So the van's been running fine all winter, except for the gas mileage has gone to crap - from 7L to 10L / 100 km. On start-up, the exhaust smells very rich and gassy for at least 2-3 minutes. If I'm doing short trips around town the fuel gauge just plummets. Once it warms up the gassy exhaust smell goes away and highway mileage is reasonable. The problem reminds me of what EchoVictor experienced in the arctic - EF12 engines burn a lot of gas when cold. So from what I've read, the fuel injection system can run in two modes: 'open loop' when the oxygen sensor is cold<600F, where the ECU guesses how much to run the fuel injectors based on engine coolant temperature, throttle, and manifold pressure sensors, etc. 'closed loop' when the oxygen sensor is warm>600F, where the ECU tunes its open loop guess based on oxygen sensor feedback. I read that open loop is set to run rich for easy drivability, so there's no stalling. But the exhaust really stinks, it seems a little much! I've checked the engine coolant sensor, its resistance is roughly in the ballpark. Spark plugs aren't fouled and indicate the mixture is OK (after a run on the highway). Distributor cap, rotor, and wires are new. Fuel and air filters have <5000km on them. Things I'm going to try: Running a few more tanks with fuel injector cleaner Unplugging manifold air pressure sensor (with engine cold idling) to test if the ECU's "limp home" substitution value is better Disconnecting the vacuum line to the fuel pressure regulator and sniffing for gas leakage (with engine stopped but ignition on and fuel pressure up) Checking the voltage at the connectors for engine coolant / manifold pressure sensors Any suggestions?
Anthony, you have it covered I think. Your milage is about the same as mine right now, right about 10L/100km ....
Well now that you mention it, maybe it's time for an update on that EchoVictor guy... I got the oil changed to synthetic 5W30. The mechanic looked everything over and agrees that the thermostat is probably no good. Shortly after that I went out of town for a month; I'll probably go back to the mechanic soon to order a thermostat & arrange to get it installed. The 5W30 sure does make a difference in starting, though; before the change the engine struggled to start at -30C and I suspected wouldn't start at all much below that; with 5W30 I have started the engine at -36C. Now, of course, the arctic is experiencing a heat wave. We actually got a degree or two above freezing today! So it was a nice day to crawl under the Domingo and add a cardboard cover to my radiator. Test drive, things were going well, the thermometer was staying mid-range, so I went all the way from Inuvik to Aklavik and back! With two warm ups, ~15 km of "city" driving (speed limit 35 km/h) and ~120km of DRIVING DOWN A FROZEN RIVER AT 70 TO 115 KM/H, BABY, YEAH!! I averaged 9.4 L/100km! That's a HUGE improvement over the 12.4 L/100km I got before. It has now become possible for me to drive my van out of here without jerrycans (though I wouldn't try!). The cardboard wasn't the only change, though. Temperature was higher (+1C vs. -11C on my previous test run in November) and the highway was smoother (cracked but otherwise bare ice road vs. gravel road with 1cm of powder snow). Still, the thermometer stayed between 1/3 and 1/2 range, where before it was pegged to the bottom. And when my toes got cold, I turned on the heater and hot air came out! I do think that masking off the radiator was the major difference though. Tomorrow I think I'm gonna drive to Tuktoyaktuk. The first 2/3 will be down the river; the last 1/3 will be driving on top of frozen salty ocean.
EV, you have to take the prize for Domingo driven in most extreme conditions! I've put a nice, easy 4000km on mine so far and I average about 10l/100km in the city right now.
OK, an update: Running a few more tanks with fuel injector cleaner - IN PROGRESS Unplugging manifold air pressure sensor (with engine cold idling) to test if the ECU's "limp home" substitution value is better - NO BETTER, JUST THROWS CHECK ENGINE LIGHT Disconnecting the vacuum line to the fuel pressure regulator and sniffing for gas leakage (with engine stopped but ignition on and fuel pressure up) - HOSE SMELLS A LITTLE BIT LIKE GAS, BUT NO GAS LEAKING FROM REGULATOR. VACUUM LEAK RAISES IDLE (as expected) Checking the voltage at the connectors for engine coolant / manifold pressure sensors - ALL GOOD - UNPLUGGING THE COOLANT SENSOR MAKES THE ENGINE RUN SO LEAN IT'S IMPOSSIBLE TO START COLD So, the only final things I can think of are that the fuel pressure regulator might be letting the rail pressure get too high, or else the injectors are worn and squirting too much gas. Assuming my van is fine, I might just try and find the right connectors to build a 'cheater box' and try to fake the resistance from the coolant temperature sensor and lean out the open loop cold start mix. The plan would be to make the coolant seem much warmer when the sensor is cold (>5000Ohm), but about the same when it's hot (<400Ohm) A 2000Ohm resistance in parallel might do the trick.
Anthony, what's the winter mix for ethanol in your area, ours was running at about 12-15% for the winter which usually leads me to drop about 10% in fuel milage (added to the colder weather driving of course).
So with the weather warmed back up to 25-30C in June, the van's fuel economy has bounced back to its pre-winter levels! Look at the nice neat chart halfway down the page here... Admittedly I did less highway driving in the winter, but a nearly 50% increase in fuel consumption in winter is pretty awful! What to do for next winter
Im late on this but just a heads up on something I did in the 1970s. IN the thermostat is a small hole that lets air or something through and it was enough to keep my 240z from ever reaching full temp until i plugged the whole with a wire, after that all was warm and I never had any problems. tom
