6 MPG, out of ideas, please help. - Page 12 - JeepForum.com
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post #166 of 510 Old 03-26-2013, 06:11 AM
86cj74.2L
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How accurate is the vac test for the cats?

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post #167 of 510 Old 03-26-2013, 06:27 AM Thread Starter
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Doesn't say. Ill take a pic of the write up later when I'm back home and also see if I can find anything else about it.
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post #168 of 510 Old 03-27-2013, 07:50 AM
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This is a quote from 98dime

I suppose I should update this a little bit. It's been a month since I replaced the aftermarket o2 sensor with a mopar one from the delaership, it took about a days worth of driving for the system to recognize the new sensor and I've had no issues since then. So for anyone out there trying to save a buck by getting an aftermarket o2 sensor don't do it! Spend the extra few bucks and get a legit mopar sensor!
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post #169 of 510 Old 03-27-2013, 08:14 AM Thread Starter
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Figures. The thing that throws me about the o2s is that I get different readings all the time. Sid cycle count pass is 64, ill get a 32 on one and a 14 on the other. The next time I look, completely different. I could understand if they always stayed within a certain range, but why all over the place like that?
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post #170 of 510 Old 03-27-2013, 10:01 AM Thread Starter
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Timing...how much do you think the timing should swing when idle? Should it even swing? I'm sitting still parked watching it stay kinda steady at 12 then it will start swinging from 8-16 degrees.
Does that actually mean anything? Lol
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post #171 of 510 Old 03-27-2013, 12:32 PM
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Quote:
Originally Posted by outofrng623
Timing...how much do you think the timing should swing when idle? Should it even swing? I'm sitting still parked watching it stay kinda steady at 12 then it will start swinging from 8-16 degrees.
Does that actually mean anything? Lol
It uses timing to control idle rpm.
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post #172 of 510 Old 03-27-2013, 01:02 PM Thread Starter
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I would've thought it would stay steady. I was just reading about what is used during idle conditions. Thinking about my stalls, rpm shifts etc...maybe that will help narrow it down.
On the plus side of things, a long time acquaintance of mine called me for something today...he just so happens to be in a good spot with Chrysler, said he will do right by me if I come in for parts. So, I feel a little better. It's gotta be better than the 15% dealer discount I get. Lol
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post #173 of 510 Old 03-28-2013, 01:24 PM Thread Starter
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Jeep goes in Monday for full diagnostic work up...
This should be interesting.

Speaking of interesting...and now knowing this, I wonder...the two post cat o2s set the scope for the precat o2s. So, the pres being new may be good but have all that different switching because the posts are dysfunctional.

They have 2 guys there that are real brains with this kind of thing...and they'll be on it.
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post #174 of 510 Old 04-01-2013, 02:42 PM Thread Starter
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So. Apparently, this is great...they charge 110/hr and consider checking a fuel economy issue a 2.5hr job. Thank goodness I know people.

So, the turnout? They don't know. They say that there are long term measurements and what not stored in the computer...measures over thousands of miles and constantly updates. There is a section they look at, I do not know what it's called, that watches the fuel and air and it swings a 64pt scale -32 to +32. One extreme to another gives them an area to diagnose. Well, mine swings from a minus 6 to a plus 9 (may be reversed, I don't recall) either way it shows nothing wrong. Lets say a plus 32 would mean a vac leak and -32 would show a fuel issue...mine only has a 15pt swing from center. So they see nothing wrong. Their only suggestion is changing the downstream o2s. But, they couldn't get the part, so...I didn't do it. He also checked the ect sensor because according to them, it could be bad but, not show in that other test as an issue.
He's had an 04 jgc 4.7 and so does his son. Said the mileage doesn't appear too far off. I disagree. Lol I know what it was doing when I got it...and what it's doing now.
As for the evap purge solenoid, same concept, without the 64pt swing test showing anything, there isn't much to go after. It appears to be running properly.
Ugh. So I guess ill wait and do the o2s and see. If that doesn't cure it I will have to start wondering if there is some kind of leak at the tank where its losing gas vapor into the air or maybe actual fuel that no one can see.
I guess one way of testing that is to just let it sit for a week and see if there is any noticeable loss. But, if its a start up or running issue, ill never know unless I drop the tank and change everything in that area.
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post #175 of 510 Old 04-01-2013, 05:45 PM
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Your LTFT's had the indication that it thought there was nothing wrong.

You going to do the downstream sensors?

Summer blend fuel is just around the corner. That may change your milage. I think winter blend is Nov 15 to Mar 15. I see at least a 2 mpg drop in winter.
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post #176 of 510 Old 04-01-2013, 06:55 PM Thread Starter
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Lmao. Everything shows that there's nothing wrong. Probably gonna do them next week.
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post #177 of 510 Old 04-02-2013, 04:51 AM Thread Starter
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My latest...

What would cause poor mileage and high fuel pressure at the rail? The fuel regulator was done 2 times, first WIX, then a Mopar...
WIX showed around 62psi steady...
Mopar shows around 58psi bouncing +/- 2psi

Add to that an overworking Evap Purge Solenoid...and sometimes a raw fuel smell.

Has to be some sort of leak or malfunction in the back near the tank. Evap System passes, hear LDP coming on, so I know thats working...

Could it be a problem with the return line? Maybe clogged or pinched or leaking so it makes the fuel regulator push more because it wont allow the right amount to go back into the return line?
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post #178 of 510 Old 04-02-2013, 05:21 AM
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Quote:
Originally Posted by outofrng623
My latest...

What would cause poor mileage and high fuel pressure at the rail? The fuel regulator was done 2 times, first WIX, then a Mopar...
WIX showed around 62psi steady...
Mopar shows around 58psi bouncing +/- 2psi

Add to that an overworking Evap Purge Solenoid...and sometimes a raw fuel smell.

Has to be some sort of leak or malfunction in the back near the tank. Evap System passes, hear LDP coming on, so I know thats working...

Could it be a problem with the return line? Maybe clogged or pinched or leaking so it makes the fuel regulator push more because it wont allow the right amount to go back into the return line?
If you were getting any excessive fuel to the engine via high fuel pressure or fuel vapor the LTFT's would be more negative then they are. The O2 sensors are the checks and balances for the entire system. And your plugs look good. If O2's would be failing (or getting too slow) your plugs would be dark.
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post #179 of 510 Old 04-02-2013, 06:59 AM Thread Starter
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I'm gonna yank plugs again and see about getting a dye to check the fuel line.
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post #180 of 510 Old 04-02-2013, 08:27 AM Thread Starter
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Fuel trims...on the new appointment have, my lt and st trims for banks 3 and 4 are extreme. We're talking +50 to -50. Now, is this a false reading or directly tied to each o2? Also I don't know why this didn't show on the other app.
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