Fuel consumption

Hallo everyone, I'm new in this forum, my name is Moreno and I'm from Italy. Here in Italy we're in many people to have a XJ and I got mine from about 3 years. Soon I will show you some pics. Well, this is my problem: From some months my XJ doens't consume fuel in good way (sorry about my english). I explain better. I checked all sensors and changed the Oxygen sensor too. All valves are in good way, but at the begin my XJ used to use one litre of gasoline to make about 7/8 Km. Since some months it stopped to do this consume and now it run with one litre to make 4 Km. I have to say that l had changed the injectors with others that one friends gave me. Those injectors are from a Dodge 4.7 and he toold me that from 88 to 91 the injectors are the same for that veicle and mine. But the color of the plastic of my original injectors are black, and those are Grey. He continue to telling me that they are right, but now l don't believe in him so much. Then, last day l wanted check if the Oxygen sensor was connect in good way. So with the key off, I unplugged the sensor and l checked the plug from the Engine. There I found 3 grounds! I don't know if it is right, but l know that one is right, but the other l think no. One, the tester was not on end of scale, but in the middle. I think that wire is that from the ECU and maybe there's a little ground there, l don't know.

Well, l hope you understood a bit what l said and hope you can help me to solve this little problem, but please fell fre to write to me if you didn't understand something.

Thank you very much!

Moreno.

P.S.

Now and before l have got on my Jeep the 31" tires, and the consume was (before this problem) close to the 7/8 Km per litre.

More information is needed. What year is the Jeep?
You do have the wrong injectors. 88-90 are the same.
Do a search on "Injectors" and "O2 Sensor"

What year jeep ?
If the fuel mileage/KM changed with the injector change I would put your old injectors back in and see if the mileage/KM goes back up.
Also spark plugs can cause issues, how long since you did a tune up on it ?

OH, your english is much better than my Italian....

ok guys...based on what he is telling us how do we get his MPG back up there....
My calculations say that at 8KM per liter equals 18.79 MPG...pretty good!
Now he is running at 4KM per liter, and that equals 9.39 MPG...not great...but only a lttle less than I am getting in my stock 2001 when driving in the city only.

Without any other symptons, I can only suggest doing a full tune up, taking it easy on the gas pedal, and maybe get back to stock injectors.

McQue said:

ok guys...based on what he is telling us how do we get his MPG back up there....
My calculations say that at 8KM per liter equals 18.79 MPG...pretty good!
Now he is running at 4KM per liter, and that equals 9.39 MPG...not great...but only a lttle less than I am getting in my stock 2001 when driving in the city only.

Without any other symptons, I can only suggest doing a full tune up, taking it easy on the gas pedal, and maybe get back to stock injectors.

Click to expand...

Oxygen sensor!!! :wave1:

Hi guys, please accepts my apologies, l forgot to telling you the year of my Jeep , it's a 89 Jeep Cherokee 4.0 Limited. Europe version for German country, so it is catalyzed (many Cherokee here in italy with the same date are not catalized).

For RichP, l had to change the injectors, becasue 2or 3 on 6 had losing fuel, so it was so dangerous run with this, So l cannot replace the new with the old, for that reason.

Crystal, the Oxigen sensor is new, but the strange thing is having all groud wires l told in my last message, Becasue on the wries are on the Oxygen plug, one if from the Eater, second from the ECU, and thirt is from ground. But reading with a tester, all 3 are on ground. So this is make me crazy :-(

For Mcque, you could have right if l could drive my Jeep like a Corvette, but these comsumpion are driving my Jeep like a old man, with using a feather on the gas pedal.

About the injectors, as l told you, are from a Dodge 4.7, that friend told me that the engine nis the same of the Grand Cherokee 4.7, so about him, the injectors are the same. For me no, becasue the bigger engine needs more fuel on the cilinders, and in my enigne no. I think the injectros from Dodge, with my original fuel system, cannot put the right fuel on my cilinders.

Last think, l cannot pretend o save more fuel, but just use the right fuel for this engine. Just little curiosity, do you know how much we pay the Gasoline here in italy? $.1.97 for each litre, so you can imagine if we use to get the gasoline like there in US, you could pay $.7.44 for one gallon!!!

So if l can consume the right fuel is good for me too

Thank for your help

Injectors from a mustang will work. Look here, you might be able to find some locally. http://www.fiveomotorsport.com/
I think you need to get the right injectors and fuel flow, those dodge injectors have to be moving massive amounts of fuel and you engine is probably running super rich.

Rich, probably you right, l add to say that some weeks ago l been to my friend mechanichs and with the right macine that read if the CO (the CO is the formula you get from the exaust system between air and gas burned) is good or not. Well, that machine said that my CO was right, but my friend told me that this is not a proof that my Jeep "burn" well the gasoline or not. Indded the catalyzator "burn" some inside of it, and the at the end of the pipe (where the machine is plugged) is easy that the machine says that everything is ok.

Really the Mustang injecors are the same of XJ 4.0?

I'll chekc thanks. but about the wires?

The cat will burn up the extra fuel, a dead giveaway of a too rich engine is a bright red glowing catalytic converter which will eventually melt or self destruct.
As far as wires, I've always used the factory dealer oem wires, cap, rotor. For plugs I have always used the stock copper core Champion plugs.

Moreno, You should try and get some injectors from another XJ. Do you have junk yards in Italy where you can go and take parts off other jeep cherokee's? Your best choice would be to buy exact replacements, it sounds like you know what is going on. I hope that we can help you out! Kelvin

Hey guys, I think Moreno is asking about the results he got when he said:
"So with the key off, I unplugged the sensor and l checked the plug from the Engine. There I found 3 grounds! I don't know if it is right, but l know that one is right, but the other l think no. One, the tester was not on end of scale, but in the middle. I think that wire is that from the ECU and maybe there's a little ground there, l don't know."
Please correct me if I am wrong, but it seems to me you would want to check the wires with the 02 sensor plugged in and the key on. Using wire peircing probes, 1 wire would be the sensor ground, 1 wire would be the sensor signal, one wire would be the sensor heater ground, and one wire would be the sensor heater voltage, 12 volts. I think the sensor heater voltage would only be there for a few seconds without starting the Jeep as the computer would shut the circuit down after a few seconds with a no start condition. (or do the older jeeps not work that way?)

McQue

McQue

Your right, the others must have their wires crossed on this one, LOL!!!!!

Sounds like our Italian friend has an all too common Case of the Renix O2 sensor wiring harness getting a little too friendly with the exhaust manifold.

Sounds like the three O2 sensor wiring harness wires got smoked by making contact with the exhaust manifold, and all three are now shorted to ground. It is a simple cut and replace job with some fresh wire and crimp connectors. This is what happens when someone moves the wires around while replacing spark plugs, plug wires and OH, FUEL INJECTORS on a Renix engine with out making sure the O2 sensor wire and harness assy is not safely relocated after the work is done so that it does not get to friendly with the exhaust manifold!

Ask me how I know this!!!!!:gag:

Oh, and if I am right, he probably burned out the fuse or fusable link on the 12 volts to the O2 sensor heater, not sure how I know that either, LOL.

Although the Fuel injectors he has may be a bit large, the Renix computer may be able to compensate by further limiting injector open time, but only if he has a working O2 sensor signal to the ECU.

McQue said:

Hey guys, I think Moreno is asking about the results he got when he said:
"So with the key off, I unplugged the sensor and l checked the plug from the Engine. There I found 3 grounds! I don't know if it is right, but l know that one is right, but the other l think no. One, the tester was not on end of scale, but in the middle. I think that wire is that from the ECU and maybe there's a little ground there, l don't know."
Please correct me if I am wrong, but it seems to me you would want to check the wires with the 02 sensor plugged in and the key on. Using wire peircing probes, 1 wire would be the sensor ground, 1 wire would be the sensor signal, one wire would be the sensor heater ground, and one wire would be the sensor heater voltage, 12 volts. I think the sensor heater voltage would only be there for a few seconds without starting the Jeep as the computer would shut the circuit down after a few seconds with a no start condition. (or do the older jeeps not work that way?)

McQue

Click to expand...

Ok guys, first all, thank you very much for all your answers and please continue to write me until we all solve this problem. Then, McQue, well maybe you're probably right, l mean that l though to replace the wires from the O2 Sensor,because l wanted to see if something was wrong. Indeed, some months ago (before l changed the O2 Sensor) with a friend l had tested those 3 wires, and 2 worked in right way, one from the 12V was ok, and after one or two second the 12V stopped to work. That wire comes from the eater. the second worked (I think) well, becasue it was the ground and the thirt l don't remeber well what signal got, becasue l think it was from the ECU. But what it make me crazy is, if one electric circuit is "open" (the key off) on those write l have not to have not "conduction". Becasue it mean that some wire is "short-circuit". But it's strange that some months ago, when l made that testing l got the positive in the right wire and the negative in the right wire too without see the short-circuit before.
Or maybe (if you know that), in the Jeep electric scheme when you have the key off all circuit is on ground. But this l think it could be so strange and "stupid".

Rich, yeah, me too about the spurg plugs and other stuff, l always used the original parts, because to be sure that nothing was wrong.

Anyway, l have got the Renix scheme and it doesn't seems that the circuit when you have the key off is all in ground, but maybe l can't read it wrong. If you want l can publish it here.

Anyway one my idea couls also to "rebuild" the 3 wires from the O2 to be sure. Do l do l right job with this?

Bye and thanks again.

Moreno.

Moreno...some info to read about testing your 02 sensor...

http://mr2.com/TEXT/O2_Sensor.html

McQue said:

Moreno...some info to read about testing your 02 sensor...

http://mr2.com/TEXT/O2_Sensor.html

Click to expand...

Great link, well written, great details and lots of usefull info etc., but he has an 89 renix, so the O2 sensor voltage test data does not apply (but the rest does apply!!!).

The 87-90 year O2 sensors do not generate voltage, they are variable resistors, and the voltage is 0 to 5 volts on the Renix O2 sensor, not 0 to 1.0 volt. The ECU supplies a 5 volt signal, and uses a reference resistor in the ECU for comparison. The sweet spot is 2.45 volts on the Renix O2 sensor. It should oscillate back and forth across the 2.45 volt mark on the Renix, but with the Renix the ECU wiring harness connections must be connected and working!!!!!

Thank great link, but my problem (I think) it is not the O2 Sensor, it is new, but the wires, maybe.