Jan Olsson Posted September 23, 2008 Report Share Posted September 23, 2008 I have noticed sometimes that the avg. MPG dropped from time to time but I've always thought that I must have been hard on the throttle or something but yesterday I had proof that something fishy is going on.. Yesterday I started the car..I did a reset on the trip meter, did also reset the "fuel used" meter. After about 15 kilometers I did a fuel stop and observed the "fuel used" counter to read 1.75 liters. The "avg. MPG" showed 13,5 l/100 km (17.4 MPG). After the fill up I started the car and instantly checked the "avg. MPG" and the fuel used counters... The avg. MPG showed 13,8 l/100 km ( 17.0 MPG) and the fuel used showed 3,5 liters or something like that. So where did the missing 1.75 liters go? (0.46 gallons) The engine was still hot, max 5 minutes stop..53 F outside.. I have noticed this phenomenom from time to time but has not been able to duplicate it and only at this temperature (about 50-60F) The fuel used counter should only accumulate the injector pulses right? Is my PCM going south? Link to comment Share on other sites More sharing options...
Jan Olsson Posted September 24, 2008 Author Report Share Posted September 24, 2008 Noticed it again today...weird. This road force imbalance is killing me. Nearest Hunter is almost 200 miles away... It makes it hard to say if the engine is running alright under load or not. I can live with the vibrations under 50F and over 57F. The tires then feels adequate..Temperature has been 55F for ages now... Can't have winter soon enough, then I'll ask them to bring home 3 sets of winter tires and have them properly road force balanced. Link to comment Share on other sites More sharing options...
adallak Posted September 24, 2008 Report Share Posted September 24, 2008 Statistics like big numbers. Yes, it sounds a little bit weired, but I would collect data based on higher mileage. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
Jan Olsson Posted September 24, 2008 Author Report Share Posted September 24, 2008 Statistics like big numbers. Yes, it sounds a little bit weired, but I would collect data based on higher mileage. You're right about that. But this is just an example. I've noticed the same thing with only 1/4 tank of gas too. MPG drops several points and fuel used adds up with a couple of liters. And the really strange thing is that I observed it last autumn, but not since then...until now. Really strange... Neither my 1988 Eldo nor the 1993 STS I had did that.. Link to comment Share on other sites More sharing options...
Jan Olsson Posted September 25, 2008 Author Report Share Posted September 25, 2008 I'll ask this question different then..Does anyone have information on how the "fuel used" meter and the "avg. mpg" meter gatheres information? In my thinking the "fuel used" counter only adds up injector puls width over time at a supposed fuel pressure and the PCM does the adding. not much to go wrong there except from the PCM right? I wouldn't mind if it always showed the same value after restarting the enginge..I feel a bit frustrated when suddenly a couple of liters is missing. Never notice it when running, always notice it after turning engine off and starting it again..Never notice it more than perhaps every 10th start. Instant economy counter seems to work alright. Link to comment Share on other sites More sharing options...
Ranger Posted September 25, 2008 Report Share Posted September 25, 2008 Correct, the PCM simply counts injector pulses to come up with fuel used. It then does the simple math to come up with AVG MPG. Link to comment Share on other sites More sharing options...
Jan Olsson Posted September 26, 2008 Author Report Share Posted September 26, 2008 Correct, the PCM simply counts injector pulses to come up with fuel used. It then does the simple math to come up with AVG MPG. Hmm. I better check the connections for the PCM. Link to comment Share on other sites More sharing options...
Jan Olsson Posted September 26, 2008 Author Report Share Posted September 26, 2008 Could it be that the PCM compares the "fuel used" and finds out that it doesn't match the fuel tank reading and compensates for that..I.e. I use fuel for 1/4 tank of gas, the fuel used shows perhaps that I've used 1/5 of gas. Next time when I turn the engine off it adjusts itself to the true values.. Could this indicate a faulty fuel pressure regulator? Link to comment Share on other sites More sharing options...
Ranger Posted September 27, 2008 Report Share Posted September 27, 2008 Could it be that the PCM compares the "fuel used" and finds out that it doesn't match the fuel tank reading and compensates for that..I.e. I use fuel for 1/4 tank of gas, the fuel used shows perhaps that I've used 1/5 of gas. Next time when I turn the engine off it adjusts itself to the true values.. Could this indicate a faulty fuel pressure regulator? I do not believe so. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.