6 MPG, out of ideas, please help. - Page 4 - JeepForum.com

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post #46 of 510 Old 03-11-2013, 06:37 PM Thread Starter
outofrng623
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I saw an o2 sensor relay today...I have a question, does it cover all 4? If it was flaking out would it be a problem? Should it trip a light? Etc...

Also, someone had asked my mileage and I haven't responded to that. 151k.

Thanks

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post #47 of 510 Old 03-11-2013, 06:40 PM Thread Starter
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Great link. Thanks
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post #48 of 510 Old 03-11-2013, 06:46 PM
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Quote:
Originally Posted by outofrng623 View Post
I saw an o2 sensor relay today...I have a question, does it cover all 4? If it was flaking out would it be a problem? Should it trip a light? Etc...

Also, someone had asked my mileage and I haven't responded to that. 151k.

Thanks
If it was bad I would think it would trip a mil light.

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post #49 of 510 Old 03-11-2013, 06:47 PM
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If it was me, I think I would try changing the temp sensor. It is cheap and quick. Just a hunch.

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post #50 of 510 Old 03-11-2013, 07:29 PM Thread Starter
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I see a lot of weird things where the mil doesn't come on. I've seen that the system won't throw a light if one o2 fails. They both have to fail. Very weird. I am thinking...and again based in this progressively getting worse over time, that you may be right. May be the tps even though I think it looked ok during the check or possibly the map. I'm going to do one at a time for giggles. Updates to follow. Lol.
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post #51 of 510 Old 03-11-2013, 07:31 PM
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I would do a compression test as mentionex before. You can rent the tester cheap and they tell you a lot. It can rule oit rings valves and head gasket
It will tell you your engines mechanical health

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post #52 of 510 Old 03-11-2013, 07:58 PM
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Originally Posted by outofrng623 View Post
I see a lot of weird things where the mil doesn't come on. I've seen that the system won't throw a light if one o2 fails. They both have to fail. Very weird. I am thinking...and again based in this progressively getting worse over time, that you may be right. May be the tps even though I think it looked ok during the check or possibly the map. I'm going to do one at a time for giggles. Updates to follow. Lol.

I am not talking the throttle position sensor, I am talking the engine temperature sensor. Although the TPS could be a problem also and is pretty cheap too.

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post #53 of 510 Old 03-12-2013, 04:03 AM Thread Starter
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I am not talking the throttle position sensor, I am talking the engine temperature sensor. Although the TPS could be a problem also and is pretty cheap too.
I caught that, was just mentioning the other things that are also on my list at this point...partially thanks to this thread.
I think I have seen the TPS for around 50, I will have to look up the parts this week...
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post #54 of 510 Old 03-12-2013, 08:36 AM
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Your "hiss" sound from the passenger side caught my eye. Is it a steady hiss or a more of a hiss, hiss, hiss to the idle of the engine(like a piston going up & down in the clynder)? My only reason for asking is due to your headgasket comment a few pages back, it sounds like my problem. Blown head gasket which i will be replacing when it stops raining here(I'm no longer in CA i live in NY too). my coolant sesnor came on today and along with my P0354 & P0304 it all made sense. My engine hisses while at idle when cold, but it does it to the rythm of the piston moving. It's air escaping from under the head via the head gasket. I had a funny smell to......realized it was a trace amount of fuel coming out where #4 is which is where my gasket is bad.
Hope this is helpful. Lets hope it's not the dreaded fallen rocker arm like i thought mine was
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post #55 of 510 Old 03-12-2013, 08:59 AM Thread Starter
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it's a steady hiss, but this morning I had a collapsed upper hose. Thermostat is about 4 months old...and truck is not overheating in the slightest. Last week I had the same issue, I replaced the cap and hose figuring the cap wasn't opening, but it happened again. So I am in process of bleeding the system and we shall see what the next few days bring. There is def air in there. Not sure if its because of the cap failing last week...so I gotta bleed and see.
Damn gremlins.
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post #56 of 510 Old 03-12-2013, 02:33 PM
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Quote:
Originally Posted by outofrng623 View Post
I see a lot of weird things where the mil doesn't come on. I've seen that the system won't throw a light if one o2 fails. They both have to fail. Very weird. I am thinking...and again based in this progressively getting worse over time, that you may be right. May be the tps even though I think it looked ok during the check or possibly the map. I'm going to do one at a time for giggles. Updates to follow. Lol.
It's not true that that the PCM won't throw a code if only one O2 sensor fails. There are individual codes for each of the four O2 sensors in your WJ which will cause the MIL to turn on. Check the P0100 to P0199 codes in the list here: http://www.wjjeeps.com/faultcodes.htm#0010

You asked about manifold pressure: The scan tool is interpreting the MAP sensor signals and displaying the Absolute Manifold Pressure or MAP. The MAP can range from 0 (a perfect vacuum) up to a maximum equal to atmospheric pressure, which has a standard value sea level value of 14.7 psi or 29.9 in Hg depending on the units being used. As altitude increases, the atmospheric pressure decreases, so the maximum MAP decreases as well. When the engine is off, the MAP in the manifold will be whatever the local atmospheric pressure happens to be. The PCM checks the MAP sensor signal as soon as the ignition key is turned on so that it will know what the maximum MAP will be when the engine starts. MAP is probably the most important value among the several others that the PCM uses to estimate intake air density.

BTW, if you subtract your vacuum gauge reading from whatever the atmospheric pressure is, the result should be close to the MAP.

EDIT: That O2 sensor relay in the PDC of your 04 is for the downstream sensor heaters.
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post #57 of 510 Old 03-12-2013, 03:34 PM Thread Starter
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Rm, thanks...
I read somewhere about the o2's it may have been the FSM...and it may have only been the readiness tests. I am going to see if I can find it.

As for the MAP. I've been trying to figure this out and I am not sure I have it down right...My scanner doesn't show bp, but I am 289 feet above sea level, which by my calc should be a bp of about 29.62 hg. When I go key on my map shows 14.5 psi, idle is 6.1 psi. Does that appear to be close to what it should be?

Thanks for the help.
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post #58 of 510 Old 03-12-2013, 09:33 PM
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Those numbers are very close to what they should be. Using your earlier reported vacuum of 18 (18 in Hg) at idle, the MAP would be 29.9 - 18 = 11.7 in Hg. Converting to psi that would be 5.8 psi, which is close to your 6.1 given that neither the MAP sensor nor vacuum gauge is a precision instrument.
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post #59 of 510 Old 03-14-2013, 04:46 AM Thread Starter
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Updates

Thanks for the MAP check and thanks everyone for the input. Right now the funds are tied up, so a compression test, smoke test and sensors are on hold until I can narrow it down a bit more. I cannot throw parts at it at the moment. Way too much stuff going on and cannot go into the wallet lol

Yesterdays adventures...

Filled up and apparently last week I did 103 miles, 25 of it was highway, the rest "city", 12.44 gallons 8.28 MPG

I took a long road trip, did 139 miles round trip. Approximately 40 of that trip was "city", but mostly 45-55 mph roads that had some stop and go. The highway was empty so it was pretty much a straight ride at about 65mph. Tested crusie throughout the trip and had no problems crusing at different speeds. Filled up when I got back, 139 miles, 9..yes 9 gallons, 15.44 mph. To me, for highway, thats still low. But, nice to see. During one startup I had a strong gas smell, other than that, no issues.

While on my trip I purchased some starter fluid, some gas additive and a mechanics stethoscope ($3, how could I not). It will be interesting playing around today to see if I can pickup any noises along the gaskets and lines...

THANKS
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post #60 of 510 Old 03-14-2013, 04:50 AM Thread Starter
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Fuel pressure question

Start the truck, check pressure, runs around 57psi, but bounces +/- 1psi (new mopar filter/reg), was 62 steady with the WIX. Isnt this a tad high still? What would cause that and...When I shut off the truck, what should the pressure be and how long should it hold for?
If there is a leak, I would imagine the pressure would slowly drop.
Thanks
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