How does YJ EFI work?

[bryanjeep]

Hey guys,
I was wondering how exactly JEep (YJ) EFI works. Does the computer look at how much the pedal is pressed. Another question is will you save more gas on the interstate in 4th gear but giving the pedal 1/4 of a push & maintain 65mph or save more gas in 5th gear giving it 1/2 to 3/4 gas pedal? Trying to adjust driving style for my commuting to school. Remember, don't know if this matters, I have 31 x 10.50 tires and stock 4.11 gears.

[XJNick]

Hi,

I'm not sure I can explain this as thouroughly or correctly as you may like, but here goes:

The Computerized system in fuel-injected vehicles monitors all it's sensors at different times during normal operation. Each sensor does a specific job by monitoring and reporting to the Electronic Control Unit (OBD I) or Powertrain Control Module (OBD II) a certain state or condition that exists in different parts of the engine and vehicle.

Your question seems to be about gas efficiency and acceleration. During normal driving, the ECU/PCM does monitor the position of the throttle through the Throttle Position Sensor. Changing the position of the throttle tells the computer you need to speed up or slow down. At the same time, you are physically allowing more air to rush into the throttle body by pushing on the pedal. The computer then will adjust the spark & injector timing to satisfy the fuel and spark needs of the engine as its RPMs change. It knows to do this through the data provided from certain sensors such as the Throttle Position Sensor (TPS)
, Crankshaft Position Sensor (CPS), Manifold Absolute Pressure sensor (MAP), Manifold absolute Temperature sensor (MAT), and others.

So to answer your question, in general the amount of gas consumed is related to engine RPMs and load. You should always try to drive in the highest gear possible if your trying to be gas efficient. However don't use such a high gear that you bog down the engine, as doing so can waste gas.

I hope this makes sense to you, as I'm writing this very quickly. Hopefully others will chime in and add anything I've failed to mention.

-Nick

	Crank position sensor A crank sensor is a component used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[dingus]

to put it simply, the lower the RPM's, the less gas it will use...

however, it puts more strain on the motor if, for example, you're doing 35 in 5th gear as opposed to 3rd gear doing 35mph... i generally try to keep the RPM's around 2500 for town driving, 2000 for highway... anything lower than like 1400 rpm's for a jeep (pretty torque-y motors) will not give very good throttle response...

[Bounty__Hunter]

Use 5th as long as it's not bogging down the motor. If you're really converned about fuel economy go back to 27" or 28" tires or start shifting early and slowing down the top speed. Cutting 10mph off the top cruising speed saves a considerable amount of fuel in our rolling bricks.

[Tug-n-pull]

Or buy a 500 dollar Escort or some other ez on gas auto just for the everyday drive to and fro. Keep the Jeep for everything else. Don't have the break in worries and if it gets keyed in the parking lot no biggie. tug

[BostonJeep]

yeah but u gotta drive it.

[bryanjeep]

So is the amount of pedal being pressed going to affect the amount of gas being shot through the injectors? The more I push the pedal, the more gas goes to engine? A lot of the time I'll give it more gas and I don't accelerate...that's another story. Jeep has no power. Oh, I wouldn't think about going to anything smaller than 31 x 10.50. Wouldn't look right on my Jeep.

[Snitty]

Originally Posted by dingus

i generally try to keep the RPM's around 2500 for town driving, 2000 for highway... anything lower than like 1400 rpm's for a jeep (pretty torque-y motors) will not give very good throttle response...

that sounds alright for a 4 cylinder... but for a 6 cylinder, i'm always driving under 1400... i will rarely drive above 2000 for more than 20 seconds

[L33TJ33P]

LOL 1400??? I am at 2500 on the Highway. I make it a habit not to go abouve 3000. Am I driving too fast?? :-D

[hi_c]

No. I run 2600 rpms to keep up with 65mph traffic. My motor has 165K miles on it.... never been rebuilt. Motor is still going, but not as good as it once was.

This goes back to the age old "2.5L Performance Mods". Get the K&N, get the exhaust improvement, and get the electric fan when you get the $.

Last resort, or first if you're wallet is fat... regear.

C

[Snitty]

my motor is running under 2000 at 70 mph

[bryanjeep]

HOW ON EATRH DO YOU GET 7OMPH AND UNDER 2000??? I go about 70 and my rpms are right below 3000 in 5th gear. Oh my crappy 2.5 deserves no more money. I am not dishing out another penny for this engine. I am done with it. My other engine is waiting to go in.

[XJNick]

I too try to always keep my Jeep under 2000 rpms. I never go above 2000 rpms unless I'm speeding up to enter a highway, etc.

At about 65 MPH on the highway I usually run right at 2000 RPMS with my 6-cylinder.

-Nick

[Snitty]

HOW ON EATRH DO YOU GET 7OMPH AND UNDER 2000???

4.0, 3.07, 31" tires... i rarely drive over 2000... and the highest I EVER take it is 3000 while accelerating in 1st and sometimes 2nd gear... and when i am in extreme stuck conditions offroad

[L33TJ33P]

Maybe I shouldn't be doing 80

[bryanjeep]

It my be the way that I am wording the question, but I still don't really have the answer I was looking for. XJ Nick did an excellent job of explaining, but one more question. What tells the injectors to spray? I it pedal position or rpms. Just because you give the pedal all it's got, that doesn't mean that your RPMs go up. Sometimes I have to stay in 3rd gear while on the interstate just to get to 60 mph. Don't even ask me what my rpms are at that point! I hate this stupid car computer stuff.

[Snitty]

the crank position sensor tells the injectors when to open, and it is a combination of other sensors that tell them how far and how long to stay open

	Crank position sensor A crank sensor is a component used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

[XJNick]

I believe Snitty is correct. The Crankshaft Postion Sensor (CPS) tells the computer what position the engine is at internally. Using this data, the computer knows when to "pulse" or send power to the injectors, which then spray.

The computer must also, however, adjust the "pulse width" of the injectors, i.e. how long they spray. It also has to sometimes advance or retard the timing of the injection pulses (as well as spark), to ensure the engine is running correctly. These functions are controlled using data from many of the sensors, but primarily the CPS, Mass Air Temp. (MAT), Manifold Absolute pressure (MAP), Coolant Temp. Sensor (CTS), Throttle Position Sensor (TPS), Oxygen Sensor (O2).

So to answer your basic question. NO, the position of the throttle does NOT directly affect when or the amount of fuel the injectors are spraying. It DOES indirrectly affect the above though through the data it sends back to the Electronic Control Unit (ECU) aka Computer.

-Nick

	Crank position sensor A crank sensor is a component used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).