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Hi all.

My 4 ltr 6 WJ built 2000 ran quite some time ok but then it started irregular idle, revs to 500 and fuming/unburned gasoline from exhaust. Lots of black stuff coming from exhaust. It seems like its getting to much fuel or 1 cil doesnt get a spark.
Sparkplugs, Map sensor, Lambdasond, injectors all new.
Doesnt give a fault once on the computer.
High fuel consumption. It gets just to much fuel somehow.
It has now 224.000 kms on the clock. Absolutely no oil consumption. I bought it 2 yrs ago with 210.000 kms and looked in good condition.
At first i thought the engine got to hot and i was right about that, visco broken, radiator stuck and sensor broken so that all fixed and it ran very well for sometime. I thought maybe the catalisor is full but trying to order 1 i couldnt even find the part so does it have one?
We live in the south of Spain so it can be very hot here but right now in Spring its about 25 C.
I've been to several garages, even the off Jeep Dealer, but no one seems to get their head around it. One said it might be the alternator but why is it running sometimes perfect and the other day its rubbish?
 

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The beast from Brazil
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8,224 Posts
When not changed yet, I would change the fuel filter/pressure regulator first. Or if you have the equipment, measure the fuel pressure at the rail. A too low fuel pressure will increase the consumption.
Do you have a scanner or can you borrow one? A scanner with live data can be of good help. When you check the fuel trims, you can maybe already see something not normal. The fuel trim figures should be less then +-10%. When there is a low fuel pressure, then the PCM will compensate with a higher fuel trim. If the trim becomes too high, then the PCM should set a fault code.
Regarding irregular idle, that is many times caused by a dirty idle air control plunjer or air canal, or the TPS is on its way out.
But I would first solve the problem of the high fuel consumption, because it could be the cause of the idle problem.
If you don´t have a scanner and can´t borrow one, but you have a smart phone, then you can buy a cheap Bluetooth (or more expensive wifi) dongle and download the free "Torque"app. This app can show you many live data, and you can erase any faults in the PCM memory. A must if you have a Jeep:brows:
 
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