-21 mpg. No real change in driving habits or distances. What would cause such a sudden drop off? Car seems to run the same as it has all summer. I have let it warm up a bit longer with the colder weather, but not that much longer. Thanks in advance...

[jtgh]

long periods of idling add up quick , 0 mpg. -30mpg subrtacts fast. ( its like a gas leak)
best , if no garage, is to put plastic on windshield , start it and drive off slowly. 45sec. warmup. is all engine needs to be ok for slow ops.
keeping rpm's low, till needle on gauge starts to move.


or
1: Thermostat , not working correctly (180F min)
2: ECU has dropped to Limphome mode.

is CEL lamp on for key on, no start , then goes out and stays out while running?

[95_tracker]

CEL is on during key on, no start condition. CEL light does not come on during running. I'll be around tonight to check feedback, but gone for a couple days of the holiday. Appreciate any feeback. Some extra info that may help. No rabbit starts, mostly hyw driving at 60 or under, thermostat and heater working fine. Cold start in moring=rapid cold idle circuit for 5 sec, down to normal idle, then slowly rev back up to cold settings over a few minutes if I let it sit

[TheZuke!]

95_Tracker,

I normally see a 3-5 mpg drop during winter without idle warm-ups.

I suspect the tighter tolerances in the drive train and stiffness of
fluids (crankcase, transmission, transfer, differentials, wheel bearing grease)
when cold may be the reason.

For instance, at the top of one long hill in town, the speed limit is
55 mph, but at the bottom it is 45 mph. I usually just take my
foot off the gas pedal at the top of the hill and let the engine do the braking.

During warm weather I need to do this about 2/10ths of a mile sooner,
and may still need to brake at the bottom. Winter time, no problem!

[jtgh]

on mine , all in gear decelerations , the fuel is cut 100% (infinite mpg all down hill , to .5mph or so)

this is part of hyper-milling. (the safe part)

[hamsta]

Things which can cause drop are:
1. Sluggish O2 Sensor
2. ECU Engine temp sensor.
3. Thermostat

[jtgh]

any sensor or actuator of the EFI system that prevents the OXygen sensor for allowing
closed loop operation, will greatly effect mpg and performance.

to detect this problem requires a scope or Tech1 scan tool.

[95_tracker]

A bit more info now that I'm back from the holday weekend. Checked the EGR feed and there is no vaccum there during warm engine at idle. No vaccum at the fuel regulator. Can't remember their names off the top of my head, the electronic solenoid closer to radiator has good vaccum and causes engine to stumble if disconnected. The other electronic solenoid next to it, closer to engine, has no vaccum at warm idle. I'll try shorter warm-ups in the morning and see if that makes a difference.

[ranger88den]

I might be mistaken, but I think my 16v has direct vacuum connection from intake manifold to fuel pressure reg. so you should have approx. 19 in.. Don't know why 8v would be different. Tracker isn't near by or I would verify.

[jtgh]

each nipple is diff. (at manifold or TB as the case may be, 8v./16v)
EVAP, full manifold vacuum at all times.
EGR, this is pORTED, it increase as you increase throttle.
FPreg. this is atmospheric. (follow tube carefully, mine to to top of air horn)

the regulator , keeps the fuel pressure constant , regardless of altitude.
or clogged air filter.


On a 95 the EGR vsv is not energized unless you have 5 conditions met,
including wheels spinning, (looks a vss to tell this)
if you want a live EGR test for newer 94/95 kicks let me know.

older ones can be done in neutral. but not the newer ones (89-95 range)
cheers.