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Old 07-20-2010, 10:06 AM   #31
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Coolant Temperature Sensor differences: The 800 Ohm hot resistance temperature sensor is different than the 185 Ohm hot resistance temperature sensor. The 185 Ohm is from the 87-90 models and the 800 Ohm is newer stuff... but dont quote me.

Probably the PCMs were reprogrammed and the temperature sensor changed from 185 to 800 Ohm to allow additional fuel for lubrication of upper engine to reduce friction.

The expression run lean and melt your pistons... those piston rings are creating a lot of friction sliding up and down the cylinder walls, with the additional fuel it lubes the cylinder walls and thus keeps the pistons and cylinder walls cool and the overall engine cooler (thicker oil and therefore higher oil pressure).

The exhaust manifolds tend to change color, crack, and blister - this is due to extremely hot exhaust gases, not from running lean but from a rich fuel mixture. The cracked exhaust manifold is not the primary reason the O2 is sending the computer on a mission to dump fuel, it is a secondary problem, the primary problem is why the fuel was enriched to the point where the exhaust gases nearly melted the exhaust manifold in the first place.

Run too lean - cook and damage the engine... run too rich - cook and damage your engine...
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Old 07-21-2010, 01:01 AM   #32
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The rubber hose collapsed or pinched leading to the gas tank on the fuel return line can cause very bad gas mileage, low oil pressure, overheating, loss of power going up hills, and so on. The high fuel pressure pushes fuel in through the injectors faster than the computer is planning to pump in, then it avalanches from there, timing gets adjusted, vacuum drops, overheating, misfires, rough idle, etc...

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Old 07-21-2010, 01:33 AM   #33
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The throttle position sensor can cause bad gas milage, rough idle & misfires, it could have a tiny wear spot from no throttle pedal position to slightly pressed. A quick test... your idle should be below 1000 rpm, say around 7-8 hundred... how easy is it to slowly increase pressing the pedal and watch the tach but stop it at exactly 1000 rpm. If it smoothly rises and you can hold it at 1000 without going over it is probably good. BUT, if you press so gently on the pedal and you still can't easily get it to slowly rise to 1000 rpm without going over try after try... then it has a worn spot. Your engine will vibrate and the reading from the TPS will too. If you have ever heard a stereo and turned up the volume control and as you did you could hear loud scratchyness until you turned it up to a certain point... that is kinda what the computer hears from that bad spot on the throttle position sensor just the same as if the volume control would (really its the same thing- just a variable resistor). But what really is going on is the wiper arm of the throttle position sensor is losing contact or not making good contact with the resistor to get a stable reading, the effect is going to maximum value or near maximum as the computer is taking a reading even if for a split second. It's like saying full throttle usually only for an instant... microseconds-nanoseconds-picoseconds--who knows but it can be just long enough for the computer to take that reading and setup the next injector cycle and adjust other engine operating parameters. Then the reading returns to normal next cycle that the computer reads the sensor, so it again setups the next injector cycle the opposite direction - idle. As long as the tps is in that spot it will act up, but during other throttle positions it performs somewhat normally- except your cruising spot... that position where the gas pedal is pressed and usually held during crusing speeds.
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Old 07-28-2010, 11:43 AM   #34
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another correction, the year of that jeep is wrong and it occurred to me the temp sensor didnt increase in value- someone had simply installed the wrong part and that is what caused it to run rich.
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Old 10-23-2010, 08:55 PM   #35
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Would clearing up a PCV valve line to the throttle body cause it to run rich?

Just clean out the PCV valve line to the throttle body, it was completely gunked up with no pressure in or out, and now it's running rich. Was running "fine" before with a gunked up line but now that it's clear, it feels as if it's flooding when I come to a stop. The engine stutters and almost dies then levels out. When I shift into 1st it stumbles a bit then catches but you can smell gas as I continue driving.

88 Wrangler 4 cyl 5 spd
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Old 10-23-2010, 09:31 PM   #36
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so a lil stumped im another crappy gas mileage on my 2.4 its automatic without a/c only had it about 2 months now but averaging about 10 mpg. oil psi is runnin around 40 eng temp on the low side. what ive done new fuel filter, spark plugs high out put ignition coil, wires and cap and rotor (nothing to fancy), oil pressure sensor (was blowing oil out the wire hole) temp sensor, have checked all vacuum lines no leaks currently jeep is loaded on a trailer and were moving to another state but will be at it when we get there just looking for suggestions on what direction to go

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fuel milage bad oil tank

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