Bad gas mileage just got worse

[SBpunk]

Ill look into it heyhar. Thanks for the heads up I would love to have something more accurate plus I like pulling crap apart on my jeep so I'm always getting one code or another hahaha .

 

[SBpunk]

Wow that is pretty awesome. I ordered one off amazon. If I knew about that I wouldnt have spent so much time looking for an XJ w/ an overhead console :S

 

[heyhar]

The Scan Gauge II is a beefier piece, but offers only four readouts. The Ultra Gauge (available only from ultragauge.com) has up to eight screens, and has a little icon in the upper right corner, looks like a halo, that denotes loop operation. Open is open, etc. Right to the left is a little heart that 'beats', when all is well. I saw it look like a 'broken heart' while in my Outback, when it was throwing an overheating code. And, the UG was only about ninety bucks. I like the digital readout for temperature that both offer.

You'll have fun with it...just don't let it distract you!

 

[Yankee]

Sorry to barge in like that but I've got the same issue... also on a 1998 XJ - I'm not getting as bad millage as you do but it's aggravating especially with prices of gas these days... 9mpg really sucks. And so, I ordered a tune-up set from rock (OMIX-ADA) and a set of reconditioned Bosch 19 lbs injectors off ebarf... do you guys think that I should order new O2 sensors as well? I do have 190,000 on the clock and god only knows if those sensor have ever been touched (I did replace cat and exhaust with Dynomax system) - truck runs perfect... just drinks a lot.

thanks...

 

[SBpunk]

I would grab up some O2 sensors. I just dropped 2 new ones in mine along with a MOPAR CPS and Idle speed control. Havent taken it out yet but its cranking up much better. EcoMike and a few others will tell you at 100k you should be replacing the O2's. You're almost at 200k so it wont hurt anything but your wallet. I dont usually support websites on forums but WeRMopar has good prices on legit OEM sensors and parts plus the shipping is holy crap fast. Two days to get to Hawaii. Its an easy job too. There is one sensor right under you intake manifold on the downpipe and the other is behind the cat. Hit them with some LiquidWrench or PB Blaster and let it soak for a bit.

 

[Ecomike]

New O2 sensors will make a huge MPG difference. Also make the sure the T-stat is not stuck open, and keeping the engine too cool.

 

[heyhar]

The second, or 'downstream' sensor has no effect on engine operation or MPGs. It merely tells the computer that the cat is there and working. The front one, on the downpipe is the one you want to replace.

I've also found a Coolant Temp Sensor that needed to be replaced. The one up near the Tstat housing. The O2 sensor and CTS are the two main ingredients in attaining closed loop operation, and MPG Nirvana!

Mike, was it you that posted testing instructions a few years back, for the O2 and the CTS. I used both to determine that the CTS was done, and my cheapo 50k miles-old O2 was very lazy. Maybe thet could be made stickys?

 

[Ecomike]

Just search here using the OEM forum advanced search tool and search "oxygen test" and "Ecomike" as the thread author for the O2 sensor testing thread. It covers 87-90 Renix and 91-95 OBD-I and 96-01 OBD-II O2 sensor testing. It is about 5-6 years old now IIRC.

The other thread you are probably thinking of is "RenX Files", but the new guy has a 98, and they are different in many ways from the 87-90 Renix, the CTS is different. The O2 sensors changed sensor type in 1991.

Also, on the late OBD-II rigs starting around 98 I recently read where the PCM does use the final post CAT O2 sensor for some fuel control but I have no details, and I doubt it has significant control of the MPG fuel usage.


For a 98, the most significant MPG items are a bad T-Stat, stuck open, Bad CTS and Bad O2 sensor(s), in the exh-manifold. Sometimes an exh-manifold crack or gasket leak, can affect the O2 sensor data!!!!

The second, or 'downstream' sensor has no effect on engine operation or MPGs. It merely tells the computer that the cat is there and working. The front one, on the downpipe is the one you want to replace.

I've also found a Coolant Temp Sensor that needed to be replaced. The one up near the Tstat housing. The O2 sensor and CTS are the two main ingredients in attaining closed loop operation, and MPG Nirvana!

Mike, was it you that posted testing instructions a few years back, for the O2 and the CTS. I used both to determine that the CTS was done, and my cheapo 50k miles-old O2 was very lazy. Maybe thet could be made stickys?

 

[Rags]

I have and seen and read so many issues with miles per gallon dropping off on Xj's with OBD 2 systems and alot of other cars and trucks with odb 2 when vehicle miles start going over 100,000....as with anything else stuff starts to wear, rings, camshaft, timing chain etc... All you can do is make sure the basics of a tune up are the best you can achieve with an engine with some miles on it...... clean injectors help, spark plugs, clean throttle body, decarb combustion chambers....... then you can move on to the engine management, If you can get access to a good scanner it will help alot to see what is going on, adjusting cam sync or distribator timing is crucial as timing chains stretch, most common thing that wears is O2 sensors, if you have no faults or check engine lights and it runs good overall invest in a good set of non universal upstream and downstream o2 sensors and if the cat convertor is original and you are up over 100k I would recommend a good replacement, they wear just like anything else and those 3 things seem to effect MPG more then anything else in my experince on a good running older engine with no faults or check engine lights or major mechanical problems.................

Also another cheap fix to boost MPG if engine is good state of tune, no check engine light and dont want to spend a ton of money on new o2 sensors and cat is to add a MAP enhancer or in other terms an adjustable MAP sensor... it fools the PCM in to showing it has more engine vacuum then your engine actually is producing, and again as I stated above engine parts do wear and engine vacuum does decrease, pcm sees less engine vacuum and uses a whole new set of fuel/timing maps to achieve that magical air/fuel mixture of 13:1 to 14:7 ...a whole other subject on short and long term adaptive memory.......

Look at this link and try to build and install one of these if everything else is running as best as you can get it within your budget and no fault codes or major mechanical engine problems..... Just a word of warning, dont try and over do the map sensor adjustment, you can make it to lean and damage stuff, or make it run to hot and actually decrease your MPG... little adjustments are the best untill you get the balance between max MPG and no chance of being to lean......... http://www.fuelsaver-mpg.com/simple-map-maf-enhancer

I built and use the single stage MAP enhancer and added a simple switch on the box to go right back to stock if the box decides to flake out or fail.......

I am going to build the 2 stage MAP enhancer so can flip from city to highway cruising to get the best MPG all around.................

I have not been here in a long time, just happen to have caught me surfin this site.......
I used to live on here years ago, but really spent to much time on here......

I wish you the best of luck and hope I could help, even just a little Alot of very friendly and knowledgeable here.......

 

[Yankee]

O2 sensor just went on the list... thanks.

 

[Talyn]

Also another cheap fix to boost MPG if engine is good state of tune, no check engine light and dont want to spend a ton of money on new o2 sensors and cat is to add a MAP enhancer or in other terms an adjustable MAP sensor... it fools the PCM in to showing it has more engine vacuum then your engine actually is producing, and again as I stated above engine parts do wear and engine vacuum does decrease, pcm sees less engine vacuum and uses a whole new set of fuel/timing maps to achieve that magical air/fuel mixture of 13:1 to 14:7 ...a whole other subject on short and long term adaptive memory.......

That will only change fuel consumption in open loop. Most of the time its in closed loop, getting feedback from the O2 sensors.

Unless the engine is modified leave the MAP sensor alone.

 

[heyhar]

To the original poster-When you get the Scan Gauge II you said you've ordered, you may encounter a problem that a few of us on this forum have noticed. The unit may shut off randomly on its own. Back in October the following thread was started, and I sent an inquiry to Scan Gauge asking about the problem. The response I got is in #8, and I posted it. I followed the recommendation, and it has worked flawlessly since.

http://www.naxja.org/forum/showthread.php?t=1091446

If you have the problem, follow the instruction, and you should be in good shape.

 

[SBpunk]

To the original poster-When you get the Scan Gauge II you said you've ordered, you may encounter a problem that a few of us on this forum have noticed. The unit may shut off randomly on its own. Back in October the following thread was started, and I sent an inquiry to Scan Gauge asking about the problem. The response I got is in #8, and I posted it. I followed the recommendation, and it has worked flawlessly since.

http://www.naxja.org/forum/showthread.php?t=1091446

If you have the problem, follow the instruction, and you should be in good shape.

Thanks for the heads up. Ill look into it once it gets here... for now OFF TO CHANGE THE FUEL INJECTORS.... again..... for the third time.... lol

 

[SBpunk]

Ok so far no change. Letting the computer reset for awhile but I tried pulling the number 1 injector and didnt change the engine like the others did. Fingers crossed

 

[SBpunk]

Ok quick question. The fuel injector cables should be showing 12+ volts right? This is what I did and the results I got.

Check the voltage on JUST the injector wires and got less than a full volt.

Checked the voltage by using the positive wire in the injector connectors and touched to the air intake manifold got 12 to 13+ volts.

Lastly I used the positive connection from the connectors to the PCM and got almost nothing

Now I'm not a complete idiot but shouldnt the PCM be grounded? If not should the negative wire on the fuel injector connectors show 12v when connected to both positive and negative? Let me know if this doesnt make sense I'm going to keep probing

The reason im asking is that I'm getting a constant P0201 and 206 code now. All the others will go away but these 2 keep coming back. Thinking something was shorted out. I have no power to the pedals now.

 

[Ecomike]

Ok quick question. The fuel injector cables should be showing 12+ volts right? This is what I did and the results I got.
Check the voltage on JUST the injector wires and got less than a full volt.

Checked the voltage by using the positive wire in the injector connectors and touched to the air intake manifold got 12 to 13+ volts.

This is why we test with NOID lights, special low power LEDs that will not damage or overload the PCM/ECU. Some systems supply a constant ground, some supply a constant 12 volts IIRC. Either way the ECU/PCM SWITCHES the other side for miliseconds only. You can NOT safely verify the switching with a multi meter. You can verify the constant ground, or constant 12 V, but only if you use the engine as a ground when testing for 12 Volts, or use ohms and the engine ground to test for a continuous ground. I forgot which is which, and IIRC it changed on the jeeps, in one of the change over years. I think the older Renix is a constant 12 volts and the ECU switches the ground on and then back off, like I said in miliseconds, which is what fires the injector, the current flow moves the solenoid in the injector.

Lastly I used the positive connection from the connectors to the PCM and got almost nothing

I hope that was just wire to wire? If yes, all you did was verify no resistance in a good wire, in which case it should not read anything.

Now I'm not a complete idiot but shouldnt the PCM be grounded? If not should the negative wire on the fuel injector connectors show 12v when connected to both positive and negative? Let me know if this doesnt make sense I'm going to keep probing

It is not a complete circuit until the ECU fires the injector, and then it is complete for only miliseconds. You DC meter will not properly register a fast DC pulse.

The reason im asking is that I'm getting a constant P0201 and 206 code now. All the others will go away but these 2 keep coming back. Thinking something was shorted out. I have no power to the pedals now.

I have no power to the pedals now.?????????

 

[SBpunk]

Eco its just chugging along. It will get me short distances but it feels like I dont have all my cylinders firing.

Ok I wasnt sure if the housing for the PCM was supposed to be grounded as well.

The noid lights are still working for all the connections. Even 1 and 6 but its throwing codes. I'm out of ideas.

 

[Ecomike]

First think is to check the #1 and #6 injectors, and any other injector with the ohm meter, and see if they all read the same resistance. If one reads <1 ohm (shorted), or a large number or over range it is bad. If they all read the same, or pretty close, might as well check all six, then assume they are good, and move on to the wiring or the computer.

P0201 (M) Injector #1 Control Circuit An open or shorted condition detected in control circuit for injector #1 or in the INJ 1 injector bank.

P0206 (M) Injector #6 Control Circuit Injector #6 output driver stage does not respond properly to the control signal.

Source:

http://www.jeepwranglertech.com/jeep-wrangler-codes-OBDII.html

http://www.cherokeeforum.com/f2/codes-p0201-p0202-p0203-p0204-p0205-47405/

I found the P020X code diag tree in my Service manual, but its bed time. I'll post it up tmorrow if i have time. Gotta get ready to take my [COLOR=blue !important][FONT=inherit !important][COLOR=blue !important][FONT=inherit !important]Jeep[/FONT][/FONT][/COLOR][/COLOR] to the trails Friday. Good luck!

FSM lists as possible causes;
Autoshut relay output circut open(no 12V to injectors)
Defective injector
Inj Control CKT wiring harness Intermittent defect
Inj Control CKT wiring harness observable defect
Injector Drivers circuit Open
Injector Drivers circuit shorted to ground
PCM defective

 

[Ecomike]

http://engine-codes.com/p0206_jeep.html

http://engine-codes.com/p0201_jeep.html

Possible causes
- Faulty fuel injector 1
- Fuel Injector 1 harness is open or shorted
- Fuel injector 1 circuit poor electrical connection
Help with this

When is the code detected?
The P0201 is set if the Engine Control Module (ECM) is detects a low or high voltage drop or resistance at the injector 1.
Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Lack/Loss of Power
- The engine may be harder to start
- Engine hesitation
P0201 JEEP Description
Engine Control Module (ECM) checks the injectors circuit resistance and monitors the voltage drop during normal operation. The ECM will trigger the P0201 code when the resistance or voltage drop at the injector 1 is out of specifications.

Read more: http://engine-codes.com/p0201_jeep.html#ixzz2Mdg1OWnP
​

 

[SBpunk]

Ok this is where I go into idiot mode. I know how to read volts and test for 12v etc but when itcomes to OHM I'm not too bright. My multimeter has settings for 200 2k 200k 20m. I'm guessing I set it to 200 right? After that how do I go about checking it? Red wire to positive side of the actual injector (probably a stupid question because its not getting any power without the connector) or to the connector itself? Sorry Eco I must be frustrating the shite out of you but I really appreciate the help. Thanks