I have a 1997 4.0 wrangler I have earler in the year put on a cold air intake which i clean regularly, performance ignition kit , alll new exhaust, along with a new TPS wich did make a big difference because i got at least 270 miles to a tank wich is not bad for the way i drive, but now with colder weather here i am only getting 180 miles to a Full tank and every once in a while the Check engine light will come on too. i noticed a big dent on the bottom of my fuel tank "from a rock i must of hit" would this over time cause a problem? My fuel gauges a little off but I was still getting good fuel milege at the time, now i dont know .My geuss is that is is a bad sensor. but not assuming anything. please help me on a solution.
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Re: Bad fuel millege
I would replace the thermostat. in the winter the system will stay rich until it is approx 195 degrees. if you put a 160 degree thermostat in for a power boost. it dont work in the winter. also rich means lots of gas lean is a little gas . good luck
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Installing a cold air intake kit like a K&N or Airaid will actually do both, give you a horsepower gain and better fuel mileage. you will notice better throttle response and you will not need to give it as much throttle to go the same speed as before and therefore you should see an increase in gas mileage(if you dont go hotrodding around!).
The 300 code is multiple misfires on cylinders. I assume you could have guessed that by the way the engine runs as you described. There are several potential causes for that, but I would start with checking your fuel pressure at the fuel rail. Should get at least 60psi for most fuel injection systems. Other causes...clogged injectors, malfunctioning map sensor, air/vaccuum leak(s), bad intake or plenum gasket(s). Check your fuel pressure and try a can of seafoam to clean out your fuel system. Check all your vaccuum/air hoses and make sure your air filter is good and not clogged. (should be replaced yearly anyway, air restriction will cause bad performance and fuel consumption) Intake and plenum test by spraying starting fluid around gasket mating to engine area and see if engine revs up (do it while idling). If you get a rev up, do it a few times. if it does it consistently in any one spot, you have a gasket leak.
Hope that helps, Mike
1994 Wrangler with 200,000 miles on the odometer. Similar problem here: Severe bucking and backfiring, and engine misses when traveling down the road. I did an entire tune-up (plugs, wires, distributor, distributor cap, and ignition coil), but got the same thing. I thought it was dirty fuel injectors, so, I poured a bottle in a few times on fill-ups. The final solution, was a bad alternator. My mechanic said it was sending voltage spikes to the computer, causing the engine bucking and back-firing problems.
What year is it?
4 cyc or V6?
I will assume you has a fresh tank of gas.
Here's a lot of to do / to check list.
clean air filter
clear air passage intake tube
clean mass air sensor MAS with electronic part cleaner
clean carb. or throttle body with carb. cleaner.
check or replace spark plug/wires/cap/rotor
change coolant (it's over due)
oil change (it's over due)
fuel filter (it's over due)
how long has this been happing..one tank of fuel or more, could have been bad gas, replace filter,, put gas dryier in fuel tank..if it continues could possibly be transmission related..the reving down doesn't sound like transmission though if tansmission was slipping it would rev up..good luck
There are several things you can do if you haven't done so already, Check voltage at ignition coil, as soon as the engine starts to turn over there should be voltage. If not, the crank sensor is not triggering the ECM quickly.... on 98-99 wranglers, this was a problem area. Check terminal connectors at the ECM, clean and secure, another area of concern.The module on the side of the throttle body is the air idle control 'motor' as jeep calls it. Over time they tend to carbon up and it results in bad air/fuel mixture and yet fails to send a fault code, you can remove & clean also the O2 sensor in front of the cat. convertor.remove & clean. Check fuel pressure, you should have some residual PSI. Treat fuel system with a good treatment...I like the Lucas products, their fuel system treatment and injector cleaner burns hot & clean. I hope these suggestions help...and the wrangler returns to top form...good luck.
clean and recharge your cold air filter, if you never had it cleaned, you can buy the recharge kit for your cold air filter, follow the instructions, if that doesn't work check your mass air flow sensor, have your mechanic clean it and test it.