Drastic MPG drop - JeepForum.com
 
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post #1 of 11 Old 08-02-2020, 02:58 AM Thread Starter
avandyck
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Hi to all.
Checking the spark plugs I installed 6 months and at least 5k miles ago, I noticed each of them were at 0.020 I re gapped them at 0.035 as the manual reads. Engine idles and runs smooth and has slightly more power, but:
today is the third day in a row that I need to put gas on the tank, I can see the DTE screen going down fast, feel like it's giving me 2 MPG now

Has anyone ever experienced something like that?
Engine was running fine before, with those 0.020-0.025 gap which is obviously not correct.

It's a 97 L6. Had the oil changed (always been on 15w40) a week before and it was working alright.

TIA for your input.

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post #2 of 11 Old 08-02-2020, 09:57 AM
kg6mov
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The two things that jump to mind are an exhaust manifold crack or a bad o2 sensor. Functionally they'll do the same thing, make the computer think you're running lean when you're not, so it dumps fuel in.


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post #3 of 11 Old 08-02-2020, 11:40 AM Thread Starter
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Quote:
Originally Posted by kg6mov View Post
The two things that jump to mind are an exhaust manifold crack or a bad o2 sensor. Functionally they'll do the same thing, make the computer think you're running lean when you're not, so it dumps fuel in.
I'm looking for cracks on the manifold, vacuum leaks or abnormal noises, can't find nothing. I have been thinking about O2 sensors but I have no codes, asides the OD not kicking in even tho I replaced the solenoid, harness, spring, fluid and filter bc of the P0783 DTC, I'm getting frustrated.
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post #4 of 11 Old 08-02-2020, 01:40 PM
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Check that your spark plug wires are correct according to the firing order. If you swapped a couple wires the unburned fuel/air mix makes it look lean to the O2 sensor (lots of extra oxygen in the exhaust). You'd think it would run rough but not always the case. Other than that I'd look at the possibility that one of the plugs cracked or the plug wire broke internally when you pulled and reinstalled the plugs. Always possible that an unrelated issue happened to pop up during the plug work but more likely that something happened during the plug work to cause the issue.
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post #5 of 11 Old 08-02-2020, 02:13 PM Thread Starter
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Originally Posted by zjosh93 View Post
Always possible that an unrelated issue happened to pop up during the plug work but more likely that something happened during the plug work to cause the issue.
Good input. Well afaik the wires are in the correct position, since I bought it. I usually unplug and plug one by one so I don't get a mess around. Maybe I'll think about something internally in those wires, but again, engine feels, sounds and idles really smooth so I'm lost. I'm guessing re gapping them plugs to what they were before and check. But I'm kinda afraid of playing the take out and back in spark plugs many times game as I cross threaded (is that correct?) a plug orifice once in another car I had.
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post #6 of 11 Old 08-02-2020, 02:13 PM Thread Starter
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This is what the wires look like
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post #7 of 11 Old 08-02-2020, 02:23 PM Thread Starter
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I'm always low on money so most of the time I run on 5 to 8 qts of gas for three days to go around nearby places, but that same amount is now getting wasted in just a short trip.
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post #8 of 11 Old 08-02-2020, 02:29 PM Thread Starter
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Photo of spark plug at 0.035 gap. Was identical to what it looked like at .020
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post #9 of 11 Old 08-02-2020, 09:52 PM
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It either has to be running real rich, or unburned gas is passing through the engine like josh mentioned, or gas is leaking out onto the ground. Or somebody is stealing it.

Wait a minute, there is another possibility. If you are only buying 5 to 8 quarts every 3 days and are relying on the computer's miles per gallon readout, you might not actually be using as much as you think. Carry some gas and drive it until it runs out maybe.
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post #10 of 11 Old 08-03-2020, 07:30 AM
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Firing order looks right in your picture. That plug looks normal. Doesn't look like it's running rich from that pic. Noticed any black smoke? Fuel smell around the engine? Anything else suddenly change about the engine?
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post #11 of 11 Old 08-03-2020, 09:46 AM Thread Starter
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Quote:
Originally Posted by RedRiverT View Post
Carry some gas and drive it until it runs out maybe.
It already ran outta gas. Ran for a minute then it struggled then died. I'll put around 15qts today and have a look at the read out.
I know I know it's just like nothing but I'm thru hard times.
I remember putting around 35 qts one day and the needle barely hit above 1/4.


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Originally Posted by zjosh93 View Post
Firing order looks right in your picture. That plug looks normal. Doesn't look like it's running rich from that pic. Noticed any black smoke? Fuel smell around the engine? Anything else suddenly change about the engine?
No smoke at all, no fuel traces around engine, two days ago I noticed a fuel smell but it went away quickly and never came back.
I can feel no changes in the engine at all besides a smoother idling and running. This is weird until I remembered that the fuel filter must be older than my grandma so I might need to replace it and have the injectors cleaned up.
Maybe it was running okay with a small gap because of that, the lack of power from the clogged pump and dirty injectors so it wasn't delivering much power to ignite such a small spark.
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