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  #13  
Old 06-11-2015, 02:24 PM
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Re: mis-fire codes but does not mis-fire

Here is the results of the fuel pressure test: 53 psi (good), flow rate at idle is 4 oz at 15 seconds and at 3000 rpms the same. the fuel pump, according to the manual should pump 16 oz per 15 seconds and not have air bubbles. The fuel passing through the pressure test bypass tube is full of bubbles that gives the fuel the appearance of being white and the best it will do is pump 4oz in 15 seconds through 4 test. What does air in the fuel mean?

So I think I need a new fuel pump. What do you think?

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  #14  
Old 06-11-2015, 03:01 PM
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Re: mis-fire codes but does not mis-fire

I wonder if the problem is the fuel pump itself, or a leak after the pump, where it can take air into the line. Did you do these tests (and having the problem as well) with less then half full fuel tank? The pump itself is normally submerged in the fuel, so cant draw in any air into the fuel. But i remember that there is an O ring above the fuel pump which could leak. That normally results in long cranking times, since the fuel returns to the tank and the fuel line will becomes full of air after engine shutdown. I never have done this flow test myself, but is it not possible that the test equipment causes air to mix with the fuel?
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  #15  
Old 06-11-2015, 04:15 PM
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Re: mis-fire codes but does not mis-fire

We are of like minds on the fuel pressure test equipment. I asked 4 clerks at AutoZone those very questions and got "uh I'm not familiar with that." So the answer is I don't know if the test equip is restricting the flow or introducing air. I'm testing at 3/4 full tank of gas.

The jeep starts up instantly and runs very well normally, unless I stomp the gas. So the air in the fuel bleed line of the tester and low flow rate have me perplexed.

So is the bottom line after 13 years, that the fuel pump is no longer capable of pumping (ignoring the air bubbles) a pint of fuel per 15 seconds?
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Old 06-11-2015, 04:55 PM
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Re: mis-fire codes but does not mis-fire

Did you check the fuel lines if they are not dented or damaged in any way, which could restrict the flow? Other than that, only opening the pump unit could maybe tell more. But the tank must be lowered for that. The fuel pump cartridge can be changed separately from the whole module, eventhough the manual tells to change it as one unit. If you can miss the jeep for some days, you could first check what is wrong inside the module, before ordering any part.
I lowered the tank once and its not that difficult to do, but it should be as empty as possible, for weight reasons.
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  #17  
Old 06-11-2015, 05:55 PM
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Re: mis-fire codes but does not mis-fire

I'm reasonably comfortable with everything pointing to the fuel pump and will replace it along with the sending unit (fuel gauge will only register 8/10th when full) in the next couple of months. When it comes to explosive liquids, I prefer to let the "professions" do the work.

Again, thanks for all your help. I will return and post the results hopefully with the fuel pump closing this chapter.

P.S. Sounds like I need the smart phone app and dongle and will look into it.

Regards
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Old 06-23-2015, 01:36 PM
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Re: mis-fire codes but does not mis-fire

I just got back from a 1400 mile round rip. CEL cam on with a 0300,0303,0306,0307 plus 3 miles from home had to toe home because it overheated. The overflow or expansion tank was overflowing and blowing coolant out the passenger side wheel well along with the radiator cap blowing coolant out of the pressure release valve. Checked for cracks, busted hoses, and leaks but did not find any. No gas fumes/bubbles in either the rad or expansion reservoir. Starts right up and runs fine but gets above 210, the fan comes on and it starts to over heat. Water Pump?

I read in the owners manual that the fuel pump filter/screen could get clogged and cause slow starts and limit speed and that it is located in the gas tank. I can live with that as long as I feather the gas peddle and let the trans shift but now I got the over heating problem. Help!
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Old 06-23-2015, 03:08 PM
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Re: mis-fire codes but does not mis-fire

Could be the waterpump yes. I heard of cases where the impeller sits loose on the shaft and hardly moves any coolant around. Also a stuck closed thermostat could be the problem. The coolant is boiling and the steam will find its way out via the overflow reservoir and eventually the radiator cap relief valve if the pressure really becomes too high.
Probably best to change the pump and thermostat now. Also have a look at the upper and lower radiator hoses and change them if they show any sign of drying cracks. If not changed lately, a new radiator cap would be on my list as well. The radiator cap should keep around 18 PSI of pressure in the coolant system, to raise the boiling point of the coolant.
Take care in not overheating this engine, because it will warp the heads and can cause valve seats to drop sooner or later.
Regarding the fuel pump filter, there is only a course screen in the inlet of the fuel pump. Sofar i didn´t hear of anybody where this screen was clogged. The filter/pressure regulator sits outside of the tank.
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Old 06-23-2015, 04:02 PM
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Re: mis-fire codes but does not mis-fire

On my list: water pump, rad cap, and thermostat. I just can't figure this out. I filled it though the rad cap and burp plug and added a 50/50 mix of coolant and filtered water to the expansion tank just below the FULL mark.The bottom hose gets warm and the top hose gets hot but the cap stays cool to the touch even when the temp is 210+. The fan kicks in at just above 210 but temp will continue to climb. How can that be?



I replaced the fuel filter/regulator, no improvement, but replacing the fuel pump is next.

Again thanks for your help
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Old 06-23-2015, 04:23 PM
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Re: mis-fire codes but does not mis-fire

If the thermostat doesn´t open, then there will be no circulation of coolant to the radiator. the coolant will start to boil and form steam, which has a much larger volume and the pressure will increase rapidly. Some of the pressure will escape to the overflow reservoir, but when the expansion is too much, the safety relief valve function of the radiator cap will vent the steam/coolant.
Same will apply when the water pump doesn´t circulate the coolant. In this way the engine can overheat, while the coolant in the radiator is still cold.
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  #22  
Old 09-25-2015, 04:18 PM
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Re: mis-fire codes but does not mis-fire

New water pump, thermostat, and radiator cap fixed the overheating problem several months ago but did not post fix. The plastic impeller on the old water pump fell off the shaft and the thermostat froze shut. The new water pump is all medal.
Re
placed the eight coils and spark plugs-made no difference. Went back to thinking it was the trans. Had Rick from Rick's Transmissions take a test ride and he said it was definitely not the transmission but could be the fuel pump or a clogged fuel rail or problem somewhere in the fuel line. Will replace the fuel pump(complete unit) tomorrow. It's been a slow process but like I said it runs fine as long as I don't stomp the gas pedal so I been in no hurry to fix the problem.
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Old 09-25-2015, 05:01 PM
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Re: mis-fire codes but does not mis-fire

Another possibility is a clogged catalytic converter, though I don't know how you'd test for that.. excess back pressure can cause a misfire..
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Old 09-26-2015, 08:23 PM
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Re: mis-fire codes but does not mis-fire

New fuel pump installed - no difference I can place the trans in neutral, floor the gas pedal, and engine will not go over 4000 RPMs. 2/3 down and I let up at 6000 RPM. Am I chasing Alice down the rabbit hole?
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